The 35mm Biogon ZM delivers beautiful drawing, excellent sharpness, no distortions, decent speed, and compact size at reasonable price. In comparison the Summicron ASPH is even more compact, particularly if one accounts for the hood, but costs far more and doesn’t deliver very much improvement in terms of optics. Here Zeiss makes a quiet statement: spherical designs are still competitive in a world gone aspherical.
When compared to the 35mm Distagon ZF/ZE, the Biogon ZM defends as much its own virtues as those of the M system itself. That is because these two lenses are as close as you can get to a fair comparison between camera systems: same field of view, same brightness, same designers, same factory, same materials, and same price. Whatever strengths or weaknesses the Biogon may show relative to the Distagon are likely to be properties of the M system itself.
It’s interesting that the ZF and ZM lens programs mirror each other not only in the choice of focal lengths to feature but also which focal lengths received the most engineering focus, the strongest implementations. Each program dedicated class-leading optics to the 2.8/21, 2/35 and 2/50 products that have cemented Zeiss’ reputation in the new millenium. For me the choice of a 2/35mm Biogon ZM T* as my 35mm lens for the M system was a no-brainer – and only partly because of its price.
This 35mm ZM is a joy to hold and use. Although it is not the smallest in its class (only the Summilux and Nokton are larger), size is not an issue with this lens. It is dwarfed by any SLR lens really, particularly ugly-duckling mid-range zooms that cover this focal length. On the M9 the lens is as good a fit as any other lens, but for aesthetic reasons I wish that the hood was rectangular like that of the Summicron.
The aperture rings found on Zeiss ZM lenses are the most enjoyable I have used. Here we find the same qualities as in the 50mm Sonnar: the movement is smooth, the detents click vigorously, and the ring has no play when settled to a stop. Even the shape of the aperture opening is more regular on the ZM lenses than other M mount lenses I have seen, but whether this makes any difference in the photographs is unclear.
Manual focus is easy and effortless with the Biogon on a rangefinder camera thanks to a fair bit of depth of field (or more appropriately, focus). The ribbed focus ring works somewhat better than the focusing tab on Leica’s lenses, at least for beginners. At first the movement on my lens had some friction but through use over time it became much more fluid.
The Biogon does not implement floating elements for focusing. The entire assembly simply shifts forward when focused closer than infinity. The latest version of the Summilux ASPH is the only lens in the M system to combine floating elements with the 35mm focal length. Such a system probably could not be implemented in the Zeiss without increasing its size and weight. At any rate, focus shift is not a problem with the Biogon so there is one less reason for floating elements to be used.
The Biogon's minimum focus distance is 0.7 meters like most M-mount lenses. This is just on the verge of being a real limitation with this lens; working with DSLR's for years has taught many of us to engage subjects at close range with wide-angle lenses. It is just on the verge however, and ultimately shouldn't cramp your style too much (unlike wider lenses, which we'll talk about on a later date).
The 35mm Biogon is a sharp lens at any aperture, but particularly so starting from f/2.8. In comparison with its sister lens, the 35mm Distagon ZF, the Biogon appears to be the sharpest. It is not always the least aberrated however – the Distagon is clearly better at f/2.
Wide-open the 35mm Biogon renders fine detail with good contrast on axis and across the field to the image borders, but not all the way to the corners. At this aperture the image corners suffer from quite strong coma and astigmatism. Astigmatism affects image quality both inside and outside the plane of focus, producing a muddy look and misshapen circles of confusion respectively (more on this below). The image area that is affected represents a very small percentage of the total image, so whether it is an issue will depend on the photographer (it hasn’t been an issue for me).
Like most wide-angle lenses for the Leica M system, the Biogon also produces a strong “hot spot” in the center of the frame at full aperture due to light fall-off in the outer regions. This is far from fully corrected by the Leica camera’s firmware when the Biogon is coded as a 35mm Summicron IV, as recommended. Besides being an image artifact, the hot spot also interacts with metering because its shape is fundamentally similar to the shape of the centerweighted metering area.
All aspects of image quality improve with the first stop down to f/2.8. Axis and border contrast become plainly excellent at this aperture, aberrations in the corners drop significantly and light fall-off is reduced to the point where software corrections produce a relatively even field brightness. Stopping down beyond f/4 brings only modest improvements over most of the image field, except for light fall-off and aberrations in the corners which both continue to improve until f/8, at least. Perfectionism notwithstanding, this lens is useful without much reservation throughout the range f/2.8 to f/8 .
The Biogon draws Bokeh very nicely, robustly one might say, but has some issues at f/2. Poorly-corrected coma flare and astigmatism in the outer image regions distort the shape of defocused point lights located there: very strongly if in the foreground, but only lightly if in the background. Absent the bespoke foreground highlights, or when using any aperture other than wide-open, the Biogon’s Bokeh is nicely rounded and almost free from distracting artifacts. On the bottom line, the combination of very high micro-contrast inside the focal plane with smooth defocus (in most situations) outside is extremely satisfying.
In other matters the Biogon is worthy of the Zeiss T* badge: it produces contrasty images even against the light, even Sunlight, with clean highlights free of halation and deep peering shadows. Internal reflections are very well controlled as well.
The 35mm Biogon is one of the most satisfying lenses ever made and the best part is that most serious amateur photographers can afford it. Unfortunately far fewer photographers can afford a digital camera that can utilize it properly. With the growing market presence of mirrorless cameras we can only hope to see one come out eventually with an APS-H or full-frame sensor to better use this lens.
Would I recommend this lens to other photographers? Yes, most enthusiastically.