Review of the LOMO Epi 9x0.2 microscope lens, adapted in two versions to the RMS standard

Material especially for Radozhiva prepared Rodion Eshmakov.

A pair of adapted LOMO Epi 9×0.2.

The LOMO Epi 9×0.2 OE-9 objective is a low-magnification achromat with an M27 mounting thread, designed for “large” research microscopes and is designed to observe an object in reflected light using illumination via a special mirror condenser located coaxially with the objective. Such an objective cannot be attached to a conventional RMS standard microscope, and whether this should be done is discussed in this article. Most of the questions about the microscope design, types of objectives and their practical use have been discussed here.

Specifications:

Optical design – 4 lenses in 2 groups, Richter aplanate, does not use special optical glasses;

Drawing of the optical design of the lens

Type of correction – achromat;
Tube distance – 190 mm (factory version);
Magnification factor – 9x (with tube distance 190 mm);
Numerical aperture (NA) – 0.2;
Focal length - 18.4 mm;
Working distance – 5.4 mm with a tube distance of 190 mm;
Cover glass thickness – 0 mm;
Immersion required - no;
Mounting type – M27 thread;
Features - microscopic lens, does not have an iris diaphragm and a focusing mechanism.

Design and adaptation of LOMO Epi 9×0.2

Due to the presence of a built-in condenser for observing opaque objects, LOMO Epi 9×0.2 has an increased body diameter and a larger thread compared to the RMS standard. The body can be easily disassembled using a clock screwdriver; it is possible to completely separate the small-sized lens block for subsequent transplantation into a new body.

Photo of LOMO 9x0.2 Epi in factory form (from the Internet).

Photo LOMO 9×0.2 Epi in factory form (from the Web).

There are two options for adapting this lens: 1) with a new tube distance of 160 mm; 2) while maintaining the tube distance of 190 mm.

In the first case, the lens will work with conventional biological and teaching microscopes in the same way as it would work on its original microscope. To do this, an extension ring 30 mm thick will be required between the previous lens mounting plane and the microscope turret to compensate for the difference in tube distances, which will lead to an increase in the parfocal distance of the lens. For such an adaptation, installing a lens block into a gutted, illicit LOMO 40×0.65 lens (spring-loaded version) is well suited. To improve image contrast, it is preferable to install a light-protective sleeve in the space between the rear lens of the lens and the mounting thread, and to protect the front lens, I made a short, dense tube for it. Photo of the adapted lens below.

The second modification option is significantly smaller in size and easier to manufacture, but entails a reduction in the tube distance by 30 mm, which means a reduction in magnification to ~8x and a likely increase in field aberrations. The lens block of the lens is easily screwed into the thread of the rear nut of the LOMO 40×0.65 lens (option without a spring) - you just need to carefully cut off the nose part of the faulty donor. A lens adapted in this way is shown in the photo below in comparison with the “long” version.

In general, LOMO Epi 9×0.2 is a more advanced version of the very, very cheap and common standard lens of old 8×0.2 educational microscopes. It differs from its progenitor Epi 9×0.2 in its larger working distance, higher manufacturing standards and the presence of coating on the lenses - all surfaces of my copies are coated except the first one. At the same time, there is information about the existence of lenses in which the first surface is coated. It is clear that this does not sound very convincing to justify converting a lens costing $5 into something similar to a lens costing $5, but we will talk about this in more detail when considering the optical properties. Apart from the nuances of adaptation, the LOMO Epi 9×0.2 is a very convenient and quite versatile lens for microscopy, which allows you to plunge into a real microworld, which is very different in scale from what is typically achieved using photographic lenses with special devices. A fairly large working distance makes it easier to work with light, which makes the lens preferable modern Chinese Plan 10×0.25, eg.

Optical properties

The LOMO Epi 9×0.2 lens has good sharpness in the central area of the frame, but suffers from pronounced spherochromatic aberrations (bright purple or yellow fringing). The lens is inferior in image quality on axis Chinese Plan 10×0.25.

When observing flat objects, sharpness drops sharply towards the edge of the frame due to the strong field curvature. At the same time, the astigmatism of the lens is corrected very well - when refocusing along the edge of the frame and using stacking, getting a sharp image is not a problem.

Image of the LOMO OMO-U4.2 reflected light object micrometer, taken on a Sony A7s and the “long” version (tube distance 160 mm) of the lens with a tube length of ~160 mm. The length of the mark is 1 mm, the division value is 0.01 mm.

The “short” version (tube distance 190 mm) compared to the “long” version (tube distance 160 mm) is distinguished by a visually larger field, which is consistent with its calculated magnification of 8x. There was no significant difference in image quality between the two versions of the adapted lens.

Image of the LOMO OMO-U4.2 reflected light object micrometer, taken on a Sony A7s with “short” and “long” lens options with a tube length of ~160 mm. The length of the mark is 1 mm, the division value is 0.01 mm.

The main advantage of the LOMO Epi 9×0.2 lens (and its progenitor – LOMO 8×0.2) is the complete absence of lateral chromatic aberrations, which allows it to be used without compensation systems (eyepieces or other devices). For comparison: the standard lens of the Biolam LOMO Plan 9×0.2 microscope has noticeable red-blue chromatic aberration, although it boasts an almost perfectly flat field. Similar Chinese Plan 10×0.25 greatly inferior in image quality to the old Soviet achromat precisely because of the indecently high level of lateral chromatism.

Image of the LOMO OMO-U4.2 reflected light object micrometer, taken on a Sony A7s and LOMO Plan 9x0.2, Epi 9x0.2 lenses with a tube length of ~160 mm. The length of the mark is 1 mm, the division value is 0.01 mm.

Image of the LOMO OMO-U4.2 reflected light object micrometer, taken on a Sony A7s and LOMO Plan 9×0.2, Epi 9×0.2 lenses with a tube length of ~160 mm. The length of the mark is 1 mm, the division value is 0.01 mm.

Due to the presence of an antireflection coating on the optics (~physical, MgF2) and a small number of optical elements, LOMO Epi 9×0.2 is also notable for its high image contrast - just compare it with the above-mentioned LOMO Plan 9×0.2 - an uncoated disgrace. Of course, Epi 9x0.2 will be better than the regular 8x0.2. In addition, LOMO Epi 9×0.2 has high light transmittance (light optical glasses) and, theoretically, can be used for UV photography - the short-wave absorption edge is 340 nm.

Light transmission spectrum LOMO Epi 9x0.2.

Light transmission spectrum LOMO Epi 9×0.2.

The following are examples of photographs (without stacking) taken using an M10 microscope and a Sony A7s camera in direct focus on both lens options. For the most part, I used the lens to photograph crystals of compounds obtained in a training workshop by 1st year students of the Faculty of Chemistry. For those interested, please indicate the objects in the photo:

1 – IPS smartphone display;
2, 3 – unknown ammonium oxorodane tungstate in an ampoule;
4 – luminescent cubane complex of copper(I) iodide with pyridine under illumination with white light and UV 370 nm;
5 – vanadyl sulfate on a copper substrate;
6-8 – hexaamminnickel chloride.

Below are examples of photos using the same link, but with stacking in Photoshop. Specifying objects:
1 – contact pad of the gas sensor chip, which I work with in the laboratory;
2 – place of soldering of the antenna contact of the substrate to the pin contact of the chip;
3 – vanadyl sulfate hydrate on a copper substrate;
4-6 – hexaamminnickel chloride;
7 – cesium-vanadium alum;
8 – cobalt(II) molybdate in two crystalline modifications – pink and gray-green;
9 – chromium(II)-hydrazinium sulfate;
10, 11 – potassium rhodanocobaltate;
12 – potassium dioxalatocuprate dihydrate;
13 – potassium-nickel schenite;
14 – Reinecke salt;
15 – unknown ammonium oxorodane tungstate;
16 – unknown ammonium oxorodane tungstate after oxidation in air.

All reviews of RMS standard microscope lenses with a tube distance of 160 mm:

Modern optics from Chinese manufacturers:

Reviews of Soviet lenses for microscopes:

Conclusions

LOMO Epi 9×0.2 is an ultra-budget (~$5-10) low magnification lens, easy to use due to its long working distance and having an acceptable level of quality for photography due to the presence of an anti-reflective coating on the optics, excellent correction of astigmatism and lateral chromaticity. I definitely recommend the lens, despite the need for adaptation and the seeming availability of modern alternatives.

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