Size and Weight Comparison
Size of a lens is an important deciding factor when comparing two lenses.Carl Zeiss Distagon T2/25 is the longer of the two lenses at 98mm. The Canon 20mm f2.8 USM with a length of 71mm is 27mm shorter. On the other hand, the Canon 20mm f2.8 USM has a larger diameter of 78mm compared to Carl Zeiss Distagon T2/25's 73mm 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. Canon 20mm f2.8 USM weighs 405g, 48% (195g) lighter than the Carl Zeiss Distagon T2/25's weight of 600g.
Below you can find the dimension and weight table of the 'Wideangle Prime Lenses in Canon EF Mount for size comparison purposes.
Wideangle Prime Lenses in Canon EF Mount for Size Comparison
Lens Mounts
Both Carl Zeiss Distagon T2/25 and Canon 20mm f2.8 USM has the same Canon EF lens mount. Some of the latest released cameras that are compatible with the Canon EF lenses are Canon 1D X III, Canon 6D MII and Canon 5D MIV.
Carl Zeiss Distagon T2/25 is also available in Nikon F (FX) mount.
Focal Range
Carl Zeiss Distagon T2/25 is a prime lens with fixed focal lenght of 25mm. When it is mounted on an APS-C sensor camera with 1.6x crop, it provides an 35mm (FF) equivalent of 40mm.
Canon 20mm f2.8 USM is a prime lens with fixed focal lenght of 20mm. When it is mounted on an APS-C sensor camera with 1.6x crop, it provides an 35mm (FF) equivalent of 32mm.