Industar-69 2.8/28 (BelOMO). Review, analysis and comparison with 7artisans 25/1.8

Material on the lens especially for Radozhiva prepared Rodion Eshmakov.

The tiny Industar-69 28/2.8 is the standard and only available (which is funny, because the I-69 was not rigidly built-in) lens for the Soviet Chaika scale cameras. These cameras had a frame size half the size of a regular film camera, that is, they were "crop mirrorless", only film ones. A large number of "Chaika" cameras were produced, so the Industar-69 is very often found for very modest money. Fans of photography and experiments with technology even in the era of SLR cameras established lens via a macro adapter, and later mirrorless users began to use this old lens after a small modification in the same way as they once used it on the Chaika.

But progress does not stand still, and for modern digital crop mirrorless cameras today there are inexpensive lenses wider and lighter, even brighter and even with autofocus. New optical glass with parameters that the USSR could only dream of, modern multilayer anti-reflective coatings... - how did all this affect the image quality of new lenses like the Industar-69? In this review of the Industar-69 lens, a comparison of the formed image with a modern budget 7artisans 25 / 1.8.

Navigation

• Technical specifications
• Design and adaptation
• Industar-69 and 7artisans 25/1.8: Optical Design Analysis
• Industar-69 and 7artisans 25/1.8: image quality
• User experience and conclusions

Technical specifications

Source: A.F. Yakovlev, Catalog. Lenses, part 2, ed. D.S. Volosov, GOI ONTI, 1971, p. 13-15.
Optical design - 4 lenses in 3 groups, "Tessar";

Focal length - 28 mm;
Calculated field of view angle – 56°;
Estimated frame size: 18×24 mm (~APS-C);
Relative aperture - 1: 2.8;
Aperture - 5 blades, without a preset mechanism;
Aperture limits - 1: 2.8-1: 16;
Minimum focusing distance (factory version) – 0.8 m;
Camera mount – thread M39×1 with a working length of 27.5 mm;
Thread for filters - no;
Features - non-standard flange focal distance makes the lens incompatible with the M39 LTM mount.

Design and adaptation

Industar-69 has a very primitive design, similar to a full-frame lens. Industar-50-2 50/3.5. However, there are no plastic parts in the lens. The I-69 helicoid is made as a simple threaded pair - when focusing, the lens block rotates. In the factory version, the focusing ring rotates by ~ 180 °, which provides a minimum focusing distance (MFD) of 0.8 m. This is very, very much for a lens with a focal length of 28 mm, but, of course, on a scale camera, with which the Industar-69 was shot, it is impossible to get into focus at a shorter distance. The aperture is controlled by a thin, not very convenient ring around the front lens of the lens. The aperture mechanism has 5 rounded blades that form a pentagon-shaped opening at F / 5.6-F / 16.

The lens has an M39×1 camera mount thread with a non-standard working distance of 27.5 mm, which is 1.3 mm shorter than the M39 LTM. To install the lens on mirrorless cameras via adapters for M39 LTM optics, it is necessary to make the lens block recessed even more by these same 1.3 mm when focusing at infinity. The easiest way to achieve this is to remove excess metal near the thread on the lens block and from the bottom edge of the focusing ring. The scale loses its meaning in this case, but on a digital camera it is of little use in principle, and you can make your own infinity mark. When reworking in this way, you can also remove both stoppers of the focusing ring, which allows you to unscrew the lens block by 4 turns and get an MDF of about 20 cm. Well, to make it even nicer, I used the adapted lens on a Sony NEX-6 camera via a macrohelicoid adapter Leica M - NEX with the M39 LTM – Leica M adapter ring – such a set costs several times more than the Industar-69 itself.

The design of the lens block is curious. Thus, each lens of the Industar-69 is rolled into a brass frame, that is, the lens is made using autocollimation assembly technology similar to microlenses. It is important that the rear lens of the objective is made in a special frame, centered by rotation relative to the other lenses before fixing with a locking ring. Therefore, in the case of obvious decentrations, expressed in the presence of asymmetrical "comical" halos around point light sources even in the center of the frame, it is necessary to loosen the fastening of the rear lens and rotate it until the spots are symmetrical. However, it is unlikely that the assembly of the lens was ideal at the factory.

As with the lens Helios-33 35/2, the blackening of the lens ends and interlens surfaces in the Industar-69 is unsatisfactory. It is easy to notice shiny edges inside the lens, which, of course, has a negative effect on the contrast of the image. However, it is difficult to expect anything else from a cheap Soviet lens.

Industar-69 and 7artisans 25/1.8: Optical Design Analysis

The four-lens Industar-69 was produced from the mid-1960s, that is, already at the time when lanthanum glass became available in the USSR. However, there are no indications that they were used in this small lens, as, for example, in Industar-61 50 / 2.8, there was none, and in reference books and other sources available to me the optical scheme with the indication of the brands of glass is not given. To assess the technological level of the objective and to establish the brands of optical materials used in Industar-69, I recorded the X-ray fluorescence spectra (Bruker M1 Mistral device) from the front and rear lenses of the objective. As it turned out, the most probable material for the front lens of I-69 is ordinary heavy crown TK20 622.567, and for the rear lens - barium flint BF16 671.473. In this case, the negative lenses can only be lead flints (TF, F, LF). There are no lanthanum glasses in the Industar-69 scheme.

Note that a similar choice of positive lens materials is found in the objective Industar-26m 50 / 2.8, which is a pre-lanthanum precursor Industar-61. It is very likely that the Industar-69 calculation is based on the Industar-26m scheme and completely repeats the choice of glass. In this case, the Industar-26m lens exists “in three forms”: half-frame (I-69), full-frame (I-26m) and medium format (Industar-29), which is quite funny.

Industar-69 lenses have a single-layer coating with a pale blue glare, probably applied by vacuum deposition of magnesium fluoride. This coating leads to some reduction in the blue region of the spectrum, but still provides better color rendering than similar chemical coating.

Thus, the Industar-69 is an old lens from the "pre-lanthanum" era, made using a very simple optical design of the "Tessar" and having a simple single-layer anti-reflective coating of the lenses. The main problems of the high-aperture "Tessars", designed without the use of super-heavy lanthanum crowns, were poor correction spherical aberrations, high level of field curvature and astigmatism, extended secondary spectrum and associated low resolution.

What can be said about a budget Chinese manual lens? 7artisans 25 / 1.8, introduced in 2017?

This lens has a larger angle of view compared to the Industar-69, and also twice as much aperture (F/1.8 versus F/2.8). However, with aperture It's not that simple: the measured pupil size of the lens is ~12 mm, which corresponds to a relative aperture of ~F/2.1, but not F/1.8, to achieve which the pupil must be 2 mm wider. The Chinese they lied again.

7artisans 25 / 1.8 uses a more complex, compared to the Industar-69 28/28, seven-lens optical design of the double Gauss type, similar to the old 50/1.4 lenses from SLR cameras.

The manufacturer does not provide information about the use of special glass in this lens, but some information about which store display these lenses are made from can be obtained using the same X-ray fluorescence analysis.

As it turned out, both outer lenses of the objective are made of materials of the heavy lanthanum flint class (CDGM H-ZLaF), including oxides of such elements as lanthanum, niobium, zirconium, yttrium, tungsten, zinc. The material of the front lens was identified by the reference sample as glass H-ZLaF4LA, which has a refractive index of, for a moment, 1.91! To understand how much this is, compare it with the refraction of water (1.33), window glass (1.52), sparkling cubic zirconia (2.15), the most refractive lens Industar-69 (1.67), the most refractive lens Industar-61 (1.74) and the most refractive glass LZOS (1.82). The rear lens of the objective is most likely made of a material with similar parameters, but due to the lack of a comparison sample, it was impossible to determine the brand of glass.

In general, the Chinese did not skimp on materials – and they did the right thing: with such lens diameters, the cost does not depend in any way on the choice of glass brand.

As expected, a modern lens has a multi-layer anti-reflective coating on the lenses. Optics 7artisans 25 / 1.8 shimmers with pink and green highlights. The coatings are designed for the spectral range of 400-700 nm. Light transmission is somewhat reduced in the blue region of the spectrum. This is probably due not only to the coating, but also to the internal absorption of light by the glass (highly refractive materials turn yellow).

It turns out that 7artisans 25 / 1.8 – is a simple technological lens of the “double Gauss” type, made using top (this is not an exaggeration) optical glasses and adequate coatings. This approach allows us to achieve a solution to many of the problems of such lenses, in particular – spherical aberration of oblique beams and higher field aberrations of the trefoil type. The use of this optical scheme in itself allows achieving better correction of astigmatism and field curvature (hence the name of the scheme - "Planar") compared to "Tessar" lenses.

Industar-69 and 7artisans 25/1.8: image quality

In general, the Industar-69 really does resemble a full-frame camera in terms of the image quality. Industar-26m 50 / 2.8. The lens has a rather soft picture with an open aperture with a pronounced soft effect. Field distortions are strongly expressed, mainly astigmatism and higher aberrations, under the influence of which the image quality drops sharply already by the middle of the field. They are also the cause of the very characteristic bokeh twist, also reminiscent of Industar-26m.

When stopping down to F/4, the sharpness in the central area increases significantly and the lens becomes quite "workable". Vignetting is reduced, contrast is noticeably increased, since the aperture cuts off "extra" beams of light reflected from the shiny internal surfaces of the lens block.

The image field, however, only returns to normal at ~F/5.6-F/8.

Below are test shots taken with the Industar-69 lens at apertures F/2.8-F/8 and the camera Sony NEX-6.

7artisans 25 / 1.8 has noticeably better sharpness in the center and across the field at an open aperture, a lower level of vignetting and more correct color rendition. This lens also has a calm bokeh without any eye-catching features. Test photos were taken with the relative aperture set based on exposure metering, and not the aperture scale, which does not correspond well to reality on this lens.

A detailed examination of the images shows that Industar-69 has a significantly lower resolution than 7artisans 25 / 1.8: in the center of the frame, at any aperture value, the Soviet lens does not catch up with the modern Chinese one. This is due to both insufficient correction of spherical aberrations and the extended secondary spectrum of the Industar-69.

Complete superiority 7artisans 25 / 1.8 demonstrates in sharpness in the middle of the field: the high level of astigmatism does not allow the old Industar-69 to achieve good quality. And only in the corners of the frame the Industar-69 turns out to be better than the Chinese lens with the aperture closed to F/5.6: for the sake of better quality at the edge of the field at F/5.6, the quality in the middle was sacrificed.

User experience and conclusions

The Industar-69 is far from ideal, and using it after more modern optics is a kind of test. The lens works poorly in backlight, has low contrast at open aperture and, frankly speaking, lacks sharpness even in the center of the frame. And with some cameras, such as Sony A3000/A3500, the lens produces color shift. Old APS-C cameras with a sensor of 16 MP or less, as well as new ones with BSI matrices, are not subject to this effect.

However, the Industar-69 cannot be called hopeless: at an open aperture, the lens produces a rather interesting bokeh pattern, which is easy to achieve when shooting portraits of cats and flowers, and by slightly closing the aperture you can get good sharpness in the center, sufficient for many subjects. The lens, again, is well suited for ultra-budget macro photography (and maybe better such option?) due to the large depth of field and ease of achieving the desired image scale. In the comments to old review On the website you can also find excellent examples of landscapes taken with the Industar-69, although the optical quality of the lens is poor for this task by today's standards.

Below are examples of photographs taken with Industar-69 and a camera. Sony NEX-6.

It is worth noting that an important feature of the Industar-69 is its size: the lens is so small and light that you can throw it with you, even if it seems not to be very necessary. A compact camera like the Sony NEX with the Industar-69 fits into a jacket pocket without any problems. Only due to these aspects, it may turn out that over a certain period of time, the owner took more photos with the Industar-69 than with a high-quality, but large-sized lens, which was often too lazy to take with you.