The 50mm Planar ZM is one of the simplest lenses ever made, yet performs more robustly and consistently than almost any other lens. It is very closely related to the more-storied 50mm Summicron-M, of nearly identical size and capabilities, that it challenges in the marketplace. This Planar is a fundamentally boring lens with its lack of buzzwords to rave about and also substantive flaws to gripe about.
In my review of the 1.4/50mm Planar ZF I emphasized the direct connection between that lens and the “double gauss” optical layout from the 19th century. In actuality the design of the ZM lens is even more closely related to this precursor, resembling more closely that of pre-WW-II designs than any other modern lens. Adding T* coatings to a lens design originally devised to maximize contrast without the use of coatings has produced a lens with phenomenal contrast and resistance to contra-light.
This is my third 50mm lens, and fourth 50mm lens review. Despite appearances this focal length is not my favorite but I admit that it is very versatile and an excellent teacher. As I experience it the M system pushes the photographer towards using 50mm more than other systems, in part because of the default choice of magnification in the viewfinder.
The 2/50mm ZM is in most ways operationally the same as the 2/35mm ZM. The two lenses share the same lens barrel, down to the last detail. For the overall description I will refer you to that review.
One small difference between the two lenses is the amount depth of field they provide, obviously with the Planar providing less of it. It hasn’t been an issue for me however because 50mm at f/2 still provides plenty of depth of field to hide small errors at most focus distances.
Besides this there is an annoying detail common to both the Biogon and the Planar, but much more so on the Planar, where the first glass element is fixed to the lens’ faceplate. A double-threaded ring is screwed here on top of the first element, with two diametrically opposed notches that I presume to serve in the assembly process. These notches have sharp corners that frequently catch threads in microfiber cleaning cloths, getting in the way of a smooth cleaning and sometimes damaging the cloths. This is rather sloppy and unusual for Zeiss.
The 0.7m close focus limit is absolutely not an issue with this lens, much as it has been for me with some other lenses in the M system. Likewise for focus shift. Like the Biogon lens this Planar is not corrected for close focus as it lacks floating elements.
The 50mm Planar ZM is not the strongest-performing lens there is at f/2, but it just might be after f/4. It also doesn’t have any major flaws at any aperture.
At the full aperture of f/2 the Planar draws with high resolution and high contrast on-axis, and good contrast over the majority of the frame. Fine detail is resolved all the way to the borders in fact, but contrast is lower there because of halation artifacts – probably due to residual spherical aberration. Although fine detail can be seen at the image corners, the micro-contrast there is extremely poor.
One stop down from the full aperture, at f/2.8, contrast and resolution in the image center improve to extremely high levels. Likewise the outer image regions now attain levels similar to what the image center delivered at f/2, but the corners still come out a bit short of useful. Halation is greatly reduced along extreme contrast edges at this aperture.
At all of the smaller apertures, from f/4 onwards and until the diffraction limit, the Planar’s performance is outstanding: extreme contrast and resolving power over the entire frame. This performance stretches to the image corners now, and even there aren’t any halation artifacts. At these apertures you will definitely encounter some moiré on the M9 camera, no matter the subject matter. Contrast is slightly lower at f/8 than it is at larger apertures.
Performance at close range is less than stated above, and degradation is perceptible when working at a couple of meters or less. Even down to the 0.7m close focus limit performance is still quite good though, and is rarely the limiting factor when you consider how poor indoor lighting typically is. Only a few 50mm lenses are available that correct for this effect, most notably the Summilux-M ASPH.
The Planar is very resistant to veiling glare when used in contra-light, particularly if you can afford to stop it down once or twice. Flares spots can be produced under the right conditions, as with any lens, though you will get large blooming patches more often than spots.
Bokeh is understated and simply excellent, with no distracting artifacts. Zones of defocus are simply blurred as if by a perfect Gaussian filter in Photoshop. The transition from focus to defocus is plain – neither abrupt nor the elongated type found in the best portrait lenses.
The 50mm Planar ZM is a very good lens, there isn't much else to say. It's unlikely that either the Summicron-M or Summarit-M lenses perform much better than this lens on the M9 camera. Its excellent performance on-axis at any aperture suggests to me that it is also an excellent choice of short telephoto lens for cropped-frame mirrorless cameras.
Would I recommend this lens to other photographers? Yes.