KO-120M 120 / 1.8 with a diaphragm and a helicoid. Review of the adapted cinema projection lens from Rodion Eshmakov

Review of the lens KO-120M 120 / 1.8 specially for Radozhiva prepared Rodion Eshmakov (instagram).

KO-120M 120 / 1.8

Being one of the first lenses converted in this version, the KO-120M looks a little awkward, but inspires respect for its appearance.

KO-120M belongs to the class of inexpensive cinema projection lenses made according to the aplanatic scheme. Unlike Triplets used in slide projectors and epidiascopes, the KO series lenses have more than 2 times aperture, but, moreover, they have uncompensated field curvature, which distinguishes them from similar in parameters projection anastigmatas of the 35KP / OKP / RO series, made according to the Planar scheme.

Among the 35KP and RO lenses, there were also aplanates, which introduces confusion in the designations. For example, the same KO-120M is also found under the name 35KP 120 / 1.8, which is why it can be confused with anastigmat produced by MMZ. The main difference between anastigmata and aplanates with equal parameters is their mass: aplanates weigh much less.

Despite the fact that a 35 mm film frame is approximately equal in size to an APS-C format frame, all Soviet cinema projection lenses of this format cover the full 36 * 24 mm frame well. Many of them also have an impressive back section, as a result of which they can be successfully used on SLR cameras (all Soviet planar lenses and aplanates with FR> 100 mm). The low price and prevalence in the secondary market with very serious optical parameters makes projection optics popular with many amateur photographers, but their use requires adaptation efforts. Original KO-120M in the "knee-length" version I have already presented at Radozhiv 5 years ago, in the same article the same lens (made 3 years ago) appears in a fully adapted form: already equipped with a real focusing helicoid and a huge luxurious diaphragm from a dead reproduction lens LOMO O-2 600/10.

Specifications [Yakovlev Handbook, v.1, p. 370]:
Optical design - aplanat, 4 lenses in 2 groups;
scheme KO-120M 120 / 1.8
Focal length - 121,05 mm;
Relative aperture - 1: 1,8;
Angle of the field of view (on 35 mm film) - 14 °;
Rear focal distance - 52,43 mm;
Light transmission coefficient - 0,9;
The weight of the original lens unit is 655 g;
Features - a projection lens, the original lens unit does not have a focuser and helicoid.
Geometric parameters of the original lens unit body:

KO-120M 120 / 1.8

KO-120M 120 / 1.8

Adaptation features

Projection aplanates are the most expensive and difficult to fully adapt projection lenses: the installation of an internal diaphragm in their housing is not possible, unlike most planar anastigmata. This is due to the large light diameter of the inner surfaces of the aplanate lenses. Thus, in order to obtain a projection aplanat with a diaphragm, it is necessary to manufacture a new housing for its optics.

KO lenses consist of only two glues, which makes life somewhat easier: a new lens unit can be made of 2 halves containing a gluing seat and connected by a diaphragm assembly. Because of this, aplanates with an installed diaphragm have a very characteristic thickening in the middle of the lens unit - it is in it that a large iris diaphragm is located with a diameter greater than or equal to the diameter of the rear lens.

The lens unit for this lens was made of steel for lack of the best at that time. To blacken the inner surface of the lens unit, gas soot applied to an adhesive base was used.

A typical view of an adapted aplanat with a thickening on the body, in which a large-diameter multi-lobe diaphragm is located.

A typical view of an adapted aplanat with a thickening on the body, in which a large-diameter multi-lobe diaphragm is located.

Focusers for such lenses can be found on AliExpress today, but for this lens, made even before they appeared on the market, a simple multi-pass duralumin helicoid was made, providing a very short minimum focusing distance (about 40-50 cm) and a soft, smooth motion of a heavy lens block.

The helicoid for this lens is made to last forever and provides comfortable focusing in any conditions.

The helicoid for this lens is made to last forever and provides comfortable focusing in any conditions.

Apertures for 120 / 1.8 aplanat can also be found on AliExpress today without any problems, but they are very expensive, and sometimes it seems more reasonable to look for an old format lens in an improper condition. In this case, a rather unusual diaphragm was used from a large and heavy reproduction lens LOMO O-2 600/10. It has a peculiar fixation of the petals and at the same time is made in a "crumbling", non-monolithic body. But its petals are almost black, and the hole is always round.

The multi-blade diaphragm will not spoil the bokeh of the lens and will allow you to use it without remorse. And you have to use it.

The multi-blade diaphragm will not spoil the bokeh of the lens and will allow you to use it without remorse. And you have to use it.

The converted KO-120M turned out to be heavy and bulky, largely due to the unsuitable material of the lens block and a large helicoid. The adaptation procedure is quite complex and difficult to perform without turning. On the other hand, you can find full adaptation options that make the most of the details of the original body and details of other lenses, for example, Igor Skupnov's "homemade lenses": http://alii.pub/6alpff" target="_blank" title="/lenses /item/c_5212.html . Such adaptation options, however, can be quite laborious due to the amount of locksmith work and inaccurate, since it is more difficult to maintain the alignment of the optical system and factory lens distances.

Optical properties

At an open aperture, the lens has a satisfactory sharpness in the center of the frame, which decreases significantly towards the edge due to the pronounced curvature of the field: the focal point shifts towards the camera when moving from the center to the edge of the frame. Within the focal surface, the edges of the image also lag behind the center in resolution due to field distortions. Spherical aberration and chromatism are the most significant imperfections in the F / 1.8-F / 2.2 aperture range. By f / 2.8, the lens becomes very sharp, although curvature of field cannot be compensated for by aperture down to f / 8, even on APS-C format. Thus, the aplanat turns out to be a very specific lens and requires a different approach to frame composition than the usual anastigmata.

On a full-frame camera, the lens has ~ 50% vignetting, which affects the bokeh: towards the edges of the frame, the discs of confusion turn into characteristic "lemon". Combined with the curvature of the field, which heightens the blur towards the edges of the frame due to the shifting of the focal point, this produces a swirling bokeh effect, which can be an appropriate artistic trick. Since the nature of the brightness distribution over the disc of confusion and the shape of the discs of confusion in the KO series lenses are very different from those in planar lenses (aka Helios-40), the bokeh of aplanates looks very peculiar and unusual. At apertures smaller than F / 2.8, background blur by the lens looks like the bokeh of a very good optically 135 / 2.8 lens, since the system aberrations (except for the curvature of the field) are almost completely gone.

Due to the presence of an extended empty space between the lenses, the KO-120M works mediocrely with light: despite blackening, it is difficult to overcome reflections. A more efficient option is to use not only good blackening, but also light-cutting apertures, but their use would lead to a sharp increase in the diameter of the body and a catastrophic rise in the cost of the lens. In general, a hood is recommended with the lens.

The color rendition of the KO-120M is biased towards warm shades and, moreover, as it seemed to me, is somewhat unusual. Most likely, this is due to internal light reflections and the (possibly) lead glass used.

Taking pictures with the KO-120M is difficult, especially with a full-frame camera, when the curvature of the field makes an extremely large contribution to the formed image. It is completely unacceptable to focus on the center point and then recompose the frame. The depth of field of the lens is very small and difficult to read through the JVI / EVI. The best helper in this case is bracketing focusing. I had to use it on the A7s as well, since precise focusing using the magnifier EVI was excruciating.

The use of the lens is most advisable on full-frame cameras, since the characteristic features of the image in the APS-C frame are less pronounced, and the aberrations at the open aperture are too large.

Below are sample photos on Canon 600D (APS-C, shooting in RAW, processing in Lightroom):

And Sony A7s (full frame, shooting in RAW and processing in Imaging Edge):

Other movie projection and movie shooting reviews:

  1. RO3-3M 2/50
  2. PO 500-1 F9 CM. 1: 2 P (review from the reader)
  3. 2/92
  4. F = 92 1: 2
  5. ОКП-6-70-1 F=70 1:1,8
  6. LOMO RO501-1 F = 100 1: 2 (+ materials from the reader)
  7. LOMO RO500-1 F = 90 1: 2
  8. 16KP-1,4 / 65 (review from the reader)
  9. 35KP-1,8 / 70
  10. 35KP-1,8 / 75 (review from the reader)
  11. 35KP-1,8 / 85
  12. 35KP-1.8 / 120 (review from the reader)
  13. 35KP-1.8 / 100 (review from the reader)
  14. LOMO P-5 F = 90 1: 2 (review from the reader)
  15. LOMO P-5 F = 100 1: 2 (review from the reader)
  16. ЛОМО ОКС1-40-1 40/2.5 (review from the reader)
  17. LOMO J-53 F = 75 1: 2 (review from the reader)
  18. LOMO J-54 F = 85 1: 2 (review from the reader)
  19. LOMO OKS1-300-1 F = 300 1: 3.5 (review from the reader)
  20. Tair-41 50/2 (review from the reader)
  21. KO-120 1: 2,1 120mm
  22. KO-90 1: 1,9 F = 9cm (review from the reader)
  23. KO-120M 1: 1.8 F = 120mm (review from the reader)
  24. KO-120M 120 / 1.8 with a diaphragm and helicoid (review from the reader)
  25. KO-120 1: 2.1 F = 12cm (review from the reader)
  26. LENKINAP RO500-1 F = 9cm 1: 2 P (review from the reader)
  27. Schneider Super Cinelux 70/2 (review from the reader)

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

Conclusions

KO-120M is a very unusual super-fast telephoto lens. Optically a rather mediocre lens, but in the skillful hands of a photographer, such optics can work wonders. The lens can provide the amateur photographer with a fantastic aperture in the case for a small amount, but a full adaptation of the KO-120M (and other aplanats) requires a significant investment of effort and money.

You will find more reviews from readers of Radozhiva here.

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Comments: 18, on the topic: KO-120M 120 / 1.8 with aperture and helicoid. Review of the adapted cinema projection lens from Rodion Eshmakov

  • Michael

    It seemed to me so in the photo or did the diaphragm on the periphery with cracks come out? Thanks for your review!

    • Rodion

      There are no gaps, the petals are so stacked and shaped so that when closed, the lower part of the diaphragm mechanism is exposed. In this case, the aperture does not "show through".

      • Michael

        Ok thanks

  • Petr Nikolaevich

    Thanks for your review! How does focus bracketing on a manual lens work?

    • Rodion

      When shooting in a series of 5-10 frames, rotate the focusing ring smoothly. One of the shots is usually in focus.

  • Sergei

    And what is the final mass of the entire structure (including the helicoid and the diaphragm)?

    • Rodion

      I think not more than 1,5 kg. Mostly the fault here is the steel lens block.

      • Oleg

        Beautiful photos, unusual bokeh but also a lot of effort

  • Lynx

    all waiting for a review of the door eyes of different manufacturers as a fishy. at least a dozen.
    Rodion, don't let me down!

    • Oleg

      Lynx buy yourself a Nikon z5 and calm down.

      • Ry

        Z5 required But you can keep dreaming about it

  • Onotole

    Damn, according to all the prerequisites, the bokeh should have turned out amazing, here there is a large aperture, and a circular diaphragm, and an uncompensated sphere and a twisted background ... But no, it doesn't insert something. Can't figure out why?

    • Rodion

      Aplanates have a very unusual spherical aberration correction profile. Not like anything else from what I had. Looks rather unusual, goes against expectations. If you take the 120 / 1.8 Planar 35KP and cut the aperture for it with “bokeh-control”, then you will get what everyone is used to and what everyone is waiting for.

      • Onotole

        Yes, probably it's still it.

  • Novel

    Interesting blur, does not directly separate objects from the background, but as if "throws" them. It would be perfect for a video, IMHO.

  • Dim

    An interesting image, even 3D, is present, it is not bad for portraits, it will add a pleasant variety to the album if you manage to remake it :).

  • B. R. P.

    Portraits are something! Especially without the twist that. I liked how he washes silhouettes of people, trees, for example. Thank you, Rodion, for the work done.

  • Molchanov + Yuri

    Interesting review. I liked the lens very much, thanks!

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