Review of a rare adapted film projection lens LOMO RO506-1 F=80 1:2

29.04.2024/1/XNUMX • XNUMX comment

Review of a rare adapted film projection lens LOMO RO506-1 F=80 1:2

Material according to LOMO RO506-1 F=80 1:2 especially for Radozhiva prepared Rodion Eshmakov.

Converted LOMO RO506-1. increase.

LOMO RO506-1 80/2 is the shortest and rarest lens in the RO50x-1 film projection line, which includes 7 lenses with focal lengths from 80 to 130 mm in different versions. The lens is very similar in every way to LOMO RO500-1 90/2except the focal length.

Technical characteristics (catalog of lenses by A.F. Yakovlev, vol. 1, pp. 335-337, GOI ONTI, 1970):

Optical design – 6 lenses in 4 groups, “double Gauss” / “Planar”;

Schematic diagram of the RO506-1 lens.

Focal length - 80 mm;
Relative aperture - 1: 2;
Estimated field of view angle - 21.5°;
Format – 18×24 mm (calculated), 44×33 mm (coated);
The back focal segment is 54.3 mm;
Frame diameter - 62.5 mm;
Features - a projection lens, does not have its own iris diaphragm and focusing mechanism.

Design and adaptation

The design of the LOMO RO506-1 is no different from other lenses in the RO50x-1 series, only the body is made of steel, which is why the lens is heavier than the common LOMO RO500-1, for example. The steel body also had lenses LOMO PO500-1 produced by the refinery. It is easy to install a diaphragm into the lens: just unscrew one of the slotted nuts holding the frames with lenses, and secure an iris diaphragm with a diameter of at least 29 mm in the sleeve between the halves of the “double Gauss”. To control the diaphragm, a slot must be made in the sleeve and in the body. It is convenient to use a Chinese macrohelicoid 25-55 mm M65-M42 as a focusing mechanism. In this case, it is easy to achieve compatibility with most modern cameras, including SLR cameras and medium format mirrorless cameras such as the Fujifilm GFX 44x33 mm format. Below are photos of the lens after adaptation.

Optical properties

LOMO PO506-1 is sharp with an open aperture at medium and close distances in the central area of the frame. The lens has a high resolving power, since spherical aberrations are corrected very well in principle (without abuse of mutual compensation), although there is some spherochromaticity characteristic of lenses of the PO50x-1 series. Field distortion is corrected perfectly for the APS-C frame and satisfactorily for the 36x24 frame: when used on a full-frame camera, image quality is limited by spherical aberration of oblique beams, astigmatism and residual field curvature, but the lens has fairly good control over coma, which can only be seen in the corners 36x24mm frame and beyond. Most field aberrations disappear at F/2.8, and at F/4 the lens has good field quality on a 36x24mm frame. It turns out that the correction of field aberrations for a 36×24 mm frame in LOMO RO506-1 80/2 was carried out in a more successful manner than in Meostigmat 90/2. But in medium format, LOMO PO506-1 is probably not the best choice, since outside the 36x24 frame the level of astigmatism and coma increases sharply.

The contrast of the formed image is good under normal conditions, at the level of other similar lenses with single-layer coating of optics. LOMO RO506-1 lenses have a single-layer coating, probably a physical type of MgF2, with a blue highlight color. This coating also works as a warm filter, but not as much as blue or purple chemical enlightenment.

Transmission spectrum of LOMO RO506-1.

In backlight, the lens tends to catch bright colored lentil-shaped highlights, “rain of the sun,” and a whitish veil. The veiling is probably due to the less than ideal condition of my specimen.

The lens has a pleasant bokeh that is devoid of swirl. Some zest is given by the light spherochromatic yellow edging of the discs, which intensifies towards the edge of the 36x24 mm frame. But in the corners of the 44x33 mm frame, the bokeh is already noticeably “spoilt” by coma and astigmatism, although at medium and short focusing distances this is not too noticeable.

The following are examples of photographs taken with full frame Sony A7s through shift adapter (medium format equivalent).

Then - photos on a full-frame Sony A7s https://radojuva.com/2022/06/a7s/ without using a shift adapter.

All reviews of film projection and filming lenses:

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

Conclusions

LOMO RO506-1 80/2, it seemed to me, better matches full-frame cameras in terms of image quality than LOMO J-53 75/2 и Meopta Meostigmat 90/2 – probably due to the compromised larger dimensions of the optical circuit. Overall, this is a very good projection lens for use with full frame cameras, although one that is extremely difficult to find. If you liked LOMO PO506-1 80/2, then first of all you should try it LOMO RO500-1 90/2, which is much easier to find.

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

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