Size and Weight Comparison
Size of a lens is an important deciding factor when comparing two lenses.Leica Summicron-M 35mm f2 ASPH is the longer of the two lenses at 35mm. The Voigtlander 40mm F1.4 Nokton Classic with a length of 30mm is 5mm shorter. On the other hand, the Voigtlander 40mm F1.4 Nokton Classic has a larger diameter of 55mm compared to Leica Summicron-M 35mm f2 ASPH's 53mm 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 80g (45%) lighter than the Leica Summicron-M 35mm f2 ASPH which has a weight of 255g.
Lens Mounts
Both Voigtlander 40mm F1.4 Nokton Classic and Leica Summicron-M 35mm f2 ASPH 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. Leica Summicron-M 35mm f2 ASPH is a prime lens with fixed focal lenght of 35mm.