LOMO lenses of the OKP series are designed for use in film projectors with frames ranging from narrow 16 mm film to widescreen 70 mm film. All lenses in the series are anastigmats, but have several options for optical design, and therefore lenses with similar parameters can have very different optical properties. Basically, OKP lenses use different versions of the Planar scheme (“double Gauss”), many of them calculated by the Soviet optician D.S. Volosov. On the Web, you can also find information about prototypes, the design and purpose of which may differ from serial lenses.
This article presents a rare (I have met for all the time among no more than 5 copies at flea markets) LOMO OKP4-80-1 80 / 1.8 lens, designed to project an image from 35 mm film. According to its design concept, it is identical to such lenses as OKP5-90-1, OKP4-110-1, 35KP-1.8 / 120 and filming OKS6-75-1. LOMO OKP4-80-1 is one of the most advanced Soviet film projection lenses, in terms of quality approaching the line Schneider Cinelux.
Specifications (Catalogue of lenses designed at the GOI, edited by Yakovlev A.F., 1970, vol. 2, p. 231):
Schematic diagram of the OKP4-80-1 lens.
Focal length - 80 mm;
Relative aperture - 1: 1,8;
Estimated field of view angle - 20°;
Estimated frame format - 16x21 mm, actually covers up to 44x33 mm;
Rear focal length - 44,63 mm (the lens is not suitable for use with SLR cameras without the use of drastic measures);
Landing diameter - 62.5 mm;
Weight - 400 g;
Features - projection lens, does not have its own focusing mechanism and iris.
Lens construction and adaptation
OKP4-80-1 outwardly does not stand out among many other similar Soviet projection lenses. Its body is a tube with two retaining rings - in front and behind, into which lenses are packed, enclosed in aluminum frames. In other words, for this lens, as well as for other LOMO projectors, an autocollimation assembly is used, which, subject to the technology (!!!), provides the best accuracy, which is very important for a six-component scheme.
I could not find a patent for the optical design of the OKP4-80-1 and similar lenses. In the literary sources known to me, the author of the calculation was also not identified. At the same time, it can be noted that the design of the lens is rather outstanding: it does not have a single gluing (the maximum number of independent correction parameters for 6 lenses has been reached) and thick lenses (the fifth component) are actively used. Ideologically, the lens resembles Schneider Cinelux 70/2, which also has one very thick lens and no glued components. We can say that both of these lenses are made at the same technological level of optics.
It should be noted that OKP4-80-1 lenses are coated with a single-layer antireflection coating typical of LOMO of the 70s with a faded violet tint, which does not introduce significant color distortions into the transmission spectrum of the lens. Some LOMO projection lenses of the late 80s and early 90s even had a multilayer anti-reflection coating of the lenses, although this was not reflected in the marking.
Unlike lenses like W-54 or PO500-1, setting the aperture in Soviet projection lenses with the "6/6" scheme is very difficult. So, in 35KP-1.8 / 120 there is simply no place for the aperture, which requires a dangerous procedure for boring the frames with lenses themselves, and in OKP4-80-1 to set the aperture in the correct place (between 3 and 4 lenses), it is necessary to make a large drank in the frame of one of the lenses to remove the iris control leash, and fix it in the frame of the other lens. These procedures, if performed incorrectly, can lead to a violation of the position of the objective lenses and a deterioration in optical quality. Since the required aperture diameter is 27.5 mm, a nine-lens iris from Industar-58U or Industar-55U lenses with a light diameter of 28 mm is excellent for installation. The diaphragm control unit is conveniently produced by 3D printing.
OKP4-80-1 has a rather small rear focal length. Although larger than 44mm (the working distance of the Canon EF mount), the rear retaining ring and the large diameter rear lens barrel will not allow you to get the lens close enough to the sensor to get infinity focus even on Canon SLR cameras. At the same time, the light diameter of the rear lens is small, which made it possible to use the M39 × 1 thread with a p/o of 28.8 mm as a mount to the camera (mounting lenses for rangefinder cameras FED, Zorkiy). Thus, with the help of the Chinese M65-M65 25-55 macrohelicoid and the M65-M39 shank ordered from the turner, the lens was adapted for mirrorless cameras.
Below is a view of the adapted lens.
After adaptation, the OKP4-80-1 is larger and more massive than most similar photographic lenses, but this does not cause any inconvenience.
LOMO OKP4-80-1 has excellent sharpness in the central region of the frame with an open aperture. Resolution is greatly reduced in the corners of the 36×24 mm frame due to pronounced astigmatism, but with aperture up to F / 8 this ailment disappears. 36×24 frame edges are good even at f/4-f/5.6. In general, the resolution outside the APS-C frame for OKP4-80-1 is lower than for Zh-54 85/2, but within the APS-C frame, which is roughly equal to the calculated one, the lens performs excellently. Of the disadvantages of the lens, one can note a very strong drop in image quality (especially at the edges of the frame) when shooting in the macro range, which was observed to a much lesser extent with W-53, Zh-54 and PO500-1.
In OKP4-80-1, the picture of residual aberrations differs markedly from RO50x-1 and Zh-5x. So, for example, OKP4-80-1 has exceptionally soft and smooth focus-defocus transitions, which is valuable in portrait photography. The lens has a low level of coma. This also affects the appearance of the bokeh of the lens: OKP4-80-1 never gives "busy bokeh" - hard, lurid bokeh. Focal disks have an inconspicuous edging, sometimes with a noticeable greenish color (spherochromatism). At the edges of the frame, the disk acquires a slightly brighter border facing the center of the frame (the effect of residual coma), and at the corners of the 36×24 frame, the disk is stretched tangentially due to astigmatism and is cut off by the lens frames (and/or the M39 mount) to a figure, reminiscent of a guitar pick. I found the bokeh of the lens to be very pleasing. A similar pattern has 35KP-1.8 / 120 with the same optical design.
The contrast of the image formed by the OKP4-80-1 under normal lighting conditions is at the level of other good lenses with single-coated optics. In backlight, there may be some drop in overall contrast without strong veiling, lentil rainbow highlights appear from bright light sources. The color reproduction of the lens is close to neutral, quite good. The camera rarely made a mistake with the white balance when shooting.
Below are examples of photos on LOMO OKP4-80-1 80 / 1.8, taken on a full-frame mirrorless camera Sony A7s https://radojuva.com/2022/06/a7s.
All reviews of film projection and filming lenses:
- RO3-3M 2/50
- RO2-2M 75/2 (review from the reader)
- PO 500-1 F9 CM. 1: 2 P (review from the reader)
- LENKINAP RO500-1 F = 9cm 1: 2 P (review from the reader)
- ЛЭТИ-60/60М F=92 1:2 (review from the reader)
- F = 92 1: 2
- ОКП-6-70-1 F=70 1:1,8
- LENKINAP OKS1A-75-1 F=75 1:2 P (review from the reader)
- LOMO RO501-1 F = 100 1: 2 (+ materials from the reader)
- LOMO RO500-1 F = 90 1: 2
- 16KP-1,4 / 65 (review from the reader)
- 35KP-1,8 / 65 (review from the reader)
- 35KP-1,8 / 70
- 35KP-1,8 / 75 (review from the reader)
- 35KP-1,8 / 85
- 35KP-1.8 / 100 (review from the reader)
- 35KP-1.8 / 120 (review from the reader)
- 35KP-1,8 / 120 (with aperture, reader's review)
- LOMO P-5 F = 90 1: 2 (review from the reader)
- LOMO P-5 F = 100 1: 2 (review from the reader)
- LOMO OKS1-22-1 F = 22 1: 2.8 (review from the reader)
- ЛОМО ОКС1-40-1 40/2.5 (review from the reader)
- LOMO OKS1-300-1 F = 300 1: 3.5 (review from the reader)
- LOMO OKS11-35-1 F = 35 1: 2 (review from the reader)
- LOMO J-53 F = 75 1: 2 (review from the reader)
- LOMO J-54 F = 85 1: 2 (review from the reader)
- LOMO OKP4-80-1 F=80 1:1,8 (review from the reader)
- LOMO OKP8-90-1 F=90 1:2 (review from the reader)
- Tair-41 50/2 (review from the reader)
- KO-120 1: 2,1 120mm
- KO-90 1: 1,9 F = 9cm (review from the reader)
- KO-120M 1: 1.8 F = 120mm (review from the reader)
- KO-120M 120 / 1.8 with a diaphragm and helicoid (review from the reader)
- KO-120 1: 2.1 F = 12cm (review from the reader)
- GOZ “KO-140” 1:2,2 F–14cm (review from the reader)
- MP RSFSR GLAVOCHTEKHPROM PLANT №6 ★ F=7.7cm ★ (review from the reader)
- MSO USSR SSD UPP-1 ★ KHARKIV ★ F-7 CM ★
- Schneider Super Cinelux 70/2
- Meopta Meostigmat 100/1.7
The names of the lenses correspond to their exact spelling on the body.
LOMO OKP4-80-1 80/1.8 is one of the most difficult Soviet projection lenses to adapt. Its optical quality is quite high, which is ensured by an advanced optical design. At the same time, the lens has a very pleasant pattern, which, together with convenient parameters, makes it an excellent tool for artistic photography. In my opinion, in terms of the combination of qualities, LOMO OKP4-80-1 can be ranked among the best projection lenses - not only Soviet ones, but in general.
You will find more reviews from readers of Radozhiva here.