Mir-25MT 3,5/30 (KMZ). Overview of the adapted lens from the endoscope

Material on the Mir-25MT 3,5 / 30 lens especially for Radozhiva prepared Rodion Eshmakov.

View of the adapted lens from the side of the front lens.

View of the adapted lens from the side of the front lens.


The lens presented in the review was designed and manufactured by Igor Porokh (aka lens_made_in_ussr). The material was prepared by Rodion Eshmakov.
Mir-25MT 30/3.5 is a complete lens of the Surprise-MT medical camera (MT stands for medical equipment) designed for use with flexible or rigid endoscopes. The camera itself is based on the Zenit-19, in addition to the Mir-25MT, along with the Surprise-MT, the Industar-50MT 50/7 lens was included. The Surprise-MT camera differs from the usual Zeniths by the bayonet mount of lenses (Zenith D type) and the image format of 18 × 24 mm, approximately corresponding to the size of modern APS-C sensors.

Specifications:

The optical scheme is a retrofocus lens, the drawing was not found. Most likely, the scheme is close to Mir-1 37 / 2.8.
Focal length - 30 mm;
Relative aperture - 1: 3.5;
Field of view angle (calculated) – 54°;
Frame format (calculated) - 18 × 24 mm (~APS-C);
Thread for filters - no;
Attachment to the camera - bayonet Zenit D;
Features - the lens does not have an aperture and a focusing mechanism.

Design and adaptation features

The Mir-25MT looks very specific: on its skinny body there is nothing but an endoscope attachment at the front lens and a bayonet with a union nut. The front is easily removed by removing three screws, exposing a small convex front lens. If the lens were full frame, it would be twice as large in diameter. But the back part to remove, it seems, you need to try. In any case, on my copy, it somehow did not give in and the lens was shelved, since the Mir-25MT 30 / 3.5 has very attractive parameters. It is also generally a difficult lens to adapt, since not only does it not have a focusing mechanism, but the lens also does not have a variable aperture.

Mir-25MT in the factory version. Photo: Evgeny Kubasov

Mir-25MT in the factory version. Photo: Evgeny Kubasov

But a very high-quality and original adaptation of such a lens was performed by Igor Porokh. I have already talked about it before. Triplet-69-3 4/40, the design of which, by the way, he changed, guided by the conclusions made in my article.

Front view of the adapted Mir-25MT.

Front view of the adapted Mir-25MT.

In this version of the adaptation, the Mir-25MT was transplanted into the Industar-61LZ focusing mechanism, and the body parts were made by 3D printing. The design is collapsible, but I did not climb inside, so as not to accidentally break anything. An EF mount is used as a mount for the camera, completely printed on a 3D printer. At the same time, the lens is fixed in my EF-NEX adapter securely and without backlash. It turns out that one engineer has mastered the manufacture of a high-precision plastic part, while the giants of thought from the Lytkarino Optical Glass Plant cannot make an EF mount in metal on CNC machines, which is incredibly delivering.

3D printed EF mount. What do you think, LZOS?

3D printed EF mount. What do you think, LZOS?

The focusing mechanism used moves the lens block when focusing by 15 mm and provides an MDF of about 16 centimeters, which allows you to work in the macro range.

Lens when focusing on infinity.

Lens when focusing on infinity.

Lens when focusing on MDF.

Lens when focusing on MDF.

The only drawback of the design is the lack of a diaphragm, but its installation in this lens would require the manufacture of a housing for lenses from scratch, which, due to the low attractiveness of the parameters, did not seem appropriate. Otherwise, the converted Mir-25MT can be considered an interesting macro lens for APS-C SLR cameras.

Optical properties

Mir-25MT is a lens for crop cameras. When focusing at infinity, it does not cover the full frame, I had to use it in APS-C mode. However, it still has a noticeable vignette.

At the only aperture available, f/3.5, the lens performs rather mediocrely at infinity: the image in the center of the frame is not sharp enough due to residual spherical aberration, the edges of the frame are highly susceptible to field distortions (coma, lateral chromatism). All these ailments could be overcome if the Mir-25MT had a variable aperture diaphragm. The lens copes much better with tasks at macro distances - here its sharpness and depth of field are quite enough.
The image contrast of the Mir-25MT is rather mediocre - the poor blackening of the interlens spaces (shine) and the inefficient single-layer amber antireflection coating are to blame. The color reproduction of the lens, although almost without distortion, is generally rather faded. In sunny weather in bright light, the lens performs very, very mediocre both in terms of contrast and in terms of color. The lens does not hold hard backlight well.

The bokeh of the lens is pleasant, uncomplicated. The background blur is reminiscent of Mir-1 37/2.8 on APS-C, so it seems to me that Mir-25MT is also a retrofocus version of the double Gauss.

Below are sample photos taken with the Sony A7s in APS-C mode.

Conclusions

By itself, the Mir-25MT is not a very attractive lens in terms of parameters or image quality. There are many types of lenses 28/2.8 or 28/3.5 for SLR cameras, which will be at least as good in image quality. Nevertheless, if the lens still fell into the hands, then the option of converting it into a macro lens, which was demonstrated by Igor Porokh, is very good.

You will find more reviews from readers of Radozhiva here.

 

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Comments: 3, on the topic: Mir-25MT 3,5/30 (KMZ). Overview of the adapted lens from the endoscope

  • Alexander Rifeev

    no offense will be said - will we get to optical photographic equipment for proctologists? :-)))

    • Rodion

      :-)))

  • Vladimir

    Oh, Pharmaceutical Garden!

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