The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 18-300 F3.5-6.3 DC OS HSM and the Tamron AF 28-300mm f3.5-6.3 XR LD 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 18-300 F3.5-6.3 DC OS HSM is the longer of the two lenses at 102mm. The Tamron AF 28-300mm f3.5-6.3 XR LD with a length of 84mm, is 18mm shorter. Besides being longer, the Sigma 18-300 F3.5-6.3 DC OS HSM also has a larger diameter of 79mm compared to the Tamron AF 28-300mm f3.5-6.3 XR LD's 73mm 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 28-300mm f3.5-6.3 XR LD weighs 420g, 28% (165g) lighter than the Sigma 18-300 F3.5-6.3 DC OS HSM's weight of 585g.
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 Sigma 18-300 F3.5-6.3 DC OS HSM and the Tamron AF 28-300mm f3.5-6.3 XR LD 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.
Sigma 18-300 F3.5-6.3 DC OS HSM is also available in Nikon F (DX) , Pentax KAF3, Sigma SA and Sony Alpha mounts.
Tamron AF 28-300mm f3.5-6.3 XR LD is also available in Nikon F (FX) , Sony Alpha and Pentax KAF mounts.
Focal Range
Sigma 18-300 F3.5-6.3 DC OS HSM has a focal range of 18-300mm and 16.7X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 28.8-480mm when used on a APS-C / DX format camera. Tamron AF 28-300mm f3.5-6.3 XR LD has a focal range of 28-300mm and 10.7X 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 - 480mm.