Russar MR-2 5,6/20mm

Russar MR-2 5,6/20mm is the grandfather of symmetrical-type rectilinear wide-angle lenses and the first 20mm wide-angle lens for 35mm Leica format rangefinder film cameras.

Designed in the Soviet Union by Mikhail Mikhaylovich Rusinov and manufactured in the Krasnogorsk factory near Moscow, the lens was awarded the highest award—“Grand Prix”—at the World Exhibition in Brussels in 1958.

Born on 11 February 1909, M.M. Russinov became one of the most respected optical scientists in USSR, he co-founded the USSR Science School of Computational Optics and discovered several optical phenomena, including aberration vignetting (1938), projection center distortion (1957), and existence of second-order aberration (1986).
The phenomenon of projection center distortion became the basis of the engineering photometry.

Back in the 1950's, the Russar MR-2's unique features left Leitz and Zeiss opticians to scratch their heads for years and ultimately, their lenses turned out bulkier and performed poorly when compared to Russar MR-2. This optical lens design was the pinnacle of its inventor's academic doctorate, defended in 1940, with U.S. patent 2,516,724 filed after WWII on August 23, 1946. Patent granted on July 25, 1950.

In 1938, the Russian optical genius Mikhail Mikhaylovich Rusinov (Roossinov) was the first optician in the world to discover and utilize the phenomenon of aberrational vignetting, which made it possible to drastically improve the natural illumination fall-off over the field of view of photographic lenses and their resolving power. Aberrational vignetting is achieved by the introduction of pupil aberrations in the front part of the optical system located between the aperture stop and the object space.

When round aperture stop is positioned on the inside of an axially-symmetrical optical system, between two symmetrical lens groups, it would, with the help of the pupil aberrations, be able to increase light entering the pupil for oblique rays. Thus, the growth of the entrance pupil compensates for the natural illumination fall-off.

This outstanding feature of Rusinov's invention increased the edge illumination of the field approximately by a factor of 2 (two) for wide-angle lenses.

The lens design consists of two, more or less symmetrical halves, one of which includes the lenses 1, 2 and 3, and the other 4, 5 and 6; each half consists of two systems of lenses - one negative and one positive; the exterior lenses 1 and 6 being negative, and the medial lenses 2, 3 and 4, 5 being positive.

The entire system of lenses has a common axis of symmetry and each of the negative lenses is separated from the positive lens by air. Both exterior negative lenses 1 and 6 have the form of greatly curved meniscus, the inner surfaces of which are slightly less or greater than a semisphere, i. e. with the inner semi-spherical surface the radial angle being 170 and 190.

Each of the medial positive lenses consists of two cemented lenses 2, 3 and 4, 5; with properly cemented surfaces for correction of aberration of incident beams, and with their convex surfaces facing the diaphragm, and the index of refraction with the concave side of the cemented lens should be greater than that of the convex side. In order to correct for distortion and zonal aberration the medial positive lenses should be thick (i. e. have a thickness of about 20% of the focal length); the surfaces of these lenses facing the diaphragm are either plane or slightly concave.

The form of the greatly curved meniscus with its inner surface approximately equal to a half-sphere of the exterior lens 1 is of great importance, because due to this fact aberrational vignetting is achieved.

Between the two halves of the objective a light filter may be inserted if properly accounted for when calculating the objective. The types of glass of all the lenses of the objective are chosen in pairs having equal refractive indexes but the dispersion of which are different in order to achieve correction for chromatic distortion and chromatic astigmatism.

By 1946 M.M. Rusinov's lens design (Russar) was documented worldwide. His patent is referenced in numerous patents related to photographic lenses.

When Ludwig Bertele was hired by Zeiss in 1951, to design a wide angle lens for Contax and Hasselblad, Bertele could not obtain master patent for the use of single meniscus at each end of the lens as Rusinov had already patented it, which forced Bertele to design a lens with compromises.

At the International Congress at Stockholm in 1956 Ludwig Bertele paid tribute to Rusinov for his highly interesting and original solution to the problem of securing adequate illumination in the picture corners etc. etc..

In 2011 Dr. Hubert Nasse, senior scientist at Zeiss and chief optical designer wrote in Camera Lens News 41 published by Zeiss Carl Zeiss AG Camera Lens Division:

In 1946 the first patent for a new kind of symmetrical wide-angle lens was applied for by the Russian lens designer Michail Rusinov. It looked as if two retrofocus lenses had been combined with the rear elements together and thus had a symmetrical arrangement of positive refractive powers close to the aperture, surrounded at the front and back by strongly negative menisci.
As of 1951, Ludwig Bertele carried this idea further and designed the legendary Biogon on behalf of Zeiss...

In 2014, Lomography and Zenit Photo in Krasnogorsk, released the Russar+ — an updated version of the 1958 Russar MR-2. The new lens is multi-coated and it's body is made out of brass and features a longer filter thread.