Lomography x Zenit New Russar+ 5.6/20 L39/M Historic Wide Angle Lens Review

Material on the Lomography x Zenit New Russar + 5.6 / 20 L39 / M lens especially for Radozhiva prepared Rodion Eshmakov.

The lens was provided specifically for the preparation of the article by the commission photo shop "Kutuzov Photo" (Moscow).

The ultra wide-angle lens for full-frame mirrorless cameras New Russar+ 5.6/20 (hereinafter referred to as Russar+) has been produced in a small series since 2014 at the Krasnogorsk plant (Krasnogorsk, Russia). This lens is the fruit of a short collaboration between KMZ and the Lomographic Society, it is a re-released rare old Soviet lens for rangefinder cameras MP-2 20 / 5.6 (year of calculation - 1956, produced at KMZ), from which it differs only in external design and, probably, in illuminating coated.

The name of the lens is associated with the name of the creator - Mikhail Rusinov - the great Soviet optician, whose merits are recognized all over the world. About how Mikhail Rusinov invented (this is really a rare, completely original Soviet lens) a modern wide-angle lens (on the Lomography website Russar MP-2 is called “the mother of all modern ultra-wide-angle lenses https://microsites.lomography.com/russar-lens/”) without distortion and with minimal vignette - read in this article and on the site Lomographic Society.

Thus, Russar + is primarily of historical interest, since it is optically identical to the legendary one (that's right - many people know it, but few people shot it, which cannot be said about Helios-40) to the MP-2 lens, and the “+” for Russar + is a greater chance of finding a well-preserved copy than in the case of purchasing a Soviet lens. It is important to understand that the Russar + lens is not a competitor to modern wide-angle lenses, among which there are such impressive parameters as ttArtisan 21/1.5 or Voigltander Ultron 21/1.8.

Specifications (according to the KMZ product catalog, Lomography catalog, GOI catalog):
Optical design - 6 lenses in 4 groups, "Russar";

Focal length - 19.7 mm;
Relative aperture - 1: 5.6;
Field of view - 94 °;
Frame format - 36 × 24 mm (full-frame lens);
Rear focal line - ~ 11 mm;
Aperture - 7 blades, stepless;
Aperture limits - 1: 5.6–1: 22;
Focusing - manual;
The minimum focusing distance is 0.5 m;
Connection with the camera - M39 thread (working length 28.8 mm);
Filter thread diameter - 49 mm;
Lens dimensions - 55 × 38.5 mm;
Mass - 95

Plots of the frequency-contrast response of the lens (MTF / CFM / MTF, the spectral function used for the calculation is unknown, lomography data):

Design and execution of the lens

Russar+ is a very small and compact lens. Its body is made of chrome-plated brass, therefore its mass is palpable and amounts to almost 100 g. For comparison, Helios-150-44, made in an aluminum case, weighs about 2 g. I really like the look and classic retro design of the lens straight from the 1950s - Russar + is a pleasure even just to contemplate.

Almost hemispherical front and rear lenses look attractive. It is important to remember that the rear lens is not protected by the frame at all, since it protrudes strongly beyond its limits - the lens requires careful handling. Any defects on the menisci will certainly be reflected in the photographs, since Russar + has a small aperture, and the lenses (especially the rear) are located close to the image plane.

The lens layout is no different from the original MP-2. The lens also inherited the inconvenient aperture ring located on the front side of the lens.

The diaphragm itself consists of 7 petals, which are noticeably shiny, which is unlikely to have a good effect on image contrast when shooting with a lens with a covered aperture. Interestingly, at the maximum relative aperture of F / 5.6, the aperture is already somewhat closed, that is, the pupil of the lens is formed by the petals, and not by the lens frame.

A closer look at the lens blur dials at f/5.6 reveals that they are rounded heptagons.

With subsequent apertures, the effect is enhanced and the corners become more pronounced. The seven-blade rounded aperture allows you to get a faint effect of a fourteen-ray star in the photo from point light sources in the frame.

A problem when using a lens can be that access to the aperture ring is blocked if a light filter is installed. It’s good that the thread for the filter is not aligned with the aperture control ring at all, as in Jupiter 12. However, this will not save you from a circus with horses when using a polarizer: the fact is that the filter thread rotates along with the focusing ring, so it would be extremely inconvenient to use gradient or polarizing filters with Russar +.

When focusing, the lens practically does not change its dimensions - the lens block moves a very small distance. The focusing ring travels a little over 180°, and the minimum focusing distance is huge - as much as 0.5 m! The distance scale of the Russar+ is greatly stretched, in combination with a huge depth of field already from an open aperture, this provides easy focusing. In most cases, it is generally enough to put the lens at the hyperfocal distance and forget about focusing.

However, I really, really dislike it when the design of the lens does not allow focusing at close distances. Therefore, I took advantage of the charm of the M39 mount with a large working length, just as I did when using lenses with mount Leica M: through a combination of the M39-M42 ring, the M42-M42 10-15 mm macrohelicoid, the M39-M42 ring and the thin M42-NEX ring, I installed the lens without losing focus to infinity on a full-frame mirrorless camera Sony A7s, being able to focus at ~12 cm (from the matrix), which is much nicer compared to 0.5 m.

With the exception of a huge MDF and a bad aperture ring, the lens has no serious flaws. Visually and tactilely, this is one of the most pleasing lenses I have ever owned.

Optical properties. Simulation in Zemax: the effect of a thick matrix filter on image quality

The Russar MP-2/Russar+ lens has a very small rear focal length of only about 11mm. As a result, the rays that form the edges of the image fall on the sensor at a shallow angle, which leads to serious problems when using a lens with digital cameras. The bottom line is that, unlike photographic film, the camera matrix has an negligibly large thickness associated with the thickness of the cover glass filter (frequency filter, spectral filter), the thickness of the color filters of the Bayer pattern, and the depth of the well of the semiconductor cell. Rays incident gently on the matrix are deflected due to refraction in the matrix filter material, which affects the balance of aberrations of the entire system. In addition, if the subpixel size is small, then obliquely incident rays may fall into the wrong cell after passing through the Bayer filter, causing colorshift - extremely nasty uncorrectable color distortion, or even not reaching the semiconductor element at all, causing additional vignetting.

To prevent color shift, it is preferable to use the lens with cameras with a low pixel density (matrix resolution 36×24 mm <24 MP). On my camera Sony A7s with a full-frame 12 megapixel matrix, there was no color shift - this was the idea at one time to take A7s.

The effect of a matrix filter can be modeled using the ANSYS Zemax software package. The problem was that I could not find the optical design of the MP-2 in the public domain, but I managed to find a diagram of a similar lens - Russar-25 97 / 6.3, which I simply scaled to 20 / 5.6 without any additional changes in the optical design . The simulation showed that the angle of incidence of the rays reaches 50° from the normal to the image plane, which is a lot - in this case, the matrix filter should really significantly affect the image quality.

For the simulated lens, a set of diagrams was calculated, which will be further used to study the effect of the matrix filter on the balance of system aberrations.

It is easy to see that the MTF graph of the lens is very similar to that presented by Lomography. Apparently, Roussar has well-corrected field curvature and astigmatism - the distribution of the contrast transfer function over the field is quite uniform, and the limitations of its values ​​are due more to the influence of spherical aberration, as evidenced by the shape of the spots and the position of the focus at F / 5.6 relative to the paraxial focus.

It is known that in most cases the filter material is glass with a refractive index of ~1.52 (such as CDGM H-K9L, LZOS K8), and the filter thickness can reach ~1.5–2 mm (for early mirrorless cameras such as Sony A7 of the first generation). Let's add a plane-parallel plate of K8 glass 1.5 mm thick in front of the image plane and refocus the lens.

Adding a plate that simulates a filter significantly worsened the image quality over the field. Distortion increased to -1% (“barrel”), astigmatism sharply increased, due to which the contrast transfer function for the tangential direction dropped noticeably after 25 ° from the axis. The effect is also clearly seen from the increase in the size of the aberration spots for the 40° and 50° points.

Thus, the Russar+ lens will perform best with cameras where the thickness of the matrix filter is small (<0.5 mm). It is worth noting that for many cameras the matrix filter can be replaced with a thinner one (up to 0.2 mm - Kolari filters), but this is a rather expensive and relatively risky procedure. Using Russar+ on cameras with a thick filter and high-resolution matrix (for example, Sony A7R, A7R2) is completely inappropriate.

Optical properties. Modeling in Zemax: Comparison with previous wide-angle lenses

Speaking about the innovation of Mikhail Rusinov in the development of ultra-wide-angle systems, I would like to give a good example demonstrating exactly how the lens he invented differed from the previous ones. To do this, let's consider an ultra-wide-angle lens of the "Topogon" type, typical of the 1940s, again interpreted by Mikhail Rusinov - his early Russar-17 with parameters 100 / 5.6, which I scaled to 20 / 5.6 without any additional changes in the optical design.

Although the specified lens is significantly better than the Russar-25 type lens in the central region of the frame, it is inferior to it at the edge of the field due to pronounced astigmatism and chromatic aberrations. But the most important thing is not even that. The Topogon/Russar-17 type lens also has pronounced vignetting - about 50% for the frame angle.

And if we also consider the fall in illumination associated with the angle of incidence of rays on the image plane, then it turns out that the illumination of the frame decreases very quickly and reaches ~ 5% of the illumination in the center of the frame in the corners. That is, the corners are, in fact, just black.

If we turn to the vignetting diagram of a Russar-25 type lens, we will find that it simply does not exist - the geometric vignetting of the lens invented by Rusinov is zero.

In general, the drop in illumination from the center to the edge of the Russar-25 type lens is much less in comparison with the Topogon/Russar-17 type lens.

In other words, the merit of Mikhail Rusinov is the creation of a fundamentally new optical scheme of a wide-angle lens, the field illumination of which is many times greater than the field illumination of previously known wide-angle lenses. The principles laid down by Mikhail Rusinov were subsequently used by the famous German optician Ludwig Bertele when creating semi-symmetrical wide-angle Biogon lenses.

My experience

When used on a mirrorless camera Sony A7s (36 × 24 mm, 12 MP) Russar + with an open aperture forms an image with good contrast, but far from ideal sharpness - and in the center of the frame there is a slight soft effect like monocle. The main reason is uncorrected spherical aberration - in the Russar wide-angle six-lens scheme, it is in principle uncorrectable and therefore controlled by aperture - just like in "Periscopeor monocle. The corners of the frame are also far from ideal - there is pronounced astigmatism. Apparently, the appearance of astigmatism is due to the influence of the matrix filter of my camera.

Chromatic distortion and coma are not observed. The level of distortion is extremely low. Illumination of the frame from the center to the corners drops by about 1.5 steps exposure and does not depend on the aperture, since it is purely related to the angle of incidence of the rays on the matrix. These distinctive features of Rusinov lenses allowed them to firmly take their place in cartography, aerial photography, photogrammetry and photo reproduction.

When aperture down to F / 8-F / 11, image quality improves significantly - the lens becomes sharp enough for most tasks.

Image contrast is good under normal conditions, despite the fact that only the inner lenses are coated. The menisci are not coated because their curvature is too great to be able to apply the coating evenly by vacuum deposition (“physical” method) or spin-coating (“chemical” method). In hard backlight, glare and a whitish veil may appear. These artifacts often look quite attractive in an artistic sense and do not interfere much.

There is not much to say about the bokeh of the lens - in most cases it will not be possible to see it. When used at very close ranges, background blur at f/5.6 is most reminiscent of bokeh.”Periscope”, but without chromatic fringing. In general, blurring is pleasant when it can be obtained.

The following are sample shots taken with the Sony A7s. It was very interesting for me to shoot with this lens, although I rarely use wide-angle lenses.

Conclusions

Although the New Russar+ is strikingly inferior in terms of parameters and optical quality to modern wide-angle lenses, it is pleasant to use it, at least for aesthetic reasons - thanks to its excellent performance and a sense of touching history. At the same time, the lens is able to show a completely high-quality, contrasting and sharp picture, practically devoid of distortion and chromatism - although not on all cameras. For a connoisseur of old classic optics and a lover of street photography, this is definitely a pleasant find.

You will find more reviews from readers of Radozhiva here.