The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Tamron AF 28-300mm f3.5-6.3 XR LD and the Sigma 18-125mm F3.8-5.6 DC 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 18-125mm F3.8-5.6 DC OS HSM is the longer of the two lenses at 89mm. The Tamron AF 28-300mm f3.5-6.3 XR LD with a length of 84mm, is 5mm shorter. Besides being longer, the Sigma 18-125mm F3.8-5.6 DC OS HSM also has a larger diameter of 74mm 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, which means it is 70g (14%) lighter than the Sigma 18-125mm F3.8-5.6 DC OS HSM which has a weight of 490g.
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 28-300mm f3.5-6.3 XR LD and the Sigma 18-125mm F3.8-5.6 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 28-300mm f3.5-6.3 XR LD is also available in Nikon F (FX) , Sony Alpha and Pentax KAF mounts.
Sigma 18-125mm F3.8-5.6 DC OS HSM is also available in Sigma SA and Nikon F (DX) mounts.
Focal Range
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.
Sigma 18-125mm F3.8-5.6 DC OS HSM has a focal range of 18-125mm and 6.9X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 28.8-200mm when used on a APS-C / DX format camera.