Material on the lens especially for Radozhiva prepared Rodion Eshmakov.
CZJ 40×0.65 lens.
Objectives with a magnification of 40x are the workhorses of light microscopes, especially biological ones: in most cases, they allow you to achieve an image scale convenient for visual observation with sufficient (for histological studies, for example) resolving power without the need for oil immersion. This article presents a relatively affordable achromatic objective Carl Zeiss Jena 40/0,65 160/0,17 (hereinafter referred to as CZJ 40×0.65), designed for use with microscopes with final tube distance.
Technical specifications
Optical design – aplanat with meniscus corrector, presumably 5 lenses in 3 groups;
The proposed optical design of the lens. The manufacturer did not provide any design information.
Type of correction – achromat;
Tube distance – 160 mm;
Magnification factor – 40x;
Numerical aperture – 0.65;
Working distance – 0.5 mm;
Parfocal distance – 45 mm (DIN standard);
Cover glass thickness: 0.17 mm (image quality is reduced when used 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 CZJ 40×0.65 objective has a housing that is almost the same length as its maximum possible size of 45 mm. All elements of the housing are made of metal. The shiny part can be twisted off, exposing the spring-loaded brass lens block of the objective, which can be removed by unscrewing the screw that limits the travel of the lens block in the wall of the housing and the aperture diaphragm near the thread that mounts the objective to the microscope. The objective lenses are crimped into metal frames, and the position of the second component is centered during assembly through four holes in the lens block manually. Do not disassemble this lens unless you are prepared to align it yourself later.
The lens has a very short working distance of 0.5 mm. Because of this, and also because of the large numerical aperture, it is not suitable for working with side illumination without any specific devices or techniques. Metallographic objectives with similar parameters usually have a working distance of several millimeters - from 2 to 5 - and with them it is much easier (but still non-trivial!) to achieve acceptable image quality with side illumination. The short working distance requires careful and gentle handling of the lens to avoid its front element poking into the sample, especially if it is not covered with clean glass. However, the lens block has some protection - a spring with a stroke of several millimeters, and therefore it will be difficult to crush the sample or the front lens of the lens in case of focusing errors. Another thing is that it will be extremely problematic to remove dirt that gets on the very small concave front lens of the lens.
The lens has good, but not ideal, light protection. An important advantage is the presence of an antireflective coating on the lenses, which is very rare for Soviet micro-optics, for example. The coating has a blue glare and is most likely magnesium fluoride applied in a vacuum. When held up to the light, the lens is noticeably yellow.
The CZJ 40×0.65 optical design uses heavy crowns, as evidenced by the detection of barium, strontium and zinc in the X-ray fluorescence spectrum (Bruker M1 Mistral). The lead signal most likely refers to the second objective lens made of lead flint shining through the front lens. The iron, nickel and copper signals refer to the material of the objective body and lens mounts.
XRF spectrum of the front lens of the CZJ 40×0.65 objective.
The spectrum of the rear lens of the objective shows zinc and barium, and apparently also relatively small amounts of lanthanum. It is difficult to conclude that this material belongs to a specific class of glass: it may be either the lowest dispersion of the available lanthanum crowns, or it may even be a phosphate crown of the type FK14. Most likely, it is still a lanthanum crown, since glasses of the phosphate crown type were not very available at that time and they would hardly have been used in an achromatic objective.
XRF spectrum of the rear lens of the CZJ 40×0.65 objective.
The CZJ 40×0.65 objective is essentially an updated version of the usual Abbe achromat, designed back in the XNUMXth century: the front element instead of a plano-convex lens is replaced by a more expensive, but very useful positive meniscus, instead of simple crowns (like LZOS K14 or Schott K7) heavy and lanthanum crowns were used, the dimensions were increased from 33 (RMS) to 45 mm (DIN), and anti-reflective coating of the lenses was applied. In the USSR in those same years, they were still producing the 40×0.65 160/0.17 MS lens, which had neither anti-reflective coating, nor progressive materials, nor improvements in the basic design, nor even a spring in the body - it was literally a copy of those same Abbe achromats of the XNUMXth century - with all the ensuing consequences.
Optical properties. Comparison with USSR analogues
In general, the calculation of a high-quality 40x lens is an extremely difficult task. With a fixed image field size, a good lens with a contrast >0.3 acceptable for modern cameras for frequencies of 45-50 lines/mm in the image space should have a diffraction-limited quality at an aperture of 0.05 for 2x magnification, 0.1 for 4x magnification, 0.25 for 10x magnification, 0.5 for 20x magnification and, it turns out, 1.0 for 40x magnification. Moreover, without immersion, it is impossible in principle to achieve a numerical aperture of 1.0. Consequently, an ideal 40×0.65 lens will have a contrast of at least 0.3 only for frequencies of 26-33 lines/mm (this is approximately the quality level of format lenses such as Industar-37 300/4.5 or medium format Industar-29 80 / 2.8), which is not enough in itself. Taking into account the presence of aberrations, it becomes clear that one cannot expect a high-quality sharp picture in principle. Indeed, these lenses were designed for the purpose of being able to see something at least somehow, for example, to count the number of formed elements of blood in a stained smear. Photographic optics also require a high level of contrast - both general and contour, and contrast of details.
Overall, the CZJ 40x0.65 produces a “soft” image with insufficient resolution and contrast. The image quality in the central area is limited by both diffraction (we repeat that “ideally” for 40x the aperture should be 1.0, not 0.65) and the high level of spherochromatic aberrations, which manifests itself as the presence of a pronounced purple-yellow fringe. To correct spherochromatism such lenses require a radical complication of the optical scheme and the use of glasses with anomalous dispersion (phosphate and fluorophosphate crowns, "special" lanthanum flints). The lens belongs to the class of achromats, and therefore the field curvature is not fully corrected. There is also a small residual astigmatism and significant lateral chromatism across the field.
The characteristics of the objective lens are not very good. But how do the Soviet achromatic objectives, which were included in the MBI, MBR, and Biolam microscopes, perform in comparison? For the test, photographs of the transmitted light object micrometer with a cover glass were taken under equal conditions using a Sony NEX-6 camera and an NPZ M10 microscope with an OI-14 condenser at a tube distance of 160 mm. The tested objectives were CZJ 40×0.65, Progress 40×0.65 without a spring (MSh), Progress 40×0.65 F without a spring (FMSh, for phase contrast observations), LOMO 40×0.65 with a spring (OX-1, a more advanced objective than MSh according to the scheme, RMS standard 33 mm).
As you can see, the CZJ 40×0.65 lens, compared to all the Soviet ones, has better sharpness, better contrast (the presence of coating has an effect), and a much smaller field curvature, and smaller (significantly!) lateral chromatic aberration. The latter allows the lens to be used for photography in direct focus. It can be noted, perhaps, that the OX-1 lens still has better spherochromatic aberration correction in the central area of the image compared to the CZJ 40×0.65, but its high lateral chromatic aberration makes the lens unsuitable for photography in direct focus. Modern inexpensive Chinese lenses have exactly the same problem.achromats и planchromats magnification greater than 10 - it is assumed that they will be used with special compensating eyepieces. The funny thing is that new eyepieces with which these objectives are supposed to work are simply impossible to buy - they are only sometimes included with some microscopes, and often a regular eyepiece comes with a microscope.
The CZJ 40×0.65 objective, although having noticeable lateral chromatic aberration, was designed as an objective that does not require special eyepieces. Thus, according to official information, this objective corresponds to Zeiss A eyepieces (from "Achromat"), which are not compensating. Late Carl Zeiss Jena objectives that do not require compensating eyepieces were also marked with the letter A in their name. Thus, the 10/0.25 160/- objective required the use of a compensating eyepiece, but the outwardly identical 10×0.25 160/- A did not.
Excerpt from the Carl Zeiss Jena information brochure.
It turns out that from the list of inexpensive and generally accessible micro-optics, this is a rare example of a 40x lens suitable for shooting in prime focus.
Below are examples of photographs taken with a CZJ 40×0.65 lens using an NPZ M10 microscope and a Sony NEX-6 camera in direct focus at a tube distance of 160 mm.
Objects in the photo: 1-2) MOF (metal-organic framework) crystals based on benzene tetracarboxylic acid with rare earth cations, oblique illumination with an OI-14 condenser; 3-6) Potassium oxalate cuprate hydrate, oblique illumination with an OI-14 condenser; 7-8) Stained thin section of spinal cord, illumination with an OI-10 condenser (bright field); 9-10) Non-single-phase sample of the pigment "manganese violet" (manganese(III)-ammonium pyrophosphate, residues of unreacted manganese dioxide and ammonium phosphate).
Then – photographs taken using stacking (Helicon Focus).
Objects in the photo: 1) Crystals of 3-formylindole obtained in the organic workshop (illumination with a KF-1 condenser, bright field); 2-8) MOF (metal-organic framework) crystals based on benzene tetracarboxylic acid with rare earth cations, oblique and direct (photo 6) illumination with an OI-14 condenser; 9-12) Potassium oxalatocuprate hydrate, oblique illumination with an OI-14 condenser; 13-14) Potassium tetrathiocyanatocobaltate hydrate (illumination with an OI-10 condenser, bright field); 15-17) Stained thin section of spinal cord, illumination with an OI-10 condenser (bright field); 18-20) single-phase sample of the pigment "manganese violet" (manganese(III)-ammonium pyrophosphate, residues of unreacted manganese dioxide and ammonium phosphate).
Conclusions
The old Carl Zeiss Jena 40/0.65 160/0.17 microscope objective from Carl Zeiss Jena Amplival/Laboval type microscopes, if you evaluate it as a photo objective, is an extremely mediocre product. If you compare it with available analogs, then this is still a very good micro objective, the main advantage of which is the ability to use with eyepieces without compensation for lateral chromaticity and with cameras in direct focus.
