The 50mm C Sonnar ZM is a very unique option for a normal lens. In a nutshell this lens looks and draws as if were a compressed version of the 85mm Planar ZF, in ZM mount. The Sonnar is unusually compact even for its focal length and speed class, but costs far less than Leica’s more modern aspherical lens of similar specifications. There are some well-known issues with this lens however, which should dampen the enthusiasm of many.
The designation “Sonnar” is most typically found on moderate telephoto lenses from Carl Zeiss, in the range of 85mm to 135mm. In this case it applies to a normal lens because its construction is fundamentally similar to that of moderate telephotos, a design choice that gives the Sonnar its unusually small size. More specifically the high magnification in the front groups is not balanced with symmetrical power in the rear groups, permitting the barrel to be shorter than what is natural for the focal length.
Today I am an at an early stage of experience with the Leica M9 and feel the desire to get faster lenses quite keenly. This Sonnar has such universal appeal on paper that I quickly settled on it for my first taste of a high speed 50mm M lens. Roger and his team at LensRentals.Com kindly agreed to send me a beautiful copy of the lens for this review.
This 50mm ZM is the smallest lens I have used thus far. It is shorter but slightly wider than the 35mm Biogon ZM (they weigh essentially the same) and is utterly dwarfed by all the SLR lenses that I have seen. The combination with the M9 is harmonious and comfortable – I suspect this is the most pleasant 50mm lens/camera combination to use and behold.
The aperture ring is one of the high points of the physical implementation of this lens. The movement is smooth, the detents click vigorously, and the ring has no play when settled to a stop. There is no way to predict how these properties will change over time, but between like-new lenses the feeling of the Zeiss’ aperture ring is superior to Leica’s.
Manual focus is comparatively easier with the Sonnar on a rangefinder camera than the 50mm Planar ZF on a reflex camera, but with one big and rather terrible caveat : focus shifts substantially at wider apertures on the Sonnar. This is due to high amounts of uncorrected spherical aberration in the drawing of the lens. The effect is pleasant for some uses, a nuisance for others, and can sometimes be avoided by deliberately focusing behind the subject.
The Sonnar ZM does not implement floating elements, and its closest focus distance is 0.9 meters. This is not a severe limitation for this focal length, but I do wish that it allowed focus down to 0.7 meters like its sister lens, the 50mm Planar ZM.
Whereas the 85mm Planar ZF manages to combine a soft look wide-open with authoritative drawing at all other apertures, the 50m Sonnar ZM struggles to find its foothold until depth of field embraces whole subjects. Bokeh and flare resistance are on a high level however, which go a long way to redeem this lens.
The Sonnar’s drawing at full aperture is difficult to characterize because it is so unevenly delivered in actual use. Occasionally you get both great detail and a smoothness that is ideal for portraits, but most of the time the best you get is mild blur.
This is because the focus shift effect places the camera’s best-focused plane right at the edge of depth-of-field (towards the back end) when the lens is used wide open. Hence the extremely narrow depth-of-field a 50mm lens would normally offer at f/1.5 becomes halved or quartered for one direction of focus error.
At smaller apertures, starting around f/5.6, the Sonnar draws fine detail with excellent contrast in the plane of focus. There is high resolution covering most of the frame that is delivered consistently. The far corners of the image field never capture meaningful detail however, even up to the diffraction limit.
Bokeh is excellent in all images made by the Sonnar. I could not observe any distracting artifacts in the defocus regions of the images shot with the lens. This lens is also very resistant to secondary reflection flare, as noted by Carl Zeiss in their promotional material, but it does suffer a large drop in contrast due to veiling glare under some conditions.
The 50mm Sonnar ZM is a beautiful lens that I simply cannot recommend. It is a very competent lens at smaller apertures but that is not ground for this lens to stand on, since I have little doubt the 50mm Planar ZM can do better. The Planar is also celebrated for its Bokeh, taking away the edge of the Sonnar’s foremost quality.
I have to wonder what this lens would be like if it incorporated an aspherical element in its design. Leica has demonstrated with the 90mm APO Summicron ASPH that Sonnar-type designs with aspherical elements are not only possible but can deliver the very highest levels of image quality. I am sure that Cosina is up to the challenge of manufacturing an aspherical Sonnar lens for Carl Zeiss.
Would I recommend this lens to other photographers? No. If Carl Zeiss ever announces a 50mm Sonnar ASPH then I would stand in line to get one.
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