Review of a rare film projection lens of the "Era" type LOMO OKP8-90-1 F=90 1:2

Material on the lens LOMO OKP8-90-1 F = 90 1: 2 especially for Radozhiva prepared Rodion Eshmakov.

The rare OKP8-90-1 90/2 film projection lens, manufactured by LOMO in the 1980s, is designed for use with wide-film projection devices, the frame of which was almost 3.5 times larger in area compared to a conventional film frame close to the APS-format. C. OKP8-90-1 differs from more common OKP3-90-1 90/1.8 lenses of similar purpose and parameters by ~8 times less weight and ~4 times length, which is achieved through the use of a simple and productive optical scheme of the “Era "(about this scheme in detail - here), invented by the Soviet optician D.S. Volosov (patent SU 182360 of 1965). In addition to the OKP8-90-1, the OKP8-100-1 100/2 and OKP6-110-1 110/2 lenses are also known, also made according to the Era optical design and designed for a frame of 70 mm film.

More articles about lenses with the optical design "Era":

• Era-6M 50 / 1.5. Experienced, low-volume lens for Zenith cameras.
• 35KP-1,8 / 65. Film projection lens for 35 mm film.
• Era-12 125/4. Reproductive lens for microfilming.

Technical specifications

Source: Catalog of lenses designed at the GOI, ed. Yakovleva A.F., 1970, v. 2, p. 287-288;
Optical design - 6 elements in 5 groups, "Era", a variation of the "double Gauss" / "Planar" scheme;

Focal length - 90 mm;
Relative aperture - 1: 2;
Field of view angle (calculated) – 34°;
Estimated image size - 22×48 mm, coated - 60×45 mm;
Case diameter - 82.5 mm;

Features - a projection lens, does not have an iris diaphragm and a focusing mechanism.

Lens construction and adaptation

LOMO OKP8-90-1 does not differ in design from narrow-film film projection lenses with a bore diameter of 82.5 mm, type RO503-1 120/2. The lens body is a tube in which two slotted nuts (in front and behind the lens) hold five aluminum frames with lenses and one interlens ring that separates the halves of the lens and is a place to install the aperture diaphragm.

Unlike lenses in the series 35KP produced by IPZ LOMO OKP8-90-1 does not have any problems with the centering of lenses in aluminum frames, so no special manipulations are required when disassembling and assembling it.

To use a lens with modern cameras, it is first necessary to choose a focusing mechanism, which is not an easy task due to the large diameter of the lens barrel. For this purpose, I literally gutted a Chinese reflex lens, sad in quality. Lightdow 500 / 6.3. Instead of the standard plastic mount with M42×0.75 thread, a specially made shank with M65×1 thread was used, which allows you to install an additional macrohelicoid with M65×1 thread with an adapter on the desired system with the ability to accurately set the working distance. For a Sony E mount camera, I needed an M65-M65 25-55mm helicoid, an M65-M42 adapter and a thin ring M42-NEX. When choosing a lens shank, it is important to take into account the large light diameter of the rear lens in order to avoid unintentional loss of aperture (aperture).

Installing the aperture diaphragm in the lens is very simple: I fixed a Chinese multi-blade iris diaphragm with a light diameter of 36 mm in a standard lens spacer using screws and a 3D-printed sleeve. Another thing is to remove the aperture control when using a focuser from 500 / 6.3 ZLO. To do this, it was necessary to make a ring using 3D printing, but still had to sacrifice the rigidity and reliability of mounting the lens in the helicoid: the lens block is held by two screws and guided by the walls of the helicoid. Unfortunately, it was not possible to achieve good installation accuracy: the design should have been revised. Nevertheless, the lens in this design is suitable for tasks related to portrait photography, shooting small objects (when using a macrohelicoid). Below are photos of the adapted LOMO OKP8-90-1.

I must say that this 90/2 lens is just gigantic in comparison. with conventional photographic lenses. Huge dimensions are the result of calculating a system with near-zero vignetting for a relatively large 22×48 mm frame, which diagonally approaches the 44×33 mm frame of modern digital medium format cameras. Also, reducing the size of an optical system is usually associated with compromises in optical quality and is therefore rather undesirable for applications where large dimensions are not a problem.

Establishing the types of optical glass in the OKP8-90-1 lens

According to information from the SU 182360 patent and data from the optical scheme of the Era-1 50/1.8 lens, the successful implementation of the Era-type optical scheme requires the use of lanthanum glasses. At the same time, a high aperture up to F/1.5 (Era-6M 50 / 1.5). However, among the Soviet lenses, I do not know of any that would use expensive lanthanum super-heavy crowns (STK). Yes, presented in the previous article the study showed that conventional barium flints (BF) are used in 35KP-1,8 / 65 instead of STK. It is of great interest how the optics “got out” when designing a medium format long-focus lens OKP35-1,8-65 8/90, which is much more demanding on materials than the 1KP-90 / 2.

I analyzed the elemental composition of the lens material of the OKP8-90-1 objective by X-ray fluorescence spectroscopy (RFLA, XRFS) using the Bruker M1 Mistral instrument, which makes it possible to obtain semi-quantitative data on the content of heavy elements in an object without destroying it. Before analysis, the lens was disassembled and a spectrum was recorded from each of the lenses. The results are presented in the table below.

It turned out that among the lenses of this objective there is not a single one that would be made using lanthanum glass. However, the presence of a large number of hafnium-containing lenses is surprising (hafnium is among the elements even more expensive than lanthanum).

According to the analysis, we can definitely say that the fourth lens of the objective is made of glass of the TBP type (heavy barium flint) - such materials have a very high refractive index (n=1.75-1.85), although with a slightly larger dispersion (v=45-30) in comparison with lanthanum STK (n=1.65-1.8, v=57-45).

It is worth paying attention to the fact that the last lens is positive and made of TF type glass (n=1.65-1.8, v=33-25). This seemingly counterintuitive choice of materials actually helps control chromatic aberration: heavy flints and many TBP glasses have a fairly large positive partial dispersion deviation from the normal straight line (similar to ED glass lenses), which makes it possible to reduce the secondary spectrum. In addition, the high refractive index of TF and TBP lenses helps correct monochromatic aberrations.

Thus, from the point of view of the materials used, LOMO OKP8-90-1 90/2 is a much more advanced lens than 35KP-1,8/65.

Optical properties

The LOMO OKP9-90-1 90/2 lens demonstrates high image quality within a 36×24 mm frame with an open aperture. Sharpness is limited by rather noticeable spherochromatic aberrations (purple green fringes), with field distortion having little effect. On a 44×33mm frame, higher-order aberrations introduce some "softness" at the edges of the image. Apertures down to f/2.8 can achieve excellent distortion correction in the center of the frame, and the edges of the 36x24mm frame get really good at f/5.6. When used on 44×33 mm cameras, to obtain a sharp image of a flat object across the entire field, it is likely that it will be necessary to aperture more due to the influence of the residual curvature of the field (in the space of objects, the focus shifts towards the photographer when moving from the center to the edge).

LOMO OKP8-90-1 is a rare projection lens that uses multi-coated lenses with green and purple highlights. Largely due to the applied coating, the lens forms an image with good contrast (even in backlight) and neutral color reproduction under normal lighting conditions. In hard backlight, due to color veiling (according to the color of the lens flare), the image may take on a greenish tint.

The lens has a fairly even bokeh, although it is noticeably distorted by colored green spherochromatic fringing. Apparently, to see its “character”, you will need to put the lens on a camera with a format of at least 60x45 mm or on a Fujifilm GFX using an expensive medium format speed booster. In general, the lens pattern is pleasant and unobtrusive, the picture is tasty and juicy.

Below are examples of photographs taken Sergey Maltsev on a medium format camera Fujifilm GFX50SII.

Next - photos on a small-format full-frame camera Sony A7s.

All reviews of film projection and filming lenses:

1. RO3-3M 2/50
2. RO2-2M 75/2 (review from the reader)
3. PO 500-1 F9 CM. 1: 2 P (review from the reader)
4. LENKINAP RO500-1 F = 9cm 1: 2 P (review from the reader)
5. ЛЭТИ-60/60М F=92 1:2 (review from the reader)
6. 2/92
7. F = 92 1: 2
8. ОКП-6-70-1 F=70 1:1,8
9. LENKINAP OKS1A-75-1 F=75 1:2 P (review from the reader)
10. LOMO RO501-1 F = 100 1: 2 (+ materials from the reader)
11. LOMO RO500-1 F = 90 1: 2
12. 16KP-1,4 / 65 (review from the reader)
13. 35KP-1,8 / 65 (review from the reader)
14. 35KP-1,8 / 70
15. 35KP-1,8 / 75 (review from the reader)
16. 35KP-1,8 / 85
17. 35KP-1.8 / 100 (review from the reader)
18. 35KP-1.8 / 120 (review from the reader)
19. 35KP-1,8 / 120 (with aperture, reader's review)
20. LOMO P-5 F = 90 1: 2 (review from the reader)
21. LOMO P-5 F = 100 1: 2 (review from the reader)
22. LOMO OKS1-22-1 F = 22 1: 2.8 (review from the reader)
23. ЛОМО ОКС1-40-1 40/2.5 (review from the reader)
24. LOMO OKS1-300-1 F = 300 1: 3.5 (review from the reader)
25. LOMO OKS11-35-1 F = 35 1: 2 (review from the reader)
26. LOMO J-53 F = 75 1: 2 (review from the reader)
27. LOMO J-54 F = 85 1: 2 (review from the reader)
28. LOMO OKP4-80-1 F=80 1:1,8 (review from the reader)
29. LOMO OKP8-90-1 F=90 1:2 (review from the reader)
30. Tair-41 50/2 (review from the reader)
31. KO-120 1: 2,1 120mm
32. KO-90 1: 1,9 F = 9cm (review from the reader)
33. KO-120M 1: 1.8 F = 120mm (review from the reader)
34. KO-120M 120 / 1.8 with a diaphragm and helicoid (review from the reader)
35. KO-120 1: 2.1 F = 12cm (review from the reader)
36. GOZ “KO-140” 1:2,2 F–14cm (review from the reader)
37. MP RSFSR GLAVOCHTEKHPROM PLANT №6 ★ F=7.7cm ★ (review from the reader)
38. MSO USSR SSD UPP-1 ★ KHARKIV ★ F-7 CM ★
39. Schneider Super Cinelux 70/2
40. Meopta Meostigmat 100/1.7
41. Projection aplanates: "Petzvali" and "Richter"

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

Conclusions

LOMO OKP8-90-1 90/2, made according to the original Era optical design, is not only a projection lens with remarkable properties, but also an example of high-quality medium format optics, which is becoming relevant today with the development available cameras. This lens has only one serious drawback - dimensions and weight, otherwise it is a real find for connoisseurs of high-quality Planars with a characteristic vintage pattern, different from the refined picture of modern optics.

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