LENKINAP OKS1A-75-1 F = 75 1: 2 P. Review of a film lens adapted for SLR cameras by Rodion Eshmakov

Material on the lens especially for Radozhiva prepared Rodion Eshmakov.

LENKINAP OKS1A-75-1 F=75 1:2 P

LENKINAP OKS1A-75-1 F=75 1:2 P. increase. View of the adapted lens from the side of the front lens.

For the lens provided for review, I thank Andrey Andrey (inst .: entomolog99).

OKS lenses belong to the Soviet line of professional filming optics like the modern Zeiss Compact Prime. The manufacturer of these lenses is LOMO or its predecessors - LOOMP and Lenkinap. In the USSR, there were other filming lenses: for example, RO seriesproduced at KMZ.

OKS optics uses a peculiar notation system of 3 numbers - OKS K-LL-M, where K denotes the type of optical design, LL is the focal length of the lens and M, probably due to the features of the mechanical design. For example, OKS75-1-75, OKS1-2-75, OKS1-4-75 and OKS1-6-75 are known with a focal length of 1 mm - all these lenses have different optical designs. However, this does not mean that OKS1-22-1 will have an identical optical design.

Currently, OKS optics are highly valued in the secondary market due to the "convenient" parameters and the myth of the high optical quality of these lenses and outstanding artistic performance.

This article presents an early OKS1A-75-1 manufactured by Lenkinap. The marking indicates that the lens was produced before 1962 (the year LOMO was formed). The meaning of the letter A in the name of the lens is unknown to me.

According to Yakovlev's handbook (1970), the OKS1-75-1 lens has the following

Specifications:

Optical design - 6 lenses in 4 groups ("Helios" / "Planar");

Schematic optical diagram of the OKS1-75-1 lens. Overlay of the first and second lenses - a typo in the catalog.

Schematic optical diagram of the OKS1-75-1 lens. Overlay of the first and second lenses - a typo in the catalog.

Focal length - 75 mm;
Relative aperture - 1: 2;
Estimated frame format - 16 × 22 mm;
Field of view angle (for the calculated frame) – 20.5°;
The back section is 48.84 mm;
Light transmission coefficient (not less than) - 0.75;
Aperture - 16 blades, no preset mechanism, adjustment without clicks;
Thread for filters - 45 × 0.5 mm;
Mass - 238

Geometric parameters of the OKS1-75-1 lens body.

Geometric parameters of the OKS1-75-1 lens body.

Despite the fact that OKS1-75-1 is designed for cameras with a frame size of ~APS-C, it easily covers the 44×33 mm frame of modern medium format cameras due to the large light diameter of the rear lens group. It is very likely that OKS1-75-1 is a modernization of one of the early Soviet lenses GOI Helios-2 1937.

Helios-2 lens card in the GOI 1963 catalog

Helios-2 lens card in the GOI 1963 catalog

In any case, OKS1-75-1 uses ordinary brands of optical glasses without the use of lanthanum or thorium, that is, it is made at the level of technology of the 40s.

Design and adaptation features

I got the lens for review already in an adapted form: the lens block was installed in a handicraft focusing mechanism of unknown origin, a macro ring with an M42 thread was used as a shank, the aperture control was made by a separate ring. The scales printed on the body parts have nothing to do with this lens.

Alteration of OKS lenses is a trivial task, since setting the aperture in them is not required and it is enough just to choose a suitable focusing mechanism, for example, a Chinese macrohelicoid. Lenses with a focal length of 75 mm or more, due to the large rear distance, can be mounted on full-frame SLR cameras, and some of the shorter focal length lenses (OKS1-50-1, RO3-3M, OKS11-35-1, OKS3-22-1) - on APS-C SLR cameras.

View of the adapted OKS1-75-1 lens.

View of the adapted OKS1-75-1 lens.

OKS1-75-1 lenses are coated with a pale blue coating, which is very typical for LOMO lenses (both film and projection lenses). A very similar coating was used by German lenses Carl Zeiss Jena 40s - 50s. Soviet photo optics, as a rule, had a brighter antireflection coating, which significantly distorted the light transmission spectrum.

All objective lenses have a pale blue AR coating.

All objective lenses have a pale blue AR coating.

However, this OCR also turns noticeably yellow, since the contribution of the blue coating to the transmission spectrum is not compensated in any way.

View of the lens through.

View of the lens through.

A distinctive feature of OKS optics is a multi-blade diaphragm, which is round at any f-number. In OKS1-75-1, the diaphragm has 16 petals. Unfortunately, the petals do not have a matte finish and introduce reflections when photographed.

View of the OKS1-75-1 closed diaphragm from the side of the front lens.

View of the OKS1-75-1 closed diaphragm from the side of the front lens.

Thus, the OKS1-75-1 design is very simple and can be used on almost any modern system after a simple modification - the adapted lens is comparable in size and parameters with Jupiter-9 85/2.

Optical properties

OKS1-75-1 seems to use a very old double Gaussian type optical design with 6 lenses in 4 groups without the use of any special materials (highly refractive lanthanum or phosphate low dispersion glasses) and has poor image quality at an open aperture. In the central region of the field, a noticeable effect of spherical and chromatic aberrations can be noted. The edges of the frame are affected by coma. With aperture up to F/2.8, the image quality in the central part becomes very good, and the corners of the 36x24mm frame come in order to ~F/5.6. It seemed to me that the projection lens I had previously LOMO J-53 75/2 demonstrated a significantly higher image quality both at long and short distances.

The lens covers the frame without problems up to 44×33 mm, which allows it to be used on Fujifilm GFX medium format cameras and shift adapter on full frame cameras.

The image contrast is average, among similar optics with a single-layer coating there are clearly best samples. The resistance to glare and veiling in backlight is weak: even the lens hood that came with the lens did not help much to avoid flare. However, it can be successfully used as an independent visual medium.

Unlike Zh and RO projection lenses, the filming OKS1-75-1 has a characteristic "helios-like" bokeh: the focusing disks have a bright edge and flatten from the center to the edge into "lemons". The influence of coma and astigmatism distorts the symmetry of the out-of-focus spots at the edge of the lens field, which leads to the appearance of a bright border on the side of the spot closest to the axis and to the deviation of the symmetry from elliptical - this enhances the effect of the “swirl” of the background and gives the effect of “scales”. As a rule, such blurring of the background has not very high-quality optical lenses - Helios-65, Helios-40, Pentacon 50 / 1.8, Boyer Saphir 75/1.9.

The following are sample photos taken with a full-frame mirrorless camera. Sony A7s. Some of the pictures were taken using a shift adapter Fotodiox Pro Shift EOS-NEX – These pictures have an aspect ratio other than 3:2.

Also examples of photographs on the lens using a medium format camera Fujifilm GFX50S shared the owner of the lens Andrey Andreev (inst.: entomolog99).

All reviews of film projection and filming lenses:

  1. RO3-3M 2/50
  2. RO2-2M 75/2
  3. LOMO RO501-1 F = 100 1: 2
  4. PO 500-1 F9 CM. 1: 2 P
  5. LOMO RO500-1 F = 90 1: 2
  6. LENKINAP RO500-1 F = 9cm 1: 2 P
  7. LOMO RO506-1 F = 80 1: 2
  8. ЛЭТИ-60/60М F=92 1:2
  9. 2/92
  10. F = 92 1: 2
  11. 16KP-1,4 / 65
  12. 35KP-1,8 / 65
  13. 35KP-1,8 / 70
  14. 35KP-1,8 / 75
  15. 35KP-1,8 / 85
  16. 35KP-1.8 / 100
  17. 35KP-1.8 / 120
  18. 35KP-1,8 / 120 (with aperture)
  19. LOMO P-5 F = 90 1: 2
  20. LOMO P-5 F = 100 1: 2
  21. LENKINAP OKS1A-75-1 F=75 1:2 P
  22. LOMO OKS1-22-1 F = 22 1: 2.8
  23. ЛОМО ОКС1-40-1 40/2.5
  24. LOMO OKS1-300-1 F = 300 1: 3.5
  25. LOMO OKS11-35-1 F = 35 1: 2
  26. LOMO W-53 F = 75 1: 2
  27. LOMO W-54 F = 85 1: 2
  28. LOMO OKP4-80-1 F=80 1:1,8
  29. ОКП-6-70-1 F=70 1:1,8
  30. Tair-41 50/2
  31. KO-120 1: 2,1 120mm
  32. KO-90 1: 1,9 F = 9cm
  33. KO-120M 1: 1.8 F = 120mm
  34. KO-120M 120 / 1.8 with a diaphragm and helicoid
  35. KO-120 1: 2.1 F = 12cm
  36. GOZ “KO-140” 1:2,2 F–14cm
  37. Vega-9 2,1 / 50
  38. MP RSFSR GLAVOCHTEKHPROM PLANT №6 ★ F=7.7cm ★
  39. MSO USSR SSD UPP-1 ★ KHARKIV ★ F-7 CM ★
  40. Schneider Super Cinelux 70/2
  41. Meopta Meostigmat 90/2
  42. Meopta Meostigmat 100/1.7
  43. RO2-2M 75/2 VS LOMO Zh-53 75/2 VS LOMO RO506-1 80/2
  44. Projection aplanates: "Petzvali" and "Richter"

The names of the lenses correspond to their exact spelling on the body.

Conclusions

My impressions of the OKS1-75-1 75/2 are mixed: with a mediocre image quality, the lens still has a pleasant and recognizable pattern. But there is the same mediocre and brighter in the picture, more aperture Helios-40 85/1.5, the cost of which in the secondary market is sometimes lower (even for the new version with multilayer enlightenment) than that of OKS1-75-1. Even ultra-cheap Helios-44-2 with a focal length of 58 mm, which gives absolutely magical results in capable hands, can be considered as an alternative with a stretch. And, of course, do not forget about the many high-quality Soviet projection lenses such as W-53, 35KP-1.8 / 75 и PO500-1, whose lens blocks are very, very affordable and easily adaptable to modern cameras. In general, OKS1-75-1 is not something about a special picture and not about quality, but rather about nostalgia and the “spirit of cinema”.

You will find more reviews from readers of Radozhiva here.

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Comments: 5, on the topic: LENKINAP OKS1A-75-1 F = 75 1: 2 P. Review of a film lens adapted for SLR cameras, from Rodion Eshmakov

  • B. R. P.

    Thanks for the review, Rodion, interesting glass, good photos. In the portraits, the model has a too conspicuous highlight on the forehead. Ask girls to “nail” such things with powder, for example.

    • Rodion

      In a good way, I had to nail it myself in Photoshop, if we talk about it ...

      • B. R. P.

        Or like this)

  • Yuriy Molchanov

    And I really like the drawing, although maybe it's all the skillful hands of the photographer. I hope someday I will be able to do something similar with my own hands. I already collect aluminum pipes.

  • Azatbek

    I got the Lomo oks1-75 lens. and tightly attached to the carcass of the film Olympus. I don’t understand how to remove it and the aperture ring does not rotate. also the lens hood. or it is fixed and cannot be removed in any way. but it gives a strange look.

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