Material on the lens especially for Radozhiva prepared Rodion Eshmakov.
Pentakta 4/40 with Contax RF/Kyiv mount and self-made adapter for Sony cameras.
German Pentakta lenses were intended for the Pentakta L100 microfiche projector manufactured by the Pentacon association in the GDR. A microfiche is a type of microfilm on which small-format photo reproductions of documents made on high-resolution optics were stored (Tevidon, Dokumar) at a decrease of 30-60 times. Projection lenses designed for reading microfiches are also high-resolution, but they usually differ from filming lenses in their design by the absence of an iris diaphragm.
In total, 3 lenses are known in the Pentakta line:
- Pentakta 2.8 / 30 - the most common, works with a frame no more than APS-C, optical design - 6/4 "Planar".
- Pentakta 4/40 (presented in this article) - a rare lens, works with a frame a little more than APS-C, optical design - 6/4 "Planar";
- Pentakta 8/85 - a rare lens, works with a frame of ~ 36 × 24, optical design 4/4 "Topogon" / "Orion".
The high resolution and very small size of Pentakta lenses are key features that make them attractive for use on today's modern cameras.
Specifications:
Optical design - 6 lenses in 4 groups, "Planar";
Focal length - 40 mm;
Relative aperture - 1:3 (in the factory it is artificially limited to 1:4);
Frame format covered – less than 32×24;
Features - a projection lens, does not have a focusing mechanism and an iris diaphragm.
Design and adaptation features
The Pentakta 4/40 case is very similar in design and execution to the Pentakta 2.8/30. The front lens block of the lens is also centered with three adjustment screws, while the rear one is assembled without surprises - as in the same Helios-44. Centering the front lens block after disassembling the lens is a mandatory and rather painstaking work that requires patience and accuracy. For alignment, all you need is a screwdriver, a camera with a lens mount, and a remote point light source.
The nut that locks the negative doublet of the front lens block also acts as a diaphragm, limiting its light diameter. Boring its hole allows you to increase aperture lens up to ~F/3. It is also possible to install an iris diaphragm between the lens blocks of the lens, but this requires turning. I installed an eight-bladed diaphragm with a light diameter of 9 mm. The hole formed by it has a fairly close to round shape.
The Pentakta 4/40, due to its relatively short rear focal length, can only be mounted on mirrorless cameras. I chose the unusual Contax RF mount as a mount, since I had a suitable body part from the lens Jupiter-8M, in which, using parts printed on a 3D printer, the lens block of the lens was installed in a convenient way. The Contax RF mount is good because it contains the focusing part right in the camera, which simplifies the design of short throw lenses. Inexpensive homemade adapters for modern systems for Contax-Kyiv lenses can often be found on sites like OLX. Moreover, today there are already factory-made adapters for using lenses. Contact RF on mirrorless cameras. I used a lens with a homemade E-mount adapter, which provides a rather small minimum focusing distance of about 30 cm at 3 turns - this, of course, is far from “macro” at this focal length, but still not bad.
Below are photos of the adapted lens and homemade adapter CRF-NEX.
Optical properties
Pentakta 40mm f/3 can only work fully with APS-C format cameras. In this case, the lens will have equivalent parameters of ~60/4, which brings it closer to the classic full frame 55/3.5 macro lenses.
On full-frame cameras, full frame coverage is achieved only at distances of less than 0.5 m, in some cases the lens can be used when cropping 4: 3 (frame format 32 × 24 mm), which I used in most cases - in APS-C mode when working with I did not switch with this lens.
As befits a microfiche lens, the Pentakta 4/40, even at the manufacturer's non-specified f/3 aperture, produces superb image quality from the center to the edge of an APS-C frame. On the 12 MP sensor of the Sony A7s camera, I did not notice any significant effect of spherical aberration, coma or astigmatism on the image. This is a very good result for an old lens: the commonly used 38-45mm f/2.8-3.5 f/XNUMX-XNUMX lenses, which are usually made according to simple Tessar schemes, have noticeable problems with sharpness at an open aperture.
The objective lenses have a single-layer antireflection coating - the same as that of the Pentakta 2.8/30. The lens is slightly yellow through the light, which is generally characteristic of old optics.
The image contrast in normal lighting conditions is good, but in the backlight there is a very noticeable veil on full-frame cameras. Within the APS-C sensor, its influence is small. The observed light scattering appears to occur on the lens rims of the rear lens block of the objective. Sometimes, in addition to the veil in hard backlight, you can observe violet reflections of lens enlightenment in photographs.
Although the Pentakta 4/40 (f/3) is hard to classify as a bokeh monster, the resulting background blur is not bad. In my opinion, this classic correct "Planar" bokeh is much more interesting than many specialized complex and technically perfect macro lenses. And a large depth of field at an open aperture is a big plus when shooting small objects, insects, flowers. Most likely, the lens would have shown itself perfectly with macro rings at a shooting scale of 1:2–1:1.
Below are sample shots on a Sony A7s full frame camera. Some have been cropped 4:3. Shooting in RAW, developing in LR (levels, selectively - vignetting correction).
Conclusions
If the widespread and well-known Pentakta 2.8/30 lens claims to be an excellent manual camera lens for APS-C cameras, then the rare "magpie" can prove itself as a compact and lightweight macro lens with good sharpness and a pleasant pattern.
You will find more reviews from readers of Radozhiva here... All Rodion reviews in one place here.
Very cute, simple and tasteful) Thank you.
Really great lens!