Soviet film projection lenses of the "KO" series are simple in design and cheap to manufacture four-lens aplanats (i.e. lenses with a curved image field) with an attractive combination of focal length and aperture ratio. There are two generations of lenses of this type: the first is represented by lenses KO-90 90 / 1.9, KO-120 120/2.1 and KO-140 140/2.2 (described in this article) with a fit diameter of 52.5 mm; while the more common lenses of the second generation are distinguished by the same relative aperture F / 1.8 for all, a large bore diameter (62.5 mm) and the letter “M” in the name - KO-90M 90 / 1.8, KO-120M 120 / 1.8 and KO-140M 140/1.8. These lenses were produced first at the State Defense Order "Geophysics" (as a copy of this article), then at the MMZ (Minsk). The earliest lenses of this type, called "Kinolux", were manufactured at the State Optical Institute in the late 1930s, but only in the late 40s, and not all of them were put into mass production.
Western serial copies, for example, Carl Zeiss Jena Kipronar or Meyer-Optik Gorlitz Kinon with a choice of focal lengths from 90 mm to 200 mm with a relative aperture from F / 1.8 to F / 2.2, may have a more respectable age. The fact is that this optical design, like many other designs of Soviet lenses (for example, Telemar - patent US 2239538 1940, FED 100 / 6.3 - US 1467804 1922, Orion - US 2031792 1934 ), apparently, was obtained during the period of relations between the USSR and Germany until 22.06.1941/XNUMX/XNUMX. The author of the scheme of these film projection aplanats is a prominent German optician Robert Richter (patent US 1843519, 1931).
Richter's aplanat uses glass grades that are well suited to the current conventional crowns of the K8 type and flints of the F2 type from the GOST catalog (IPZ / LZOS). For this reason, there is no particular reason to consider Western lenses of better quality in terms of scheme calculation and correction in comparison with Soviet ones, although the quality of blackening and light protection can vary significantly and greatly affect the image.
Optical design - 4 lenses in 2 groups, aplanat;
Focal length - 140 mm;
Relative aperture - 1: 2.2;
Frame format (calculated) - 18×24 mm, covers 44×33 mm;
Landing case diameter - 52.5 mm;
Features - does not have a focusing mechanism, attachment to the camera and an iris diaphragm in the factory.
Lens construction and adaptation
The KO-140 lens has a very primitive design - it is a hollow tube with two screw-in frames, each of which contains a two-lens gluing. Despite the ribbing of some internal surfaces and the presence of a light protection diaphragm, KO-140, like many others Soviet lenses, has an initially low overall contrast of the formed image due to the poor quality of the blackening of the internal surfaces of the case - the paint is quite shiny. Due to better blackening, the reputation of Carl Zeiss Jena Kipronar lenses is much higher compared to KO lenses, and the cost is literally orders of magnitude higher than that of Soviet lenses, although the level of performance of the optical part is practically the same. But, unlike Kipronar, all KO lenses have coated optics.
To install the KO-140 lens on a modern camera, first of all, you need to find a focusing mechanism with the right mount to the camera. The diameter of the rear half of the lens is 52.5 mm, which makes it quite easy to choose a focusing mechanism for the KO-140 - you can use the bodies of optically faulty old lenses (for example, Telear-N 200 / 3.5), but the best option would be a Chinese macrohelicoid type M58-M58 25- 55 or 36-90 mm. The rear focal length of the KO-140 is ~60 mm, so the lens can be used with small-format SLR cameras by choosing, for example, an M42 thread as a mount. However, for use with medium format cameras, you will need a large aperture mount - Canon EF or Fujifilm GFX - to avoid vignetting.
The greatest difficulty in adaptation is the installation of the aperture in lenses of the KO type. There is no place for setting the aperture in the lens barrel itself, because, unlike planar lenses, the inner diameter of the housing corresponds to the diameters of the light beams passing through the lens. In the past, I usually made adaptations with a complete redesign of the lens barrel, making it with turner from scratch or leaving in the factory form only frames with lenses. This required a lot of material and turner time, which automatically made the adapted lens the most expensive in terms of cost among ordinary Soviet projectors. But this time I applied a simplified version of adaptation: only two small parts were made, in which an iris diaphragm with a light diameter of 50 mm was mounted (this is even more than required). The hollow tube-body of the KO-140 lens was cut into two halves, each of which was attached to the corresponding part of the diaphragm assembly so that the original lens distance was preserved. To ensure the coaxiality of the lens components, the position of one of the halves of the body was adjusted by screws with control for the symmetry of the aberration spot of the image of a point light source on the axis.
In my version of adaptation, a macrohelicoid M58-M58 36-90 mm with a specially made M58-M42 shank was used as a focusing mechanism. A 67 mm filter thread has also been added. Photos of the adapted KO-140 are shown below.
It's funny that the KO-140 at a focal length of 140 mm has a very long length (~250 mm from the front lens to the image): the optical design of two positive components, in principle, always has a length greater than the focal length. Also for Richter or related lenses Petzval schemes lens spacing is required the greater, the larger the required focal length and aperture, while the rear focal length usually has to be reduced in this case. As a result, it turns out that the 140 mm lens is slightly smaller in size than the Chinese ultra-cheap super-telephoto zoom Jintu 420-800 mm F / 8-F / 16, which is shown next to the KO-140 in the photo above. On the other hand, the mass of the KO-140, even after adaptation, is small, since most of its body is occupied by air: the lens is much lighter than a projector similar in parameters with a “double gauss».
KO-140 has high sharpness in the central area of the frame at an open aperture. On-axis image quality is limited by spherochromatic aberrations. According to my observations, the sharpness of Richter's aplanats in the center is often higher than that of lenses of the Planar type, similar in terms of parameters and technological level, but they are much inferior to the Planars in terms of the field. So, KO-140 has pronounced astigmatism, field curvature and strong lateral chromatic aberration on the edge of the frame 36 × 24, as a result of which it will be possible to obtain a high-quality image in the field only with F / 5.6-F / 8, and it will not be possible to get rid of chromatic aberrations by aperture. When refocusing, you can get a fairly sharp image at the edge of the 36 × 24 mm frame already at F / 2.8-F / 4, but the corners still suffer too much from astigmatism. In the center of the frame, the lens has excellent sharpness down to f/2.8 - much better than most old 135/2.8(3.5) lenses I know.
For clarity, here are three photographs taken on the KO-140 with apertures of F / 2.2, F / 2.8 and ~ F / 5.6, as well as 100% crop from the central region and the periphery of the frame.
It is easy to see how quickly the longitudinal chromatic aberration in the center of the frame, although the edges are too blurry even at ~F / 5.6 due to the curvature of the field and astigmatism.
It turns out that the success of correcting spherochromatic aberrations in the absence of special types of glass in Richter aplanats depends very much on the relative aperture: even aperture of 1/3-2/3 stops of EV greatly improves image quality. Apparently, for this reason, the KO-140 has a relative aperture of F / 2.2, and not F / 2. However, the newer KO-140M lens, with the same concept and the same simple glass brands, has aperture F/1.8! How much does this affect image quality? The answer can be given by modeling the Richter lens in ANSYS Zemax.
I entered the parameters of the lens from US patent 1843519 and zoomed to a focal length of 140 mm so that the lens covers a frame with a diagonal of 58 mm (corresponds to a 44 × 33 mm frame with a small margin) with vignetting of no more than 60%. The aperture stop was located directly on the plane-parallel third surface of the lens. Next, we simulated the size of aberration spots, the longitudinal chromatic aberration curve, the astigmatic field shape, and distortion for aperture ratios F/1.8 and F/2.2 in the spectral range 400–700 nm (spectral function of a typical CMOS array). The results are shown in the charts below.
As you can see, with aperture from F / 1.8 to F / 2.2 (2/3 EV), the size of the spots has greatly decreased - ~ 3 times for the center of the frame and ~ 1.5-2 times for the edge of the frame. In this case, the longitudinal chromatism decreased by a factor of ~1.5, and the spherical aberration of wide beams was also eliminated.
The uncorrected curvature of the field and astigmatism together determine the characteristic pattern of the KO-140 lens and the like: blurring of the background when moving from the center to the edge does not decrease, as in the case of conventional fast lenses due to geometric vignetting, but on the contrary, it increases as the focus point moves closer to the image. At the same time, the foci of the tangential and sagittal beams strongly diverge from when the center of the frame moves to the edge, which leads to greater defocusing of the sagittal beams, as a result of which the bokeh of the lens does not look scaly, but twisted. Aplanats of Richter “twist” the background much more than lenses with similar parameters Petzval scheme, where the divergence of the sagittal and tangential beams (i.e. astigmatism) is much smaller. At the same time, Richter aplanats with a smaller focal length (for example, KO-90 90 / 1.9) rotate the background much more than aplanats with a large focal length, but the image quality across the field is higher for long-focus options.
The contrast of the generated image strongly depends on the quality of the blackening of the internal surfaces of the lens block and on the presence / absence of light protection elements - diaphragms, fins. My adapted lens performed well in normal lighting conditions, although it is not uncommon for backlight to appear fogged in some parts of the frame. The color reproduction of the KO-140 is generally good for a single-coated lens. The pink-purple highlight coating does not adversely affect the color on photographs, since the lens has too few borders - glass-air, carrying enlightenment, so that it significantly affects the light transmission spectrum of the lens.
When used as a camera mount, the M42 thread KO-140 easily works with a 36 × 24 mm frame, but, as experience has shown using an adapted lens with shift adapter, on 44×33 mm medium-frame cameras, it is better to choose an EF mount as a mount for leveling the vignette. This also applies to other lenses - KO-90 (M), KO-120 (M), KO-140M, LOMO P-5.
The following are sample photos taken with a Sony A7s full-frame camera using shift adapter EOS-NEX.
Next - photos on Sony A7s taken without using a shift adapter.
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.
The film projection lens KO-140 140/2.2 can rightly be called the best in the KO line in terms of image quality. Despite the primitive optical design, the lens has sufficient sharpness for many tasks with a peculiar pattern unusual for other lenses, as well as impressive parameters. KO-140 140 / 2.2 is well suited for 44 × 33 mm format cameras - as a "boxy" portrait lens (EGF = 108 mm), and for crop cameras - already as a sharp aperture telephoto lens.
You will find more reviews from readers of Radozhiva here.