The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 24-70mm F2.8 DG OS HSM and the Canon 28-135mm f3.5-5.6 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. Sigma 24-70mm F2.8 DG OS HSM is the longer of the two lenses at 108mm. The Canon 28-135mm f3.5-5.6 IS USM with a length of 97mm, is 11mm shorter. Besides being longer, the Sigma 24-70mm F2.8 DG OS HSM also has a larger diameter of 88mm compared to the Canon 28-135mm f3.5-5.6 IS USM's 78mm diameter.
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 28-135mm f3.5-5.6 IS USM weighs 540g, 47% (480g) lighter than the Sigma 24-70mm F2.8 DG OS HSM's weight of 1020g.
Below you can find the dimension and weight table of the Standard Zoom Lenses in Canon EF Mount for size comparison purposes.
Standard Zoom Lenses in Canon EF Mount for Size Comparison
Lens Mounts
Both the Sigma 24-70mm F2.8 DG OS HSM and the Canon 28-135mm f3.5-5.6 IS 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.
Sigma 24-70mm F2.8 DG OS HSM is also available in Sigma SA and Nikon F (FX) mounts.
Focal Range
Sigma 24-70mm F2.8 DG OS HSM has a focal range of 24-70mm and 2.9X zoom ratio . When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of 38.4 - 112mm.
Canon 28-135mm f3.5-5.6 IS USM has a focal range of 28-135mm and 4.8X zoom ratio . When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of 44.8 - 216mm.