SPECIAL  AND  INTERESTING  LENSES  PRODUCED  BY CARL ZEISS JENA AND CARL ZEISS OBERKOCHEN:

 TESSAR 21cm f/4,5, TESSAR 13,5cm f/6,3, ANASTIGMAT 110mm f/8, APO-TESSAR 30cm f/9, TESSAR 40mm f/3,5, TESSAR 23mm f/2,8, TESSAR 105mm f/3,5, LUMINAR 16mm f/2,5 e 25mm f/3,5, SONNAR 2,5cm f/1,4, APO-GERMINAR 375mm f/9, DOKUMAR 47mm f/5,6, BLASENKAMMEROBJEKTIV ZEISS JENA 39mm f/8, BLASENKAMMEROBJEKTIV ZEISS S-DISTAGON f/11, P-FLEKTOGON 35mm f/2,8, JUSTIER OPTIK  JO-1  14mm f/14, S-PLANAR 120mm f/5,6 in M46x1, S-PLANAR 25mm f/1,6 4050A°, S-PLANAR 50mm f/1,6 4360 A°, S-PLANAR 95mm f/2,1 4360 A°, UV-PLANAR 60mm f/4, S-DISTAGON 27-32mm f/1,5 T*, MIROTAR 500mm f/4,5, N-MIROTAR 210mm T= 0,03, TELE-TESSAR 500mm f/8 AND SPIEGELOBJEKTIV 500mm f/4.

 

 

10/12/2012  (UPDATED  04/02/2015)

 

This article required a lot of preliminary job for researches as well as acquisition of unusual pieces, in some cases expensive, and I want to consider it a sort of Christmas gift dedicated to my many friends and enthusiasts of this topic.

To paraphrase the famous maxim "the phylogeny summarizes the Ontogeny", the evolution of the Zeiss brand, in it's multiform and suffered corporate transformisms and reorganizations, embodies a bit 'the history of modern photography itself, a great mother who has always introduced new technologies and formed skilled technicians which, like seeds carried by the wind, in turn have brought success to other famous companies, often reaching the top of their design offices, and of course the Zeiss production, structured between pre-war Carl Zeiss Jena and Zeiss Ikon and postwar Carl Zeiss Jena, Carl Zeiss Oberkochen and Zeiss Ikon Stuttgart, is really huge, a real triumph of forms and models: in this context, I have isolated a cross selection, with a broad spectrum of lenses produced in various periods and intended for a broad range of usages, even unknown to most people: the only common denominator is the famous brand name that identifies them.

The first set of objectives rightly honors the Tessar type project. the famous masterpiece by Paul Rudolph unveiled in 1902; thanks to its simple construction, flare resistance even in absence of antireflection coating and excellent performance, at the time matched only by much more complex convertible models, featuring even 8 lenses, this optical project arose an immediate and overwhelming success and became the most copied model in the world: there is no company involved in the production of objectives, were them for taking, reproduction or enlarging purposes, which had not conceived at least one lens based on the classic 4 lenses - 3 groups Tessar type; modern and emblazoned interpretations (Ai-P Nikkor 45mm f/2,8, Leica Elmar-M 50mm f/2,8 new), credited with excellent performance, confirm that the famous "Adlerauger" (the eye eagle) is still truly actual.

The first example we consider brings us back to photography adolescent dawn: it is a Carl Zeiss Jena Tessar 21cm f/4,5 in BBM (brass barrel mount), that is with straight brass barrel and without leaf shutter; the front ring shows the 142.294 patent number of the Kaiserliches Patent Office, registered on April, 25 1902, and the serial number 111.389 whitnesses a production restricted to August 1909, well 113 years ago ... At the same time the famous Burgess Shales were discovered in British Columbia, with their exceptional Cambrian fauna preserved so well that, for the first time, we studied the soft parts of the trilobites, a distant event which now belongs to the history of paleontology.

 

 

This objective whows a magnificent rètro livery and a N60 screw mount (Normalfassung 60mm); the Tessar 21cm (then 210mm) f/4,5, designed for 13x18cm plates, was characterized by a surprisingly long commercial life, through two world wars and several recomputations, and was produced from autumn 1906 until spring 1980, with a Carl Zeiss Jena serial range between about 80,000 and 10.833.987 ... The ferrule which keeps the rear doublet can be unscrewed, thanks to a knurled power take on the bottom of the lens, while the two individual lenses are removable together, unscrewing the black front rim, in turn separable into two pieces by removing the central lens, screwed on the back of the removed ring: in this way all air-to-glass surfaces of the lens can be easily accessible for cleaning and we can also inspect the diaphragm, featuring 16 blades and nearly circular; this latter does not report logarithmic aperture values but simply the corresponding diameter of the iris in millimeters, from 39mm to 3mm.

I have performed preliminary tests with this lens, and do not hide the emotion felt in reviving such a dated, historical piece: at full aperture (39mm) the performance is quite soft (but it must be considered that the 100% monitor observation - taking into account the real original format, not exploited - would correspond to parse a file of about 20,000 pixels by side, that is a hypothetical screen of more than 7 meters, so it's definitely a too severe valutation. taking in count the age of the lens and the moderate magnification applied to a 13x18cm plate); stopping down the iris to 17mm we get the best compromise between aberrations suppression and diffraction, and the lens le ts you record a really unexpected resolution, at least in the central areas, accompanied by a good contrast even if devoid of the micro-contrast "wickedness" typical of lenses equipped with modern coatings (completely absent here), but - unfortunately - a residual undercorrected spherical aberration involves a quite visible focus-shift (backfocus), so, wanting to take full advantage of the high performance guaranteed at 17mm (approximately f/12, 5), it is highly advisable to focus directly at the working aperture. Further closing to 8mm (about f/22 + 1/2), the focus plane is more stable but, of course, the sharpness is affected by diffraction, so the optimal aperture is f/11 or so.

It 's interesting to note that the objective is engraved as an f/4,5, while the original patent relates to an f/5,5 ... If we consider that the maximum aperture of the iris has a diameter of about 39mm, the latter would correspond to geometric aperture of about f/5,4, corresponding to the patent data but not to the official ones...

For those interested to have a vague idea of how it this Tessar 21cm f/4,5 performs today, here

THE LINK

to a brief test that I did with this lens.

This other exemplar of Tessar lens in brass barrel mount is instead a small but delicious 13,5cm f/6,3, probably at the time mounted on an Ernemann Heag Series XII camera for 9x12cm plates; also in this case the iris aperture is calibrated in mm (from 21mm, that is f/6,4, to 3 mm, i.e. f/45) and the serial number 165.789 can frame it chronologically with accuracy: when this little brass gem was produced, in the North Atlantic still floated bodies of missings of the Titanic tragedy, the Italian Navy had just occupied the island of Rhodes, sparking the Italian-Turkish war and the new bell tower of St. Marco in Venice, after the collapse of 1903, was inaugurated with great pomp: in fact, this Tessar came out of Jena works in April-May of 1912, just 100 years ago.

 

 

The 1902 Tessar type formula is the result of a long and painful optimizing job deployed by Paul Rudolph for over a dozen years; the starting point for its development is certainly the Zeiss Protar, designed in 1890 and, during the first years of production, marketed under the Anastigmat brand name; the lens that follows actually belongs to this generation and it looks interesting because it is a Zeiss Anastigmat 110mm f/8 produced in March 1896 by Krauss, the Zeiss-based subsidiary in Paris (and Stuttgart): a true alter ego that was active until the early '900.

 

 

The lens proposed here (with the main statements of his patent, registered in April 1890), is small in size and was originally fitted to a mahogany wood plate; the barrel is made of burnished brass and, as usual, the stopping-down references for the iris actually indicate the diaphragm hole in millimeters; notice how the data in the front ring are manually carved, removing the black lacquer and displaying the bare brass.

 

 

The lens features a pleasant vintage appearance, showing all its 117 years; on the side of the barrel can be seen the 15.031 serial number, which actually fits the production in March 1896.

 

 

As mentioned, this Zeiss Krauss Anastigmat 110mm f/8 is equipped with a classic Protar type core, consisting of two asymmetric glued doublets, a solution that reduces the air-to-glass surfaces to just 4, a forced choice to maintain a high contrast without coating; beside the section of the original patent are placed the two cells with the doublets (easily removable from the barrel) and, on the inner side, can be seen the serial matching number of the lens (to avoid misunderstandings during the assembly or subsequent maintenance) and also a mysterious "C320 F5065" code. The maximum aperture of 16.2 mm allowed by the iris ring would correspond to a theoretical value of about f/6,8, perhaps officially rounded to f/8 considering the absorptions and reflections of the system; the maximum theoretical aperture, according to the patent data, should be around f/5,6 but the Protar formula still suffered from excessive spherical aberration and therefore the maximum value allowed by production exemplars was prudently reduced.

 

 

The various components disassembled and displayed in sequence; note how the iris diaphragm, comprising 10 blades and nearly round, appears partially closed even at full aperture, a solution that reduces the inner flare; also the black matt passivation of the blades is a truly actual solution which, curiously, was not present in much more modern lenses, such as the Zeiss for Hasselblad and Contarex of the '60s, equipped with diaphragms shining like mirrors ...

 

 

In an effort to correct the spherical aberration and improve the flatness of field, in 1893 was also introduced a Protar version with the latter group consisting of 3 glued lenses instead of 2 (Series IIa, Zeiss diagram n° 008), then produced in 90, 110, 136, 167, 205, 244, 295, 350 and 433mm focal lenghts; the rear glued triplet solution will be then evoked by one of the rarest and most famous lenses in history, the Leitz Anastigmat 5cm f/3,5.

 

 

As history teaches, Paul Rudolph combined the rear doublet of the Protar with the front group of the Unar, thus obtaining the immortal Tessar.

 

The following image was realized precisely with this lens, used at full aperture f/8.

It's clear that, with some care, this lens from the nineteenth century can still give satisfaction; notice how the lens' formula, featuring only two lenses groups, allows a good contrast even without coating.

Another "classic" Tessar is the first 5cm f/2,8  for Contax rangefinder: the Tessar brought to f/2,8 represented the end point of many revisions of the original project implemented by Willi Merte and Ernst Wandersleb with the intention to raise the aperture of this lens from f /6,3 up to f/5,5, f/4,5, f/3,5 and - in fact - f/2,8. The fast version was patented in Germany in July 1930, the first prototype of 5cm f /2,8 (Versuch 1931 n° 4) was born in 1931, with serial number 1.239.697, and the first serial batches were produced starting from the same year.

The first group of Tessar 5cm f /2,8 made in bayonet mount for the newborn Contax Ia was assembled in January 1932, when were prepared 850 pieces ranging between the serial numbers 1.309.001 and 1.309.850; the exemplar displayed below actually belongs to this series.

 

 

The lens, mounted on a contemporary Contax Ia, is collapsible and shows a counter-clockwise bayonet mount with the distance scale applied to the camera body (suitable only for some objectives), a typical feature of this popular camera; notice how its finish is still influenced by art-dèco suggestions.

 

 

The lens is aesthetically pleasing although clearly dated; the finish is nickel, which is typical of that period and destined to be superceded very soon by the chrome plating process; obviously the lens lacks anti-reflective coatings and features a virtually round iris diaphragm; the aperture values are shown on the front plate, as for the Leitz Elmar 5cm f/3,5, however the adjustment is by far more practical thanks to the wide ring with knurled perimetral power take; the lens mount is a small mechanical masterpiece, with the bayonet coupling that must coexist in confined spaces with the mechanism that allows to extract the collapsed lens and block in turn it's barrel in working position; definitely a true classic, even if its performance has never fully convinced, relegating it to the role of "last" choice behind the jewels Sonnar 5cm f/1,5 and f/2 and Tessar 5cm f/3,5, less fast but truly biting.

 

 

The diagram summarizes the original f/2,8 Tessar patent, signed by Merte and Wandersleb, with its geometrical parameters and the characteristics of the involved optical glasses.

The fertile progeny of the Tessars, over time, has ennobled also mid-low range cameras, sharing with these bodies - rated to budget - the outstanding relationship between quality and production cost typical of this formula; in this regard, two good examples are represented by the Carl Zeiss Tessar 40mm f/3,5 for the Rollei 35 and the Tessar by Rollei 23mm f/2,8 for the the Rollei E110 (and their versions 35T and A110): the first for the 135 and the second for the 110 film format.

 

 

The Rollei 35, a masterpiece of the genial engineer Heinz Waaske, who designed it between 1965 and 1966, is an all metal little gem of micro-mechanics that, at the time, stunned by the extraordinary compactness, although obtained by sacrificing the rangefinder, combined with extremetely guessed aesthetic solutions that made him a true object of design; built with the ruggedness and accuracy typical of the House, it made use of the best german know-how in related fields: Franke & Heidecke mechanics, Gossen light meter, Deckel Synchro-Compur shutter (wonderfully miniaturized) and Carl Zeiss Oberkochen lens: what we could ask for more?

 

 

The Tessar 40mm f/3,5 coupled with this camera was first produced by Zeiss Oberkochen (as the example shown, with its congruent serial number); the Tessar 40mm lens from Carl Zeiss equipped all the exemplars Made in Germany and, till the end of the available stocks, even those made in Singapore; since then, the Rollei obtained from Zeiss the grant to produce the lens by itself, with identical specifications, and it was thereafter marked Tessar Made by Rollei.

It's interesting to note that, despite the destination to a mid-range unit, this Tessar is designed without skimping on the endowment of modern optical glasses; in particular, the first and the last lens are made with lanthanum Flint optical glasses of Schott LaF3 and LaF2 class, while many Tessar lenses designed in the previous decades, and also intended for prestigious equipment, did not avail themselves of Rare Earths materials. The dimensions shown in the patent (diagonal field of 56° and f/3,5) perfectly match the characteristics of the production model.

 

 

The other Tessar considered here is the 23mm f/2,8 "Made by Rollei" model fitted on the the Rollei A110 and E110 cameras, also daughters of the visionary Heinz Waaske (who conceived them in 1972-73) and characterized by a body that is a balanced and admirable synthesis of ergonomics/functionality and design, all calibrated to the target of the potential buyers, that is those which approach to photography for the first time; even in this case, although it is a device for size 110 film cartridges, the Rollei brand (which, in the meantime, moved bag and baggage to futuristic factories in Singapore) did not come to terms with quality and durability, creating an all-metal body and free of mechanical tolerances that is placed on another planet than the competition ; its metal shell, collapsed when in resting position, opened discovering the viewfinder and the lens, while the cocking of the shutter and the film advance were performed by closing and reopening the same shell, as it is on Minox subminiatures.

It's interesting to note that all the controls delegates to the adjustment of the device, the shooting and the release of components are made of plastic of fluorescent orange color, then easily identifiable by an inexperienced user; in particular, the toothed lever system placed under the front plate, operated with the thumb of the left hand, controls the focus of the Tessar lens, adjustable from 1m to infinity, and a transparent green indicator in the viewfinder indicates the relative area of zone focus, selected among the five available options: 1 meter, portrait half-length, 2 meters, group of people, scenery to infinity; of course the focus is not exact but craftsmen probably relied on the large depth of field allowed the focal length of 23mm.

Even the iris, to keep costs down, is simplified and reduced to two simple, opposed guillotines with a V-shaped groove, asymmetric and similar to the section of a river with a gentle slope from the shore; at the top of the camera there are three predefined steps and graphically identified with bright light, dim light and low light: a switch allows you to choose the appropriate aperture, modifying the mutual positioning of the guillotines; selecting the middle value, the hole left by the special shape of the two metal plates is at least surprising (see details in the illustration) and is similar to a star with 4 points, with 2 sharp top and 2 rounded corners: I do not think that this is the optimal configuration for an even optical performance over the whole frame or a nice bo-keh in blurred backgrounds, but, probably, those who invested, all in all, a modest amount to buy this gem, perhaps the first "real" camera "of their life, has been pleased anyway with the results.

 

 

The Tessar lens mounted on the Rollei A110 and E110 was designed by Carl Zeiss in 1960, initially with a 25mm focal lenght, then reduced to 23mm to perfectly fit with the 110 film format; this lens allows an angle of view of 50°, corresponding - in the 135 film format - to a widened standard lens of approximately 45 mm, a choice certainly apt for non-specialist, universal use, while the maximum aperture of f/2,8 can be considered reasonable for the product category.

Even in this case, the tiny Tessar has been designed without paying attention to saving: apart from the sophisticated multi-layer coating treatment applied by Rollei, its optical core provides the first glass lens realized with lanthanum Crown glass type Schott LaK10 and the fourth lens grinded from lanthanum Flint glass type Schott LaF21, two materials with a good balance between high refractive index and low dispersion.

Over time, the Tessar type proved to be a very versatile formula and gave birth to lenses with very different angle of views and targets, from the Carl Zeiss Jena Apo-Tessars for photo-engraving to the 76° wide-angle Tessar for Contax (albeit with aperture reduced to f/8) to the historical Tele-Tessar lenses with focal lenghts 3,5 - 4 times longer than that of a standard; the same basic shape, in inverted position, has been used by various brands also to conceive objectives for reproduction and macrophotography at high ratios, and perhaps the most famous example in this field is represented by the Zeiss Luminar 16mm f/2,5 and Luminar 25mm f/3,5, special optical systems intended for the Zeiss Ultraphot macro- and microphotographic device which allow, respectively, reproduction ratios up of 40:1 and 25:1: Both lenses use a reversed Tessar type formula, standard or slightly modified.

 

 

These Zeiss Luminar 16mm f/2,5 and 25mm f/3,5 lenses were available for the Contarex outfit and belong to the first of three (or four) series, produced before 1967-68 and characterized by twin knurled rings (one to control the iris and the other as a function of power take) with 90° edges and, as you can see, both of these lenses rely on a reversed Tessar optical formula, standard for the 25mm (right) and modified for the 16mm (in left), obtained by adding a fifth lens in front of the glued doublet; both lenses, if used at full aperture to avoid diffraction, offer a very high resolving power, despite the high magnification, demonstrating the great potential expressed by this immortal optical scheme.

 

The lens shown here is instead a Carl Zeiss Jena Apo-Tessar 30cm f/9, a classic process-lens for graphic arts that exploits the Tessar formula with apochromatic status for lithography; the basic lens uses an R55 mount (ie "rohr" - tube - 55mm in diameter), assembled on a very fine pitch helicoid and equipped with a drilled plate for fixing.

 

 

This sample is historically interesting because it was produced in December 1943 and testifies to the corresponding raw materials shortages in Germany at the time: the barrel is made of aluminum alloy (anyway high quality), because brass was intended for ammunitions, and the lens is finished with gray enamel because in the last years of war chromium stocks (normally supplied by the Scandinavian countries) were virtually finished and, moreover,chrome-plating the aluminum used for the barrel would not have been possible.


The next lens under review, in turn, can be considered historical for the implications underlying its optical scheme: it is the Carl Zeiss Jena Sonnar 2,5cm f/1,4 fitted on the 16mm cine camera Zeiss Ikon Dresden Movikon 16 built in 1935.

 

 

This cine camera, presented at a time of great excitement for the german film activity and on the eve of the famous Berlin Olympics, immortalized in the famous film by Helene Riefenstahl, was an all metal little jewel built with precision and mechanical tolerances typical of the Zeiss Ikon golden age; among it's characteristics we find the spring-driven motor with broad autonomy, starting with self-timer, 4 shooting rates from 12 to 64 fps, 4 shutter aperture angles from 180° to 30°, programmable sequences, direct and 90° angled with prism viewfinders, single frame shot, hole finder for direct focusing on the focal plane, crank for fades and Carl Zeiss Jena interchangeable lenses, rangefinder coupled with automatic parallax correction; among the most important accessories there are a magnificent, multi-focal turrel finder and a range of optics, with bayonet mount, including the rare Topogon 1,3cm f/3,5, the Tessar 2cm f/2,7, the very fast Sonnar 2,5cm f/1,4, the Sonnar 5cm f/2,8, the Sonnar 7,5 cm f/44 and the Tele-Tessar 18cm f/6,3 (the latter uncoupled).

 

The Carl Zeiss Jena Sonnar 2,5cm f/1,4,on the 16mm film format, covers an angle of about 30°, corresponding to the classic standard cine lens; this exemplar appears to be the 493° of a batch of 500 units produced in April 1935 and it is therefore one of the first Sonnars of this kind produced for the Movikon 16; obviously it lacks lenses coating (a specific hood was provided, shown in the image above) and its almost round iris closes from f/1,4 to f/22: the large maximum aperture, excellent for the time, combined with the minimum shutter speed of 1/25" allowed by the 12 fps frame rate with shutter set to 180°, allowed to operate even in dim light.

The lens focuses from infinity to 1m and incorporates a casing with an auxiliary lens that, with the rangefinder extracted sideways in working position, facilitated the focusing operations, while the power take of the focus ring (placed at 7 o'clock), engaged by a pivot to a ring provided with toothed sector, also commanded the automatic insertion of a reduction frame in the viewfinder to compensate the parallax at minimum distances; considering also the bayonet mount, made with the usual precision, this small 1935 lens is a true masterpiece of optics and mechanics, arrived at the absolute completion after the war with the introduction of anti-reflection coating.

 

 

The optical scheme of the Sonnar 2,5cm f/1,4, thanks to the angle of view reduced from the classic 46° to about 30°, rather than rely on the typical configuration already used in the Sonnar 5cm f/1,5 for the Contax rangefinder refers directly to the prototypes of the Ernostar f/1,4 designed in the late '20s by Ludwig Bertele for Ernemann, just before the corporate merger with the Zeiss Ikon; the young Bertele calculated, for the company in Dresden, the famous f/2 and f/1,8 lenses for the camera Ermanox, then it was taken over by Zeiss Ikon and immediately commanded the rechensbuero of Carl Zeiss Jena, not even thirty: in this phase he evolved his former Ernostar f/1,8 into the Sonnar f/1,5, combining the front module of the first (single lens plus triplet) with a more complex rear group, featuring 2 or 3 glued lenses in place of the single element fitted in the Ernostar; in our case, due to the view angle reduction and the small film size covered, Bertele got an f/1,4 lens replicating the basic architecture of the Ernostar f/1,4 prototype, developed in the latter stages of his career at Ernemann,  maintaining the single rear element of this latter.

 

 

In the Sonnar 2,5cm f/1,4 for Movikon 16, calculated by Bertele in 1930, we find the typical glued triplet which characterizes the Sonnar of the '30s, consisting of a flint glass, a low refraction and low dispersion Fluor Crown glass melted by fluorides and a lead Dense Flint with high refractive index and high dispersion; the matching means that the central, low dispersion collective element creates a chromatically under-corrected doublet with the first, collective lens and a chromatically over-corrected doublet with the third, dispersive lens. In the Sonnar f/1,5 lens is present another glued triplet at rear, in which the strong curvature in the collective contact surfaces between the second and the third lens corrects better coma and spherical aberration compared to the previous Ernostar f/1,4 prototype, but in the case of our Sonnar 2,5cm f/1,4 this complex module has not been necessary due to the reduction of the field angle, then it was maintained the single rear element provided in the original configuration of the Ernostar from the '20s.

The four lenses described below are post-war productions of the Carl Zeiss Jena DDR, designed over a period of time between mid '50s and early '70s, and each of them, as well as being unusual if not unknown, for various reasons is particularly interesting.

Let's start with a lens for graphic arts, functionally similar to the well-known Nikon Apo-Nikkor, Rodenstock Apo-Ronar, Schneider G-Claron, Goerz Red Dot Artar and the like; this Carl Zeiss Jena Apo-Germinar 375mm f/9 belongs to a family of lenses for various film formats, with focal lengths between 140mm and 1.200 mm, which were calculated between 1955 and 1957 by Harry Zoellner; particularly, this model is very interesting because it was specifically created  for diffraction descreening.

 

 

The exemplar shown above was produced in late 1961 and adopts the original, symmetrical formula with 6 air-spaced elements conceived by Zoellner in 1957; as we will see, soon after, in 1962, the scheme was revised and amended in a classic 4 elements - 4 groups formula, like the aviar or Apo-Ronar, and were actually built only 67 exemplars of Apo-Germinar 375mm f/9 with 6 elements like the one presented here; this glass and brass monster, weighing almost 2kg, is also interesting for another practical aspect: unlike other types of Apo-Germinar, designed for reproduction in conventional graphic arts, this model was explicitly designed to copy originals which, in turn, had already been printed with screen printing, facing the same problem that meet the users of modern flatbed scanners when they have to implement the "de-screening" of the scanned originals; in this case, to cancel the original screen raster shall be the phenomenon of diffraction introduced by the iris stopping down.

This special Apo-Germinar 375mm f/9 offers an extremely wide range of apertures from f/9 to f/256, a value that would allow an exaggerated depth of field, frankly useless shooting flat originals, resulting also in a progressive occurrence of diffraction which reduces the resolving power to the various apertures; in the front section of the barrel there are two mysterious, additional scales: the first indicates the resolution of the screen raster present on the original, with two different measured values, and the other selects the reproduction scale adopted, compared to the size of the subject to be copied, with values ranging between 10% and 1000%; by combining each other the reference parameters on the two scales, the series of adjustments will set the most appropriate aperture so that diffraction would cancels the original's screening with the minimum degradation of sharpness physically necessary ... Of course, the lens can also be used for life size (1:1) conventional reproduction, exploiting, at this magnification, a diagonal of 620mm well and using the optimum lens' aperture shown with a red dot on its scale (f/16 + 2/3); this beautiful piece by Zeiss Jena DDR features a 72mm mount screw and a rather narrow visual angle, as it's common with this kind of lenses, equal to 46°.

 

This close-up better shows the series of dials with scales that operated in cascade; to define the optimal aperture for descreening the original, at first you must turn the dial with alternate knurls until the white enamel diamond is placed in front of the proper resolution of the original's screen (Rw and Ra values), then you have to match the other end of the diamond with the value of the reproduction scale, shown on the second numerical ring, and it will automatically set the required aperture, shown by the triangular reference mark placed above the aperture scale.

 

 

This diagram shows the changes introduced in the formula of the Carl Zeiss Jena Apo-Germinar: Harry Zoellner in mid '50s, designed the optical system on the left, with 6, symmetrically arranged, air spaced elements, and all models were equipped with this optical core, including the 375mm displayed above; in 1962 the range was revolutionized and the focal lengths between 240mm and 450mm adopted the classic 4 elements - 4 groups core (represented in the center), while the 140mm, the 180mm and the focal lenghts from 600mm upwards relied on a new scheme (right), always computed by Zoellner, which maintains the 6 air spaced elements in symmetrical arrangement but with different structure.

Harry Zoellner, the father of this Apo-Germinar, was a true german optics eminence; having chosen to remain in the Democratic Germany, fatally he was not well known in the West for the systematic boycotting of the products and the disinformation managed to art that, during the years of the Cold War, were the order of the day; vice versa Zoellner, after directing the mathematical department of optical calculation at Voigtlaender, Brunswick, from 1946 to 1977 leaded the Rechensbuero for lenses computation of Carl Zeiss Jena DDR (moreover, after 1963, he will also head the department of research and development for photography), and in his long and brilliant career he will design many famous lenses of the brand as well as make an important contribution to the birth of the first computer for the optical design used in Jena, the famous and gigantic ORPEMA. So I thought it was a duty to create a small profile of this great man, allowing everyone to know his unquestionable merits.

 

Another Carl Zeiss Jena DDR really unusual and relatively unknown lens is the Dokumar 47mm f/5,6; calculated in 1969 by Wolf Dannberg (the Zoellner right arm and father of the Flektogon 20mm) and Joachim Schilling, the Dokumar 47mm f/5,6 was a moderately wide (about 60°) reproduction lens with f/5,6 fixed aperture and high resolution that was fitted on a repro device to create microfiches on 35mm non-perforated film, produced by Zeiss Jena as well and called Dokumator Aufnahmengeraet DA7.

 

 

In this picture the Dokumar 47mm f/5,6, whose berrel is bare like a lens for slides projector, is fitted inside the original mount that permitted to fix the objective to the matching repro-camera; the threaded rings allow you to accurately tune te focus draw and fix it, preventing unwanted movements. From the first glance impression, later confirmed by the technical data, the scheme recalls a symmetrical wide-angle lens fo the Biogon or Super-Angulon type.

 

 

In this front view you can see two interesting anomalies in the series of engravings of this particular exemplar: for the Dokumar 47mm f/5,6 Carl Zeiss Jena has assigned serial numbers lots equivalent to 1.490 pieces (being special optics we can not know whether all objectives have in fact been assembled), produced between 1971 and 1981, and all individuals have the standard writing with Carl Zeiss Jena (without DDR) and the serial sequence (eg: 9.363.525); in this case is added the designation DDR and, instead of the serial, is engraved a 4-digit number; I examined another specimen similar to this, with numbers like that, and I'm guessing that this is a large supply, specific for a single contractor, perhaps governmental.

 

 

The Dokumar 47mm f/5,6 is a lens that adopts a configuration of the Super-Angulon type, exploiting 8 lenses in 4 groups arranged almost symmetrically with respect to the fixed diaphragm; schemes of this kind usually allow field angles between 90° and 105° but, in this case, it was decided to limit the coverage to just 59.5°, obtaining a very high resolution even at the edges and limiting the vignetting according to the Lambert law, for which progression is functional to Cos³ Theta and not to the classic Cos⁴ Theta, ensuring a brightness in the corners higher than 70% of that measured on axis (value which increases to over 90% with an optional ,concentric ND filter, adopted rarely and only with very critical subjects).

The lens, applied to the Dokumator Aufnahmengeraet DA7, can reduce opaque or transparent originals with scales ranging from 1:30 (A0 from a distance of 1.532mm) and 1:7.5, reproducing them in microfiches on special, non-perforated 35mm microfilm rolls with high resolution; the useful format of the obtained microfiche (Nutzformat) is 28x40mm, with a coverage of 53.5°, while the overall field exposed (Schwaerzungsfeld) is equal to 32x45mm, which corresponds to a field circle diameter of 53.4 mm and an angle of view of 59.5°.

The distortion is corrected in a virtually perfect way: the relative value is below 0.1% and the absolute is less than 5 microns over the whole field.

As shown in the graphic, the Dokumar 47mm f/5,6 also equipped repro-cameras of the types 551674, 550452 and 542112.

 

(credits - sheet: Carl Zeiss Jena)

I encountered substantial difficulty to find images illustrating the Dokumator Aufnahmengeraet; this original Carl Zeiss Jena sheet shows the previous model, the DA5, for a smaller format and equipped with a Dokumar 38mm f/5,6, otherwise it is identical to the DA7 on which was applied our 47mm f/5,6. As can be guessed, this is a big bench for microfilming equipped with a plane provided with a complex lighting systems and a column on which is placed a camera with special bulks for 35mm non-perforated film; I ignore the overall technical characteristics and the series of controls on the board would suggest the presence of a possible vacuum pump for sucking the originals and keep them flat on the ground; these devices have been extensively used for microfiches making also by the HVA (Hauptverwaltung Aufklaerung), Department of the Ministerium fuer Staatssicherheit, better known as the STASI, for applications easy to understand.

As in a chess game, even the Western counterpart has developed a very similar instrument, called Zeiss Mikrobox: it also reduced the flat originals on microfiches with reduction ratios from 1:8 to 1:30, replicating the parameters of the Zeiss Jena Dokumator, and was equipped with a lens designed in 1974 by Erhard Glatzel and his alter ego Hainz Zajadatz, deriving it from the classical Biogon scheme by Ludwig Bertele: this objective has a focal length of 40mm, shares with the Dokumar the fixed maximum aperture f/5,6 and was called Carl Zeiss S-Biogon.

 

 

As you can see, the 40mm f/5,6 by Glatzel is a "real" Biogon, very orthodox, which differs from the classical f/4,5 - 90° model for minor details, mainly the sickle-shaped first element.

 

The S-Biogon 40mm f/5,6, of which is reported the patent extract related to the production model, guaranteed in turn a very high resolution (one speaks of more than 300 l/mm, in the zones of the field which are more favorable), however, with the intent to miniaturize the Microbox repro device, its angle of field is greater than that of the Dokumar 47mm f/5,6 and this entails a vignetting at the edges in the order of 1 f/stop, unacceptable for the specific use, which requires the almost systematic adoption of the concentric ND filter, not essential for the Dokumar; incidentally, it seems that also the Foreign Intelligence Office of the DFR, so as not to be outdone, has made extensive use of the Zeiss Mikrobox ...

 

 

The original resolving power data of the Dokumar 47mm f/5,6, perilously recovered, are extremely favorable: the aerial resolution is 260 l/mm constant from the center up to 10mm off-axis, passes to 220 l/mm at 17.5 mm off-axis and settles to 200 l/mm at the far edges of the permitted range (26.7 mm off-axis); of course this theoretical resolving power must deal with the photo-sensitive material used, but even in the worst operating conditions the resolving power at the edges does not fall below the minimum value of 135 l/mm.

 

 

Even the original MTF values are also high: in these diagrams are reproduced the contrast transfer modulation parameters (MTF) measured on axis (red line) alongside with the corners, with sagittal (green line) and tangential (blue line) orientation, at spatial frequencies ranging from 0 to 260 cycles/mm, all at 1:30 and 1:7.5 reproduction ratios: these readings are extremely severe, if we consider that - usually - the optics are tested at 10 and 30 or at 10, 20 and 40 cycles/mm ... The parameters show that on axis, under favorable conditions, at 1:30, contrast transfer is still present (10%) at 260 cycles/mm, while the edges are extinguished at almost 250 and almost 225 cycles/mm, depending on the reading orientation, with curves slightly less at 1:7.5.

These values are obviously excellent, well in excess of those permitted by conventional taking lenses, even of the highest quality.

The third Carl Zeiss Jena DDR lens that's looked at is an highly specialized one that very few have had the pleasure to see live: it is the Blasenkammerobjektiv 39mm f/8, developed in 1968 by Eberhard Dietzch, deriving it from a Flektogon 20mm schema, also designed by himself.

 

 

The Blasenkammerobjektiv 39mm f/8 is a very special lens developed to capture the path of nuclear tracks in a special 5 meters per side "bubble chamber" set up in the "City of Science" in Dubna (Russia): these charged particles are liberated in the chamber, filled with a transparent, unstable liquid, in this case heated hydrogen. The hydrogen is usually entered starting from very cold and compressed to 5 atmospheres; immediately before the particle beam is released, the pressure in the chamber is reduced suddenly, expanding the volume of the chamber with a piston and bringing it to 101% of the initial volume; passing through the hydrogen, the particles release energy that bring the hydrogen to boiling along their path, creating a trail of small bubbles; the particles pass through the 5 meters chamber in just 15 nanoseconds, making it impossible to identify them, but bubbles of boiling hydrogen takes about 1/100" to form, thus creating a trace that can be photographed.

The Blasenkammerobjektiv serves precisely to photograph the traces of these paths, highlighted by bubbles generated during the boiling of the medium; to the optical system, very complicated, belong two enormous front menisci, one of which is in direct contact with the pressurized hydrogen, in addition to other refraction correctors, while the basic scheme is similar to that of an f/2,8 retrofocus lens with a 90° field; the complex features a 39mm focal length, an f/8 wider aperture (with f/11 -  f/13 working aperture), a field angle of 88° and a distortion within the 1,5% range.

 

 

This bubble chamber, exposed outside, in a CERN facility, is similar to that just described. On a 3,7m sphere like this, always at CERN in Geneva, was applied a lens produced by Zeiss Oberkochen which performed the same functions of the Carl Zeiss Jena Blasenkammerobjektiv 39mm f/8; it was a special S-Distagon with semi-fisheye structure and a series of rear field lenses in order to get a telecentric projection; the objective worked in contact with large concentric menisci (another similarity shared with the Zeiss Jena version) and allowed a wider angle of field, 106°, albeit accepting a distortion of about 20%, while the working aperture was f/11; so here it's optical scheme.

 

Look at the great overall similarities with the Carl Zeiss Jena Blasenkammerobjektiv, from the front menisci to rear field lenses; the basic formula is of the Distagon type but, for ease, it does not completely corrects the distortion, not to further complicate a project already so critical.

 

 

In this image the nuclear tracks highlighted by the boiling medium were photographed  in a context similar to that described above and are really fascinating.

Another Carl Zeiss Jena DDR unusual lens  is the P-Flektogon 35mm f /2,8, designed as well by Eberhard Dietzsch in 1973 and also known inside the company with the code SO-3.1 (Sonderoptik 3.1) assigned by the Operativ Technischer Sektor (OTS) of the former DDR Ministerium fuer Staatssicherheit, the famous STASI.

 

This objective, similar to a "tandem" X-ray lens lacking its mate, equipped a Pentacon-derived 24x36mm SLR camera called GSK and was intended for surveillance tasks; its characteristic, beyond the long backspace registration required by the travel of the mirror, from which the name Flektogon, consisted of an extremely advanced entrance pupil, combined with a front lenses group of  reduced diameter, and this device was used by STASI to oversee and photograph the interior of rooms through holes in doors or walls; the particular optical scheme has resulted in a distortion of 5%, quite high in absolute but irrelevant for the particular intended use.

For the GSK STASI surveillance camera the Carl Zeiss Jena had conceived a series of four lenses, all suitable for shooting through small openings: the P-Flektogon SO- 3.1 35mm f /2,8 just described was in fact supported by an SO -3.2 50mm f/28 (a Biotar-derivated double Gauss lens), a SO-3.3 75mm f /3,5 (with Tessar formula) and an SO- 3.4 135mm f / 3.5 (a remake of the famous Sonnar with same characteristics); notice the special mount with protruding front lens and the focus ring with cine-like "follow focus" rack.

The Carl Zeiss Jena, during the years at the height of the Cold War, he realized many other special lenses for the Operative Technical Sector of the STASI, several of which were true jewels for miniaturization and optical complexity; one of the most interesting among them was named JO-1 (Justier Optik 1) and constituted the optical system of a surveillance device called Beobachtungscomplex II; the Beko II was composed of a module with a camera and large eyepieces for better vision to which was applied a metal tube of 30mm in diameter and 436,7mm in length inside of which was inserted the JO-1 objective, a complex system with 16 lenses in 10 groups featuring a 14mm focal lenght and f/14 fixed aperture. This optical system provided for a front module with great eye relief (conceptually similar, if you will, to the P-Flektogon just described) with a secondary relay system carrying the image to the other end of the tube, where a 24mm circular image was impressed on 35mm film; the front optical system features the entrance pupil in a position such as to allow the acquisition through a very small hole and the device was operated inside specially equipped hotels (where usually resided members of the enemy intelligence): in fact, in these hotels the dividing walls of some rooms were equipped with through apertures, 30mm in diameter, which shrank at the end like a cone, leaving only a small hole hardly detectable; the Beko II tube was inserted inside these holes  up to hit the tapered end that coincide with the small opening that faces the room of the unaware occupant.. The optical system covers a well 102° angle of view with a resolving power ranging from 105 l/mm on axis to 60 l/mm at the extreme edges of the 24mm image circle and the illumination, thanks to the telecentric path, to far corners ensures even 55% of the axial flow, an excellent value for a half angle of field of more than 50°. It was also available a shorter periskop lens, a SO-3,5 17mm f/5, framing as well a 24mm imaging circle and providing a 80° field.

 

 

It should also be noted that there was another device, called Beko, which was similar to Beko II and based on camera Exa Ic with eyepieces.
The image shows BeKo equipped with a SO-3.5 17mm f/5 lens, with 80° angle of view.

 

 

Here we have an image of the Beko II equipped with Carl Zeiss Jena Justier Optik JO-1; the camera shutter speeds usually ranged from 30 ", to compensate for the f/14 limited aperture.

 

 

 It's interesting to note that unoffical reports emphasized how these "service holes" were most often carved in the wall next to the bed: perhaps our spies, rather than intelligence, were looking for something itchy to get away from the routine?

Now let's ideally cross the Iron Courtain (in those days up) and come back to Carl Zeiss Oberkochen to analyze some very interesting products of that company: the first subject is an unusual variant of the well-known and appreciated Zeiss S-Planar 120mm f/5,6 for the 6x6cm format (Hasselblad 500 series and Rollei SL66) and specifically optimized for shooting at close range and reproductions.

The most famous model is certainly the Hasselblad "C" version with built-in leaf shutter and dual finish, satin chrome or black anodized, with or without T* multi-coating, depending on the production time (between 1968 and 1982), but few know that the Zeiss brand has developed three versions of macro lenses for the 6x6cm format (S-Planar 120mm f/5,6, S-Planar 135mm f/5,6 bellows and Makro-Planar 120mm f/4) even in straight barrel, without shutter, intended for repro-cameras and characterized by an M46x1mm threaded mount, typical for this kind of equipments; furthermore, perhaps at the request of some manufacturer of technical cameras, has provided the S-Planar 120mm f/5,6 also in a configuration similar to that of classical large format lenses, with Synchro-Compur #0 leaf shutter and optical shells screwed at both ends, removable for mounting on plate; are also known some rare examples of the later Makro-Planar 120mm f/4 T* assembled in the same way, in 1989-90, but using a Copal #0 shutter (an all-black versions like the customized one for Nikon) instead of a Deckel, an unusual solution for Zeiss.

 

 

The two unusual options just described: the optical core is identical to that of the conventional S-Planar for Hasselblad and Rollei but the mount is substantially changed; at left a version with Synchro-Compur MXV #0 leaf shutter, intended to the plate of technical equipments like the Linhof, at right the model with simple barrel and M46x1mm thread that, through an intermediate plate (not shown here), was applied to repro-cameras; both lenses were produced before and after 1972, so there are examples lacking the T* multi-coating and others, such as those illustrated, which are equipped. Incidentally, this leaf shutter by Deckel, Munich, is very similar to the one inside the Zeiss Hasselblad "C" lenses and, of course, was adopted by the Zeiss Stiftung because it directly controlled the company through its shareholding..

 

 

The Zeiss S-Planar 120mm f/5,6 T* in M46x1mm beside a classic Zeiss  Hasselblad Makro-Planar 120mm f/4 CF T*: the greater compactness of the first, with a tailored barrel tightly wrapped around the lenses core, is noticeable.

 

 

The lens in M46x1mm mount shows the classic "screw wasp" shape, typical of large format lenses for leaf shutter; note the aperture ring scaled between f/5,6 and f/32, as in the conventional Hasselblad model, and the engravings on the front ring, which are also identical to those placed on the optics for the famous Swedish camera; the optical core was unchanged but the diaphragm, rather than the Spartan 5-blades iris typical of the Synchro-Compur shutter, employs an 11 blades structure, more rounded by far.

It's difficult to define how many exemplar of this kind was built because the matching serials correspond to batches of normal production Hasselblad lenses, then they were lenses' cores prodived for the Hasselblad "C" mount and then diverted to this configuration; statistically, almost all samples with T* coating fall within a batch of serials similar to that of the lens shown here, (for example, 6,130,072 and 6,130,155), while the versions lacking the T* are usually grouped into batches of serials in the order of 5.150.000 , 5.720.000 or 5.792.000; in the first case are known two exemplars with serial 5.150.124 and 5.150.350.

Incidentally, the serial numbers of the T* specimens I known fall into three lots of S-Planar lenses (317 pieces from 6.129.735 to 6.130.052 + 80 pieces from 6.130.053 to 6.130.132 + 102 pieces from 6.130.133 to 6.130.234) which were officially produced in 1978 in Hasselblad "C" mount: from these official figures is not possible to infer whether the optical cores then applied to barrels in M46x1mm mount have been taken "patchy", crafting a handful of specimens, or if whole batches (such as the second and the third, which includes the two known serials of the T* fitted M46x1mm version) were actually fully intended to the version for reprocamera; in any case, the production is decidedly limited, in the range of 200 units for the model with multi-coating. Even the serials of the older versions, without T*, officially belongs to batches of lenses produced in Hasselblad "C" mount, then an exact census of this optics is impossible.

 

 

The mount is really simple and the apertures are continuously adjustable, without click-stops on exact or intermediate positions; the front cell of the lens can be unscrewed, allowing access to the iris and for cleaning the inner optical surfaces, while the rear shell is fixed: in fact, as it's maximum diameter is less than that of the mount thread, it is not necessary to remove it to fit the lens on its plate.

 

 

The presence of multi-layer coating is evident in this image.

 

 

 

I believe that the S-Planar 120mm f/5,6 is still an highly relevant lens because, like the rare and famous S-Planar 50mm f/4 for Contarex, has been optimized for short distances without compromises; in fact, the almost symmetrical double Gauss formula with 6 lenses in 4 groups, typical of high-resolution lenses for reproduction, has been specifically adjusted to provide the maximum flatness of field, astigmatism correction, contrast and resolving power at the reproduction ratio of 1:5, to which corresponds, approximately, a field of view (or projection, reversing the equation) of 30x30cm; the same way, also the S-Planar 50mm f/4 for Contarex, realized in just 400 pieces, was optimized for a reproduction ratio of about 1:10; the decision to move the "sweet spot" of these objectives so unbalanced towards the close range, adopting schemes so sensitive to small changes of the mechanical draft, led to a visible deterioration at infinite, defined as curvature of field and peripheral astigmatism, to the point that for the S-Planar 120mm f/5.6 might be discouraged the use at these distances, if you want an appreciable and uniform performance, while in the S-Planar 50mm f/4 even the focusing helicoid physically precludes the adjustment to infinite!

All the other macro lenses for the medium format, the S-Planar (then Makro-Planar T*) 135mm f/5,6 bellows and the Makro-Planar 120mm f/4 T*, in order to deliver an acceptable corner performance even at infinite settings, were optimized for the intermediate reproduction scale, penalizing the performance at minimum distances; therefore, to date, the S-Planar 120mm f/5,6 is unsurpassed at close range, as underlined by the experience of professionals and also confirmed by the official MTF diagrams measured at 1:5.

 

 

The official Zeiss diagrams, measured at the 1:5 reproduction ratio, show that the S-Planar 120mm f/5,6 features a lower distortion than that of the other models (about 0,1%, virtually metric, against 0,4 to 0,5%), a visibly higher microcontrast (highest curve, relative to 10 cycles/mm) and also an higher definition of the details (lower curve, referring to 40 cycles/mm), the whole thing despite being stopped down only by one f/stop (from f/5.6 to f/8) against the two stops of the other models (from f/4 to f/8 the 120mm f/4 and from f/5,6 to f/11  the 135mm f/5,6).

The values of the S-Planar 120mm f/5,6 at f/8 are so high (considering the short conjugate, which always leads to a physiological lowering of the curves) to compete with those of a good 6 elements enlarging lens for the same film format and used at a similar magnification ratio (5x); aware of this detail, many years ago I conceived a crafted adapter ring to apply this special S-Planar for repro-cameras to conventional photographic enlargers, which allowed me to print at the same reproduction ratio (1:5 = 5x = 30x30cm print from a 6x6cm film format) my Hasselblad negatives with excellent results and the fetishistic satisfaction of a 100% Zeiss powertrain.

Another really special and unusual lens coming from the Zeiss Oberkochen works is the S-Planar 25mm f/1,6 4050A°.

 

 

This objective was the fulcrum of a special equipment for high resolution micro-lithography which, via direct step and repeat procedure on the silicon wafer, made it possible to create the masks of microchips; these optics, if you will, can therefore be considered as the foundations of all the modern technology, since the applied micro-electronics now manage every aspect and manifestation of our life.

The S-Planar 25mm f/1,6 - despite the enormous purchase price - was assembled in a simple and bare barrel of anodized aluminum, there is no focus devices (delegated to a kind of microscope integrated into the apparatus, with less than 1 micron critical precision), and neither an aperture control ring, since these optics, in order to obtain the maximum resolving power, must avoid diffraction and work at the widest possible aperture, in this case a fixed f/1,6; furthermore, since the maximum theoretical resolution is also affected by the wavelength of light used, with the progress of technology become necessary to produce microchips of such a small size and with so miniaturized slopes to call into question a resolving power incompatible with the wavelengths of the visible light; has then started to study and optimize objectives that exploited light with a wavelength shorter and shorter, coming in more modern and complex models to use the ultraviolet band at less than 2000A°, which entails unimaginable complications (quartz lenses, spaces in vacuum or filled with helium, etc.).

The-S-Planar 25mm f / 1.6 was produced from 1974 to 1980, so it does not belongs to this generation of extreme lenses, assembled with more than 30 quartz and fluorite elements and that cost hundreds of thousands dollars each; however, it is very interesting because, in this sprint towards the theoretical extreme resolution, represents one of the first cases in which it was abandoned the visible light in order to exploit the ultraviolet; in particular, this objective was provided in three different versions, characterized by the inner production codes 10 77 37, 10 77 38 and 10 77 39: the first was optimized for a wavelength of 4800A° (F' line, cadmium blue line), the second to 4360A° (g line, blue mercury line) and the third, the most extreme and identical to the one shown here, worked at 4050A° (h line, violet mercury line), that is already into the utraviolet light, invisible to naked eyes.

The combination of the aperture f/1,6 with a special, "diffraction limited" optical formula, virtually perfect, and these working wavelengths entailed a maximum theoretical resolution, respectively, of about 1.300, about 1.430 and about 1.540 lines/mm, breathtaking values and almost unbelievable.

The objective in question was optimized for an 1:10 reproduction ratio, so it focused a mask, with the final model of the microchip, 10 times larger than the actual size and produced with a resolving power of 150 l/mm, projecting it's shape on the silicon wafer with a 10 times reduction and a resolving power, which is necessary to keep all the details of the scheme, up to 1.500 l/mm.

This lens was designed by Zeiss Oberkochen for the German firm founded by Felix Mann, who was one of the pioneers in the design of machines for microchips micro-lithography with the "step and repeat" method; this objective, and other similar ones, always made by Zeiss, went to be fitted to models designed by Felix Mann and produced by GCA Corporation - Burlington Division - Burlington, Massachusetts (USA), such as the GCA - Mann 3600 and GCA - Mann 4800 steppers; here you are some informations about these unusual and expensive equipments.

 

Mid '70s advertising for the GCA Mann 3600 apparatus ; inside, above the base for the silicon wafer, was fitted a Zeiss S-Planar 25mm f/1,6 like the one illustrated above.

 

 

An illustrated brochure of the next model, featuring better performance, called GCA - Mann 4800.

 

 

Of course, being devices developed in the first half of the '70s,  were served by computer hardware and software that today can make you smile... This image, concerning a soft update for the GCA - Mann 3600 made by the H & L Associates study , shows a pattern generator function screen, on which the technician, in practice, drew the traces of the microchip that the apparatus would have reported on the silicon wafer.

 

 

If it was not enough the impressive resolving power of 1.500 l/mm, this particular specimen is further desirable for its special engravings: first, instead of the classic Carl Zeiss S-Planar lettering, we find the name Oberkochen Opton Pl-S, typical of objectives to be exported or marketed in some countries of the Warsaw Pact in which the Judgment of the Courts had granted Carl Zeiss Jena the use of the related brand names; in addition, the serial number is atypical (the S-Planar 25mm f/1,6 lenses were produced in the range of 5.767.646 - 6.371.184; a further, huge batch of 1.750 numbers was allocated but not followed) and refers to the classic, prototypical Zeiss serials: in fact, were assembled two pre-series exemplars for shows with the normal name Carl Zeiss S-Planar and serial numbers 2.589.535 - 2.589.536, and two similar examples, for expositions above the Iron Curtain, characterized by Oberkochen Opton S-Pl lettering and serial numbers 2.592.427 and 2.593.428; the  illustrated item is one of the latter.

Of course those are lenses that have nothing to share with photography itself, however they are very interesting, both for the very high technical content and for the essential contribution provided to the whole mankind, which is liable for the technological level and the same standard of living that characterizes the modern age. To use it in the conventional manner is also impossible because of its short draft, however, reversing the device, you would get a 10x super-macro lens with frightful resolution; of course the extremely shallow depth of field given by the f/1,6 fixed aperture would make practically mandatory the recourse to multishot stacking technique, using a sideshift table of extreme precision, in order to appreciate very tiny focus variations, in the order of microns...

With regard to the production, would be actually assembled 175 exemplars for 4800A°, 250 pieces for 4360A° and 217 other objectives for 4050A° (plus four prototypes). A huge batch of serials (1.750 numbers) was given years later for the intermediate 4360A° model, but there is no evidence that these objectives have been actually produced, as sometimes happens with Zeiss Oberkochen numerations.

Another lens belonging to this series that I managed to recover is the S-Planar 95mm f /2,1 M 1:5 nA = 0.20 4360 A°;  it was also intended to match steppers for the manufacture of microcircuits and contrary to what happened with the 25mm f /1,6 just described the suitabel image size was much larger.

 

I want to emphasize that Zeiss was very active in the field of special lenses for industrial use, and although each type has been produced in very limited runs, even just three examples, the sequence of models is much broader than you can imagine; here is a certainly incomplete list of the different models until 2000, namely those easier to classify: S-Planar 45mm f/1, S-Planar 38mm f/1,1, S-Planar 42mm f/1,1, S-Planar 68mm f/1,1, S-Planar 38mm f/1,2, S-Planar 42mm f/1,2, S-Planar 46mm f/1,2, S-Planar 60mm f/1,3, S-Planar 65mm f/1,3, S-Planar 37mm f/1,4, S-Planar 41mm f/1,4, S-Planar 75mm f/1,4, S-Planar 69mm f/1,5, S-Planar 125mm f/1,5, S-Planar 14mm f/1,6, S-Planar 25mm f/1,6, S-Planar 31mm f/1,6, S-Planar 50mm f/1,6, S-Planar 40mm f/1,7, S-Planar 0,1mm f/2, S-Planar 210mm f/2, S-Planar 95mm f/2,1, S-Planar 100mm f/2,8, S-Planar 14mm f/3,3, S-Planar 48mm f/3,9, S-Planar 32mm f/4, S-Planar 60mm f/4, S-Planar 74mm f/4, S-Planar 135mm f/4, S-Planar 195mm f/4, S-Orthoplanar 50mm f/4, S-Orthoplanar 60mm f/4, S-Planar 0,4mm f/5, S-Planar 0,42mm f/5, S-Planar 0,43mm f/5, S-Planar 0,48mm f/5, S-Planar 32mm f/5,6, S-Orthoplanar 105mm f/5,6 ed S-Planar 60mm f/8: really a comprehensive and varied series indeed, ranging from lenses for microfilm (S-Planar and Orthoplanar 50mm f/4, 60mm f/4 and 105mm f/5,6) to those for laser medical (the very short focal lengths) to those designed for microlithography of microchips; precisely the larger models in this category, which also includes the S-Planar 25mm f/1,6 just discussed, reached impressive prices, even 500,000 DM of the time!

The optical schemes of these special lenses for micro-circuits are usually kept confidential by their brands, with the intention to avoid providing incentives to competitors in areas where the economic interests are relevant; in this case I was are to provide the sections of the already described S-Planar 25mm f/1,6 and also of a boosted version, the S-Planar 50mm f/1,6 which, given the same NA= 0,28 aperture, working wavelength and resolving power, allowed an useful format with a diameter of 14,5mm instead of 8mm.

 

 

The version of S-Planar 50mm f/1,6 4360 A° was produced since 1974 in 1.196 exemplars and was significantly larger than the 25mm f/1,6: the barrel diameter is 81mm in the front and 8,45mm at the widest point, it has an overhang of 146,5 mm from the frame stop (160mm all inclusive), it features an M 76x1mm threaded mount and weighs exactly 1.599g.

 

The essential and massive barrel of the Zeiss S-Planar 50mm f/1,6 4360 A°; the engravings, carved and lacquered on the outside surface of the barrel, bear the Carl Zeiss trademark, the serial number and the S-Planar 1:1,6 f = 50mm wording, while the reference to the working wavelength, in bright orange color, is placed on the locking ring coaxial to the front lens.

 

Close detail of the front area.

 

The two Zeiss S-Planar 50mm f/1,6 and 25mm f/1,6 in actual scale: the difference in size is very important, starting from the the threaded mount (M 76x1mm and M 39x1mm, respectively), all for simply increasing the useful microchip image circle from 8mm to 14,5mm while maintaining a similar resolution.

 

Overall image which includes two samples of the S-Planar 95mm f/2,1 4360 A° (the middle belonging to the last production batch), the S-Planar 50mm f/1,6 4360 A°, the S-Planar 25mm f/1,6 4050 A° and the Nippon Kogaku Ultra-Micro-Nikkor 55mm f/2 5460 A°, which is also intended for primitive microchip masks engraving apparatus; this latter uses a longer monoband frequency, positioned inside the visible range (yellow-green), and its resolving power is lower - so to speak - than that of Zeiss ones: about 550-600 l/mm.

 

This short article, extracted from Zeiss Inform N°85 (1977) was written by Erhard Glatzel and refers to the two objectives S-Planar 25mm f/1,6 and 50mm f/1,6 described above and their relative optical sketches.

 

This graphic better shows the S-Planar 50mm f/1,6 4360 A° scheme and its light bundles; the last converging element operates uncording to the Luboshez principle, focusing the beams of a smaller imaging area and increasing the relative brightness; the output beams are absolutely telecentric, thanks to the reduced size of the image circle compared to the diameter the last lens. Basically you could almost consider this objective as a 10x microscope lens, reverted and beefed up in size.

As you can see, these are asymmetric formulas, more advantageous when the reproduction ratio is not life-size (in this case it provides for a 10x reduction); the lenses are split and the objective tends to be composed of multiple modules, according to the denomination "bulge lenses", adopting schemes that in slang are called "relaxed lenses", with dispersive front elements (unusual with such fast lenses) and forces distributed over many components; schemes similar in concept have been used in Zeiss super-fast wide-angle lenses for cine purposes, albeit with different choices of glasses for the changing needs of the spectral band; precisely this latter, and the approach to shorter and shorter wavelengths in order to obtain a very high resolution, has driven the evolution of this series of S-Planar lenses, as shown by the following diagram.

 

 

We can observe how the sketches of these S-Planar lenses became more and more complex simply passing froma a 4.360 A° wavelenght (the threshold of visible light) to 3.650 A°, in the near ultraviolet range: an apparently limited spectral variation which entailed, however, the adoption of very complex patterns, a kind of "bulge lenses" practically composed by two modules which are comparable to a "tandem" of objectives mounted one reversed in front of the other; the reason for this complexity lies in the fact that, approaching shorter and shorter wavelenghts, the modern, high refractive/low dispersive optical glasses, full of Rare Earths oxides, are no longer able to transmit these bands, forcing the designers to use glasses of more traditional conception and with tamer refractive/dispersive relationships; all this has imposed to multiply the number of the elements to compensate for the above described deficiencies.

Another extremely interesting and rare piece that came from the prestigious Zeiss Oberkochen factory is the Zeiss UV-Planar 60mm f/4, a lens designed in 1965 and patented in 1966 that, thanks to the special materials used in the mold of  it's lenses, is transparent to ultraviolet light starting from a 320nm wavelength, with a percentage of transmitted light at 350nm practically equal to that afforded in visible light (which, let's remember, begins at about 430nm wavelength); the pictures of this intriguing and extremetely rare lens were kindly provided by my brotherly friend Dr. Klaus Schmitt of Weinheim, Germany, which I thank a lot for his kindness; the Dr. Schmitt is a leading authority in the field of multispectral and UV photography and manages a very interesting blog where he shares his fascinating experiments, accessible at the following link.

http://photographyoftheinvisibleworld.blogspot.com/ 

 

 

The Zeiss UV-Planar 60mm f/4 shows a simple mount, similar to that of an enlarging lens, and devoid of focus ring; the lens mount is a LTM 39x1/26" thread and the only available control is the aperture ring, ranging from f/4 to f/22 and controlling a simple, 5 blades iris; the UV-Planar, with production code 10 42 00, covered a field angle of about 45° on the classic 32x45mm Schwaerzungsfeld on non-perforated 35mm film and is optimized for a ratio of 1:10, with an useful range between 1:8 and 1:12.

From the optical standpoint, the Zeiss UV Planar 60mm f/4 is based on a Gauss asymmetrical scheme with 5 lenses in 4 groups that, in order to ensure adequate transparency in the ultraviolet band up to 320nm, were produced using special materials.

 

 

The header of the related patent, issued in March 1966.

 

 

The Gauss asymmetrical scheme with 5 elements in 4 groups of the UV-Planar 60mm f/4; it seems that, in 1961-62, had been calculated a model with a Gauss formula featuring 6 lenses, finally replaced by this version, but I did not find any evidence to confirm that.

 

 

The complete design parameters of the UV-Planar let us understand the reason for its transparency to UV spectrum up to 320nm; in fact, the refractive/dispersive values of the lenses lead back to materials particularly suitable for this purpose: the first lens is made of lithium fluoride, the fourth and the fifth of calcium fluoride, the third of Schott FK-3 Fluor-Crown glass based on fluorides, with low dispersion, and the second, to equilibrate the system, of Schott F1 Flint glass with medium-high dispersion. The three fluorite elements allow the passage of UV light at wavelengths well shorter than the nominal 320nm, and also the FK-3 glass, while not reaching the limits of lithium and calcium fluorides, goes further than this limit; in practice, the "cut filter" of the system is the Schott F1 Flint glass type used in the second front element, which starts to transmit in any appreciable way around 320nm and ensures a light flux of 90% at 350nm, where the other elements of the optical schema are already at optimal peaks; the F1 glass does not contain oxides of Rare Rarths which, with their warm blend, abruptly raise the threshold of light frequencies exploitable, and therefore guarantees the necessary coverage toward the ultraviolet spectrum, albeit more limited compared to the fluorides materials of the remaining lenses of the scheme; note the exceptionally low dispersion guaranteed by the elements in fluorite, as confirmed by the Abbe number Vd = 95,2 of calcium fluoride, and even the value of Vd = 99,27 of lithium fluoride.

As mentioned, the Zeiss Oberkochen UV-Planar 60mm f/4 lens is a very rare and produced in small quantities: immediately after his design were built some exemplars with the classic Zeiss prototypical serials 2.5xx.xxx: specifically, two specimens with serial numbers 2.583.219 and 2.583.220, followed by some twenty pieces ranging between 2.587.001 and 2.587.020 (two examples are documented: 2.587.004, the one shown, and 2.58.4017). These pre-series UV-Planars were followed by ther 10 pieces produced around 1977 (serial numbers from 5.917.199 to 5.917.208) and 20 exemplars made around 1987 (serial numbers from 6.720.393 and 6.720.412), for a total score of just above 50 pieces.

Remaining in the field of limited edition special lenses by Zeiss Oberkochen, the following model is truly unusual: it is the Zeiss S-Distagon 27-32mm f/1,5 T*, a lens which at first glance leaves us perplexed because it is difficult to imagine what could be it's actual use.

Also in this case the pictures were kindly shared by my dear friend Dr. Klaus Schmitt from Weinheim (Germany), the leading expert of special purposes lenses, which I thank again for the grant.

 

 

The Zeiss S-Distagon 27-32mm f/1,5 T* is assembled inside a barrel devoid of iris ring or traditional focus helicoid and, by the first look, it appears that was built for very particular purposes: in fact, this model was the relay-lens of a photo-rendering device that reproduces movies and dumps them on tape, taking (on a kind of moviola) the film in motion and focusing the image on a video tube, from which signal was made the master (probably, considering the production period, destined to VHS videotapes). The f/1,5 large maximum aperture was likely necessary to get very fast shutter speeds and capture many frames as quickly as possible, while the reduced focal range (27mm to 32mm), in my opinion, was exploited only to the two extremes, thereby rapidly selecting two different film formats to be reproduced.

 

 

In fact, at front of the trimmed out barrel, there is a ring which allows to select two positions under the designation "35" and "C", probably at the two ends of the allowed range; the practically flat front lens and the type Distagon architecture, which allows, at the same aperture, a longer infinite registration, indicates the search for a construction as far as possible telecentric , as required by the output video tube. This lens was designed in 1980 and was produced in dribs and drabs, until 1992, in small batches between the serial numbers 6.423.255 and 7.301.355, for a total of just 440 pieces.

As a last step in this walk I kept a piece that is a lens of exceptional optical/mechanical quality plus a great symbol/fetish/icon of Zeiss sound quality and, by extension, of the strongest Made in Germany way-of-life: it is the famous Carl Zeiss Mirotar 500mm f/4,5, a super-telephoto, high aperture catadioptric lens (based on the use of mirrors) which, since the presentation, was an hyperboles' receptacle: unmatched optical quality, perfect and solid mechanics, embarrassing size and light weight, unsustainable price ...

It's funny to note that, looking online, these are countless articles, references and reviews for the golden era Zeiss Mirotar lenses (500mm f/4,5 and 1000mm f/5,6) and how pratically each one, by discriminating true informations from the rhetorical trappings and the continuous repetition of the laconic official sheets, do not contain any data actually new and concrete; let us seek to fill this gap.

The Mirotar is an extremely attractive lens not only as a summation of the absolutes but also for the intriguing human backstory behind its conception and that, until now, have never been pointed out; first things first.

The Mirotar project, directly calculated as a 500mm and then oversized and scaled to 1000mm, was realized in 1960 by Helmut Knutti, was assisted by Alfred Opitz, a fellow of his barely known by the general public and specialized in prisms and reflective silver surfaces; both these mathematicians had cut their teeth in the '50s designing several generations of Zeiss binoculars and, though little known in the field of photographic optics, they were two highly experienced professionals.

The Mirotar, starting from September 1960, was patented in Germany, Switzerland and France and surprised as it was the sensational debut of a company that had never grown in its DNA passion for mirror lenses, but indeed - as we shall see - an earlier design of the Zeiss Jena "sister" had paved the way for this great project.

Talking about the figure of Helmut Knutti, few people know that, again in 1960, he computed for Zeiss Oberkochen another 500mm lens, radically different in concept: it was a conventional refractive lens that allowed the 6x6cm format and with maximum aperture reduced to f/8 to cope with the bottleneck introduced by the classic Synchro-Compur shutter used in the Hasselblad "C" series: it is the equally famous Zeiss Tele-Tessar 500mm f/8, produced from 1961 to 1982 and which was also one of the two objectives, together with the Zeiss Biogon 60mm f/5,6, to be brought effectively on the lunar surface, as unequivocally confirmed by the technical reports of the Apollo missions.

I was very fascinated and a little stirred to realize that the two most famous 500mm lenses produced by Zeiss in the modern era, although conceptually dissimilar, are children of the same father; placing them side by side on the same shelf of my living room, with the two cases in contact , I even imagined that Herr Knutti, from the afterlife, smiled smug and I hope, therefore, that he will not be affected if I imagined for him the nice nickname "the Zeiss 500mm man"...

The 500mm f/4,5 Mirotar was initially produced in a batch of 200 units, ranging between the serial numbers 3.513.210 and 3.513.409 and assembled in 1963; the same year it was offered for sale in Contarex mount, the prestigious 35mm SLR system by Zeiss Ikon Stuttgart which was on the market since late '50s.

 

 

The lens was delivered inside a semi-rigid bag made of black cowhide lined in red velvet; the lid was equipped with a double closure, lockable with a key, while the bag was supported by a long black leather strap held in place by four passers studded on the bottom and sides of the bag itself; the belt was split into two segments, each with chrome buckle and holes at the opposite end and mutually fixed to create a single, adjustable element.

The belt had a large non-slip shoulder strap to better distribute the weight and, inside the bag, there were elements shaped and lined with the same velvet that keep steady the heavy lens; on the sides of the interior there are four more ties with snap buttons, designed to hold in place the spare contrast filter holders, of which one was always slotted  inside the lens and three stored this way.

 

 

The Mirotar body is finished alternately in leather and gloss black enamel with the visible metal parts nicely machined from solid; overall we immediately feel the taste of a very solid object, conceived without frills and aesthetic concessions but all voted to the functional requirements and, of course, one perceives just as easily the excellent build quality.

 

 

The front cap, unique in its kind, is large and fixed with a bayonet, while the rear cap, made by pressed metal and anodized, is standard and identical to that fitted to the other Contarex lenses; in the picture you can see that the lens, unlike other reflex objectives, does not feature an inner focus device actuated modifying the distance between the mirrors: the optical core is fixed and sealed by a filter turrel, ensuring an assembly of extreme precision and protection of the internal mirrors from dust and moisture, and the focus is set in a conventional way, thanks to a large black leather bellows, with a complex hexagonal shape, splayed with conical outline, which at the rear is fixed to a black lacquered slab and that focuses thanks to the travel of two straight rack and pinion guides, embedded in the baseplate and controlled by two knurled aluminum side knobs machined from solid.

 

 

Removing the cap, is shown the impressive "monocle" of the Mirotar that, unlike other catadioptrics, features two front menisci elements with the frame of the secondary mirror fixed inside the second's inner surface with such a skill that it seems to literally melt the glass, without any trace of glue or unevenness. The front ring shows the names "Carl Zeiss Mirotar 1:4,5 f = 500mm Lens Nr3153xxx Made in Germany" with a fixed orientation and steady for all samples; the lenses feature coating but, of course, being an objective produced in 1963, it is not the famous T* multi-layer.

 

 

The front axial view lets us understand the structure of the solid base plate and shows, at 2, 6 and 10 o'clock, the position of the metallic pivots which act as constraints for the cap's bayonet. Its design, vaguely archaic, with disquieting ancestral recalls, is combined with maximum functionality and this realization can be rightfully considered a true design object ...

 

 

...how could we ignore, in fact, the surprising similarities between the front view of the Mirotar 500mm and the CD player with motorized plexiglass cover and side lighting of the famous hi-fi player Bang & Olufsen Beosound Overture?

 

 

The side view with Contarex camera mounted (in this case a Super Electronic) returns the real proportions of the Mirotar 500mm f/4,5: it is a lens featuring a 151mm diameter for 235mm in length (with bellows completely collapsed) and 193mm in height - considering the baseplate and the handle - and the use freehand, also made impossible by the position of the focusing knobs, is definitely off limits because of the important masses involved: in fact we have 4.610g for the bare lens, to which must be added 39g of side filter slot, 6g of rear cap and well 308g of front cap, for a total of 4.963g: also in this case, as will occur to the Contarex Vario-Sonnar zoom lenses, Zeiss has chosen the way of optical and mechanical perfection without any compromises in terms of ease of use or compactness/maneuverability: everything is sacrificed to the image quality, and the users must resign themselves to exploit the Mirotar strictly on a tripod of adequate strength, finalizing the excellent reproduction permitted by this objective with a careful and meticulous commissioning as well.

 

 

The bellows allows a large focus excursion, thanks to the long rack rails embedded in the base, allowing to focus the Mirotar between infinite and 4m; obviously you can not display the corresponding distance on a focus scale nor rely on markers for the depth of field or infrared correction; the structure remains very rigid and devoid of mechanical backlash even at minimum distances due to oversizing of the pieces, worthy of an armored car, and the wide residual portion of the two guides remaining iniside the structure.

 

 

These four frames allow us to better detailing the architecture of the Mirotar, starting from the large and extremely sturdy baseplate for the tripod, made from solid aluminum and fixed to the base with four large screws; on the support plane are carved black lacquered cuts that improve grip and create a geometric pattern that adds further weight to the similarity between this lens and a design object; as you can see, from the embossed base come out the focus racks knobs while the black lacquered spaces that connect the relative guides to the back slab, at infinite, are in abutment against the base itself, making the guides disappear completely.

In the upper part of the lens is placed a strong handle made with flexible synthetic material and sliding inside the two massive anchoring plates, which are also carved from solid with a geometric shape and characterized by a leather top to cover the large fixing screws and a quick aiming sight, similar to that of a weapon.

 

 

The Mirotar 500mm f/4,5 applied to a black lacquered Contarex Super Electronic with the Zeiss Contarex Vertieb cubital logo, a very rare version that is certainly appropriate for this prestigious lens; note that, in both cases, everything is mere functionality while maintaining an objectively attractive design.

 

 

The standard equipment of the Mirotar, in addition to the caps and the supplied bag,includes four filter frames (also characterized by an essential and graphic design), each of which supports a Zeiss coated filter with S49 thread, a narrow mouunt (3mm) and chrome finish; a frame must always be inserted into the slot placed at the rear of the lens, at 3 o'clock, and the supplied filters are UV, yellow, orange and infrared.

 

 

The detail highlights the quick tracking system placed on the mounting plates of the handle and borrowed from the sights of weapons, a solution that is not unusual on high-power telephotos.

 

 

In addition to the lens and the filter slots, the front cap itself is a true design object, made of aluminum covered with leather and featuring a large central, embossed button, also made of aluminum, decorated with a black insert and the Carl Zeiss achromat logo; the interior of the enormous cap is covered with blue velvet and three screws fix an auxiliary ring on which are carved the bayonet flanges that engage the pivots provided in the front of the lens, anchoring the cap; the contact points with the lens are velvet coated, so it is impossible to spoil the Mirotar with frequent mounting and dismounting of the cap.

 

 

The profile views do appreciate the considerable overhang of the central handle; its knurled aluminum edge provides excellent grip and the overall implementation of the cap is truly functional: it is a carefully and intelligently designed detail.

 

 

The Zeiss Mirotar 500mm f/4,5 side by side with the well-known Nikon Reflex-Nikkor 500mm f/8 new catadioptric lens; the japanese objective, featuring a decidedly slower maximum aperture and equipped with an optical scheme designed for maximum compactness, shows compact size and an extremely limited weight, if compared to the Teutonic giant: it seems to observe a yacht with his rescue tender... Moreover, as mentioned, the Zeiss have searched for the highest optical quality and mechanical precision, every other element was secondary and expendable.

 

A similar path was also put into practice by Zeiss itself when, in 1997, from the serial number 8.117.791, produced a new version of 500mm Mirotar: this lens, made in Japan by Kyocera, followed the footsteps of Japanese competitors, adopting an f/8 maximum aperture and exploiting a design focused on compactness, as we can easily guess watching this objective next to the f/4,5 predecessor; also the optical design is radically different and leaves the two front menisci with the secondary mirror behind them, adopting an helicoid focusing system which exploits floating of internal elements. This objective is finally usable hand-held, with due precautions, but its optical performances has never been up to that of the original large aperture Mirotar lens.

Credits: Mirotar 500mm f/8 T* kindly supplied by Ugo Marinelli

 

 

The lens data are shown on the typical front "button" bearing the secondary mirror;, notice that it is referred the T* surfaces coating, absent in the previous Mirotar. This lens should have been produced in a single batch of 3.000 units, included between the serial numbers 8.117.791 and 8.120.790.

Credits: Mirotar 500mm f/8 T* kindly supplied by Ugo Marinelli

 

 

 

 

Paradoxically, in a camera system in which the fastest shutter speed was 1/1000", the unusual and high maximum aperture of the Mirotar 500mm f/4,5 could be a problem, especially if the body, for precautionary, was loaded with a 27° DIN film: the risk that, in bright sunlight, you could not avoid overexposure was concrete, as - like for all the conventional catadioptric lenses - the Mirotar does not incorporate an iris diaphragm to reduce the widest aperture.

To overcome this problem, engineers have provided a second set of filters, this time of ND type (Neutral Density): neutral gray filter which does not change the color rendering (in color pictures) or tonal display (gray tones reproduction in black and white) but, simply, cut light in excess; observing the Mirotar from the rear, therefore, we find at right the slot that allows to fit the frame bearing the main filter (indicated in orange color) and, at left, a rotating turret (in yellow) , placed between the bottom of the lens and the plane on which flows the slotted filter frame, which incorporates three filters: one is transparent and does not change the image or the brightness, while the remaining two are gray ND filters which absorb a quote of the passing light, thus simulating the luminous flux corresponding to a theoretical f/8 and f/11.

These filters are moved thanks to the knurled side of the revolving turret, a sector which protrudes on the left bottom of the lens allowing the photographer to make it rotate; the rotation mechanism features three snap-on marks, corresponding to the correct positioning of the three filters , while the selection is permitted by engravings of the of actual brightness (4,5, 8 and 11) marked in white on the side of the tower and visible from outside; in predetermined positions the corresponding aperture value matches a red arrow placed on the barrel.

The presence of a transparent filter, apparently useless, is explained by the fact that the mechanical draft of infinite is calculated taking into account the optical interaction of the two filters (slotted and rotating) always in place: if, working at f/4,5, the transparent filter on the turret is missing , the backfocus conjugate is changed.

 

 

If we peek through the fully extended bellows, observing the rear portion of the barrel which remains hidden inside, can be seen as the metal that surrounds the rear filter is not finished in any way but it looks crude, and are even visible milling circles of the material: it is a very strange choice, considering the high level of the overall finish and the astronomical cost of the article; since even the bellows themselves are critical and may reflect stray light on their inner surfaces ( Remember the ... Sorrows of young Weston?), one would assume that the whole rear assembly of the Mirotar is not a shining example of  scattering light suppression, although, in practice, have never been detected problems in this regard.

As history teaches us, the Mirotar 500mm f/4,5 was available for the whole commercial life of the Contarex system, sipping little by little those famous 200 units assembled in 1963; in the '70s, with the closure of the Zeiss Ikon Stuttgart and the elimination of programs for cameras' domestic production, the lens was diverted to Rolleiflex and Contax-Yashica systems, and it is widely accepted that have immediately been produced new exemplars upgraded to these specifications; the facts are slightly different.

First, by analyzing the production list, it appears that the only Mirotar assembled after the historic batch of 200 pieces dated 1963 (serials from 3.153.210 to 3.153.409, plus four prototypes showing serials 2.513.249, 2.513.250, 2.522.721, 2.522.722) would be 15 scanty units built in the mid-'80s, originally made with Contax-Yashica mount and ranging between the serials 6.740.699 and 6.740.713; an additional batch of serial numbers for 100 further exemplars in Contax-Yashica mount was assigned for the year 1994 but there is no evidence that has ever been built, probably due to lack of demand resulting from the high price.

In practice, excluding the 4 pre-series exemplars, the Mirotar 500mm f/4,5 lenses actually produced to be marketed would be only 215, of which no one officially assembled in Rolleiflex mount, while the first exemplar actually made with Contax Yashica bayonet saw the light in mid-'80s, 10 years after the launch of the Contax RTS, in which system the Mirotar was instead regularly catalogued from the beginning.

If for 10 years were not assembled lenses with Contax-Yashica bayonet and were never directly produced exenplars in Rolleiflex mount, one wonders which objectives have been delivered to the customers of this latter system and how it has been satisfied, until mid-'80s, the demand of the Contax users!

 

 

This image is interesting; besides showing the aluminum pawl which acts as a clutch and adjusts the resistance of the focus knobs, it clearly illustrates the rear focusing slab; as you can see, this latter - proceeding from the base upwards - is defined by two parallel planes: at about three quarters of the structure, it shrinks with a double curve at obtuse angles until reaching the ring integral with the bellows and which also holds the camera body mount; this ring has a further, evident narrowing compared to the section of the slab, creating a sort of step with a curved profile, and between this slab's ring and the actual Contarex mount there is an intermediate spacer ring, finished in black, which incorporates also the unlocks for camera rotation.

Well, this IS NOT the slab designed and applied to the 200 Mirotar lenses produced in 1963 but a model conceived by Zeiss in the '70s to allow a simple exchange of the bayonet mount (thus allowing you to easily convert a lens to Contax-Yashica mount or Rolleiflex or whatever); the main and only difference between the Mirotar for Contarex and those supplied since the '70s for Contax-Yashica and Rolleiflex lies exactly in this mechanical element; regarding to my exemplar, therefore, whether it has been marketed in the '60s with the original Contarex slab and then, at the request of the owner, in the '70s was converted to Contax using the factory new design slab, or, as we will detail better, it is a unsold exemplar for the system Contarex, remained for years in warehouses, and factory-converted to Contax, as new, in order to be marketed only in the '70s; in every case the back slab has been updated to the new model and the suitable Contarex mount would be one of the interchangeable "bottoms" fitted on request ...

Therefore, this objective would share an interesting story: born in Contarex mount in the '60s, converted to Contax in the '70s, fitting the new slab with interchangeable bottoms (directly by request of the owner or factory-updated, brand new), and then reconverted to Contarex in the '80s or '90s, applying to the new slab one of the interchangeable optional mounts.

Now let's see how does it differs the original Contarex 1963 slab by the advanced model of the '70s.

 

 

As you can see, the original Contarex slab (left) proceeds from the bottom narrowing thanks to the rear surface inclined inward; the bending under the mount is single and the integral ring that holds the bellows and the bayonet has the same thickness of the slab that generates it; more, the mount is secured by six screws applied to the ring coaxial to the bayonet itself, inside it, and the lever that releases the camera rotation runs in a slot directly cut in the ring integral with the slab. Conversely, in my exemplar, with "type Contax" updated slab and the optional Contarex bayonet applied, the slab proceeds linear, narrows sharply with a double bending, the integral ring supporting bellows and bayonet is far thinner and the thickness missing is recovered by an additional washer, interposed between the slab's ring and the bayonet, which also incorporates the release for camera rotation; as you can see, there are no fixing screws in the inner ring, coaxial with the bayonet, while, inside the sleeve, are observed notches for disassembly; precisely the reduced thickness of the anchoring ring earns to draw a few millimeters, sufficient to provide for interchangeable mounts for various camera systems, including the Contarex itself that, when this variation was launched, was still officially distributed - albeit briefly - by the Zeiss Contarex Vertieb.

Of course, honoring its reckless love for the complex mechanical, Zeiss did not conceive these interchangeable bottoms to allow an easy replacement by the owner, as was the case - for example - with the Tamron Adaptall lenses, since the mount is fixed with a sequence of concealed screws which surely make life difficult for those who don't know the schema.

 

 

To clarify, look at the bayonet of this Mirotar example: just to the left of six o'clock it can be seen the head of a seventh screw, abnormal and screwed in depth, that peeps out in the lower floor of the bayonet; a twin-screw is located in a position diametrically opposite, hidden from sight by the outer bayonet ring itself; if we remove it, by unscrewing the 6 standard screws, we expose the two additional screws. Removing even these, we can exploit their threaded holes in the metal as "inspection wells" and, by rotating the bayonet thanks to its release for shooting vertically, after a rotation of about 90°, through these holes become visible two further, concealed screws, the removal of which is done by using the "wells" of the first two...

Mechanical complication aside, the synthesis of the whole matter lies in the fact that all the samples of Mirotar 500mm f/4,5 marketed for Rolleiflex 35mm and all those for Contax-Yashica (except the 15 famous lenses made in the mid '80s) other they are not than Contarex objectives belonging to the batch of 200 units built in 1963, remained unsold until the extinction of their original system, modified brand new at Oberkochen applying the new slab and its related camera mount, and then sold to customers of these two new systems; a direct corollary of this observation is the fact that the lenses actually sold in original Contarex mount, between the beginning of the '60s and early '70s, are far fewer than the 200 built, since to this theoretical figure we must subtract all the unsold exemplars factory "recycled" for Contax and Rolleiflex.

 

(credits - advertising: Yashica Co.)

An indirect confirmation of the foregoing is provided by this Contax advertising, dating back to the mid-'70s: the picture shows two Mirotar reflex lenses on which are plugged Contax RTS camera bodies and, apparently, there is nothing abnormal but, if we carefully observe the serial number of the 500mm, naively left in plain sight, we note that it is the lens n° 3.513.345, which is the 136° exemplar of the 200 assembled for Contarex in 1963 ... Also in other Contax advertising images with the whole lens system the 500mm Mirotar shows a unmistakable Contarex serial number, belonging to the same batch. They are therefore lenses unsold for a dozen years in stock, exhumed and equipped with the new slab and its Contax yashica mount.

 

 

This sketch shows how the reduced section in the main ring on the new model slab, which has a draft at infinite of well 49,7mm, leave room enough to set up any kind of lens mounts; in this case, I pointed out the useful 4,2mm with respect to the Contax-Yashica mount draft. Interestingly, the scheme is approximate and, while correctly bringing the thinner ring with its "step", the outline the slab, tilted with Single-fold, goes back to the original Contarex model, creating even more confusion. As a side note, it should be considered that the device for release and vertical rotation of the camera is embedded in the interchangeable "bottom" itself and then, using self-made adapters, you lose the ability to rotate the body.

Since we are disclosing unusual contexts and details, let's go further, analyzing the characteristics of the lens and the accessories related to one of the only 15 exemplars assembled after the 1963 clump, thanks to the images of a specimen currently on sale.

 

 

Despite the production of this exemplar dates back to the mid-'80s, it is clear that the lens - apart from the new case, the serial number engraved on the front and the famous back slab already thoroughly discussed - is absolutely identical to the original model of 1963, right to the last detail, and also the glasses coating, despite the improvements introduced for several years now, it seems the same of the original Contarex lenses. This absolutely slavish conformity made glitter the suspicion that these 15 posthumous exemplars, in fact, have been assembled with parts or production surplus of individual items made at the beginning of the '60s for the batch of 200 Contarex Mirotar lenses and then stored in the factory until then; if this suggestive hypothesis were supported by tangible evidence, one could say that, in practice, the Mirotar 500mm lenses were produced only in 1963 and only for Contarex cameras, and all other exemplars for Contax-Yashica and Rolleiflex are only vestigial residues of this original "big bang".

 

 

Also the monumental front cap equipping the 15 exemplars made for Contax-Yashica is absolutely identical to the original for Contarex, and the only variant is represented by the central, applied disc, which has been updated to the contemporary Zeiss logo; also in this case it could be a surplus production from 1963 recycled for this small batch.

Another over-structural variation that is found in the 15 mid-'80s exemplars for Contax is relative to the filter slots.

 

 

Compared to those originally provided with the 1963 Mirotar for Contarex, the protrusion of the frame with respect to the body of the lens has been increased, also including a knurling, with the clear intention to get a better grip; also, the thickness of the metal in the raised edges has been increased to stiffen the structure and allow to eliminate the portion of the edge itself surrounding the S49 filter, now screwed on a flat surface and without perimetric obstructions, allowing in this way to unscrew and tighten the filter with ease (an operation that, in the previous model, was difficult because of the raised overhang a few millimeters from the frame of the filter), and, finally, the filter mount is no longer chrome but black, definitely a choice dictated by the desire to reduce the flare. Of course, these filters are simple exterior accessories, easy to make, and these variations do not affect the hypothesis previously made and relative to the assembly of these 15 Mirotar lenses using primary components produced in 1963.

The Zeiss Mirotar 500mm f/4,5 has always been credited with very high performance and superior to those of any other catadioptric lens product from the competors, both benefiting from the conception of the project and the wide aperture (less diffraction), not to mention the virtually cleared assembly tolerances; the following diagram shows the MTF figures measured at the widest aperture available on 6 telephoto 500mm lenses made by Zeiss over the past 50 years, including the Tele-Apotessar Contax 500mm f/5,6, which remained at the prototype stage, 3 of which intended to the 24x36mm and the remanining for the the 6x6cm format.

 

 

The values expressed by the Mirotar are indeed impressive and such to rival the performances of an high quality 50mm standard lens stopped down to it's optimum aperture; particularly, the microcontrast (low spatial frequencies, highest curve) is very high, which is unusual in a catadioptric lens that has to deal with interreflections, and the contrast transfer at 40 cycles/mm (lower curve) shows unusually high values that promise an high resolution of details, in addition, the excellent consistency of the curves from center to edges and the negligible differences between the sagittal and tangential measurements describe a lens in which field curvature, astigmatism and lateral chromatic aberration are excellently suppressed.

In fact, the Brand itself declared that the frames obtained with the Mirotar, due to it's high resolution, could be greatly enlarged and that the correction of chromatic aberration was so good to allow shooting infrared performing the focus in visible light, removing the IR filter, without the need of any further focus correction, despite the focal length and the large aperture that make critical every minimum variation of this parameter; in comparison, the other telephotos play a role of supporting actors and is indicative to notice that also the most modern Zeiss Mirotar 500mm f/8 T *, designed many years after favoring compactness and produced in 1997 by Kyocera, Japan, in a batch of 3.000 units, not even approach the theoretical resolving power of the burly ancestor, confirming the fact that the Mirotar by Helmut Knutti was really aimed at the highest image quality, accepting without rethinking the overall dimensions and consequential costs, Zeiss style!

As I mentioned early on, surprised that at Zeiss Oberkochen, a factory that had never ventured into the production of reflex lens, come out of nowhere a gem like this, without prodromes and a fertile substrate for reference, but in fact the football assist was provided five and a half years earlier by the colleagues and rivals of Carl Zeiss Jena: in 1954 the two great mathematicians Harry Zoellner and Wolf Dannberg, already widely cited above, applied themselves at the design of a very fast 500mm catadioptric lens, which was patented in January 1955 and subsequently went into production with the Carl Zeiss Jena Spiegelobjektiv 500mm f/4 brand name.

 

 

This lens,  produced in black and green mimetic finish, this latter for military use (the main target of this project), shows very interesting and rational optical/mechanical features , many of which will be then taken up in the Mirotar, from the polygonal cradle, integral with the barrel and equipped with focus knobs, to the incorporated revolving turret for the filters; particularly, the architecture of the optical system, of Bouwers-Maskutov type with two glass front menisci, is extremely similar to that which, years after, will be put on paper by Knutti and Opitz when they concretized the Mirotar 500mm. The only substantial difference between the Carl Zeiss Jena precursor and the Oberkochen follower concerns the focus: the Spiegelobjektiv focuses by moving internal elements, controlled by alumimun knobs, without any change in the physical length of the lens, while the Mirotar uses, as seen, a rear auxiliary bellows.

 

 

The statements from the Zeiss Mirotar and the Zeiss Jena Spiegelobjektiv patents confirm the great conceptual similarities; the Mirotar seems more devoted to generic color shoot that requires greater control of chromatic aberration, pursued not only by the couple of rear field lenses (made with glasses featuring different refractive/dispersive characteristics) but also working by up and using for the two huge front menisci two optical glasses whose parameters are very similar but not identical; whereas, the Zeiss Jena Spiegelobjektiv arises to exploit a slightly wider aperture but probably it was specially developed for military long-range shooting with band-cut red filters and black and white film, not seeking the absolute perfection in the suppression of chromatic aberration, which is nonetheless well corrected in a catadioptric lens, since all the elements and built-in filters are made with the same BK7 glass type, with the exception of the second lens of the rear doublet, made of type F3 Flint glass.

 

 

In these wonderful schemes, created especially by my dear friend Pierre Toscani, starting from the mathematical parameters of the project, we can better appreciate the magnificent architecture of the two lenses and the extension of the fundamental flare-stoppers up to the limit permitted by the light flux necessary to cover the expected format; the theoretical aperture of the Mirotar would be f/4 and, with the limitations due to the system quotas, corresponds to a T = 4,7, while the Spiegelobjektiv, which theoretically would be an f/3,6 lens, exhibits a T = 4,2. Both lenses show an afocal front group and a 9 diopters module, confirming the great similarities they share.

The Zeiss Jena 500mm f/4 Spiegelobjektiv, for architecture and speed, was certainly a milestone that created many influences and suggested an archetype whose seed sprouted not only at Oberkochen, in fact, in 1976, the soviet David Volosov (a resonant surname of that Confederation's optics, with distinguished predecessors) patented the schema of a 500mm f/4,5 catadioptric lens also structurally similar to the 500mm from Jena and Oberkochen: evidently, these two speed and performances champions were now a prestigious landmark to imitate.

 

 

Statements from the Soviet patent n° 569.999, based on drawings filed in 1976, which illustrates the 500mm f/4,5 catadioptric lens; despite its simplicity, the section highlights the characteristics proper to the two german reflex lenses which preceded him.

Returning to Helmut Knutti and the two 500mm lenses he designed in 1960 for Zeiss Oberkochen, it must be said that, in the concept of the Tele-Tessar 500mm f/8 for Hasselblad "C", his idealistic aspirations were ballasted by specific technical constraints: from a side the extra-low dispersive FK1 glass, although already patented jointly by Zeiss and Schott  Jenaer Glasswerke at the end of the '50s, was not yet available for an industrial mass-production; on the other hand, the widest aperture, as mentioned earlier, was bound to the useful diameter of the Synchro-Compur leaf shutter (24mm), forcing the designer to limit the maximum value at f/8.

  Moreover, Herr Knutti came from the design of binoculars and traces of specific know-how acquired in this particular practice transpire also from the draft of the 500mm Tele-Tessar lens, in which he gave up even the use of a tamer low-dispersion glass like the type FK5 (Abbe number Vd = 70.4), at time already commonly spread, using instead, at the rear, a refined hyperchromatic doublet, in which are involved two glasses (in this case the Flint F2 and the Dense Crown SK16) characterized by almost identical refractive indexes (therefore, from this point of view, it behaves almost as a single lens) and substantially different dispersion, much greater for the Flint and lower for the Dense Crown.

 

 

This arrangement summarizes some highs in Helmut Knutti's life, all concentrated in 1960: the Zeiss Contarex Mirotar 500mm f/4,5 and the Zeiss Hasselblad Tele-Tessar 500mm f/8 together with their patents' statements and optical diagrams currently drawn starting from these parameters.

 

 

The confidence of Herr Knutti with the construction of binoculars is evident even looking at the external barrel of the 500mm Tele-Tessar Hasselblad: if we compare its front section with these Zeiss Jena ASEM military monocles, produced in 1914, we find striking similarities, including the accessory shoe placed in the front, enamelled ring: in practice, an aesthetic directly transposed!

 

 

Diagrams and unpublished sections that display the position of the optical cores inside the respective barrels; notwithstanding the obvious structural differences and the substantially different film formats, both lenses, in their own way, provide exciting images and, considering that the Tele-tessar was part of the outfit for NASA missions on the lunar surface, we can safely say that their designer left an extremely important and imperishable heritage.

To end the overview on 500mm German objectives, I would like to mention also the Carl Zeiss Jena Fernobjektiv 500mm f/8, a lens with a glorious birth sinking in the '30s, when the same, simple optical system, an achromatic doublet, powered the Fern 50cm f/8 for Contax rangefinder; this lens, conceived in 1932, mechanically defined in summer 1933 and produced for Contax from 1934 to the end of the war, was revived by the newly formed Carl Zeiss Jena DDR and remained in production from 1948 to 1964. This interpretation is historically interesting because, in the limited interregnum in which german Dritten Reich and Stalin's Russia cooperated for an exchange of materials and technical information, in the 30s, its optical design was shared directly between the Jena technicians and the russian colleagues, so that, subsequently, the GOI Leningrad defined a lens which optical characteristics were absolutely identical.

 

credits - collezione: Pierpaolo Ghisetti

 

The front view of this sample of Fernobjektiv 500mm f/8 shows a serial number from early 1954, when it was produced a batch of 125 lenses in M42 mount; the red T indicates the surfaces coating, certainly very noticeable thanks to the intense color of the front lens. The objective, in practice, is a long hollow tube, with manual iris and helical focus decentralized toward the forepart, and the optical unit, consisting of two lenses glued together, is positioned at the front, in the first centimeters of the barrel.

CONVERSION OF THE MIROTAR 500mm f/4,5 TO MODERN CAMERAS LENS MOUNT

Since the Mirotar illustrated in this article is fitted with the '70s updated bellows slab of "Contax type", with a draw clearance at infinite of 49,7 mm and interchangeable revolving mount, I proceeded to remove the original Contarex bottom (in an absolutely reversible way and without structural changes) by availing of the support and the effective skills of my friend Cristian Fattinnanzi, a photographer specialized in the "custom" transformation of lenses; I am therefore grateful to Cristian for the goodwill and for his valuable help.

 

 

The interchangeable bottoms produced for the Mirotar 500mm f/4,5 updated slab are fixed to the frame by 4 screws, 2 of which can be removed through the relative holes and the other two are instead hidden and we need to unlock the camera rotation system and turn the outer ring until, after a rotation of about 90°, within the "wells" of the first 2 screws appear the others, ready to be unscrewed in turn; in the case of the Contarex mount, whose bayonet is particular, first we need to remove the outer ring, fixed by 6 screws, to access those below. The slim interchangeable bottom, which incorporates the whole release and rotation mechanism, weighs a good 85 grams and the bayonet is carved from solid stainless steel of the highest quality, while the rotating device is absolutely free of backlash: overall, it is a mount in full harmony with the quality of Zeiss high range products.

 

 

The friend Cristian captured while beginning the disassembly of the original ring.

 

A scketch quickly materialized on paper, in order to evaluate the thickness necessary to allow mounting of modern cameras, equipped with bulky handles, without compromising the focus to infinite.

 

 

The Mirotar 500mm f/4,5 with the "Contax type" slab and the interchangeable bottom removed; notice the step between the slab itself and its ring, that's much more subtle: this space allows to fit the original bottoms, held in position thanks to 4 screws inserted into the threaded holes highlighted by the graphics; as a further compliance with the typical Zeiss love for mechanical complexity, sometimes an end in itself, the holes are not equally spaced (in practice they mark the vertices of a rectangle) and also their orientation is not congruent to predefined positions (such as "12 o'clock", "3 o'clock" and so on), which leds to a lot of problems when it was necessary to drill the new adapter ring maintaining the required allocation...

I asked directly to Zeiss if were still available, somewhere, original interchangeable bottoms, at the time supplied as spare parts on request (also a simple Contax-Yashica mount would have been fine) but I was told that they were all "cleared"(SIC)...

 

 

At the end of the surgery, the Mirotar has been given a new life, thanks to a Canon EOS mount that allows the use of really modern cameras and to focus with extreme precision using the live view at high magnification; the graphics show the lens with its new bayonet and the bottom bearing the previous mount; the only restriction imposed by the change is the inability to turn the camera vertically without moving the lens, since its mechanism is built into the removed ring.

 

 

More precisely, as, once removed the original bottom, the available draft was plentiful, the lens was fitted with a 42x1mm threaded ring which, in normal conditions, enable us to reach the infinite with various millimeters of residual travel; to enable the actal Canon EOS bodies to rotate without interfering with the slab, on the abutment of the 42x1mm ring was applied an hard resin spacer obtained by lathe, about 2mm thick, which acts as a stop for the further 42x1mm - Canon EOS adapter ring; this thickness keeps the abutment plane of the Canon bayonet far enough from the slab to ensure the mounting of the relative cameras while, removing the resin spacer, also a Nikon body (with an infinite draft of 46,5 mm, against the 44mm of Canon EOS) can focus to infinity, using a 42x1mm - Nikon adapter stripped of his field lens. Further, thin calibration adhesive thicknesses were applied to the resin spacer to allow the 42x1mm - EOS ring to tighten remaining in phase to keep the EOS body perfectly horizontal.

 

 

Here is the final appearance of the lens; to clear the risk of unwanted reflections, I enamelled the inner surface of the 42x1mm threaded ring and the edge of the fitting 42x1mm - EOS mount with an extremely opaque, matt-black acrylic enamel , while the contact pins with microchip are useful for an application that we will see later...

 

 

The result of this work discloses unedited operating scenarios and bound only to the imagination of the operator; moreover, the primary 42x1mm mount with plentiful draw, albeit subject to the limitations for bodies rotation caused by the slab profile, does not circumscribe the lens use to Canon EOS, as the following image shows:

 

 

Here are some camera bodies I have applied to the Mirotar with modified mount: Nikon F2AS, Contax ST, Pentax MX, Canon F1 new and Icarex S 35 TM, all with adapters from 42x1mm screw to the corresponding  camera bayonet (without field lens for the Nikon, not necessary), except the Icarex that, of course, fits exploiting the native 42x1mm mount. In this way the Mirotar becomes a popular national instrument that crosses transversely, and happily, the cameras factions.

 

 

...and here is the reason for which it was adopted a ring with microchip: the Canon Extender EF 2x II is a good focal extender but incorporates a chip which corrects the resulting focal lenght and aperture parameters in the metadata transmitted to the camera body; whereby, in absence of the prime lens chip, the doubler provides an error which physically prevents the unit to shoot, also manually. In this case we got a 1000mm lens with a relative aperture f/9 and an effective value around T = 9.5.

The following image is a reproduction of the first test shot made with the Mirotar 500mm f/4,5 applied to a Canon EOS 5D MkII, taking from about 2,3 km away in a day characterized by winter mist and therefore unsuitable to squeeze the 100 % of the lens' performances ... The image and its 100% crops show, however, that the strange adaptation between a catadioptric lens built just 50 years ago (1963 - 2013) and a modern full-frame digital SLR camera works perfectly.

 

 

To end with flourish, I would like to describe another Mirotar version produced by Zeiss for mere military and surveillance uses: it is the famous Carl Zeiss N-Mirotar 210mm T = 0,03, a lens produced since 1977 in just 43 pieces and characterized, on his debut, by a really stratospheric selling price, next to the 50,000 U.S. Dollars.

the N-Mirotar 210mm (where N stands for-Nacht-or Night) is an extremely sophisticated instrument consisting of a fast, catadioptric primary lens of 210mm focal length, a system with 3-stage image intensifiers, cascaded, connected by optical fibers, and a rear relay lens composed by a telecentric tandem of 2 objectives, the first inverted in front of the second, which pick up the intensified image from the fluorescent screen placed behind the series of intensifiers and focus it on the focal plane of the camera.

Credits: for all the following pictures the  N-Mirotar 210mm was kindly supplied by Ugo Marinelli

 

 

In this picture, along with classic Mirotar 500mm f/4,5 and 500mm f/8 T* lenses for conventional photography, there is also the special N-Mirotar 210mm, born for hand-held night photography thanks to the image intensification; the rear mount is a Contax-Yashica bayonet and this objective, formally, belonged to this system, although it was provided only  on special order and it was necessary, between order and delivery, to wait up to one year . The N-Mirotar features anatomical grip incorporating a trigger that activates the intensifier, powered by dry batteries; the front lens is protected by an unusual soft rubber plug with two waist belt, one of which always anchored to the objective to avoid losing it inadvertently; the phosphors of the intensification system must be protected from direct light, even when the device is switched off, then the cap needs to be kept always in position, except at times when the system is operating.

 

 

Another group picture with these exceptional and rare objectives in which it is clear that the primary lens of the N-Mirotar is a catadioptric, architecture chosen for its compactness, taking into account the space required by the three-stage image intensifier and the corresponding rear relay-lens.

 

 

the N-Mirotar 210mm measures 365mm in length by 98mm in diameter with a maximum height (from the base of the handle to the top of the front frame) of about 222mm; the primary objective has a single front meniscus, on the inner surface of which is placed the secondary mirror, while the two field lenses are positioned in the hole of the primary mirror, making the system very compact, and their displacement allows the focus, managed by an external lever: the focus ranges between infinite and 20m , a considerable distance that limits the use of the N-Mirotar to long range surveillance. The primary objective has a focal length of 210mm and its actual brightness has never been officially declared: some sources referred even f/1,2 but, quotas in hand, the theoretical aperture should be around f/2,5 and the actual one, taking into account the central obstruction, in the range of  f/3 - f/3,2.

The image produced by the catadioptric 210mm lens is captured by the cascaded intensifiers, consisting of 3 modules connected by optical fibers, which provide to intensify the light a total of 80.000 times; the image produced by the intensifier, now reduced to a monochromatic yellowish-white vision, is displayed on a circular screen from which it is focused by a rear relay-lens, a kind of macro lens actually consisting of a tandem of cascaded objectives, projecting it on the focal plane of the Contax camera; this couple of objectives, with the first inverted in front of the second, has certainly been inspired by similar systems used in the old X-ray diagnostic apparatus, in which the faint image of the fluoroscope is captured by a lens and telecentrically projected towards a second objective that provides to focus it on a video tube: also in this case the two objectives, usually fast, are mounted with the rear lenses that face the screen source and the final output, exactly as in the N-Mirotar.

If we look at the architecture of the schemes, we can easily recognize in the two modules of the relay-lens an inverted Planar combined with a Sonnar type; since in the cascaded and reversed objectives, usually, it is suggested to use a secondary lens with focal lenght approximately twice than the reversed primary objective, if I was naughty I could almost assume that at Zeiss, to save time and money designing an objective that had been planned for a limited production, they could have simply combined a Contax Planar 50mm f/1,4 with a Contax Sonnar 100mm f/3,5, which diagrams, from what we can guess from the graphics, are virtually identical to those of the two modules at the rear of the N-Mirotar.

The final image is monochromatic and covers a 30mm circle (therefore, it impresses only partially the 24x36mm format, like some fisheye lenses), with a field angle of about 8°; the maximum brightness of the lens, of course, is difficult to quantify, nevertheless Zeiss data claim that the gain with respect to an f/1,4 aperture is about 2.500x, which means 11 f/stop, corresponding to a luminance of  T = 0,03, which allows to work at night without lights support; in fact, using a 400 ASA - 27° DIN film, with full moon (10^-1 lux) it was possible to shoot at 1/500", with a quarter moon (10^-2 lux) with 1/60" and moonless, in the glow of the stars (10^-3 lux), with 1/4"; of course, the final image is not figurative tout court, showing a low resolution and flattened tones but it is highly effective for the intended purpose.

 

 

The focus is ensured by an external lever, folding and provided with a recess for the finger, which slides in a slot of the objective, moving the inner field lenses; of course is not present a reference scale and an accurate focus is anatomically difficult, but in this case it was privileged the ergonomics and easy to use in predictably difficult and hectic situations; next to the focus lever is also visible the rugged fastener for the soft rubber cap.

 

 

The N-Mirotar, by reason of its highly specialized use and its breathtaking price, was produced in extremely limited runs and the main customers were the intelligence agencies; even the specimen in question, the sixth produced in 1980 on a lot of 10 pieces, was initially provided to some U.S. agency or Government organization and subsequently declassified and sold as a no longer needed surplus, but on the barrel remained stickers that bear witness to the original destination ("property of the Government of the United States") and the related bar codes and pin number. In detail can also be appreciated the main switch with three positions (turned off, always on, switched on manual activation) and its trigger; to compact the system the handle can be removed through the metal ring visible in the picture.

As mentioned, the official production was of 43 pieces, as follows: 10 examples between serial numbers 6.081.404 and 6.081.413, 10 units ranging between 6.145.956 and 6.145.965; 10 specimens between 6.280.369 and 6.280.378; 7 units between 6.578.727 and 6.578.733 and 6 pieces included between the serials 6.845.788 and 6.845.793, all fitted with Contax-Yashica bayonet mount.

 

 

The barrel that incorporates the rear tandem relay objectives is easily removable, allowing you to inspect the screen on which the series of intensifiers project the image and on whose surface the secondary objectives focus; one can not overlook the fact that this lens constitutes the ultimate epigone of similar systems designed at the end of the war for the armed forces of the Dritten Reich and identified by the name "project UHU": in this case there was a very fast front lens combined with an active infrared projector (or for passive action, if they were following thermal tracks), an high voltage cathode ray tube, which transformed the infrared into a visible fluorescent image, and a secondary optical system which allowed to view it easily.

The N-Mirotar was powered by two common 1,5v "AA" dry cell batteries, placed at the connection point between the barrel and the handle, in a compartment accessible by removing the screw shown in the photo with a coin; the claimed range for a set of batteries is about 30-40 hours of continuous operation, so pretty good.

On request were available two accessories for direct vision (applicable in place of the rear barrel bearing the secondary lenses and the bayonet mount) and much more compact: monocular the first and binocular, with separator prism, the second: personally I've never seen a single live exemplar.

 

 

The N-Mirotar was delivered in a suitcase; in our exemplar are still present government stickers identifying the contents, with their pin numbers: a Contax 137 MA Quartz and a NVD (acronym for Night Vision Device) Zeiss N-Mirotar. The central sticker is interesting, because it says "demonstration model", perhaps a sample used to train specialized operating men and therefore not used on the field, which justifies its good state of preservation; the inscription referring to the completely reconditioned camera body probably indicates a subsequent overhaul carried out before the disposal of the kit for the sale.

 

The interior of the case shows the shaped padding and other elements of the kit, such as a still sealed shoulder strap and the keys to the case locks, certainly a not too effective defense in a world of intelligence professionals...

After this long and hopefully exciting sharing, is evident as the articulated Zeiss production, in all its corporate forms, is relevant not only in numbers but also extremely differentiated, a vast sea with many inlets still unexplored and within which lie, as we could ascertain, true pearls of great interest for technological contents, performances, specialized application areas and, why not?, also the mere appeal for collectors.

Best wishes to you all.

(Marco Cavina)

(Texts, equipment, photographs and graphics by Marco Cavina, unless otherwise indicated)

 

 

CONTACT              PHOTOGRAPHIC  TECHICAL  ARTICLES