Progress microscope objective 9x0.20 190-P (OM-13P)

Material on the lens especially for Radozhiva prepared Rodion Eshmakov.

OM-13P 9×0.20 190-P.

The 9×0.2 190-P (OM-13P) objective was included in the optics kit for Soviet polarizing (petrographic) microscopes. In fact, the OM-13P is a variant of the common and inexpensive standard objective of biological microscopes LOMO 8×0.2 M42, but without stress in the lenses and for the final tube distance of 190 mm versus the usual 160 mm. And here is a similar one in parameters LOMO Epi 9×0.2 (OE-9) – similar in design, but optically still a different objective. The 9×0.2 190-P objective can be used on conventional microscopes with a finite tube distance, but parfocality will be lost, and the magnification will be the same ~8 times as M42The version of the lens presented in this review has an anti-reflective coating on the lenses, but not all OM-13P lenses were coated.

Technical specifications

Source – reference book “Computational Optics”, ed. MM. Rusinova, L., 1984, p. 338.
Optical design - 4 lenses in 2 groups, aplanat;

Drawing of the optical scheme of the lens.

Type of correction – achromat;
Tube distance – 190 mm;
Magnification factor – 9x (with tube distance 190 mm);
Numerical aperture – 0.2;
Focal length - 18.1 mm;
Working distance – 8.14 mm;
Parfocal distance – 25 mm;
Cover glass thickness – 0 mm (designed for use without a cover glass);
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

The lens is made in a very compact case made of chromed brass. The lenses are enclosed in metal frames, there are no manually centered elements: you can disassemble the lens for maintenance without much risk of not being able to reassemble it later.

The objective has a standard mount to the RMS type microscope, but due to the non-standard size of 25 mm, problems may arise when using it: some microscopes, due to the short stroke of the focusing mechanism, may not be able to focus with this objective, in addition, other objectives in the revolver may interfere with focusing, resting against the table. There are special extension rings, placed between the objective and the microscope, which will allow the use of any objective with a tube distance greater than 160 mm without interference.

The optics of this specimen have an anti-reflective coating, most likely MgF2, applied in a vacuum chamber. In terms of light transmission, the OM-13M lens is better than the uncoated one. LOMO 8×0.2 M42, but is inferior to the lens LOMO Epi 9×0.2 OE-9.

Light transmission spectra of lenses 8×0.2 (M42), 9×0.2 Epi (OE-9), 9×0.2 190-P (OM-13P).

The quality of light protection is generally quite low: the inside of the lens does not have a matte coating and ribbing, which is why parasitic light reflections occur. Lens LOMO Epi 9×0.2 OE-9 made much better quality.

The working distance of the OM-13P is quite large (8.14 mm) and is comfortable when working both in transmitted and in lateral reflected light. In this, the lens is practically no different from LOMO 8×0.2 M42 with a working distance of 8.6 mm. This similarity is not accidental: the OM-13P is obviously a slightly recalculated version M42. At the same time, the lens OE-9 9×0.2 Epi has a working distance significantly smaller - 5.4 mm, and therefore it is definitely not a minor conversion M42.

Optical properties

The lens has the same optical characteristics as a regular one. LOMO 8×0.2 M42, but has a slightly better image contrast. When used in a system with a tube distance of 160 mm, the OM-13P lens is inferior in image quality across the field to the lens 8×0.2 M42 due to pronounced astigmatism. Both lenses are inferior LOMO Epi 9×0.2 OE-9 in terms of image quality both in the center and across the field. Modified Chinese Achromat 10×0.25 It turns out to be the best option for image quality in the central area, but suffers from astigmatism at the edge of the APS-C frame.

Overall, the image quality produced by the OM-13P lens is very mediocre, the lens Epi 9×0.2 I liked it much better.

Below are examples of photographs taken with a Sony NEX-6 camera and an OM-13P lens at a tube length of 160 mm.

Objects in the photo: 1-3 – MOF (metal-organic framework) crystals with benzenetetracarboxylic acid and rare earth cations, dark field illumination with an OI-10 condenser; 4-5 – MOF (metal-organic framework) crystals with benzenetetracarboxylic acid and rare earth cations, oblique illumination with an OI-14 condenser; 6-14 – crystals of an organic compound on the vessel walls in mixed illumination (side and transmitted light of different temperatures), 15 – MOF (metal-organic framework) crystals with benzenetetracarboxylic acid and rare earth cations in reflected light under side illumination.

Next, some examples of photos using stacking.

Objects in the photo: 1 - crystals of 3-chloro-1-phenylpyrazole under dark field illumination with a KF-1 condenser (aperture for 90x objective); 2-3 - crystals of phenylenediamine under dark field illumination with a KF-1 condenser (aperture for 90x objective), 4-6 - MOF (metal-organic framework) crystals with benzenetetracarboxylic acid and rare earth cations, dark field illumination with an OI-10 condenser, 7 - MOF (metal-organic framework) crystals with benzenetetracarboxylic acid and rare earth cations, oblique illumination with an OI-14 condenser; 8 - MOF (metal-organic framework) crystals with benzenetetracarboxylic acid and rare earth cations in reflected light under lateral illumination.

Conclusions

The Progress 9×0.20 190-P (OM-13P) lens is quite mediocre and has no significant advantages over the most common 8 × 0.2, and much less convenient to use on a conventional microscope due to the non-standard parfocal distance. It makes sense to use this lens only on those microscopes for which it was originally intended, where it is one of a set of similar parfocal lenses.