The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Tamron SP 35mm F1.4 Di USD and the Voigtlander 20mm F3.5 SL II for their suitability to various photography scenarios:
Size and Weight Comparison
The 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 20mm F3.5 SL II weighs 205g, 74% (600g) lighter than the Tamron SP 35mm F1.4 Di USD's weight of 805g.
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 the Tamron SP 35mm F1.4 Di USD and the Voigtlander 20mm F3.5 SL II 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.
Tamron SP 35mm F1.4 Di USD is also available in Nikon F (FX) mount.
Voigtlander 20mm F3.5 SL II is also available in Nikon F (FX) and Pentax KAF mounts.
Focal Range
Tamron SP 35mm F1.4 Di USD is a prime lens with fixed focal lenght of 35mm. When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of 56mm.
Voigtlander 20mm F3.5 SL II 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 a 35mm (FF) equivalent of 32mm.