The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Tamron AF 18-250mm f3.5-6.3 II LD and the Sigma 50-500mm F4.5-6.3 DG OS HSM 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 50-500mm F4.5-6.3 DG OS HSM is the longer of the two lenses at 219mm. The Tamron AF 18-250mm f3.5-6.3 II LD with a length of 84mm, is 135mm shorter. Besides being longer, the Sigma 50-500mm F4.5-6.3 DG OS HSM also has a larger diameter of 104mm compared to the Tamron AF 18-250mm f3.5-6.3 II LD's 74mm 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. Tamron AF 18-250mm f3.5-6.3 II LD weighs 430g, which means it is 1540g (78%) lighter than the Sigma 50-500mm F4.5-6.3 DG OS HSM which has a weight of 1970g.
Below you can find the dimension and weight table of the SuperZoom Lenses in Canon EF Mount for size comparison purposes.
SuperZoom Lenses in Canon EF Mount for Size Comparison
Lens Mounts
Both the Tamron AF 18-250mm f3.5-6.3 II LD and the Sigma 50-500mm F4.5-6.3 DG 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 T8i, Canon 90D and Canon SL3.
Tamron AF 18-250mm f3.5-6.3 II LD is also available in Nikon F (DX) , Sony Alpha and Pentax KAF mounts.
Sigma 50-500mm F4.5-6.3 DG OS HSM is also available in Pentax KAF3 , Sony Alpha, Sigma SA and Nikon F (FX) mounts.
Focal Range
Tamron AF 18-250mm f3.5-6.3 II LD has a focal range of 18-250mm and 13.9X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 28.8-400mm when used on a APS-C / DX format camera. Sigma 50-500mm F4.5-6.3 DG OS HSM has a focal range of 50-500mm and 10.0X zoom ratio . When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of 80 - 800mm.