Review of Petzval's adapted film projection lens LOMO P-6M F=12cm 1:1.6

Material especially for Radozhiva prepared Rodion Eshmakov.

Adapted LOMO P-6M 120/1.6.

LOMO P-6M 120/1.6 is an aplanat cinema projection lens made according to the Petzval scheme. All lenses of the P-6, P-6M series have a relative aperture of 1:1.6 and are much less common than P-5 lenses with a relative opening of 1:2. The P-6M 120/1.6 lens was intended for 35 mm Kolos-type film projectors. True, given the gigantic size of the lens, I would add one “s” to the name of the projector.
The P-6M lenses are of interest as, perhaps, one of the fastest Petzval lenses that can be found. This review presents a version of the LOMO P-6M 120/1.6 lens adapted for mirrorless cameras. I thank Andrey Andreyev (inst: entomolog99) for the lens unit provided.

Technical characteristics (“Catalog. Lenses”, A.F. Yakovlev, edited by D.S. Volosov, 1970, vol. 1, pp. 373-374):

Optical design – 4 lenses in 3 groups, Petzval lens;

Drawing of the optical design of the LOMO P-6M lens.

Focal length - 120 mm;
Relative aperture - 1: 1.6;
Estimated frame size – 15.2 x 21 mm, covered ~60 x 60 mm;
The back focal segment is 56.1 mm;
Landing diameter - 82.5 mm;

Lens dimensions LOMO P-6M 120/1.6.

Weight - 1360 g;
Features: projection lens, does not have an iris diaphragm, a focusing mechanism or attachment to the camera.

Design and adaptation

The lens consists of two “halves” in brass frames, screwed into a steel tube body. The front glued component and the third lens are rolled into the frame, the rear lens can be removed. The lens glass has an anti-reflective coating of a violet-pink hue, while the P-6M turns yellow when exposed to light. The light protection of this lens is sad: the space between the lens elements is poorly blackened and very shiny. To obtain at least an acceptable level of contrast, it is necessary to install a ribbed light-cutting sleeve with a matte black finish. In addition, a deep lens hood is very useful for the lens.
LOMO P-6M 120/1.6 is not easy to adapt for shooting with modern cameras, especially SLRs, due to the huge size of the body and the relatively small rear segment. Same as lens adaptation ОКП8-90-1 90/2, I used a low quality lens body like Samyang 500 / 6.3, since the Chinese still don’t make inexpensive ones helicoids for bore diameter 82.5 mm.

Another problem during remodeling is the selection and installation of the iris diaphragm. It is almost impossible to get apertures with a diameter of more than 65 mm, and in this lens, it is likely that it should be located closer to the front lens, which has a light diameter of ~75 mm. Even if the required diaphragm is found, its installation will be complicated by the need alterations of the body itself lens block, there will be problems with the drive output when using a focuser from a 500/6.3 reflex lens. In general, a fully competent adaptation of the P-6M 120/1.6 requires excessively large investments, so a compromise was found with the installation of a fixed lens diaphragm with a diameter of 65 mm in a shank with an M65×1 thread. The choice of M65×1 thread is due to the availability of inexpensive adapters M65-GFX for use with Fujifilm digital medium format cameras. For use with my camera, a special M65-M42 adapter was also made, which, together with a thin ring M42-NEX provides the required working distance for the Sony E system.

The main disadvantage of the described adaptation method is the dual-functioning diaphragm. Being located in the wrong place for this lens, the iris diaphragm restricts the edge beams to a greater extent than the central one, increasing the vignetting of the lens during use and thereby influencing the nature of his drawing. However, even such an aperture is very useful for the lens.

Below are photos of the adapted lens.

LOMO P-6M is very large and heavy, especially when compared to something like KO-140 140 / 2.2. Despite the size and weight, focusing with this lens is not that difficult thanks to the ergonomics of the body Lightdow 500 / 6.3.

Optical properties

LOMO P-6M 120/1.6 is the most “soapy” of all the lenses I have ever owned, not counting the projection one periscope "Glavuchtekhprom". The level of spherochromatic aberrations at an open aperture is simply monstrous; the difference in the focus position for blue and red rays at an open aperture is measured not in tens or hundreds of microns, but in millimeters. The level of astigmatism outside the ~APS-C frame is incredible - at medium-long focusing distances it is not always clear whether it was a focus error on an object at the edge or whether the lens itself is so “good”. And yes, usually it’s the lens itself – suitable only for the central composition.

The aperture allows you to solve, to a greater or lesser extent, problems with optical quality, but, being behind the lens, it also introduces vignette, as can be seen in the examples below.

The image contrast, even after adding light protection, leaves much to be desired. The lens is very afraid of backlight and side light. Apparently you need a good lens hood.
LOMO P-6M 120/1.6 gives a specific expressive bokeh, practically devoid of twisting at an open aperture (if vignetting was not introduced during adaptation). Due to the colossal level of spherochromatic aberrations, each bokeh disk in the central region has an orange bright edging (highest spherical aberrations + chromatism) and a bright region in the center (3rd order spherical aberration). At the edge of the frame, discs may develop tails due to high levels of astigmatism.

The following are examples of shots taken with a full-frame mirrorless camera. Sony A7s. The photographs were, in most cases, significantly enhanced to increase contrast when developed RAW.

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 + Review, analysis and comparative test of the adapted projection lens 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. LOMO P-6M F=12cm 1:1.6
22. LENKINAP OKS1A-75-1 F=75 1:2 P
23. LOMO OKS1-22-1 F = 22 1: 2.8
24. ЛОМО ОКС1-40-1 40/2.5
25. LOMO OKS1-300-1 F = 300 1: 3.5
26. LOMO OKS11-35-1 F = 35 1: 2
27. LOMO W-53 F = 75 1: 2
28. LOMO W-54 F = 85 1: 2
29. LOMO OKP4-80-1 F=80 1:1,8
30. LOMO OKP8-90-1 F=90 1:2
31. ОКП-6-70-1 F=70 1:1,8
32. Tair-41 50/2
33. KO-120 1: 2,1 120mm
34. KO-90 1: 1,9 F = 9cm
35. KO-120M 1: 1.8 F = 120mm
36. KO-120M 120 / 1.8 with a diaphragm and helicoid
37. KO-120 1: 2.1 F = 12cm
38. GOZ “KO-140” 1:2,2 F–14cm
39. Vega-9 2,1 / 50
40. MP RSFSR GLAVOCHTEKHPROM PLANT №6 ★ F=7.7cm ★
41. MSO USSR SSD UPP-1 ★ KHARKIV ★ F-7 CM ★
42. Schneider Super Cinelux 70/2
43. Meopta Meostigmat 90/2
44. Meopta Meostigmat 100/1.7
45. RO2-2M 75/2 VS LOMO Zh-53 75/2 VS LOMO RO506-1 80/2
46. Belar-2 2,5/90 (MMZ). Review of a rare slide projection lens adapted for modern cameras
47. Projection aplanates: "Petzvali" and "Richter"

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

Conclusions

LOMO P-6M 120/1.6 is “aperture ratio for the sake of aperture ratio.” It is difficult to say how useful the lens was in general even when used for its intended purpose - obviously, Petzval’s use scheme without modern materials is completely inadequate for such parameters. Adapting a lens is difficult, it’s hard to wear, and when shooting with an adapted lens on a small-format camera, it’s difficult to get a sane result. All this makes P-6M lenses attractive only to a narrow circle of enthusiasts. It seems much more appropriate to use aplanate lenses with more moderate parameters - P-5 90/2 or KO-120 120 / 2.1.

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