Belar-2 2,5/90 (MMZ). Review of a rare overhead projection lens adapted for modern cameras by Rodion Eshmakov

Material on this lens especially for Radozhiva prepared Rodion Eshmakov.

Belar-2 2,5/90 (MMZ). Review of a rare overhead projection lens adapted for modern cameras by Rodion Eshmakov

View of the lens after adaptation. In the foreground is a Fotodiox EOS-NEX shift adapter.

The beginning of perestroika gave birth to many new projects that had previously been shelved by conservative government officials in a country with an inefficient planned economy. Most of them were never developed subsequently due to the devastation and confusion caused by the collapse of the USSR. Some of them have just been restarted in the last few years (like lenses "Rubinar"produced by LZOS), and some of them, apparently, have sunk into oblivion hopelessly, as well as"The era that did not become an era”, and a number of other interesting lenses.

This article is devoted to a rare and little-known overhead projection lens Belar-2 2.5/90 manufactured by MMZ (Minsk). Apparently, he was supposed to replace two lenses at once: a budget Triplet-5 100/2.8 and more expensive aperture 35KP-1,8 / 100 (in the frame for the Peleng projector). With its parameters, it resembles Leitz Colorplan overhead projection lenses (early biometar-like and late zonnar-like), but optically has nothing to do with them.


Optical design - 5 lenses in 5 groups, development of the "Triplet" / "Tessar" scheme;

Optical design of Belar-2 90/2.5.

Optical design of Belar-2 90/2.5.

Focal length - 90 mm;
Relative aperture - 1: 2,5;
Covered format – up to 44×33 mm;
Rear focal line - ~ 60 mm;
Features - a projection lens, does not have a focusing mechanism, aperture and attachment to the camera.

Optical Design Features

Yes, perhaps, this is an infrequent example of independent and original work of domestic optical engineers, which was recorded in a patent SU 1429074 A1 dated 07.10.1988/XNUMX/XNUMX. The above information about the optical design of the lens is taken from there and it is worth paying attention to it a little.

Firstly, the lens does not contain any glued lenses. This is a very reasonable solution for projection optics, allowing the lens to be used in projectors with high power lamps that get very hot. There is no gluing even in high-quality film projection lenses Schneider Cinelux. Due to the greater power of the lamp, there is no need to use super-aperture large-sized and expensive lenses.

Secondly, the optical scheme itself does not cause obvious associations with any of the known lenses. It would be tempting to call it "triplet with speed booster, but no: the last two lenses have a total negative optical power. Nevertheless, there is one clue: the Ukrainian Arsenal plant produced a rather interesting compact camera Kyiv-35 with an MC Korsar 35 / 2.8 lens - another child of perestroika. The lens has a five-lens design, in which the analogy with the widespread Tessar four-lens design is clearly traced.

Optical design of MS Korsar 35/2.8 (patent SU 1278769 A1

Optical design of MS Korsar 35 / 2.8 (patent SU 1278769 A1)

It is easy to see that by splitting the three-lens component of the MC Korsar lens, we get the Belar-2 90 / 2.5 scheme: even the aperture position is the same for both lenses. Thus, Belar-2 is a distant (already very) descendant of the good old Tessar.

Thirdly, as many as 3 lenses out of 5 are made of super-heavy lanthanum crown STK-19. This type of glass is actively used by optical enterprises in Ukraine and the Russian Federation (IPZ, LZOS). For example, KMZ used it to create Zenitar 50 / 0.95.

Optical glass palette on the Abbe diagram from the official website of LZOS. The grades of glass used in the Belar-2 lens are marked in red.

Optical glass palette on an Abbe diagram from the official website of LZOS. The grades of glass used in the Belar-2 lens are marked in red.

The use of heavy lanthanum glasses makes it possible to better deal with monochromatic aberrations of the system by reducing the radii of curvature of the optical surfaces. However, even in those years it was not some kind of high-tech: the Japanese, represented by Komine, produced tantalum glass lenses, which has even more "interesting" characteristics.

However, in addition to the scheme itself, its implementation is also important. This 90 / 2.5 lens was produced by 2 Belarusian enterprises, and under different names.

All that remains of the original body of my lens is the title ring with the manufacturer, parameters and lens name. The number looks pretty interesting.

All that remains of the original body of my lens is the title ring with the manufacturer, parameters and lens name. The number looks pretty interesting.

A small series of MMZ lenses was called Belar-2. At the same time, much earlier, the lens became known to the community of photographers as, apparently, the serial MS Diar-2 (factory Diaproektor, Rogachev).

Photo of the MC Dear-2 lens with an intact lens block. Photo provided by Andrey Andreev

Photo of the MC Dear-2 lens with an intact lens block. Photo provided Andrey Andreev

Despite the differences in markings, it is indeed the same lens, as the documents say, received by Sergey Mankeev from representatives of the Rogachev plant.

Published photo of documentation from the Diaprojector plant. Original scan from Sergey Mankeev.

Published photo of documentation from the Diaprojector plant. Original scan from Sergey Mankeev.

It can be noted that the lenses of the Belar-2 and MC Dear-2 lenses have finally received a multi-layer anti-reflection coating of green and purple hues, which is typical for Belarusian optics (for example, MS Helios-44-3), although it is not indicated in the marking of my lens. The transmission spectrum of my lens was studied by spectrometry in the range from UV to near IR. With the help of one more additional test, a final result was obtained, suitable for calculating the light transmission coefficient of the lens.

Belar-2 transmission spectrum in the range from 380 to 1100 nm.

Belar-2 transmission spectrum in the range from 380 to 1100 nm.

It can be noted that this type of coating provides maximum transmission in the yellow-orange region (650 nm). The spectrum has a rather complex profile with pronounced absorption in the blue region (380–480 nm). Expect 'warmed' colors and issues with auto-mount from lens white balance camera due to the transmission profile.

The light transmission coefficient of the lens in the visible region of the spectrum (380 - 800 nm) is 0.83, in the near IR (800-1100 nm) - 0.55. This is not bad for an optical scheme with 10 glass-to-air surfaces and primitive multilayer (namely, two- or three-layer) enlightenment. If the coating were single-layer, the transmittance would hardly exceed 0.7 (similar to 16KP-1,4 / 65).

In a word, Belar-2's enlightenment gives good light transmission and is able to compete for contrast, but hardly for color reproduction.

Lens adaptation

Belar-2 (as well as MS Dear-2) is made in a body similar to overhead projection "triples" design. My lens had completely soured threads on the title ring and rear nut, for which it was sawn without pity. No pity - because the case is not at all suitable for installing a diaphragm: its outer diameter would be too large. The multi-bladed diaphragm I chose had a light diameter of 36 mm, which is enough even with a margin.

Belar-2 lenses turned out to be rolled into brass and aluminum pancakes, which, in fact, on the one hand, simplifies assembly, and on the other hand, creates some difficulties. The new housing for the lenses and aperture was made to order from 2 parts, the locking nut of the front part is combined with the nose thread 40.5x0.5 for filters - the dimensions of the lenses allow the lens to be made compact. Detail drawings can be viewed here (link) for 1 file, link for 2 file).

Unfortunately, the correct assembly of such a multi-component circuit was not easy to implement. The workmanship of lens parts and the quality of the original project also had an effect. One way or another, after some time, the lens was very misaligned, which was especially clearly seen when trying to use it on a Sony SLT A55v crop camera. The reason for this was too large an inner diameter of the front of the lens block. The problem was solved by using shims to achieve lens alignment and prevent backlash.

Another common problem with lenses with metal frames is thermal degradation of the frames. This problem concerns exactly projection optics (Zh, RO, 35KP, OKP series), which undergoes constant thermal cycling during operation. As a result, the geometry of frames changes, lenses can fit loosely in them, change position under the influence of gravity, and lenses in projectors rarely roll during use. Thus, it turns out that many of the projection lenses that look perfect on the outside turn out to be completely unusable. And it is far from always possible to align them, especially in the native building.

I've probably even been lucky enough to make a housing where the lenses sit loose enough to achieve concentricity in the easiest way possible.

After assembly, the lens block was installed in the Chinese M52-M42 25-55 mm macrohelicoid, the working length was set to ensure compatibility with all modern cameras, including Nikon F mount cameras.

Below are photos of the appearance of the lens, including in comparison with aerial photography medium format Uran-27 100/2.5, as well as on the camera Sony SLT A55v.

From the point of view of ergonomics, the lens turned out to be good: the helicoid corresponds in its parameters to the focal length of the lens, provides sufficient focusing speed and a comfortable minimum focusing distance. The case has very small dimensions, especially in comparison with Soviet projection planars. These qualities, as well as the optical properties of the Belar-2, have made it one of my favorite lenses.

Optical properties

Belar-2 has, perhaps, outstanding characteristics. It is very sharp in the center of the frame and at the same time has good field aberration correction - much better than six-lens and (especially) five-lens 100/2 (2.8) class planars. Of the residual distortions, there are minor spherical aberrations, a coma noticeable at the corners of the frame, as well as “classic” purple-greens that are quite noticeable in some scenes. chromatic aberration (spherochromatism).

Another notable feature of Belar-2 is the frame area covered: the lens without vignetting works on my full-frame camera with a shift adapter, providing a frame format of 36x45 (4:5) or 24x56 mm (2,33:1) (about how this works , mentioned here). Even outside the calculated working field, the image quality is quite good. For this reason, I took a lot of photos with this lens using the Fotodiox EOS-NEX shift adapter. Good results can also be expected when using speed boosters with this lens.

The contrast of the image formed by the lens is good. This merit belongs mostly to the applied antireflection coating. However, enlightenment is insidious: it can give a rather unpleasant green veil in hard backlight. It also has a complex spectral profile, which is why the camera often makes the wrong choice. white balance. One way or another, the color reproduction of the lens definitely has its own characteristics.

It's funny that in terms of bokeh, Belar-2 looks more like biometars (in the USSR - "Vega"), to which the lens has nothing to do: in the central part of the frame, the out-of-focus disks have a slightly pronounced yellow-green edging, and along the edge they turn into asymmetric lemons due to the influence of the coma. Such an observation serves as further evidence that the picture of the lens circuit diagram in itself means little - each circuit can be implemented in different ways, giving almost any result. In this case, the tessar-like lens is designed so that nothing remains of the tessar image, except perhaps a very moderate drop in resolution towards the edges of the frame. MS Corsair 35 / 2.8, by the way, differs little from its four-lens progenitor in design.

Below are examples of photos on the Sony SLT A55v APS-C camera, taken by Andrey Minchenko. The lens was not aligned at that time.

The following are examples on a Sony A7s full-frame camera, taken with the help of a shift adapter (“shift mounts”, pictures without EXIF). Part of the photo was taken on the lens before adjustment. On a full-frame camera, the difference is minimal, especially when looking at previews.


Belar-2 (or MS Dear-2) is an excellent projection lens. Its modification for installation on the camera has a number of serious difficulties, but the result is definitely of interest. Perestroika and post-Soviet "wind of change" although he didn’t even leave tens of thousands of these and other interesting lenses, he laid the foundation, ideas for modern optical engineering on the territory of the states of the former USSR, which will someday still show themselves. I hope that not only in tank NVD и KABah.

You will find more reviews from readers of Radozhiva here... All Rodion reviews in one place here.

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Comments: 4, on the topic: Belar-2 2,5 / 90 (MMZ). Review of a rare overhead projection lens adapted for modern cameras by Rodion Eshmakov

  • B. R. P.

    Not Colorplan, but not bad)

    • Rodion

      And Colorplan seems to be no better. Not even better.

  • Andrei

    The lens is from the category, outside is Frankenstein, and inside is a prince.
    Nice picture for something like this.

  • Shiryaya scorch

    The Wind of Change not only left no lenses, the whole country was gone to these sounds. And right now, under the version of the song 2.0 ... Well, you understand ....

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