The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Tamron AF 28-75mm f2.8 XR LD and the Sigma 17-50mm F2.8 EX DC OS HSM 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. Tamron AF 28-75mm f2.8 XR LD weighs 510g, which means it is 55g (9%) lighter than the Sigma 17-50mm F2.8 EX DC OS HSM which has a weight of 565g.
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
Both the Tamron AF 28-75mm f2.8 XR LD and the Sigma 17-50mm F2.8 EX DC OS HSM 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 AF 28-75mm f2.8 XR LD is also available in Nikon F (FX) , Sony Alpha and Pentax KAF mounts.
Sigma 17-50mm F2.8 EX DC OS HSM is also available in Pentax KAF3 , Sony Alpha, Sigma SA and Nikon F (DX) mounts.
Tamron AF 28-75mm f2.8 XR LD has a focal range of 28-75mm and 2.7X 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 - 120mm.
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.