The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Tamron AF 18-200mm f3.5-6.3 XR II LD and the Sigma 18-250mm F3.5-6.3 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 18-250mm F3.5-6.3 DC OS HSM is the longer of the two lenses at 101mm. The Tamron AF 18-200mm f3.5-6.3 XR II LD with a length of 84mm, is 17mm shorter. Besides being longer, the Sigma 18-250mm F3.5-6.3 DC OS HSM also has a larger diameter of 79mm compared to the Tamron AF 18-200mm f3.5-6.3 XR 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 18-200mm f3.5-6.3 XR II LD weighs 398g, which means it is 230g (36%) lighter than the Sigma 18-250mm F3.5-6.3 DC OS HSM which has a weight of 628g.
Below you can find the dimension and weight table of the SuperZoom Lenses in Sony Alpha Mount for size comparison purposes.
SuperZoom Lenses in Sony Alpha Mount for Size Comparison
Lens Mounts
Both the Tamron AF 18-200mm f3.5-6.3 XR II LD and the Sigma 18-250mm F3.5-6.3 DC OS HSM has the same Sony Alpha lens mount. Some of the latest released cameras that are compatible with the Sony Alpha lenses are Sony A68, Sony A77 II and Sony A58.
Tamron AF 18-200mm f3.5-6.3 XR II LD is also available in Canon EF , Nikon F (DX) and Pentax KAF mounts.
Sigma 18-250mm F3.5-6.3 DC OS HSM is also available in Canon EF , Nikon F (DX), Pentax KAF3, Sony Alpha, Sigma SA, Canon EF, Nikon F (DX), Pentax KAF3 and Sigma SA mounts.
Focal Range
Tamron AF 18-200mm f3.5-6.3 XR II LD has a focal range of 18-200mm and 11.1X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 27-300mm when used on a APS-C / DX format camera. Sigma 18-250mm F3.5-6.3 DC OS HSM has a focal range of 18-250mm and 13.9X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 27-375mm when used on a APS-C / DX format camera.