Soft achromat 135 / 2.8. Review from the reader Radozhiva

Review of soft achromat 135 / 2.8 from technical gluing (presumably part of the MBS lens) specially for Radozhiva, prepared Rodion Eshmakov.

Soft achromat 135 / 2.8

Soft achromat 135 / 2.8

This lens was custom made, but no one expected such a result. It would seem that the picture that can be obtained using achromatic gluing is obvious: sharpness in the center and a blurry edge, but by chance this lens turned out to be a component of a more complex lens (aplanat or achromat), which has completely different properties.

Lens Specifications:
Optical design: two lenses glued together, achromat.
Diameter: 50 mm
Focal length: ~ 140mm

Adaptation features
Gluing fell into my hands completely naked, its origin is not known for sure: the seller indicated only its origin from some set of spare parts. Its front surface is rather strongly convex, the rear is enlightened and almost plane parallel.

The whole adaptation was to fit the lens into the ordered frame, which was naturally attached to the case of the gutted Korean Karenar 135 / 2.8 (the lens was purchased with bad lenses).

The diaphragm remained from the Korean donor (despite the distance from the lens, it functions correctly), a helicoid with a 15 mm stroke is quite sufficient for such gluing. The lens is pretty neat.

Soft achromat 135 / 2.8


Soft achromat 135 / 2.8

Optical properties
Contrary to expectations, the lens does not form a sharp image in the center of the frame on an open aperture: the resulting image is clearly mitigated by spherical aberration. At the same time, a good correction of chromatism and even some compensation of field distortions can be noted. The profile of spherical aberration, completely different from the classical achromat, greatly influenced the lens side: it is extremely unusual and interesting, it frankly reminded me of Vega-22 bokeh and other biometars.

When the aperture is closed to F / 5.6, the lens becomes sharp in the central region of the frame, while the bokeh almost aligns and becomes ordinary.

The optimal result is achievable in the region of ~ F / 3.5 - when the form of blurring of the background is maintained at a sufficient sharpness.

conclusions
The work on this lens clearly demonstrated the variety of achromats: it turned out that gluing with under-corrected spherical aberration (components of more complex achromats or aplanates) can give a very unusual and interesting result when shooting.

Thank you for your attention, Eshmakov Rodion

You will find more reviews from readers of Radozhiva here.

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Comments: 16, on the topic: Soft achromat 135 / 2.8. Review from the reader Radozhiva

  • Sergei

    Achromatic bonding from two lenses works quite well with a relative opening of 4 or more closed. What did you demonstrate when analyzing gluing from 8x30 KOMZ binoculars in one of the previous reviews.

    • rudzil@yandex.ru

      I have already managed to visit lighter ones, who also confidently worked in the center with an open one. The aperture of the classic achromat determines not the sharpness in the center, but the size of the central sharp area. The same achromat is not classical, because served clearly as a component of a more complex (but still - achromatic or aplanatic, and not an anastigmatic lens) system. Nevertheless, it turned out to be very interesting, therefore the review lies here.

    • Iskander

      Yes, that is right. But achromat, achromat, strife, as the author of the article correctly noted. I once experimented with achromat 50h330mm from the telescope ZT-4 20h50, the article is on this site. It is rather dark, the relative aperture is about 7, but chromatism is very noticeable, I think, because of the large focal length at which it is quite difficult to correct the divergence of beams of different colors. In general, as a photo lens, he disappointed me, so I returned it to my native tube, where it belongs :-) For visual observations, it is almost perfect.
      At the same time, one of the lens glues from the MBS-2 microscope (the one that is biconvex) paired with the native eyepiece gives a clearer picture without noticeable aberrations, and all this despite a noticeably higher aperture ratio - about 4,3. Focal about 150, diameter 35.
      It would seem that a finished, calculated achromat for the telescope should give out much better quality than the half of the lens from the microscope. But in reality, it’s not so simple. I’m just now adapting this glue for a DSLR.

  • anonym

    Respect to Rodion!

    • zengarden

      Give Rodion any glass - he will make a lens out of it :)

  • Ilyas

    too sad to see the picture (

    • Rodion

      Explain?)

  • anonym

    In general, the garbage is full

    • anonym

      Yes. It is so indeed.

      • Vitaly N

        Quiet with myself ...

        • Noa

          All who do not subscribe become Anonymous. So this is not necessarily the same site visitor

          • Arkady Shapoval

            Yes exactly. And “Anonymous” above are different.

  • Vitaly N

    It is a pity that there are not enough clean portraits in the photo, they are somehow "spy" :) - the bokeh is very interesting.

  • Molchanov Yuri

    Bokeh is beautiful. Thanks to the author for the review and would like to wish successful experiments.

  • Vladimir

    Lens in garbage….

  • Rodion

    Recently I was finally able to unravel the origin of this gluing. This should be the front lens of a 100mm f / 2 cinema projection lens such as a Petzval 4/3. The 90/2 Petzval on hand gives a picture identical in nature of distortions when the rear lens group is removed.

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