Review and test of the LOMO M42 8x0.2 achromatic microscope

Material on the lens especially for Radozhiva prepared Rodion Eshmakov.

8x0.2 lenses from LOMO and Progress factories.

8×0.2 lenses from LOMO and Progress factories.

The 8×0.2 objective is the most common Soviet microscope objective, which was standard for a huge number of microscopes of various purposes - from school to research. The optical design of this objective was invented in the 42th century, and the M1930 objective (this is its official code) was produced at various enterprises (Progress, LOMO, LZOS ...) from the ~44s until the end of the XNUMXth century. With a high degree of probability, this particular objective will be the only one that survived on an old microscope found at a flea market or in a garage. And this same objective is one of the most balanced in terms of properties of old micro-optics - given the low price and ubiquity, it can be called a kind of Helios-XNUMX for microscopy.

Technical specifications

Source: Handbook "Computational Optics" ed. MM. Rusinova, L., 1984, p. 336.
Optical design - 4 lenses in 2 groups, aplanat;

Schematic drawing of the optical design of the lens

Type of correction – achromat;
Tube distance – 160 mm;
Parfocal distance – 33 mm;
Magnification factor – 8x;
Numerical aperture – 0.2;
Focal length - 18.1 mm;
Working distance – 8.6 mm;
Cover glass thickness: 0-0.17 mm;
Chromatic difference of magnification – 0% (for lines F, C);
Immersion required - no;
Mounting type – RMS standard (4/5” x 1/36” thread);
Features - microscopic lens, does not have an iris diaphragm and a focusing mechanism.

Lens design

LOMO 8×0.2 has small dimensions (parfocal distance 33 mm) and a large working distance of 8.6 mm, which makes it convenient when working with side light.

The design of the objective is very simple. The chrome-plated brass body has a slotted nut on the side of the thread for attaching to the microscope, which fixes the lenses. The objective has a non-adjustable design, so you can unscrew the nut and remove the lenses in the autocollimation frames and the interlens insert, if necessary for cleaning. It is very useful to blacken the shiny space between the lenses with matte black paint to increase the contrast, but I did not disassemble the specific objective presented in the review.

Image quality

LOMO 8×0.2, although a primitive lens, has a number of important advantages in comparison with even some modern optics. Thus, this lens has minimal lateral chromatic aberration, and, despite the pronounced curvature of the field, is characterized by corrected astigmatism for the field within the APS-C frame. This means that it is possible to achieve acceptable image sharpness at the edge of the frame, especially when using stacking. Below are test photos of an object micrometer and a smartphone display using an 8×0.2 lens and a Sony NEX-3 camera on a modified MBI-1 microscope.

This lens also has only 2 groups of lenses, due to which the image contrast, even with all the shortcomings in the form of poor blackening and lack of enlightenment, is better than that of the more “advanced” Soviet planachromat LOMO Plan 9×0.2. With modern Chinese achromat 10×0.25 after blackening and aperture setting to NA=0.2, the old 8×0.2, of course, can no longer compete in contrast, just as it can no longer compete with its own version for observations in reflected light – Epi 9×0.2 (OE-9).

The downside of the M42 8×0.2 is the mediocre image quality overall: the picture is full of spherochromatic aberrations, which are very annoying in some situations. Apertured to 0.2 Chinese Achromat 10×0.25 is a much higher quality lens.

Crops of photographs of the reflected light object micrometer OMO (division value 0.01 mm), taken with the help of Sony NEX-3 and LOMO Plan 9x0.2, 8x0.2 and modified Chinese achromat 10x0.25 160/0.17 lenses.

Crops of photographs of the reflected light micrometer object OMO (division value 0.01 mm), taken with the Sony NEX-3 and lenses LOMO Plan 9×0.2, 8×0.2 and modified Chinese achromat 10×0.25 160/0.17.

Also see comparison of 8-10x lenses here.

Examples of photos taken on LOMO 8×0.2 and Sony NEX-3 without stacking are shown below.

List of objects in the photo: 1-3) Titanium disulfide, 4) o-Aminophenol, 5-6) Cobalt sulfate contaminated with basic sulfate, 7) Potassium bisoxalate cuprate, 8) Sugar crystal.

Then – photos on the Sony A7s with the tube length increased to ~190 mm.

List of objects in the photo: 1) Crystals of iron(III) acetylacetonate on test tube glass, 2) Chips of hard alloy, 3) Iron(II, III) oxoacetate, 4-6) Zirconium sulfide-disulfide, 7) Ammonium polyoxomolybdate(V, VI)-132, 8) Ammonium molybdochromate.

Next is a photo using stacking on a Sony NEX-3.

In the photo: 1-3) Titanium disulfide, 4) o-Aminophenol, 5) Cobalt sulfate contaminated with basic sulfate, 6) Sugar crystal.

And examples on Sony A7s with stacking at a tube length of ~190 mm.

List of objects in the photo: 1) Hard alloy chips, 2) Iron(II, III) oxoacetate, 3) Ammonium polyoxomolybdate(V, VI)-132, 4) Ammonium molybdochromate.

All reviews of RMS standard microscope objectives with a finite tube distance (160-190 mm):

Modern optics from Chinese manufacturers:

Reviews of Soviet lenses for microscopes:

Carl Zeiss lenses:

Lenses from other manufacturers:

Lambda 10/0,25 160/-

Conclusions

Among all the old micro-optics, the most common and cheapest in the post-Soviet space LOMO 8×0.2 is a rare example of a quite tolerable lens even by today's standards, which is suitable for photography in direct focus. Yes, the lens is far from ideal in terms of image quality, but it is also devoid of the most critical shortcomings, and a simple procedure for blackening the interlens space will also improve the already not-so-bad contrast. Therefore, do not disdain the old 8×0.2 achromat - it can be used for its intended purpose.

RADOJUVA