This review is done with a Leica M9. Image comparisons are screen shots from a RAW editing tool. Click on images for full resolution.
Let’s start by coding the Biogon 21 mm. The Leica internal menu only offers two 21mm options: Elmarit-M 21mm f/2.8 and Elmarit-M 21mm f/2.8 ASPH. The Super-Elmar-M code is recognised by the M9 but cannot be manually selected in the menu. Since one of the black marks of the Super-Elmar-M code falls exactly on a screw on the Biogon bayonet mount, manually coding the Biogon as Super-Elmar is a bit difficult. For the purpose of this review I will then only use the menu options of the M9. Here the results of shooting a white wall boosting contrast and saturation to max:
According to this website the lens should be conned as Elmarit-M 21mm f/2.8 ASPH. Vignetting is indeed improved compared to the uncoded version, but the non-ASPH coding seems a better choice. Zeiss suggests to code the lens as Elmarit-M 28mm f/2.8 (IV) (source: could be read in some blog and Zeiss customer service confirmed it to me in a personal email). To verify that I did a second test (the real Leica Super-Elmar-M is taken as reference):
Indeed the 28mm is good, but I don’t like having the incorrect focal length info in the EFIX.
The Elmarit-M 21mm f/2.8 ASPH is really not a good option. As it can be seen in this “real-life” comparison the corners becomes reddish…
The first test compares the two lenses at max aperture (if you shoot stars) and at f/8 (a more suitable aperture for landscapes). My conclusion: wide open the Leica is maybe a very tiny bit sharper in the center but it is also not as fast as the Zeiss. At f/8 the results are indistinguishable in terms of sharpness. The Zeiss lens is however a bit more contrasty.
Second set of images shows the same scene as above taken at f/4 and f/5.6. My conclusion: the Zeiss lens is a bit more contrasty, but both lenses deliver the same details: sharpness is substantially identical.
The castle of Brescia (Italy) is now moved to the edge of the frame in the set of images below. My conclusions: the Leica shows better sharpness and higher contrast on the edge of the frame. At f/8 the gap to the Zeiss Biogon is however small (but at least in terms of contrast, visible).
In this final comparison I increase the sharpness and sharpness fall-off adjustment on the Zeiss Biogon. The difference to the Leica (left to its standard values for sharpness) becomes very subtle:
Both at f/5.6. Which is which?
Bokeh and subject separation
Subject separation with 21mm is not very strong but the difference between f/2.8 and f/3.4 is visible, The Zeiss moreover has shorter minimum focus distance (also with rangefinder coupling it goes below 0.7 m). The next shots are at 0.7m for both lenses.
Here another scene (Leica above, Zeiss below):
And the zoom version:
Both lens have a controlled flare.
The Leica Super-Elmar-M 21mm f/3.4 is optically the best lens of the two. If you intend to shoot landscapes at f/8, no-one will ever be able to tell if you used the Super-Elmar-M or the Zeiss Biogon T* 2.8/21 mm ZM (provided the vignetting of the Biogon is corrected).
Since I swap lenses once in a while, I want my lenses to be coded on the flange – the via-the-menu lens coding is for me not an option. Unfortunately the 4-screw mount of the Biogon makes coding on the flange a bit difficult. Online you could buy third party flange with ready-to-be-coded holes that fit the 4-screw mount of the Biogon but one screw will have to be sacrificed, i.e. the flange will connect to the lens with only 3 screws. I have not tried this option and kept the Leica lens for my digital M.