Review of the adapted projection lens Meopta Meostigmat 2/90 f62,5

Material on Meopta Meostigmat 2/90 especially for Radozhiva prepared Rodion Eshmakov.

Adapted Meopta Meostigmat 90/2. increase.

Czech film projection lenses Meopta, among which there are several lines with different optical designs and main parameters, are usually considered by enthusiasts as a higher quality alternative to Soviet lenses in the series Ж и Ro. Indeed, these lenses have some significant differences in optical design from Soviet ones that are worthy of coverage. This review presents the Meopta Meostigmat 90/2 lens, adapted for use with modern cameras.

Specifications:

Optical design – 6 lenses in 4 groups, “double Gauss” / “Planar” type, diagram not found;
Focal length - 90 mm;
Relative aperture - 1: 2;
Frame format - 16×21 mm (calculated), 44×33 mm (covered);
Landing diameter - 62.5 mm;
Features - a projection lens, does not have its own iris diaphragm and focusing mechanism.

Design and adaptation

The lens differs little in appearance from the Soviet projectors of the RO and Zh series: the Meostigmat 90/2 aluminum body is barrel-shaped with a diameter of 62.5 mm. If it weren’t for the standardization of mounting diameters in projection devices, the lens could have been much lighter and smaller in size - something like LETI-60M 92/2 – because the rear lens is quite small. However, the length of Meostigmat 90/2 is significantly shorter than the Soviet one with the same parameters PO500-1.

Meostigmat 90/2, like many other Meopta lenses, is assembled without the use of an autocollimation assembly, which simplifies the precise positioning of optical elements on the axis. In other words, the objective lenses are not rolled into metal frames and can be removed from the body. The ends of the lenses are blackened - and quite well, although this blackening tends to fall off. The use of bulk assembly did not negatively affect the optical properties - my specimen does not have any problems with the centering of the optics.

According to the technological level of the optical design, Meostigmat 90/2 can be classified as a late “dolanthan” lens of the “double Gauss” type: according to X-ray fluorescence spectroscopy, the lens uses glass like barium flints BF13 640.483 – BF16 670.473 as materials for the positive front and rear lenses ( and the same).

X-ray fluorescence spectrum of the front lens of the objective lens. Zr, Sn – instrumental artifacts, Ba, Zn, Sr, Pb, Sb, As, K are detected.

The conversion of the lens is simple and similar to the procedure for adapting the Soviet projection lenses RO and Zh: in the space between the halves of the double Gauss, an aperture with a light diameter of 36 mm and an external diameter of 50 mm can easily be placed, to control which you need to make a slot in the lens body. As a focusing mechanism, the best option is the Chinese macrohelicoid type 25-55 mm M65-M42, which will allow the lens to be used on almost any modern camera, incl. on SLR cameras. Below are photos of the converted lens.

Optical properties

Meopta Meostigmat 90/2 is a high-quality lens that is sharp at medium distances with an open aperture. In the central area of the image, the resolution is limited by the size of the secondary spectrum and residual spherical aberrations; along the edge of the frame, a decrease in contrast and resolution is noticeable due to the spherical aberration of oblique beams, coma and astigmatism. Spherochromatic aberrations (color fringe) at the open aperture of the lens, as it turns out, are significantly less than those of the PO500-1 90/2, but the level of field distortion is higher - and this despite the fact that Meostigmat has a higher level of geometric vignetting. Only at apertures below F/5.6 does the Meostigmat 90/2 demonstrate really good image quality over a 36x24 mm frame field.

The image contrast under normal conditions is quite good, comparable to the level of other similar lenses with single-layer coating of optics. Meostigmat 90/2 lenses have an anti-reflective coating of yellow, amber color, which increases light transmission in the short-wave region, which is problematic for yellowing heavy flints, and makes color rendering more neutral in comparison with “blue optics”.

Transmission spectrum of the Meopta Meostigmat 90/2 lens.

The Meostigmat 90/2 has a drawback related to its behavior in backlight: for the fifth surface of the lens at a certain angle, total reflection of light is observed, as a result of which the lens acts as a mirror for light sources outside the frame, causing the appearance of bright lentil flares. For this lens, the use of a hood is justified.

Lens bokeh is not like the background blur of lenses like PO500-1. It does not have chromatic fringing, in the central area of the frame the blur is almost neutral due to the mutual compensation of spherical aberrations, and at the edges of the frame one can observe the pronounced influence of the spherical aberration of inclined beams in combination with astigmatism and coma: the bokeh disk turns into an asymmetrical lemon with a bright fringing with predominance of its outer part.

Despite the small size of the rear lens, the Meostigmat 90/2 works well with shift adapters on full frame cameras and is therefore suitable for medium format cameras such as the Fujifilm GFX 44x33mm format. Below are photos using shift adapter and full frame mirrorless camera Sony A7s.

And more examples of frames at Sony A7s more.

All reviews of film projection and filming lenses:

The names of the lenses correspond to their exact spelling on the body.

Conclusions

Meopta Meostigmat 90/2 is a good projection lens that can be easily adapted for modern cameras. The lens differs in design from Soviet ones, but it cannot be said that it has any superiority over Soviet lenses type RO or Zh, since it is made at the same technological level, implying the same significant compromises in correcting aberrations. It makes sense to search for this particular lens only if there is interest in its specific picture, otherwise there are available and inexpensive PO500-1 90/2 и Zh-54 85/2 – the best choice for the enthusiast.

You will find more reviews from readers of Radozhiva here и here.

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