Minolta MC Rokkor-PF 1:1.4 f=58 mm. Review of the modified lens

Material on the Minolta MC Rokkor-PF 1:1.4 f=58 mm lens especially for Radozhiva prepared Rodion Eshmakov.

Modified Minolta 58/1.4.

Modified Minolta 58/1.4. increase.

Minolta MC Rokkor-PF 1:1.4 f=58 mm (hereinafter referred to as Minolta 58/1.4) is a classic high-aperture lens for SLR cameras, the first version of which was released back in 1961. The lens belongs to the conventional first generation of especially fast (F/ > 1:1.5) standard lenses for SLR cameras and has a focal length of 58 mm - exactly the same as the RE Auto-Topcor 58/1.4, Nikon Nikkor-S 58/1.4 produced in the same years, Canon FL 58/1.2, and also - less aperture Carl Zeiss Jena Biotar 58 / 2, Helios-44 58/2, Takumar 58/2 – the list is not exhaustive. The choice of the unusual focal length of 58 mm was due to the need for opticians at that time to choose a compromise between image quality, the complexity of the optical design and the rear focal length, the latter requiring at least 38 mm to work with SLR cameras.

There are 4 versions of the Minolta 58/1.4 lens, two of which belong to the Auto Rokkor-PF line and have a single-layer anti-reflective coating on the optics, and two to the MC Rokkor-PF line, already with multi-layer coating of the lenses. The latest version of the lens was produced from 1969 and had, according to some sources, a slightly redesigned, but fundamentally the same optical design. This is indicated by the same letters PF in the name, meaning the number of lens groups - P, “penta”; and the number of lenses is F, the sixth letter of the alphabet. Review of this factory version of the lens already on the site, and this article is about a modified lens of the latest version with a new aperture and focusing mechanism.

Factory specifications of the lens:

Optical design – “double Gauss”, a variation of the “Planar” design, 6 lenses in 5 groups;

Schematic diagram of Minolta 58/1.4.

Schematic diagram of Minolta 58/1.4.

Focal length - 58 mm;
Field of view - 41 °;
Design frame format – 36×24 mm, covered – 44×33 mm;
Relative aperture - 1: 1.4;
Aperture limits - 1: 1.4-1: 16;
Aperture - 6 petals, "jumping";
Minimum focusing distance (MDF) - 0.6 m;
Thread for filters - 55 mm;
Camera mount – Minolta MD mount;
Mass - 275

It should be noted that the Minolta 58/1.4 is a unique lens among its analogues, since it uses a simple six-element design, while all old 50-58 mm F/1.4 lenses for SLR cameras have a design of at least 7 elements. The only exception is a rare and interesting Soviet lens Era-6M.

Lens modification and adaptation

The Minolta 58/1.4 has a rather unpopular mount that is not used in modern cameras - the Minolta MD mount. Of course, it is possible to use it on mirrorless cameras via an adapter, but about tilt-shift adapter then you can forget. Another obvious drawback of the factory lens is the 6-blade aperture, which creates nuts in the bokeh even when the aperture is limited slightly. Finally, the focusing mechanism provides a good, but not as convenient as we would like, minimum focusing distance of 0.6 m (0.55 m for Helios-44).

I received the lens in a mediocrely modified form for Canon EF, with broken aperture control. Therefore, it was decided to completely replace the aperture in the lens with a round ten-blade one, and the focusing mechanism with a macrohelicoid with a much larger stroke than the factory one - to ensure a short minimum focusing distance and a more convenient connection to the camera (M42 thread).

Replacing the aperture in the Minolta 58/1.4 is not difficult - the lens block consists of a housing into which the front and rear halves of the “double Gauss” are screwed into the thread. The diaphragm is fixed in the housing with screws and can be completely removed. There was enough space for a new diaphragm with a light diameter of 29 mm, but its drive, of course, had to be changed, which required making a through groove in the body. The aperture control ring was made using 3D printing. The lens block with the aperture ring was installed in the macrohelixoid using a bushing made by 3D printing. The minimum focusing distance when using a 17-31 mm macrohelicoid was reduced to ~0.35 m, which is already great.

The modified lens is shown in the photo below.

The modification deprived the lens of the original vintage design of the MC Rokkor line, but endowed it with much greater functionality compared to the factory version. The M42 mount lens can be mounted on most cameras via an available adapter. The practical helicoid turned out to be much more convenient than the original focusing mechanism when shooting, and the aperture is now just pleasing to the eye, and it can be used flexibly without worrying about the quality of bokeh. I believe that later all the plastic parts will be replaced by metal ones for reasons of aesthetics and reliability.

Optical design

The lens uses a simple six-element “6/5” design, which is not far removed from the classic “6/4” Helios-44 58/2. Nevertheless, aperture Minolta 58/1.4 is twice as high as Helios-44. It is logical to assume that optical materials made it possible to achieve such an increase, and therefore it was interesting to consider the elemental composition of the glass from which the objective lenses are made using the method x-ray fluorescence (Bruker M1 Mistral).

The glass in the first objective lens contains strontium (Sr), lanthanum (La), cadmium (Cd) and barium (Ba), as well as hafnium (Hf), arsenic (As) and probably zirconium (Zr). The glass does not contain lead or niobium. Taking into account the analysis of patent documentation, this glass apparently belongs to the family of heavy lanthanum flints with a refractive index n~1.74-1.78 and a dispersion coefficient (Abbe number) v~40-45. The closest analogues in the GOST catalog are STK19, STK16.

X-ray fluorescence spectrum of the front lens of the Minolta 58/1.4 lens.

X-ray fluorescence spectrum of the front lens of the Minolta 58/1.4 lens.

The rear lens element is made of a material that contains lanthanum (La), cadmium (Cd) and small amounts of strontium (Sr), niobium (Nb), hafnium (Hf), zinc (Zn) and probably zirconium (Zr) . The material probably also belongs to lanthanum flints with n~1.70-1.75 and v~45-50.

X-ray fluorescence spectrum of the rear lens of the Minolta 58/1.4 lens.

X-ray fluorescence spectrum of the rear lens of the Minolta 58/1.4 lens.

The fourth objective lens contains significant amounts of lead (Pb) and zinc (Zn), as well as relatively small amounts of barium (Ba) and arsenic (As). Such glass definitely belongs to flint or heavy flint glass with n~1.62-1.66 and v~31-35. Analogues in the GOST catalog - F4, TF1.

X-ray fluorescence spectrum of the fourth lens of the Minolta 58/1.4 lens.

X-ray fluorescence spectrum of the fourth lens of the Minolta 58/1.4 lens.

It can be noted that the materials used in the lens use rather toxic elements, such as cadmium (comparable to mercury in toxicity) and lead - modern lenses have long tried not to use such glass (following RoHS).

Thus, the Minolta 58/1.4 uses fairly advanced optical materials (heavy lanthanum glass) to achieve an acceptable level of image quality at high aperture. Similar in focal length and similar in design, Helios-44, for example, does not use lanthanum glasses in the optical design - for its technological level of performance aperture F/1.4 is unattainable.

It is important to note that the Minolta 58/1.4 does not use thorium glass, so there is no risk of confiscation at the airport due to increased levels of radiation.

Optical properties

The quality of the image formed with an open aperture is poor by today's standards. One can observe pronounced spherochromatic aberrations associated with the appearance of a soft effect on contrasting boundaries, as well as colored (purple-green) fringing. Sharpness decreases significantly from the center to the edge of the frame due to higher order aberrations and coma. You can significantly improve image quality in the central region by stopping the lens down by just 1/3-1/2 stop - this eliminates most of the higher-order spherical aberration, significantly increasing image contrast and visual sharpness. This is why a round aperture is especially useful for a lens. Below are examples of photos taken on a full-frame mirrorless Sony A7s camera, taken wide open and stopped down to 1/3 EV.

Good image quality across the field can be achieved by apertures up to F/5.6-F/8. Users of medium format cameras with a 44x33mm sensor will probably have to use F/8-F/11.

Due to the high level of chromatic aberrations (extended secondary spectrum), the resolution of the lens in the center of the frame is limited even at closed apertures. Therefore, you can’t expect any miracles in macro photography or in other scenarios where attention to the smallest details is required - just like in the case of other old 50/1.4 lenses.

The objective lenses use multi-layer coating, shimmering with amber, green and purple highlights. The manufacturer called it “achromatic”, implying a minimal negative impact of the coating on the color rendition of the lens (which often happens if the coating is chosen incorrectly, with very formal approach). I recorded the light transmission spectrum of the lens and also assessed the light transmission coefficient.

Light transmission spectrum Minolta 58/1.4.

Light transmission spectrum Minolta 58/1.4.

What you need to pay attention to is the smoothness of the spectral curve. Although its shape is similar to the curve of a lens with a single-layer coating, the same on all lenses (like Izyumsky 16KP-1.4 / 65), but it is generally higher in intensity (i.e. in the region of high light transmission values) and does not have “dips”. In the range of 400-780 nm (visible spectrum), light transmission is ~86%, which is a good result for such an old lens. In the near-infrared range of 800-1100 nm, light transmission is 72%, which is also better than many other lenses with multi-layer coating of optics. The maximum light transmission occurs in the yellow-green region – ~550 nm. Thus, in the absence of light scattering effects, the lens only slightly shifts the tone to the green region, and the color temperature to warm shades, but does not introduce serious distortions of individual colors, as happens in the case of uneven spectral curves with several maxima. Consequently, the manufacturer in this case turned out to be honest, and the lens under normal shooting conditions should have good contrast and color rendition - and this is actually the case. But in backlight, especially with an open aperture, the Minolta 58/1.4 easily catches veils (including colored ones, usually greenish), rainbows and glare. However, these artifacts can be used for artistic purposes.

The bokeh of the lens is worthy of attention. The background blur looks bright and organic. Unlike many other lenses of the 50-58/1.4 type, the edging of the bokeh disks does not sharply intensify towards the edges of the frame (the spherical aberration of oblique beams in the Minolta 58/1.4 is not strong), so the bokeh does not look “rattling” in the corners of the frame (compared to the later Minolta 50 / 1.4). The bokeh disk border facing the center of the frame is somewhat brighter than the one facing away from the center, and therefore in some situations the blur takes on the character of scales and is somewhat reminiscent of the bokeh of 50 mm lenses with a Sonar. One way or another, the Minolta 58/1.4 stands out in terms of image quality among lenses with similar parameters.

Minolta 58/1.4 covers a 44x33 mm frame, albeit with a noticeable drop in illumination towards the corners of the frame. Moreover, its equivalent parameters correspond to a 45/1.1 lens on a 36x24 mm frame. Excessive coverage allows the Minolta 58/1.4 to be used with tilt-shift adapters on full-frame mirrorless cameras, including horizontal shift. The following are photographs taken with shift adapter on a full frame Sony A7s camera.

More examples of photos from the Sony A7s are below.

Conclusions

Minolta 58/1.4 is one of the old lenses of the 50-58/1.4 class that stands out for its image character. It’s probably not the best in terms of sharpness, but the creators did a great job of high-quality coating of the optics, thanks to which the lens has good color rendition and contrast; and abandoned the use of yellowing thorium glass. Some inconvenient nuances of the lens, such as the hexagonal diaphragm, turn out to be fixable: the modification described in this article allows you to turn the Minolta 58/1.4 into a convenient and fairly universal high-aperture art prime.

You will find more reviews from readers of Radozhiva here и here.

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Comments: 7, on the topic: Minolta MC Rokkor-PF 1:1.4 f=58 mm. Review of the modified lens

  • Dmitry Kostin

    Nice design on the lens.
    Thanks for the review!
    In Kutuzov there is now his relative 58/1.2 converted to Canon for 45k.

  • Igor

    Excellent, detailed review, like all reviews from Rodion! I have a “younger brother” of this 58/1,8 lens - the design is very similar. For a portrait on a cropped crop it is suitable, on a full frame, further than 2 meters a mirror on a nickel catches. The only point in the review that somewhat surprised me was the unexpected statement that you shouldn’t expect any special resolution from the old 50/1,4... BUT WHAT ABOUT RE AUTO TOPCOR? Personally, I was very impressed by the Topkors, both 1,4 and 1,8 (58mm). Are there any “Koshinovsky” (not Tomioka!) “color reflexes” produced for Porst? I would very much like to hear your opinion about them. Compared to Minolt’s vaguely romantic drawing, the above-mentioned ancient animals are, well, just razors🤣 (IMHO) And the review, Wonderful!👍🙏👌

    • Rodion

      If I have a chance to try them, then, of course, I will try to tell you about my impressions

  • Vlad

    Off topic of the review, but still. Among widths, most manufacturers have three lines: large-expensive-professional with f1.4, medium-sized with f1.8-2 and compact-budget with f2.8. Question: why doesn’t anyone produce cheap, compact 50-85-135/2.8? I wouldn’t mind giving up the compact 85/2.8 for about $200-300. Or are there some technical restrictions on this?

    • Rodion

      Sony has an old 85/2.8 zonnar (by design, not by name). Perhaps sales are predicted to be low for such optics, which is why they don’t make them.

  • Paul

    An interesting adaptation, but the authenticity of the lens is completely lost. With a native macroring, a macrohelicoid is not needed.
    Installing a multi-blade aperture is also interesting, although I don’t understand why: the whole process of shooting with such glasses is on an open aperture, and at 8, as one of my friends said, “they are all the same”; Whether there are 6 aperture blades or 12 does not matter.

    • Paul

      An example photo from this lens (open aperture) in medium format (Fujifilm GFX 50R camera).

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