Review and test of the Voigtländer Ultron 1:2/28 (Type II) rangefinder with Leica M mount

Material on the Voigtländer Ultron 1:2/28 lens especially for Radozhiva prepared Rodion Eshmakov.

Voigtländer Ultron 1:2/28 (hereinafter referred to as Ultron 28/2) is a modern wide-angle, fast prime lens, released in 2021 for rangefinder cameras with a Leica M mount. Ultron 28/2 belongs to the line of vintage optics (“Vintage line”) ") and is Voigtländer's fastest full-frame 28mm lens, although Leica also has a 28/1.4 lens. Despite the fact that formally Voigtländer is a German company of Austrian origin, since 1999 all lenses have been manufactured and developed by the Japanese company Cosina.

Reviews of other Voigtländer optics:

• Voigtländer Braunschweig Heliar 1:4,5 F=13,5cm (1928)
• Voigtlander APO-Lanthar 90mm F3.5 SL N / AI-S
• Voigtlander Nokton 58mm F1.4 SL N / AI-S
• Voigtländer Ultron 21mm F1.8 Aspherical (Leica M)

Specifications (with manufacturer's pages):

Optical design – semi-symmetrical, 10 lenses in 7 groups, 1 aspherical element, 2 lenses made of material with anomalous partial dispersion;

Focal length - 28 mm;
Field of view - 74,51 °;
Estimated frame format - 36 × 24 mm;
Relative aperture - 1: 2;
Aperture – 10 “straight” blades;
Aperture limits – 1:2-1:22, stepwise adjustment (with half-stops);
Focusing - manual only, autofocus is available on mirrorless cameras when used with a special adapter;
The minimum focusing distance is 0.5 m;
Thread diameter for filters – 39 mm (О_о);
Camera mount - Leica M mount (with the ability to interface with a rangefinder);
Dimensions - 51.4 × 36 mm;
Weight - 230 g;
Additionally – available in 2 design options (Type I and type II), type II – in 2 color options (silver/black);
The cost is ~$700.

Design and execution of the lens

To prepare the material, I was given a completely new lens in a box. As is the case with Ultron 21/1.8, the delivery package is very modest and includes only the lens with caps, a warranty card and a booklet from the manufacturer.

Ultron 28/2 is made in a pseudo-retro style in an aluminum case with silver anodizing. There is also an option in black. On the body you can find the designation of the focal length in large numbers (in case you forget), a standard set of scales - the depth of field scale (it is not clear how it was calculated), markings of the aperture control ring, a distance scale in feet and meters.

The case also has a bayonet mount for a lens hood. Both the lens hood mount and the camera mount are made of chromed metal.

Ultron 28/2 type II lenses differ from type I only in the design of the body, and the key difference is in the way the lens focusing ring is controlled: if in type I it is made like in all normal manual lenses - in the form of a ring with notches for fingers, then in type I II they did something purely “hair-drying” - the focusing ring is completely smooth, completely unintuitive (in the sense that it is difficult to recognize it in the blind), but with a special leash-rest for the finger. Apparently a tribute Elmar 50/3.5. I didn’t like this method of focusing, and this focus was very annoying even when I was using it 7artisans 35/2 LM, but this is a matter of habit and taste.

The focusing ring has a very short angular travel - only 90°. The minimum focusing distance (MDF) is 0.5 m, which is a lot for a lens with a focal length of 28 mm - you can forget about shooting small objects. The limitation of MDF is due to the purpose of the lens for rangefinder cameras, where, due to parallax, focusing at a distance of less than a meter is generally quite difficult. However, the latest versions of the same Leica M cameras already have Live View, and therefore such MDF does not cause anything but bewilderment.

It’s good that when used on mirrorless cameras, the lens can be mounted via a macrohelicoid type adapter Laina LM/EM Mount, which allows you, firstly, to reduce the MDF of the lens to an acceptable level, and secondly, it makes it possible to focus using such a simple, understandable and humane ribbed ring.

The Ultron 28/2 diaphragm looks and is designed the same as Ultron 21/1.8, and consists of 10 matte black L-shaped petals (similar to the aperture blades Helios-103).

This shape of the petals makes it possible to achieve an almost linear movement of the aperture ring, and also helps to obtain a pronounced effect of a ten-rayed star from point light sources in the frame in the range from F / 2.8-F / 11 due to the formation of a hole in the shape of a regular decagon with clearly visible angles. In the F/11-F/22 range, the lens pupil appears round.

Aperture control is completely manual, with one ring. Fixed values ​​from F/2 to F/22 are available for installation, with intermediate clicks of the ring between the marks. Due to the inability to smoothly adjust the aperture, the lens is of limited suitability for video shooting.

As a result, there are no doubts about the manufacturing quality of this light and compact lens, nor any complaints about its appearance, although the focusing method of this version is not for everyone. It is better for the chooser to try both lens options in his own hands - both type I and type II.

Optical design: anomalous dispersion lenses

Ultron 28/2 is an almost symmetrical lens in its optical design, however, in the design, only the first 2 lenses, according to the manufacturer, are made of glass with anomalous partial dispersion, while the last lens is made of “regular” glass, but has an aspherical surface shape.

What does this gobbledygook even mean? The bottom line is that successful correction of chromatic aberration in a simple lens system requires two factors:

• A combination of positive lenses with low dispersion (higher Abbe number) with negative lenses with high dispersion (small Abbe number) - the difference should be as large as possible, but the flight of fancy is limited here by reasonable values ​​​​of the refractive index, which is usually higher, the greater the dispersion (smaller Abbe number).
• Combined positive and negative lenses must be made of materials with similar partial dispersions (PgF) for the short-wavelength part of the working spectrum (in the range between the spectral lines g and F of the blue-violet region of the spectrum).

Dispersion is determined by the dependence of the refractive index of the material on the wavelength. The Abbe number is associated with the difference in refractive indices at the boundaries of the working wavelength range - for the red and blue regions of the spectrum. Relative partial dispersion PgF characterizes how large the dispersion in the blue region of the spectrum is relative to the dispersion over the entire operating wavelength range.

The trouble is that if the required difference in Abbe numbers could be achieved with glasses of the XNUMXth century, then the second condition, mandatory for obtaining well-corrected chromatism or even apochromatic systems, is much more difficult to fulfill, because the particular dispersion of glasses is usually strongly correlated with the general one and the dependence PgF from the Abbe number represents an almost straight line for most materials (the so-called “normal straight line”). This fact is due to the fact that dispersion is strongly related to the chemical composition of the glass: usually, to increase the dispersion, an increase in the content of lead oxide (or its substitute in lead-free glasses - tungsten oxide, titanium oxide or tellurium oxide) is required, hence the observed proportionality.

The desired deviation of the partial dispersion from the normal line is as positive as possible for positive lens materials and as negative as possible for negative lens materials. But usually the opposite is true - excellent lanthanum crowns usually have a very large negative deviation (see the picture below STK19), and heavy flints with high dispersion have a very large positive deviation (see TF10).

That is, it turns out that lanthanum oxide makes it possible to reduce the partial dispersion, but does not make it possible to increase the general dispersion sufficiently and, moreover, greatly increases the refractive index. And lead oxide makes it possible, for example, to increase the overall dispersion, up to a certain point having little effect on the increase in the private one. Thus, a new possibility opens up: if the material contains significant amounts of both lanthanum oxide and lead oxide, then as a result it will have a negative deviation of the partial dispersion from the normal straight line and a relatively high dispersion in general, although the refractive index will be quite high . Such glasses are called “special flints” or “flints with anomalous dispersion” or, as in the case of Ultron 28/2, “glasses with abnormal partial dispersion”.

Since the front and rear objective lenses, which are similar in design, are made of “special” and “ordinary” materials, it was possible to directly compare their chemical composition using the method of X-ray fluorescence spectroscopy (XRF, XRFA, XRFS) to conduct semi-quantitative elemental analysis. Measurements were performed on a Bruker M1 Mistral instrument, which is insensitive to elements lighter than argon and always detects zirconium (Zr) and tin (Sn), which are contained in the components of the instrument. Below are pictures of the recorded spectra.

Note that significant amounts of niobium (Nb), lanthanum (La) and barium (Ba) are recorded in the spectrum of the front lens. The presence of a rubidium (Rb) signal indicates a high potassium content in the glass, but the presence of copper (Cu), nickel (Ni) and zinc (Zn) lines in the spectrum is due to the fact that when recording the spectrum, part of the beam also interacted with the metal frame lenses. No lead was found in the material, which is not surprising - due to RoHS requirements, manufacturers try to avoid the use of lead-containing materials.

Significant amounts of lanthanum (La), tungsten (W), tantalum (Ta), niobium (Nb), and zinc (Zn) are detected in the rear lens material. Tungsten oxide is known to greatly increase the refractive index and dispersion of a material, and is only found in lenses that correspond to “ordinary” glass. “Anomalous” glass contains lanthanum and niobium as the main modifying additives, and it is niobium that contributes in this case to an increase in the overall dispersion while maintaining a negative deviation of the partial dispersion from the normal straight line. Most likely, the front lens material has a refractive index of no more than 1.75 and an Abbe number of ~50 (Hoya NBF1 or CDGM H-TF5), while the rear lens material may have a similar or higher refractive index with an Abbe number of ~30-35.

Optical properties. Comparison with 7artisans 28/1.4 (Leica M)

The Ultron 28/2 lens, according to the manufacturer, is optimized for use with Leica M-mount rangefinder cameras, but not mirrorless cameras. This means that the lens is sensitive to the thickness of the matrix filter and requires a thin protective glass on the sensor, similar to that found in Leica M cameras. Otherwise, lenses sensitive to filter thickness exhibit a severe reduction in image quality at the edge of the frame due to increasing field curvature and astigmatism. This effect is described in detail in the review New Russar+ 20/5.6.

One way or another, the idea of ​​how this lens works on conventional mirrorless cameras looks useful, so when working with it I used the camera Sony A7s.

I also compared the optical quality of the Ultron 28/2 and Chinese lenses. 7artisans 28/1.4 (Leica M), for which the same scene was filmed with both lenses at different aperture values, and then 100% crops of the resulting images were examined.

Below is the first series of shots taken on the Ultron 28/1.4 at apertures from F/2 to F/11.

Next is a series of photos on 7artisans 28 / 1.4 at apertures from F/1.4 to F/11.

Then - 100% crops from the resulting photographs.

Similarly, the second series of frames taken on Ultron 28/1.4 at apertures from F/2 to F/8.

Now on 7artisans 28 / 1.4 at apertures from F/1.4 to F/8.

And 100% crops from the received photos.

Note that with apertures F/2-F/2.8 Ultron is better than 7artisans 28 / 1.4, in terms of image quality in the central area of ​​the frame, but in the corners of the 36×24 frame, Ultron is inferior to the Chinese lens at all considered apertures - probably due to the effect of the thick matrix filter of the Sony A7s camera, since the nature of the observed optical distortions indicates a high level of astigmatism and transverse chromatism.

In addition, it is clearly noticeable that, compared to 7artisans 28 / 1.4 The Ultron 28/2 lens has the best level of image contrast. This is not a testing artifact: the Ultron 28/2 really has an excellent quality anti-reflective coating on the optics and an unproblematic blackening of the internal surfaces of the lens. The applied lens coating provides a fairly even light transmission profile, thanks to which the lens has very good color rendition.

Ultron 28/2 is not afraid of backlight, does not catch large birds and is not prone to veiling, especially at an open aperture. The colors are rich and rarely require any intervention.

Thanks to its symmetrical circuitry, the Ultron 28/2 has very low distortion.

The disadvantage of the lens is quite strong vignetting at apertures F/2-F/2.8. Due to the high level of geometric vignetting, the lens has a characteristic bokeh with clearly visible, but not tacky/Helios-like “lemons”. At the same time the same 7artisans 28 / 1.4 has an even lower level of geometric vignetting at an open aperture of F/1.4, for which it is enough to compare the bokeh of the lenses: 7artisans 28 / 1.4 at F/1.4 + at F/2 + Ultron 28/2 at F/2

The following are sample photos on the Ultron 28/2 and a full frame mirrorless camera Sony A7s.

Conclusions

Voigtländer Ultron 28/2 is a successful implementation of a compact, fast wide-angle lens for rangefinder cameras. The lens is of high quality, the image is characterized by excellent contrast and high quality, but to achieve the best results it is preferable to use the lens with cameras that have a thin matrix filter. An alternative to Ultron 28/2 could be Chinese 7artisans 28 / 1.4 (Leica M), which, having greater aperture and better image quality, has very compromised contrast and color rendition.

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