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 bonding 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). Here 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 in the “real-life” comparison below 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 contract, visible). A sharpness fall-off adjustment in the RAW editing tool however makes the difference between the two glasses from f/5.6 and above disappear.
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) entirely disappears: