Implementation of vignetting control “in glass and iron”. Material from the reader Radozhiva

Overview of the adapted medium format Vega-23 150 / 3.5 lens from the Racurs camera, as well as a description of the implementation of vignetting control “in glass and iron” prepared Radozhiv's reader - Rodion Eshmakov.

Vega 23

Vega 23

Vega-23 is a standard lens of the “Racurs” pavilion medium format cameras. Like the camera itself, the lens is quite rare - indirectly, this can be judged by the four-digit serial number and by the occurrence in the secondary market. It is surprising that this instance fell into my hands already redone (and very high quality), and, apparently, a very, very long time ago - it is possible that in Soviet times. The lens served as a successful model for testing such an interesting function as vignetting control.

Lens specifications (hence):
Optical design: Vega \ Biometar, 5 lenses in 4 groups; рисунок
Focal length: 150 mm;
Relative bore: 1: 3.5;
Native format: 6x7 cm, in fact it covers no less than 8x8 cm;
The field of view angle in the native format: 33 degrees diagonally;
Aperture blades: 8 pcs., 16 pcs. (for the monitored instance);
Filter thread: 58x0.75 mm
Diameter for smooth nozzles: 62.5 mm;
Features: a factory-made lens is built into the board with an electromechanical shutter. A copy from the review is a rework with the saved optical part.

Features of adaptation and design

Unfortunately, I did not have the opportunity to get acquainted with the design of the lens in the factory version. Although it is worth noting that due to the bulky shutter mechanism and mounting boards, this lens will be difficult to use on familiar cameras without a radical rework. Factory Lens.

This copy was competently redone by an unknown craftsman, apparently, in Soviet times: the lens-like lens-blocks clean of tears were placed in a shabby case Vega-12B while maintaining the distance between the lenses (as evidenced by unspoiled sharpness). At the same time, the standard eight-petal aperture was replaced by a beautiful round sixteen-petal aperture - apparently from some kind of large format lens. Aperture adjustment is carried out by turning the entire front lens block.

View of the aperture Vega-23.

View of the aperture Vega-23.

In general, the idea of ​​turning the lens block to adjust the aperture is often used by DIYs, as with small masses of the optical part, it is possible not to output aperture control by means of special rings, etc. However, this is justified only when the lens block does not rotate during focusing - as in this adaptation option, for which the housing was chosen Vega 12.

Vega-23 in the Vega-12B case.

Vega-23 in the case Vega-12B.

The lens unit itself is very simple and austere: ordinary slotted nuts lock the lenses, rolled into metal washers and shining with pink or blue single-layer coating. The design is very typical for simplified Soviet lenses (almost all magnifying lenses are an example of this). The lenses of Vega-23 are quite thick, the lens is not easy - it weighs about 500 g.

View of the lens with a covered aperture in the light. The yellowness of the glass is noticeable.

View of the lens with a covered aperture in the light. The yellowness of the glass is noticeable.

Although the lens was in the housing Vega-12BIt turned out that it can not be used in this form with cameras like Kiev-6 - there was a strong flight for infinity. However, after evaluating the difference between the working segments, it turned out that the converted lens should be used with a 40 mm macro ring. Indeed, after acquiring and installing such a ring, focusing on infinity was achieved with a small (about 1,5 mm) overrun. All this indicates how the master responsibly and prudently approached the work on the lens.

2 adapters and a macro ring - all that is needed to use the adapted Vega-23

2 adapters and a macro ring - all that is needed to use the adapted Vega-23

Optical properties

Thanks to competent adaptation, the lens can be easily used both on medium-format cameras with B mount (aka Pentacon Six, P6) and on small-format cameras (via an adapter from P6 to the desired system). I used a lens on the camera Canon 600D (APS-C, crop factor 1.6) and used not all of its potential, but only a small part of the center of its field of vision. Given the lack of information on this lens on the Web and photos from it, it would be interesting to try it on a 6x6 cm format.

Like all Vega lenses, this one is pretty high quality. Already with an open aperture, it shows good sharpness - a rare lens for such a large frame has a good resolution with an open one. The most pronounced in Vega-23 are chromatic aberration: The pre-focus area is purplish red and the pre-focus is green. This suggests that the secondary spectrum is very wide - i.e. HA fixed by today's standards is bad. Although, I believe that in their native format they make a not so significant contribution to the image. Of course, residual spherical aberrations are also observed (and the profile of spherical aberration is characteristic of biometars - the circle of a defocus has a brightness that does not increase towards the edge, which is not entirely customary). It was possible to find field aberrations only along the edge of the lens field, which is not used on small-format cameras - finding a circle of blur in the edge on one side indicates a coma. On covered apertures, the lens shows a very high resolution, limited by the same chromatism.

The absence of aberrations also means some “scarcity” of the image of the lens: it does not have unusual bokeh, any special behavior in the focus area. But this also means high optical quality - the better the lens, the less surprises it produces.

Single-layer enlightenment copes well in normal lighting - the contrast is not bad. But in the backlight, it falls sharply, a veil appears (although, most likely, this is due to reflections in the adapter and the macro ring). The lens in bright backlight catches large pink-purple highlights. The color rendition is shifted to a warm area.

Because the lens is designed for cameras with a large frame (6x7 cm), then in a small format it does not have any vignetting. It is on this feature that an interesting function is based that can be implemented with almost any lens.

Vignetting and bokeh control in hardware design

Vignetting (i.e., uneven exposure of the frame, usually a decrease in illumination from the center to the edge) is one of the most important characteristics of the lens. As a negative effect, vignetting is usually mentioned when considering wide-angle lenses, but at the same time it plays a very significant role in the formation of images of such well-known lenses as Helios-40, Zeiss Planar 50 / 1.4: it is it that is responsible for “twisting” the bokeh of the first and “feline” eye ”of the second. It - a common means of focusing attention on a central object - is often superimposed with the help of software.

It is easy to notice that the CZJ Pancolar 80 \ 1.8 has a vignette and is absent in the RO500-1 90 \ 2, similar in characteristics and scheme, and in the photo we see that Pankolar spins the background, and PO500-1 - no. If we compare the optical schemes, we will notice that the projector has both groups of lenses of the same size - both the front and the rear (therefore it is so large and heavy), while the Pankolar rear group is much smaller than the front in terms of light diameter (which makes it light and compact).

vega-vingetting-article-16

Comparison of CZJ Pancolar 80 \ 1.8 and PO500-1 90 \ 2 schemes: the rear group of Pankolar lenses is much smaller than the front in diameter. In RO they are very close in size.

vega-vingetting-article-17

This is the key: the size limitation of the rear lens group is essentially the factor that determines the format that the lens can cover. It can be covered in different ways. We say “with a margin” when we use only the central part of the lens's field of view and observe uniform illumination of the frame. We say - "back to back" - when we do not observe black fields, but we notice uneven illumination and darkening corners. We say - "with a vignette" - when we see black fields around the frame. Almost all photographic lenses are designed "back to back": this allows you to reduce weight and size, save expensive optical glass. Most cinema projection lenses are designed with a large margin (the PO50x-1 lenses often cover the SF, although they are essentially designed for APS-C).

Schematic representation of the effect of the size of the light diameter of the rear lens group on the defocus circle in bokeh

Schematic representation of the effect of the size of the light diameter of the rear lens group on the defocus circle in bokeh

This immediately gives rise to the idea: what will happen if you control the light diameter of the rear lens group during shooting? This means setting a variable aperture in the lens, made "with a margin" to cover the frame. This diaphragm, again, should not work as an aperture, which means it should be installed far from the "optical center" of the lens (a kind of "center of mass" - the point that will be the center of an ideal single lens, which our lens is equivalent to). How far is it? For a conventionally symmetrical (planar, aplanat type) lens, “far” starts a little further from the rear lens, and for a triplet / tessar-like lens, at least half of the rear segment. For a retrofocus lens, it is possible that the second diaphragm will need to be mounted flush against the rear lens assembly. I must say that “far” has a limit of “very far” - when the diaphragm begins not only to introduce vignetting, but to crop the image. So, you must not set the aperture too close to the matrix (this applies primarily to mirrorless cameras, where there is such an opportunity).

Installation options for the second aperture of vignetting control (K.V.) in lenses of different schemes

Installation options for the second aperture of vignetting control (K.V.) in lenses of different schemes

Back in 2015, I tested this idea with ordinary Industar-23U. Even in such a performance, she showed her worth. The same effect was noted when using the well-known projection device F-92 92 \ 2 LETI-60M with a lens diaphragm (from Industar-23U). And already this year, the Chinese are preparing a new line of optics, in which it is precisely for the purpose of controlling vignetting additional aperture! Needless to say, how versatile can a lens made in this way be?

Frankly, Vega-23 is not an interesting lens for the implementation of such a scheme due to the absence of any features of the picture in a small format. But she may be a good model.

Implementing a two-diaphragm scheme with SF optics in a small format is an extremely simple task. It is only necessary to install a circular multi-lobe (better than 9) aperture in the adapter type P6-M42. I used a microscopic diaphragm with a diameter of 36 mm that fits perfectly with my adapter. I am almost sure that the Chinese will in the future master the production of factory adapters with a built-in diaphragm precisely for controlling the vignette (there are already rings with a diaphragm - these are adapters of the EF-NEX type, where the manual diaphragm works instead of the electric one).

Photo of P6-M42 adapter with integrated diaphragm

Photo of P6-M42 adapter with integrated diaphragm

Photo of P6-M42 adapter with integrated diaphragm

Photo of P6-M42 adapter with integrated diaphragm

Photo of P6-M42 adapter with integrated diaphragm

Photo of P6-M42 adapter with integrated diaphragm

Below I will give the result of such a modified adapter with Vega-23.

Changing the nature of bokeh (twisting enhancement) with closing the second aperture

Changing the nature of bokeh (twisting enhancement) with closing the second aperture

Changing the nature of bokeh (twisting enhancement) with closing the second aperture

Changing the nature of bokeh (twisting enhancement) with closing the second aperture

Changing the nature of bokeh (twisting enhancement) with closing the second aperture

Changing the nature of bokeh (twisting enhancement) with closing the second aperture

Paired photos - the effect of closing the aperture on the picture of the lens (1 frame - open second aperture, 2 - covered)

vingetting-article-bokeh-1vingetting-article-bokeh-2vingetting-article-bokeh-3vingetting-article-bokeh-4vingetting-article-bokeh-5vingetting-article-bokeh-6vingetting-article-bokeh-7vingetting-article-bokeh-8vingetting-article-bokeh-9vingetting-article-bokeh-10As you can see, when closing the second diaphragm, the depth of field does not change, the edges become darker, and in the side the circles take the form of a “cat's eye”. In addition, the camera tries to make a mistake with the exposure and overexposure the center (metering mode for the entire frame) - it is better to use metering in the central region of the frame. The increase in contrast is also noticeable in some cases - the diaphragm cuts off spurious rays and reduces their re-reflection. With a strong closure of the second diaphragm, it begins to work as an aperture and increases the depth of field. If you close both the aperture and the zalino diaphragms, then you can come to the effect of the keyhole - the picture will be enclosed in a circle bounded by a black field. The stronger the aperture diaphragm is closed, the sharper the circle border. And the stronger the second aperture is closed, the smaller the circle in size.

The effect of the "keyhole": the second diaphragm is very closed, the aperture varies from 1: 3.5 to 1:11.

The effect of the "keyhole": the second diaphragm is very closed, the aperture varies from 1: 3.5 to 1:11.

The effect of the "keyhole": the second diaphragm is very closed, the aperture varies from 1: 3.5 to 1:11.

The effect of the "keyhole": the second diaphragm is very closed, the aperture varies from 1: 3.5 to 1:11.

The effect of the "keyhole": the second diaphragm is very closed, the aperture varies from 1: 3.5 to 1:11.

The effect of the "keyhole": the second diaphragm is very closed, the aperture varies from 1: 3.5 to 1:11.

In conclusion, I will cite photos taken on Vegu-23 in different conditions.

Conclusion

A relatively rare lens for medium format cameras, Vega-23, has good quality, but its dimensions are excessive for a small format lens, and the picture does not have any features. Meanwhile, it turned out to be a suitable lens for the implementation of an interesting scheme with two diaphragms, opening up new possibilities in photography.

Thank you for your attention, Eshmakov Rodion.

You will find more reviews from readers of Radozhiva here.

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Comments: 21, on the topic: Implementation of vignetting control “in glass and iron”. Material from the reader Radozhiva

  • anonym

    the master worked hard for fame, sharp sharpness, and very beautiful background blur.

  • Alexey de Paris

    An interesting review from an enthusiast! You need to add more photos of different plan to the review.

  • zengarden

    Great article, entertaining! And such a rare combination of theoretical and practical knowledge and direct hands :) Rodion continues to amaze ...
    In general, the second aperture for medium format optics is probably almost an optional condition (especially on the crop), because the contrast is noticeably reduced from flares due to too large frame coverage. For a long time I have been thinking of inserting a similar "cut-off device" into the adapter for Vega-12B, but there it is necessary to somehow calculate the size of the hole, and I'm in this nicht ferstein :(

    • Valentine

      Experimentally choose: for the experiment cut out circles from cardboard, then replace with something solid.

      • Rodion

        Yes, just calculate the diameter of the conical light beam at the proposed installation location of the circle. The light cone is a body obtained by rotating a trapezoid with base 1 in the form of the diameter of the rear lens and base 2 in the form of the camera diagonal length. The geometry is normal.

        • Valentine

          Rodion, thanks, great article. And Vega is interesting and your technical calculations. I agree that the calculation is NOT complicated. True, I didn't count myself, I just covered my Canon FD 85mm to see how much vignetting would be on a focused frame and how much the twirl would go in the background. It turned out like this (above without vignetting, below with vignetting; the first column is the focus area, the second and third are the near and far parts of the background).
          Canon FD85

        • Iskander

          Rodion, something is wrong here. According to this logic, a lens with a rear lens diameter larger than 36mm (inner diameter of the M42-EOS adapter) - cannot be used on a 36x24 matrix (43,27mm diagonal)? Will the adapter cut corners?

          • Rodion

            Will means. And many lenses are designed with this in mind. Or excluding. Like the Zenithar 50 / 1.2, which has a large rear lens and is shielded by a Nikon mount, for example. Because of what, in the comments under the review, the lens was accused of overestimating aperture. The lens is not in business there, just an attempt to mount it on Nikon is a failure. Nobody likes this system for the tight limits on the size of the rear lens.
            Canon lenses of type 85 / 1.2 have a large rear lens - and their aperture is cut by the bayonet and the shaft of the camera's matrix: in the bokeh, circles of confusion are cut off by the shaft and electrical contacts and so on.
            So the discrepancy between the size of the rear lens and the mount is a frequent and widespread phenomenon, one might say. It leads to some losses in real aperture ratio and to an increase in vignetting.

    • Eugene

      I inserted a plastic cover from the front zenith lens into my sf pentacon-sony adapter, cut a hole in it and inserted a black back tube from the rangefinder industrial 50 into this hole. The result was a cut-off. During testing, I found out that when photographing on a crop the camera does not need a cut-off, there is not enough light coming from behind a narrow window, but you need to ff.

  • Ivan

    Great stuff! Thanks for the review.

  • Michael

    Typo: "The lens unit itself is very simple and ascetic."
    A good article and interesting experience, however, eludes the meaning of practical application. Unless to make a good image is not very with a pinwheel a la Helios. Thanks to the author

    • Arkady Shapoval

      Fixed

  • Andrew Biliy

    an EOS-NEX adapter with a built-in diaphragm just for this (mentioned in the text) on Ali I saw this here link

    • Rodion

      This diaphragm serves to replace the electrical one, which cannot be controlled. The vignette for her is a side effect and, possibly, harmful, because the diaphragm there is not a fact that it is in the right place.

  • Alexey

    Great review. Thank you. But the lens is mediocre, such a complex alteration is clearly not worth it.

  • Rafael morales ruiz

    Hola. Soy un enamorado de las viejas lentes soviéticas con las cuales (Zenit 11 y 12 y Zenit-E con Helios 44-M4, Helios 44-2 e Industar 50-2) comencé en el mundo de la fotografía. Ahora trato de adaptar las viejas lentes de formato medio y gran formato a mi Canon 1Ds Mark II, por lo general con buenos resultados, con este toque “vintage” de estos objetivos. Curiosamente ha caído en mis manos, precisamente, el Vega 23, nº 3310, del cual se habla en este artículo. Si pudiera le mandaría fotos. Todavía me cuesta algo acostumbrarme al mismo. Pero voy obteniendo resultados. Precisamente estaba buscando información en internet sobre el Vega 23 porque estaba observando que tenía muchas más palas que las iniciales 8, para poner esta información en mi Facebook (Rafael Morales Ruiz), donde voy a colgar unada conot esografía tom objectiv Las vueltas que da el mundo, verdad? Un saludo desde España.

    • Rodion

      Hello! The fact is that I, the author of the article, is the person who sold you this lens on Ebay. To contact me, email me - rudzil@yandex.ru ... Also I can give you information some about this lens if you need it. Gracias!

  • The F

    Fuck. Really interesting article. I will keep in mind tk. very much from the "Helios" picture with a swirling backdrop. If I ever get a mirrorless camera, I will definitely try to cut something like that.
    Thank you.

  • orarve

    Masterpieces of St. Petersburg painting Perov Vasil

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