Size and Weight Comparison
Size of a lens is an important deciding factor when comparing two lenses.Carl Zeiss Biogon T2/35 ZM is the longer of the two lenses at 68mm. The Voigtlander 40mm F1.4 Nokton Classic with a length of 30mm is 38mm shorter. On the other hand, the Voigtlander 40mm F1.4 Nokton Classic has a larger diameter of 55mm compared to Carl Zeiss Biogon T2/35 ZM's 52mm diameter.
Weight of a lens is as important as its external dimensions, especially if you are planning to hand hold your camera and lens combination for longer periods. Voigtlander 40mm F1.4 Nokton Classic weighs 175g, which means it is 65g (37%) lighter than the Carl Zeiss Biogon T2/35 ZM which has a weight of 240g.
Lens Mounts
Both Voigtlander 40mm F1.4 Nokton Classic and Carl Zeiss Biogon T2/35 ZM has the same Leica M lens mount. Some of the latest released cameras that are compatible with the Leica M lenses are Leica M11, Leica M10 and Leica M Typ 262.
Focal Range
Voigtlander 40mm F1.4 Nokton Classic is a prime lens with fixed focal lenght of 40mm. Carl Zeiss Biogon T2/35 ZM is a prime lens with fixed focal lenght of 35mm.