Modification of Tair-3 1:4,5 F=30 cm (KMZ), adapted for medium format cameras. Analysis of the optical design of "Tair"

Material on Tair-3 especially for Radozhiva prepared Rodion Eshmakov.

Tair-3 1:4,5 F=30 cm (hereinafter referred to as Tair-3) is a long-focal lens for small format cameras, produced at KMZ and ZOMZ in various versions:

• Tair-3 1:4,5 F=30 cm P, KMZ - technical version of the lens, without a focusing mechanism;
• Tair-3 1:4,5 F=30 cm, KMZ, “Grand Prix Brussel” - option for Zenit cameras with M39 or M42 mount (presented in this article);
• Tair-3 4,5/300A (Tair-3A), ZOMZ – option for SLR cameras, has a replaceable “A” type shank, usually equipped with a shank for M42 thread;
• Tair-3-FS 4,5/300, KMZ – version for the Photosniper photogun, two possible color schemes (white и black ), special focusing mechanism, replaceable shank type “A”, usually equipped with a shank for M42 thread;
• MC Tair-3S 4,5/300, KMZ – a late version of the lens for the “FS-12” photo gun, multi-layer coated optics, a special focusing mechanism, a replaceable “A” type shank, usually equipped with a shank for M42 thread;
• Exotic technical options: Tair-3N and Tair-3T - versions of Tair-3 1: 4,5 F = 30 cm P with modified lens mounts and anti-reflective coating.

This review is dedicated to the first production version of the Tair-3 lens, designed for small format SLR cameras - Tair-3 1:4,5 F=30 cm, KMZ, "Grand Prix Brussel" - but adapted by an unknown craftsman for use with medium format cameras with a Pentacon mount Six.

Specifications:

Optical design – “Tair”, 3 lenses in 3 groups (doublet with meniscus field corrector);

Focal length - 300 mm;
Relative aperture - 1: 4,5;
Aperture – 16 blades, stepless adjustment;
Aperture limits - 1:4,5 - 1:22;
The minimum focusing distance is 3 m;
Thread for light filters – M72;
Mounting to the camera (factory version) – M39 thread or M42 thread;
Features: There is a rotating tripod socket.

Optical design "Tair": educational program

The Tair optical design was patented (SU 78122, November 3.11.1944, XNUMX) by a famous Soviet optician David Samuilovich Volosov in 1944, although it was probably invented a little earlier, judging by the known examples of the lens of a photographic gun intended for reconnaissance, the FS-2 300/4.5, produced in 1943.

As indicated in the title of the patent, the lens is a combination of two elements previously known to optics - a two-lens achromatic doublet, which itself is very often used as a lens for binoculars and telescopes, and an almost concentric meniscus corrector with near-zero optical power, already used to correct curvature fields in Petzval projection lenses and aplanate microscope lenses.

Perhaps D.S. Volosov was not the first who came up with the idea of ​​combining an achromat doublet with a corrective meniscus - due to the simplicity and obviousness of this idea, however, he was definitely the first who was able to take into account the emerging technological nuances of this arrangement: 1) in Tair lenses the meniscus is made with a sufficient deviation from concentricity, so that it can be manufactured quite easily; 2) the distance between the doublet and the meniscus in the lens is chosen so that the total length of the lens system does not exceed 150 mm, which allows for sufficient accuracy of the mutual centering of the lenses during assembly. Subject to compliance with the specified technological requirements D.S. Volosov achieved excellent correction of field aberrations for an impressive field size of ~8-10°, thus constructing the simplest possible long-focus anastigmat lens. Moreover, decades later, the authors of the work “The Existence of Local Minima in Lens Design” (DOI: 10.1364/ILD.1990.LMC2) with the help of computer calculations it was shown that the layout of the Tair lens is the most optimal for a three-lens long-focus lens of all possible options.

The Tair lens differs from most similar lenses in that it is a long-focus lens, and not a telephoto lens in the technically correct sense of the word. The difference between these concepts lies in the relationship between the focal length and the total length of the system: a telephoto lens has a total length from the first surface to the image approximately equal to its focal length (in the case of Tair-3 - 96% of the focal length), while a telephoto lens is much shorter its focal length. Refusal of tele-shortening is one of the factors that made it possible to effectively combat the aberrations of such a simple system and provide high performance in comparison with lenses of similar complexity (see Tele-Tessar 1: 6,3 Willi Merthe) aperture 1:4,5.

Let us repeat the main thing once again: with its extremely simple design and the use of the most common optical materials, the Tair type lens is the best possible lens option for small angles of a similar technological level. In other words, until a 10° ~1:4.5 telephoto camera has a dozen lenses, aspherics or low-dispersion glass (which is also accompanied by a more complex design), it will not be able to provide image quality that is fundamentally better in comparison with a “Tair” type lens.

To clearly illustrate this, using optical modeling in Zemax, we will compare the optical quality of the Tair-3 lens and a typical four-element telephoto lens from the GDR patent DD 30118 (15.7.1964) Meyer-Optik with parameters 500/5.6, scaled to 300 mm at a given field of view angle of 10°.

To begin with, we note that the optical design of the 78122/300 lens given in the SU 4.5 patent does not quite correspond to the Tair-3 lens: the shape of the lenses in the latter’s doublet was different, although all the thicknesses and, characteristically, the shape of the meniscus turned out to be the same. According to the simulation data of both lenses, the Tair-3 lens has mutually compensated spherical aberrations of the third and higher orders, while the patented design does not imply such correction of spherical aberration of the higher orders.

The use of mutual compensation of spherical aberrations improves image quality at an open aperture, but leads to some deterioration in quality at smaller apertures. Indeed: the Tair-3 lens at an open aperture has significantly better image quality compared to the version from the patent, incl. better calculated resolution (55 mm-1 versus 50 mm-1). At small apertures, quality is determined more by chromatic aberration than by residual spherical aberration, and therefore lenses behave in a similar way.

lens type Orestegor 500/5.6 from the DD 30118 patent is a four-lens anastigmat, the aperture position of which I had to guess for reasons of lens size and astigmatism correction. By the way, the lens diameters were chosen so that vignetting was no more than in the Tair-3 lens

This telephoto lens has a total length of 89% of the focal length, and, in fact, its optical design is ideologically similar to the Tair lens discussed in this article: the front group of lenses is still an achromatic doublet, and the rear element is nothing more than a split on two lenses there is a correction meniscus, which is clearly visible in the outlines in the diagram.

The length of the German lens from the first to the last lens, equal to 212 mm, looks doubtful. It would be more difficult to center the optics in this lens than in the Tair-3, and if you remember the fact that this lens was actually produced with a focal length of 500 mm, then you only want to sympathize with the GDR engineers.

The German telephoto uses a composite rear meniscus to provide better correction: the positive flint lens Schott F4 617.366 (i.e. n=1.617, v=36.6), oddly enough, serves to correct chromatic aberration due to the large value of the relative partial dispersion in blue range, and the increased number of surfaces makes it possible to combat spherical aberration. Does this give it an advantage over the Tair-3 lens in image quality?

In the central image area, the lens is indeed better than the Tair-3 at wide open aperture. In this case, it is difficult to judge the image quality by the field, since the patent, as a rule, does not provide the final version of the lens calculation, and the arbitrariness of determining the aperture position does not bode well.

It turns out that the Germans managed to shorten the scheme and improve the quality? But no, because the same “open aperture” of this lens is 1:5.6, not 1:4.5. The Tair-5.6 lens, “squeezed” to F/3, behaves better than the German one, which is confirmed by the fact that it is extremely difficult to beat the Tair in terms of image quality without using high-tech optical materials or complicating the optical design.

Now, after realizing the genius of D.S.’s invention. Volosov, let us return to the consideration of its specific instance.

Design and modification of the Tair-3 lens

Tair-3 is made entirely of metal, and therefore weighs much more than modern lenses like 70-300/4-5.6 – this is not a plastic travel lens at all. The large mass, however, reduces the amplitude of hand tremors when shooting and serves as such a “passive stabilizer.”

The aperture ring is located on the nose of the lens, and just behind it, closer to the camera, is the focus ring. Ergonomics up to version Tair-3A I haven't grown here yet. Thus, the focusing ring is narrow and inconvenient, and during focusing, the lens unit of the lens moves rotationally and translationally along with the ring, which makes some convenient focusing techniques implemented with the lens inapplicable Tair-3A, in which the focus ring does not move progressively.

The lens helicoid stroke is also less than that of Tair-3A, as a result of which the MDF is only 3 m, and not 2.2 m, like the later version. For some subjects, 3 meters is too far; I often ran into MDF when working with this lens.

The aperture control of this lens version is single-ring, stepless, without a preset mechanism. It is extremely inconvenient to change the aperture value blindly, without looking up from the sight. The solution would be either a preset mechanism, as in Tair-3A, or step adjustment. However, when changing the aperture it is also very easy to lose focus, so it is better to set the desired aperture before you start sighting. The iris diaphragm mechanism has 16 matte dark blades and always produces a round opening, which is a nice bonus.

The lens has a rotating ring with a tripod foot, which allows you to mount the lens in any desired orientation. The further body part, which had the inscription “Grand Prix Brussel” on it, was lost from my lens when the mount was replaced with a P6 mount by an unknown craftsman. Also, at the same time, the corrugated light-protective bushing of the shank was removed, which is why, when focusing, the highly reflective inner surface of the helicoid was exposed.

In general, this lens has a lot of problems with light protection: in the space between the second and third lenses of the lens there is not a single light cutter, not a single ribbed surface. The smooth anodized walls of the lens block reflect obliquely falling rays of light, thereby causing strong veiling of the image. The solution is to install ribbed bushings made by 3D printing and additionally painted with matte black paint and carbon black. Print-ready models available via link. Installation is carried out after unscrewing the front lens block, secured with three screws.

Bushings can be placed in each cylindrical section of the lens, but when calculating it is important to make their clearance large enough so as not to introduce vignetting into the optical system, especially for the axial beam.

After fixing the bushings with a couple of drops of cyanoacrylate glue, it is advisable to additionally deposit soot on the inner walls of the lens block, which is a much blacker and matte material compared to any paint.

The effect of the modification performed is demonstrated in the next section.

As a result, we can say that this version of the Tair-3 lens is very “raw” in design. The lens has far from the best ergonomics, especially when compared with the late Tair-3A, which in its black lacquer coating feels nothing less than a “Mercedes”; The light protection measures also look unsatisfactory. The fact that this lens received the Grand Prix at the World Exhibition is nothing less than the merit of D.S.’s original optical design. Volosov, but not of a mechanical design.

Optical properties

Tair-3 has moderate sharpness with an open aperture, limited mainly by spherochromatism. Aperture up to F/5.6-F/6.3 allows you to reduce the influence of longitudinal aberrations and significantly improve image quality. On modern high-resolution sensors, the lens will never allow you to achieve pixel-by-pixel detail, but you can get a pleasant experience from working with it when used, for example, with full-frame cameras with sensor resolutions up to 24 megapixels.

As for the image quality across the field, as shown in the earlier diagrams of the frequency-contrast characteristics of the lens, Tair-3 is best suited for cameras of the 36x24 mm format, although it can also be used with cameras of the 44x33 mm format. But on the medium format 6x6 cm, the use of the lens as a regular telephoto is doubtful due to the high level of astigmatism at the edges of the frame. Another thing is that in the 6x6 format the lens will be the equivalent of a full-frame 150/2.3 - which is quite a portrait lens, and the bokeh of Tair-type lenses is always excellent, and beyond the calculated field it’s also quite remarkable.

Despite the fact that the Tair optical design does not control distortion well, even on the 6x6 format its level does not exceed +3.5%.

The contrast of the image formed by the lens directly depends on the quality of light protection. Even a lens hood will not save the situation if everything in the lens block is shiny. So, the lens in the form in which I received it had absolutely no good contrast - the veiling was incredibly strong, and it was simply unbearable to shoot at the slightest hint of backlight. Below are sample photos taken with the Sony A7s and the lens before installing the light protection sleeves. All photographs have been post-processed to increase contrast.

Once the light protection is installed, the lens is simply unrecognizable - even without a lens hood, the image contrast is quite high and rarely needs serious correction. And this is far from the only case when the contrast of the image is determined not by layers of enlightenment, but by the blackening of surfaces, light-cutting diaphragms and light-protective fins. Below are examples of photos on the Sony A7s and the lens after installing the light-protective sleeves.

Conclusions

This version of the Tair-3 lens is not so good due to low usability and the need for independent modification. In general, in terms of optical quality, Tair-3 lenses are not just good, but better in comparison with many other old lenses of the 300/4.5 class. Considering its price on the secondary market, Tair-3 is a very good manual lens for studying the super-television range. I recommend that those interested in this lens pay attention first of all to the option Tair-3A.

You will find more reviews from readers of Radozhiva here и here.