Material especially for Radozhiva prepared Rodion Eshmakov.
Achromat 4×0.1 in the revolver of the NPZ M10 microscope.
The vast majority of entry-level microscopes from different brands are equipped with simple 4×0.1 achromat lenses. This review examines the simplest and cheapest lens ($7) from those found new on the Chinese marketplace. This 4×0.1 achromat comes in a variety of external design options and will be the very first low-magnification objective for many beginning microscopists. Some information about microscopic optics, terminology, classification, methods of application is given here .
Technical specifications
Optical design – 2 lenses in 1 element (achromatic doublet);
Type of correction – achromat;
Tube distance – 160 mm;
Lateral chromatism (increase chromatism) – ~0%;
Magnification factor – 4x;
Numerical aperture – 0.1;
Focal length - 30 mm;
Relative aperture – ~F/4;
The estimated image field size is 18 mm;
Parfocal distance – 45 mm;
Working distance – 18 mm;
Cover glass – 0.17 mm (in fact, its use is optional);
Immersion required - no;
Mounting teak – RMS standard (4/5” x 1/36” thread);
Features - microscopic lens, does not have an iris diaphragm and a focusing mechanism.
Lens design and modification
The Achromat 4×0.1 is made in a black metal body using only two plastic elements - an ergonomic ribbed ring (for easy installation of the lens into the revolver socket) and an aperture diaphragm. It is known that the same lens also exists in a silver version with a slightly different design.
The size of the 4x0.1 lens is very similar to the 10x0.25 from the same set, but the optical design of the lens occupies only a small part of the body. Almost the entire visible length of the lens is its decorative “hood,” which is chrome-plated on the outside and inside and certainly does not benefit the image contrast. In order for the lens image to be more contrasty, this tube must be coated on the inside with matte black paint.
The lens is very easy to disassemble: you can unscrew the outer decorative part with the painted markings, then it will not be difficult to unscrew the shiny tubular lens hood. All that remains is the lens itself, very small in itself. It is impossible to remove the only glued lens from it - it is rolled into the frame. Note that there is no point in completely getting rid of decorative details: the blackened tubular hood plays the role of light protection.
Despite the completely primitive optical design, they did not forget to apply an anti-reflective coating with a purple tint to the lenses. Most likely, the coating on the surfaces of the doublet has 1-2 layers. This coating has virtually no effect on color rendering. The short-wavelength limit of light transmission is ~340 nm.
The light transmission spectrum of achromat is 4×0.1.
According to X-ray fluorescence analysis, the lens uses modern light or barium crown in combination with barium flint. This combination is designed to provide a good degree of correction of chromatic aberrations, but the two-lens design is, in principle, not designed for use with large fields.
X-ray fluorescence spectrum of the front lens of a 4×0.1 objective. Found: Ba, Sr, Sb, K, traces of Pb. Detection of Zr, Sn – instrumental artifact, Cu, Zn – background of metal structural elements around the lens.
Like most 4x lenses, this achromat has a long working distance, which is very convenient when working with side lighting. You can further increase the working distance by removing the decorative elements of the lens barrel.
Photos of the lens (after blackening) are shown below.
Overall, the 4×0.1 achromat is a typical super-budget lens. Primitive optics in a beautiful but rustic body with artificially increased dimensions “for solidity” and without light protection.
Image quality
As befits an achromat-doublet, the lens forms a sharp image in the central area of the field. There are small but still noticeable spherochromatic aberrations (purple and yellow fringing). But as you move away from the center, the quality quickly decreases due to the field curvature and astigmatism inherent in such an optical design. It is impossible to achieve a high-quality image at the edge of the field even with refocusing.
Direct comparison of 4×0.1 achromat with a slightly more expensive one (10$) plan-achromat 4×0.1 Plan showed that the doublet is completely inferior to a more complex lens - both in image sharpness in the center, and (especially!) in image quality across the field, and in overall contrast.
Images of the LOMO OMO-U4.2 reflected light object micrometer, taken on a Sony A7s and 4×0.1 achromat and 4×0.1 Plan achromat lenses with a tube length of 160 mm. The length of the mark is 1 mm, the division value is 0.01 mm.
The following are examples of photographs taken with an achromat 4×0.1 160/0.17 (after blackening) and a full-frame mirrorless camera Sony A7s, mounted on a modified NPZ M-10 microscope (tube distance 160 mm).
List of objects in the photo: 1 – micrometer object OMO-U4.2, 2 – nickel shenite, 3 – potassium oxalate cuprate hydrate, 3 – copper shenite, 5 – gas sensor chip platform with platinum contacts (manufactured in Uzhgorod, Ukraine) , 6 – crystals of manganese(III) acetylacetonate, 7 and 8 – crystals of ammonium persulfate in polarized light, 9 – crystals of ammonium hydrogen phosphate in polarized light, 10 – polycrystalline silicon.
Then - photos taken with stacking in Helicon Focus.
List of objects in the photo: 1 – nickel chenite, 2 – copper chenite, 3 – gas sensor chip pad with platinum contacts (manufactured in Uzhgorod, Ukraine), 4 – crystals of manganese(III) acetylacetonate, 5 and 6 – ammonium persulfate crystals in polarized light, 7 – ammonium persulfate crystals in polarized light, 8 – polycrystalline silicon.
All reviews of RMS standard microscope lenses with a tube distance of 160 mm:
Modern optics from Chinese manufacturers:
- Review of the low magnification lens 2/0.05 160/- (no-name, China). Problems of constructing low magnification lenses for microscopes
- 4x0.1 160/0.17 achromat (China, no-name)
- Microscopic optics on a camera. Review of microscope lens Plan 4x0.1 160/0.17 (China, no-name)
- 10x0.25 160/0.17 achromat (China, no-name) - modification and test
- Review of the Planachromat microscope lens Plan 20x0.4 160/0.17 (no-name, China)
Reviews of Soviet lenses for microscopes:
- LOMO Epi 9x0.2 (adapted)
- LOMO 10x0.4 L (OM-33L) - modification and test
- Review of achromat microscope lens LOMO 21×0.4 190-P (OM-8P)
Conclusions
In truth, there is no point in specially purchasing the item in question. 4×0.1 achromat: by paying a couple of dollars more you can buy a very successful lens 4×0.1 Plan. It makes sense to use a 4×0.1 achromat only when it is already available, and the quality of the image across the field is not so important - it is able to perform its function as a survey lens for a cheap microscope.
