Film shooting Helios-33 2/35 (KMZ), adapted for Sony cameras

Material on the lens especially for Radozhiva prepared Rodion Eshmakov.

Adapted Helios-33 35/2 on Sony NEX-6.

The Helios-33 35/2 lens was intended for use with film cameras with a frame format of 16x22 mm (~APS-C), but later also became a fairly common technical lens like some lenses OKS series. This review presents exactly this technical lens, adapted for cameras with Sony E bayonet mount.

Technical specifications

Source: A.F. Yakovlev, Catalog. Lenses, part 2, ed. D.S. Volosov, GOI ONTI, 1971, p. 189-190.
Optical design – 6 lenses in 4 groups, Helios/Double Gauss type;

Drawing of the optical scheme of Helios-33.

Focal length - 35 mm;
Relative aperture - 1: 2;
Field of view - 46 °;
Covered frame format – APS-C;
Aperture - 8 blades, without a preset mechanism;
Aperture limits - 1: 2-1: 16;
The back focal segment is 23.3 mm;
Thread for filters - no;
Minimum focusing distance (factory setting) – 0.5 m;
Camera mount (factory version) – C-mount.

Design and adaptation

The lens in the factory version was intended for technical cameras (possibly video cameras with a vidicon) with a standard C-mount and was equipped with a simple focusing mechanism with a large minimum focusing distance (MFD) for such a focal length. Unfortunately, I did not think to take photos of the lens before adaptation, although I should have. Here - as in the joke: "smart thoughts haunted him, but he turned out to be faster." The main disadvantage of the original design was precisely the excessively large MFD, so the lens block of the lens was transplanted into a Chinese macrohelicoid 17-31 M42-M42 using a 3D printed sleeve.

The result is a very compact lens with convenient focusing in a wide range, which, using thin rings with M42 threads, can be installed on many systems - Sony E, Fujifilm X, Nikon Z, EOS M. I used a ring M42-Sony E  for using the lens with the Sony NEX-6 camera.

The lens aperture is controlled by turning the ring on the front part. The aperture value marks are applied to the ring. In total, the Helios-33 has 8 aperture blades, forming an opening in the shape of a regular octagon.

Unlike a mass-produced lens Helios-44 58/2, the Helios-33 lens uses an autocollimation lens block assembly, the essence of which is that each lens of the lens is enclosed in a metal frame, which is machined so that the center of the lens exactly matches the axis of rotation. Due to this, as well as due to the better accuracy of setting the diameter of the metal frame compared to a glass lens and the greater length of the frame compared to the edge of the lens, the autocollimation assembly allows for a smaller gap between the wall of the lens block housing, smaller errors in lens shift and tilt during assembly, and therefore allows for better centering of the lenses during lens assembly. However, if the technology is violated, the result may be terrifyingThe use of an autocollimation assembly dramatically increases the cost of the lens.

Because the Helios-33 35/2 lenses are rolled into metal frames, it is impossible to correct the poor quality blackening of the lens ends, typical of USSR optics: as you can see from the photo of the lens, they are very shiny, which negatively affects the image contrast and the behavior of the lens in backlighting.

Unlike LOMO OKS or projection lenses Ro, having a physical coating of the MgF2 type, deposited in a vacuum, the lenses of the Helios-33 objective are chemically coated (SiO2, applied by the spin-coating method, single-layer).

Light transmission spectrum of Helios-33 35/2.

The maximum light transmission is at 540 nm, the lens has a greenish-yellow tint when viewed through. The enlightenment has a pink glare.

I would really like to call Helios-33 35/2 a large-scale copy of the lens Helios-44 58/2, but, as it turned out, these are fundamentally different lenses. Thus, in the 1963 GOI album-catalog by E.B. Lishnevskaya for the Helios-33 lens (card 49.01) it is indicated that the brands of optical glass used are TK6, F1, TK10, BF17.

Helios-33 lens card in the GOI 1963 catalog

By the way, the card number corresponds to the year and month of lens development, i.e. Helios-33 was calculated in January 1949. For most lenses in this catalog, outdated names of optical glass brands are indicated. Thus, it is reliably known that TK6 glass is the current LZOS TK16, TK10 is LZOS TK20, and with BF17 it turned out to be a little more complicated: its number has undergone a less obvious change and it does not correspond to BF27 glass (607.440). There is an opinion on the Internet that this material is similar to BF16 glass 671.473, but in the book by D.S. Volosov "Photographic Optics" on page 306 the parameters of BF17 are designated as 608.462, which corresponds to the current LZOS BF25 material. To confirm that the material of the rear lens of the objective corresponds to BF25 glass, X-ray fluorescence spectra (XRFS Bruker M1 Mistral) of this lens and the rear lens of the objective were recorded. LOMO OM-2 Plan 9×0.2, which is reliably known to be made of barium flint BF25, and the front lens of the objective New Jupiter-3+ 50/1.5, made from BF16.

As expected, the XRF spectrum of the rear lens of the Helios-33 turned out to be identical to the spectrum of the rear lens of the objective Plan 9x0.2. The spectrum of the front lens corresponds to TK16 glass. The optical diagram of the lens with the indication of the relevant materials is given below.

Drawing of the optical diagram of Helios-33 35/2 indicating the current brands of optical materials LZOS.

Helios-44, unlike Helios-33, has a different choice of optical materials: instead of TK16 and TK20 glasses, the highly sought-after TK14 613.606 is used with the same refractive index but lower dispersion, the F1 flint is replaced with the lightweight LF7 578.411 flint with lower refractive index and dispersion, and instead of BF25, the heavier BF16 671.473 glass is used.

Drawing of the optical diagram of the Helios-44 58/2 lens with indication of the current brands of optical glass.

In this way, Helios-44 Overall, the Helios 33 should have better aberration correction (especially field curvature and astigmatism) than the Helios 0.66, since these lenses are otherwise very similar, including the ratio of the back focus to the focal length, which is XNUMX for both lenses.

Optical properties

Helios-33 35/2 has quite good sharpness in the center of the frame with the aperture wide open. At the edge of the field, sharpness noticeably deteriorates, mainly due to the characteristic of lenses of this type spherical aberration of oblique beams, which plays a major role in the formation of the characteristic bokeh. Residual spherical aberrations disappear in the central area at F/2.8, and at the edges of the frame – at F/4-F/5.6. Helios-33 35/2 has a very good correction of field curvature and astigmatism, because only the corners of the frame at F/5.6 remain somewhat blurry. Below are test shots on Helios-33 35/2 and the camera Sony NEX-6 at apertures from F/2 to F/5.6, as well as 100% crops of photographs.

In practical terms, the main drawback of the lens is its very poor performance in backlight. This is not so much due to the single-layer chemical coating, but to the previously mentioned low quality of blackening and matting of the inner surfaces. Stopping down the lens to ~F/2.8 helps to increase the overall contrast and reduce glare.

The expected advantage of Helios-33 is its very characteristic and recognizable bokeh with the so-called twisting effect. More advanced LOMO OKS lenses with similar parameters differ noticeably in the pattern. But the recipe for "that very" bokeh is simple - a low level of coma and trefoil, a high level of spherical aberration of oblique beams and 50% vignetting.

Examples of images taken with Helios-33 35/2 and Sony NEX-6 are given below. The shooting was done in RAW with subsequent correction (mainly contrast and dynamic range) in Lightroom.

Conclusions

Helios-33 35/2 is a pretty good and interesting lens in terms of its properties. Its expressive bokeh is especially attractive. However, this lens is much inferior in terms of contrast and sharpness, for example, Pentakta 30 / 2.8 (~F/2-2.2 after adaptation), which I once had with Helios-33. At that time, the difference seemed so significant to me that I simply could not bring myself to take any shots with Helios, which was very disappointing with its reduced image contrast and did not impress at all with its quality across the field at an open aperture. Today, Helios-33 has a lot of sharper, more contrasty and high-aperture competitors from China, although none of them have similar bokeh. So, in a sense, Helios-33 is the only one.