Adapted projection lens LETI-60/60M F=92 1:2 (KOMZ)

Material on the lens LETI-60 / 60M F = 92 1: 2 especially for Radozhiva prepared Rodion Eshmakov.

Adapted projection lens LETI-60/60M F=92 1:2 (KOMZ)

Adapted projection lens LETI-60/60M F=92 1:2 (KOMZ). increase.

The lens of the LETI-60/60M F=92 1:2 overhead projector is a simple six-lens anastigmat made according to the classical 6/4 scheme of the Helios/Planar type (hereinafter I will simply call the lens Helios 92/2). Compared to projectiontriplets"This lens is both faster and of better quality, but, moreover, its execution is much simpler than that of film projection anastigmats of the type PO500-1.

Due to the prevalence and cheapness in the secondary market, Helios 92/2 has become one of the most popular lenses for homemade products, but it’s quite difficult to find a really high-quality and full-fledged version of adapting this lens: often, when adapting, an unsuitable aperture is installed (or not installed at all), which leads to the loss of the relative aperture, an unsuccessfully selected focusing mechanism with a small stroke is used and no work is carried out on additional blackening of the internal parts of the lens block. This article presents an adapted lens, devoid of these shortcomings. Also on the site there are reviews of this lens in different versions with the simplest adaptation:

Specifications:

Optical design - 6 lenses in 4 groups, "Helios" / "Planar";

Optical scheme of the lens from the instruction manual for the LETI-60M projector.

Optical scheme of the lens from the instruction manual for the LETI-60M projector.

Focal length - 92 mm;
Relative aperture - 1: 2;
Covered frame - 44×33 mm, calculated frame - 36×24 mm;
Features - the lens does not have a mount to the camera and an adjustable aperture.

Design and adaptation

The overhead projection lens Helios 92/2 differs from film projection lenses primarily in the assembly method. So, in overhead lenses (exception - Belar-2 90/2.5) most often used is the usual bulk assembly of lenses with interlens spacers. It is believed that this assembly method does not allow achieving good lens centering, and therefore it is used only in lenses that are fairly simple in design and not very demanding on image quality. Film projection lenses (except Minsk 35KP-1.8 / 85, 35KP-1.8 / 100 and simple four-lens aplanats type KO) in the USSR were assembled by the autocollimation method, which consisted in the fact that each lens of the objective was enclosed in a separate aluminum frame, centered individually in a special lathe-type machine, after which the frame was machined - during bulk assembly of the lens, consisting of lenses rolled into frames, the centering conditions were performed automatically . True, if the technology was not followed, complete darkness and decay turned out, which is very difficult to correct - for example, all the Izyum 35KP-1.8 / 65 lenses that I saw (3-4 pieces), as well as most of the Izyum 35KP-1.8 / 75 (2-3 pcs) were with impressive decentering straight from the factory.
Despite the fact that Helios 92/2 has a simple design of the lens block, I did not find any significant decentering problems with it - the aberration spots are quite symmetrical.

Helios 92/2 has a very small case diameter - 45 mm - which makes it easy to choose a focusing mechanism for it. Moreover, many lenses retained their native simple focuser with a pin and a groove on the lens block. I used a Chinese M52-M42 36-90 mm macrohelicoid to adapt the lens, because I find it preferable when the lens has a small minimum focusing distance - my version has an MDF of only 22.5 cm! This is even less than specialized macro lenses like Vivitar (Tokina) 90/2.5 (39.3 cm.)

But installing the diaphragm turned out to be a rather non-trivial task, although there is a place for it between the halves of the lens, since the light diameters of the adjacent lens surfaces are 32 and 29 mm, and the outer diameter of the body is simply not enough to install most diaphragms with the desired light diameter. And the diaphragm itself is not easy to find. For example, you can install a nine-petal iris from lenses Industar-55U or Industar-58UBut aperture lens will then become equal to approximately 1:2.1. Therefore, having carried out a couple of experiments on installing the diaphragm from Industar-23U into this lens (the result is F / 2.5) back in 2015, I postponed the issue until the necessary irises with a diameter of 29 mm with a fairly small outer diameter appeared. Fortunately, such diaphragms, and even ten blades, are now really sold by the Chinese - and I managed to return to the topic of fully adapting the Helios 92/2 lens - one of the lenses with which my passion for projection optics began.

To install the diaphragm, it was necessary to make a groove on a lathe from the nose of the lens to almost the fourth lens, leaving a small rim. Thus, the diaphragm and the lens were in close proximity, thanks to which it was possible to maintain a full aperture ratio of the lens 1: 2.

Also, during assembly, all interlens spacers were matte blackened - this is very important for this lens. The bevels of the lens lenses have a good blackening from the factory, but have been processed additionally.

Using the 3D printing method, the necessary parts were made to fix the aperture control ring (taken from the body of some no-name Japanese-Korean lens type 35 / 2.8) and threads for 52 × 0.75 mm filters. A threaded ring for filters for such a lens is a must, because the version described in the review (similar to the one presented here) the front lens protrudes beyond the plane of the frame and can be easily damaged.

The final view of the adapted LETI-60 / 60M F = 92 1: 2 lens is shown in the photo below.

It is easy to see that with the same parameters as the RO500-1 90/2, Helios 92/2 turns out to be much lighter and less overall.

Optical properties

Helios 92/2 does not make any surprises - at an open aperture it is not the sharpest lens, the influence of spherical and chromatic aberrations is noticeable, field distortions also appear at the edges of the 36 × 24 mm frame. With apertures up to F / 5.6-F.8, you can achieve high image quality across the entire field. In my opinion, on a full-frame camera, Helios 92/2 is very similar in behavior to Helios-44 58/2 on crop 1.5.

The image contrast, provided that the inter-lens inserts are blackened, is quite good under normal lighting conditions and is on the level of other good lenses with a single-layer anti-reflection coating. In the backlight, Helios 92/2 catches bright rainbow highlights, ring glare, veil (its density greatly decreases after blackening) and other joys that can be used for artistic purposes. Color rendition - typical for lenses with violet coating of lenses - with green, since light transmission is maximum for the yellow-green range.

In terms of artistic qualities, the lens is very similar to other Helios - for example, 44 и 40. At the same time, in comparison with Helios-40, the LETI-60 F = 92 1: 2 lens is much easier to handle - mainly due to greater sharpness in the open (Helios-40 you can cover up to F / 2, but remember what shape its aperture is?), better color reproduction and contrast, and finally less mass.

Below are examples of photos taken on a Sony A7s full-frame camera.

As well as Helios-40 85 / 1.5, Helios 92/2 can be used without restrictions with digital medium format cameras such as Fujufilm GFX (44 × 33 mm) or with full-frame cameras through tilt or shift adapter.

Conclusions

Projection F=92 1:2 from LETI-60/60M is a nice and predictable lens with a classic vintage picture. I recommend trying it to anyone interested in unusual optics - even in the version without aperture, you can take a lot of good photos with this lens. I advise you to purchase adapted options only if the aperture is selected and installed in the lens in the right way.

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

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

You will find more reviews from readers of Radozhiva here.

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Comments: 19, on the topic: Adapted projection lens LETI-60/60M F=92 1:2 (KOMZ)

  • Vladimir

    Thanks for the review!

  • Vladimir

    My copy on Fujifilm x-A1

  • TSerg

    Rodion, so the aperture in your adaptation option is between 3 and 4 lenses or between 5 and 6? And to which lens is the aperture block closer?

    • Rodion

      Between 3 and 4 of course. Closer to 4.

      • Tserg

        Thanks for the reply.

  • Ilya

    hello, not at all a specialist in cameras, rather an amateur who likes the idea of ​​“getting together and spending time in photographs”, now I use the Canon EOS 1100D as the main camera for photography, but in which case I use the Google Pixel 6 Pro phone, which frankly is not inferior in places
    I would like to look after a new camera, the only priorities for the camera are the speed of creating photos, the presence of minimal bluetooth / Wi-Fi for transferring files to the phone for viewing, if possible, a folding screen, but that is not necessary
    sorry, if off topic, it's hard to understand the vocabulary of photographers with a swoop)

    • B, R, P.

      It's all to bzk. Sony, Fuji, Panasonic, etc.

      • Ilya

        rather, they are not interested in the BZK themselves, I want to take a closer look at the DSLRs, the option does not inspire

        • B, R, P.

          Among DSLRs, there are very few devices with abilities that inspire you.

        • Tserg

          Before them, it’s already pizno to be surprised, for more than an hour having splinted. More r_k-p_vtora dehto z virobniki will release top DSLRs. Ale, judging from your first post, you can’t buy your own top-end DSLR. And in a couple of years there will be no more spare parts for this category of cameras. What is it? Bathe old rubbish with crowded personnel and leather workers? It’s better to spend money once during the singing period to accumulate money and buy bzk. Yakshcho Vee on Kenoni, why can't they rule you? Tim is better, that the lenses of their DSLRs through the adapter can work on their bzk without any back and front focus and other nuances.
          Listen to more informed people and don’t waste pennies for nothing on what you already have.

          • Tserg

            on those who have already lived themselves.

  • zzz

    why cut the lens block body and insert the diaphragm? Who in their right mind would use this glass with a hole clamped? they buy it for the open

    • Rodion

      The lens works great in macro at f / 4-f / 8, in the f / 2-f / 2.8 range it does an excellent job with portraits. Aperture maneuver to control aberrations is a very important thing when shooting, it is foolish to deny it.

    • Rodion

      In the photo gallery above, many were taken at f / 2.8-f / 5.6.

  • Johann Carl Friedrich Gauss

    Rodion, hello, thanks for your reviews.
    At F = 92, they sometimes recommend an aperture from Industar I-11M 300mm f / 9 (inner diameter seems to be 30mm, a lot of petals).
    Have you considered this option?
    Are there any advantages or disadvantages (from a technical point of view) compared to Chinese?
    And maybe you have data on the size of the diaphragm block in the I-11M (diameter, thickness)?
    Thank you.

    • B. R. P.

      This is from the pavilion camera, or what?)

      • Rodion

        I-11 f/9 - a series of reproduction optics with a reduced secondary spectrum (made on the basis of APO Tessar f/9).

        • B. R. P.

          Thanks for the advice Rodion.

    • Rodion

      No, I didn't. It is very common for reproductions, and the diaphragm itself is arranged inconveniently. She might as well be unremovable.

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