The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 17-50mm F2.8 EX DC OS HSM and the Canon 17-55mm f2.8 IS 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 17-55mm f2.8 IS USM is the longer of the two lenses at 111mm. The Sigma 17-50mm F2.8 EX DC OS HSM with a length of 92mm, is 19mm 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. Sigma 17-50mm F2.8 EX DC OS HSM weighs 565g, which means it is 80g (12%) lighter than the Canon 17-55mm f2.8 IS USM which has a weight of 645g.
Lens Mounts
The Sigma 17-50mm F2.8 EX DC OS HSM has the Canon EF lens mount whereas the Canon 17-55mm f2.8 IS USM has the Canon EF-S lens mount. Some of the latest released cameras that are compatible with these mounts are Canon T8i, Canon 90D and Canon SL3 for the Canon EF Mount and Canon T8i, Canon 90D and Canon SL3 for the Canon EF-S Mount.
Sigma 17-50mm F2.8 EX DC OS HSM is also available in Pentax KAF3 , Sony Alpha, Sigma SA and Nikon F (DX) mounts.
Focal Range
Sigma 17-50mm F2.8 EX DC OS HSM has a focal range of 17-50mm and 2.9X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 27.2-80mm when used on a APS-C / DX format camera. Canon 17-55mm f2.8 IS USM has a focal range of 17-55mm and 3.2X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 27.2-88mm when used on a APS-C / DX format camera.