This is description of this part:
LOMO microscope objective with 40x magnification, intended for second-type phase contrast and for use with the LOMO KF-5 condenser.
Basic parameters of this objective:
Manufacturer: Lomo (ЛОМО)
Magnification: 40x
Correction: achromatic
Engraving on the objective: 40 0,65 Ф-2 ЛОМО
Numerical aperture N.A.: 0,65
Working distance: 0,55 mm
Tube length: 160 mm
Parfocal length: 33 mm - a so-called short barrel objective
Cover glass: yes, 0,17 mm thick
Phase contrast: yes, type F-2 (Ф-2), which means there are two phase rings inside the objective
Immersion: no (dry objective, sometimes called an "air immersion" objective)
Specimen protection: no, the objective has no spring-loaded mechanism
Thread: RMS
Work in brightfield without phase contrast: possible, but even the manufacturer states in the manual that the image quality is worse than with an objective without phase rings inside
A very important note: two phase rings inside an objective bring to mind variable phase contrast (PhZ at PZO or PhV at Carl Zeiss Jena). With LOMO, however, this is rather something like a "second type of positive phase contrast". LOMO states in the manual (https://laboratorium.dp.ua/item/68) that one image is obtained when light passes through both rings (with the condenser iris diaphragm open) - and a different one when the diaphragm is closed far enough that light no longer reaches the outer, wide ring and only the inner ring works. The manufacturer recommends viewing the specimen in both modes, because together they give a more reliable idea of its structure. The contrast stays positive (thicker or denser parts of the specimen appear darker against a bright background), and both modes differ from work with the single-ring "Ф" objectives and the LOMO KF-4 condenser (ЛОМО KФ-4), where both the objective and the condenser diaphragm have only one ring. So the resulting effect does change - but this is not variable phase contrast; the change is stepwise (either-or), not continuous.
The objective presented here fits the LOMO KF-5 condenser (ЛОМО KФ-5). That condenser has a mounting diameter of 37 mm and is very often used on microscopes from other makers, among them Carl Zeiss Jena and Olympus (especially Olympus CH). With a suitable build-up ring fitted (3D printed, for example), this condenser is commonly used in microscopes with a 39,5 mm condenser seat as well. The instructions for setting up LOMO KF-5 phase contrast can be found here: https://scopica.ru/proj/ustroystvo-dlya-nablyudeniya-metodom-fazovogo-kontrasta-kf-5/
This is a so-called short barrel objective, with a parfocal length of 33 mm. It is very commonly mounted on a 12 mm extension, which allows it to be used in microscopes that require objectives of 45 mm length. Professional adapters with protective optics, metal adapters and the popular 3D printed DIY solutions all work here.
LOMO objectives are very popular with owners of microscopes from other makers. Because of the historical links, owners of Carl Zeiss Jena microscopes treat them as an obvious substitute for those German objectives.
This objective fits practically any microscope from any maker, provided it has an RMS thread and accepts objectives with TL=160 mm and a parfocal length of 33 mm (or 37 / 45 mm if a suitable adapter is used). A few such microscopes are listed in the "compatibility" section, but that is not a complete list.
What is this part needed for?
- if you own a microscope with the LOMO KF-5 phase contrast condenser but are missing the 40x F-2 objective from the set
- if you have such a set, but the LOMO 40x F-2 objective in it is damaged or in very poor condition
- if you are curious about this variety of phase contrast and want to experiment with this objective on other condensers, to get interesting and non-obvious results
