Review of the format reproduction lens OF184m 1:9 F=15cm P (Industar-11M, LZOS, 1959)

Material on the lens prepared especially for Radozhiva Rodion Eshmakov.

OF184m 1:9 F=15cm (hereinafter referred to as OF-184M) belongs to the line of Soviet reproduction lenses of the type Industar-11 F/9, developed in the 1940s on the basis of the German Carl Zeiss Jena Apo-Tessar (literally - "Tessar-apochromat") F/9 lenses from the 1930s. Industar-11 lenses were available with focal lengths from 150 to 1200 mm, and all of them had a field angle of about 40 °, that is, they were intended for large format. The longest focal length versions have a very large frame size and are also very rare, and therefore are of great interest to both collectors and large format shooters. And the shortest focal length lens in the series was never produced under the name Industar-11: it can be found as OF184 (KMZ, GOI), OF184M (LZOS) or OB-56 (LOMO). This article is dedicated to the OF-184M lens, produced in 1959 at the Lytkarino Optical Glass Plant.

Specifications:

Optical design – 4 lenses in 3 groups (1 element made of glass with anomalous dispersion – special flint), “Tessar”;

Focal length - 150 mm;
Relative aperture - 1: 9;
Aperture - 12 blades, stepless;
Aperture limits - 1: 9-1: 32;
Calculated field of view angle – 35°;
The calculated field diameter is 95 mm, the actual frame covered is 10×12.5 cm;
Estimated shooting scale – 1:5;
Resolution for the calculated field size (center/edge) – 100/100 lines/mm (unibrom photo paper No. 3);
Back section – ~145 mm;
Mounting thread – M39×0.75 mm;
Weight – ~80 g;
Features – reproduction lens, does not have its own focusing mechanism and camera mount.

 

Design and adaptation

The OF-184M lens body is made of brass, so it has a noticeable weight for its size. The slotted nuts holding the lenses are secured with screws for reliability, which is rare in Soviet photo lenses. The lens itself is enclosed in metal frames, meaning the lens has a precise autocollimation assembly. The lens frames do not dangle in the body, so there are no questions regarding the quality of assembly and adjustment.

The only moving element in the lens is the aperture, which is controlled by a single ring without clicks. The shape of the aperture opening is almost round due to the presence of 12 blades. Unfortunately, they are not matted and are quite shiny. However, with a maximum aperture of F/9, you will hardly want to stop down the lens.

The lens optics have a single-layer anti-reflective coating with a pronounced violet glare. This is probably a chemically applied (spin-coating) SiO2 gel - as on many other Soviet lenses. When held up to light, the OF-184M is noticeably yellow.

The lens is pointless but easy to use on any modern camera - for this you will need an M39-M42 ring, which can be screwed onto the M39×0.75 thread of the lens by one or one and a half turns, a Chinese macrohelicoid of the M42-M42 25-55 mm type, a set of M42-M42 macro rings and an adapter from the M42 thread to the desired system. It is also easy to install the OF-184M on large-format cameras. Thus, the lens easily fits into the shutter of the Copal Press No. 1 type. Given the size, the OF-184M can be a small-sized standard lens for folding cameras 9×12 or 4×5”.

Industar F/4.5 vs Industar F/9: Why make a new one if you can stop down the old one?

Among the Industar type lenses in the USSR, as is known, there were many alternatives with a focal length of 150-300 mm and more aperture – up to F/3.5. This leads to a logical question – was there any point in producing a separate line of optics with low aperture, or it would be possible to stop down the aperture with the same success for lenses like Industar-55U 150 / 4.5, eg?

In order to find an answer to this question, I have modeled in Zemax the optical properties of the standard format lens Industar-37 300/4.5, the scheme of which is available to me. Then the calculation of the lens with the parameters 300/9 2w=50° was made using the optical materials specified in the GOI catalog for OF-184M, with the same or more stringent restrictions of the design parameters. The optical quality of the calculated and original lenses at F/9 was compared by analyzing the diagrams of aberration spots, aberration graphs and the frequency-contrast characteristic (MTF) for the visible spectrum region of 400-700 nm (~CMOS RGGB). The results are given below.

The graphs show that at F/9, the Industar-37 lens has greater uncompensated spherical aberration and significantly greater astigmatism and field curvature compared to the calculated Industar-11 analogue. The high level of astigmatism is an obstacle to the Industar-37 lens achieving a good level of image detail across the field. The less fast version of the lens copes much better, as evidenced by the MTF diagrams.

Moreover, at an aperture of F/9, the specially designed lens has a significant advantage in resolving power in the central area of ​​the image: 90 lines/mm versus 60 lines/mm for the Industar-37.

Meanwhile, for the 8×10” (18×24 cm) format, a resolution of 100 lp/mm is a lot. Such lenses, in combination with high-resolution film (such as Mikrat, for example) or a scanning ruler, allow obtaining highly detailed images. For enthusiasts, a lens such as the Industar-11m 300/9 can become the basis for a compact (folding) small-format long-focus lens.

Thus, the calculation of a special line of lenses with an aperture of F/9 for reproduction installations was entirely justified: the existing Industar lenses with a relative aperture of F/4.5, even after recalculation for work at finite distances, would not be able to provide the necessary image quality.

OF-184M – apochromat or not? And Carl Zeiss Jena Apo-Tessar?

Industar-11 lenses (including OF-184M) are analogs of German Carl Zeiss Apo-Tessar, as noted earlier. It can be noted that Zeiss lenses are positioned as apochromats (the prefix "Apo"), while Soviet ones are not. Does this mean that Industar-11 lenses have lost the degree of correction of chromatic aberrations achieved in German Apo-Tessars?

In fact, neither the Apo-Tessar F/9 nor the Industar-11 are apochromatic objectives – astronomers hunting for long-focus APOs can relax. The above diagrams of longitudinal aberration for the Industar F/4.5 and F/9 objectives show that the magnitude of the secondary spectrum is approximately the same for the Industar-11 and Industar-37, and the correction itself corresponds to an achromat.

However, some techniques are used to improve the correction of chromatic aberration in lenses such as Industar-11/Apo-Tessar. For example, the lens design includes OF1 glass, which belongs to the class of special flints. This means that the dispersion of the material in the short-wave region of the spectrum has a strong negative deviation from the usual one. More about optical materials and their application here.

The famous Soviet optician D.S. Volosov in his book “Photographic Optics” notes [pp. 450-451] that in lenses of the Industar-11/Apo-Tessar type, due to the selection of optical materials, the secondary spectrum is reduced by only 15%, which has no practical significance, and Apo-Tessar received its name for advertising purposes.

OF1 glass, according to its parameters, belongs to the crown-flint class and is used in many other Soviet lenses that do not claim to be called apochromats: Industar-22, Industar-50, Jupiter 3, Jupiter 9, Industar-51 (and the rest: Industar-36, Industar-37)…

To obtain a true apochromatic system, the optical scheme must also include special crowns – phosphate or fluorophosphate glasses with a strong positive deviation of dispersion in the short-wave region of the spectrum – and the following condition must be met: the difference in the Abbe numbers (dispersion of the glasses) of crowns and flints must be no less than 16 [D.D. Maksutov, “Astronomical Optics”, 2nd ed., pp. 225-237]. In the OF-184 objective under consideration, this difference is only 12, and not even for “anomalous” glasses, and therefore there is no talk of any apochromatic correction.

Optical properties: small format

On a digital small format camera, the lens demonstrates excellent sharpness without compromises with an open aperture. However, the open aperture of this lens is F/9. Aperture OF-184M is 2.8 times smaller than the typical F/10 for a small format lens with such a focal length! However, leading manufacturers of optics for modern mirrorless cameras also offer "dark" lenses.

The image contrast depends greatly on the adaptation method. It is highly desirable to have light-cutting diaphragms behind the rear lens in the space between the lens and the camera and high-quality blackening. The lens would also benefit from a hood. I used the lens without a hood, attaching it to the camera using a set of macrohelicoids and macro rings, additionally blackened with soot. Light cutters and a hood were not used. The image contrast was not high - better than that of old uncoated optics, but worse than that of regular telephoto lenses like the Jupiter-11.

OF-184M has an anti-reflective coating for the visible region with a transmission peak at 550 nm (green-yellow). The coating noticeably distorts the transmission spectrum, although the camera usually copes with the installation white balance. Due to the absence of heavy glass (lead flints), the short-wave light transmission limit is at ~330 nm. Thus, the lenses of the Industar-11 family are well suited for shooting on blue-sensitive photographic materials or even in the UV range.

Due to the high degree of correction of aberrations, the lens has a smooth, uniform bokeh across the entire frame from regular disks with an indistinct bright edging. The bokeh is less expressive than that of another similar, but even older lens 150/8 aplanatic objective, but the sharpness of the OF-184M is much better.

The following are examples of photographs taken with a full-frame mirrorless camera. Sony A7s.

The lens is also suitable for use with tilt-shift adapter or for medium format cameras such as Fujifilm GFX with 44×33 format. Photos taken with the adapter Fotodiox EOS-NEX on Sony A7s are presented below.

OF-184M as a standard lens for 4x5” cameras

Andrey Kulikov helped me test the OF-184M lens on a Linhof Technica 4×5” film camera (Instagram: andros__zz). The lens was installed in the Copal Press No. 1 shutter simply by friction.

Some of the pictures were taken on blue-sensitive sheet film for X-ray machines, which has a low resolution. They were exposed and developed as a film with a sensitivity of 100 units, the developer was metolal.

One successful shot was also taken with panchromatic sheet film Fomapan 400. Developer – Rodinal.

The OF-184M lens provides a sharp image across the entire field and in the 4×5” format, which is significantly larger than the calculated one, even when used at long distances, for which the lens was not originally designed. At the same time, even when shooting a full-length portrait, you can achieve a noticeable separation of the subject from the background. The lens bokeh is uniform across the entire field.

Conclusions

OF-184M is an exotic vintage lens, which is mostly of historical interest. However, if desired, it can be used to shoot on small-format cameras, producing sharp images. The most promising scenario for using the lens is as a standard lens for 4×5” (or 9×12 cm) cameras, or for its intended purpose – as a photo enlarger/reproduction lens for film and photo paper.