The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Canon 10-18mm f4.5-5.6 IS STM and the Sigma 10-20mm F3.5 EX DC HSM for their suitability to various photography scenarios:
Size and Weight Comparison
Size of a lens is an important deciding factor when comparing two lenses.Sigma 10-20mm F3.5 EX DC HSM is the longer of the two lenses at 88mm. The Canon 10-18mm f4.5-5.6 IS STM with a length of 72mm is 16mm shorter. Besides being longer, the Sigma 10-20mm F3.5 EX DC HSM also has a larger diameter of 87mm compared to Canon 10-18mm f4.5-5.6 IS STM's 75mm 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 10-18mm f4.5-5.6 IS STM weighs 240g, which means it is 280g (53%) lighter than the Sigma 10-20mm F3.5 EX DC HSM which has a weight of 520g.
Lens Mounts
Both Canon 10-18mm f4.5-5.6 IS STM has the Canon EF-S lens mount whereas the Sigma 10-20mm F3.5 EX DC HSM has the Canon EF 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-S Mount and Canon T8i, Canon 90D and Canon SL3 for the Canon EF Mount.
Sigma 10-20mm F3.5 EX DC HSM is also available in Pentax KAF3 , Sony Alpha, Sigma SA and Nikon F (DX) mounts.
Focal Range
Canon 10-18mm f4.5-5.6 IS STM has a focal range of 10-18mm and 1.8X zoom ratio which has a 35mm equivalent focal range of 16-28.8mm when used on a APS-C / DX format camera. Sigma 10-20mm F3.5 EX DC HSM has a focal range of 10-20mm and 2.0X zoom ratio which has a 35mm equivalent focal range of 16-32mm when used on a APS-C / DX format camera.