The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Canon 20-35mm f3.5-4.5 USM and the Canon 17-40mm f4.0L USM for their suitability to various photography scenarios:
Size and Weight Comparison
The size of a lens is an important deciding factor when comparing two lenses. Canon 17-40mm f4.0L USM is the longer of the two lenses at 97mm. The Canon 20-35mm f3.5-4.5 USM with a length of 69mm, is 28mm shorter. On the other hand, there is no difference between the max diameters of these lenses, both coming at 84mm.
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. Canon 20-35mm f3.5-4.5 USM weighs 340g, which means it is 160g (31%) lighter than the Canon 17-40mm f4.0L USM which has a weight of 500g.
Below you can find the dimension and weight table of the Wideangle Zoom Lenses in Canon EF Mount for size comparison purposes.
Wideangle Zoom Lenses in Canon EF Mount for Size Comparison
Lens Mounts
Both the Canon 20-35mm f3.5-4.5 USM and the Canon 17-40mm f4.0L 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.
Focal Range
Canon 20-35mm f3.5-4.5 USM has a focal range of 20-35mm and 1.8X zoom ratio . When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of 32 - 56mm.
Canon 17-40mm f4.0L USM has a focal range of 17-40mm and 2.4X zoom ratio . When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of 27.2 - 64mm.