The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Tamron 18-200mm F3.5-6.3 Di II VC 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. Tamron 18-200mm F3.5-6.3 Di II VC is the longer of the two lenses at 97mm. The Sigma 18-125mm F3.8-5.6 DC OS HSM with a length of 89mm, is 8mm shorter. Besides being longer, the Tamron 18-200mm F3.5-6.3 Di II VC also has a larger diameter of 75mm compared to the Sigma 18-125mm F3.8-5.6 DC OS HSM'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 18-200mm F3.5-6.3 Di II VC weighs 400g, which means it is 90g (18%) 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 18-200mm F3.5-6.3 Di II VC 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 T8i, Canon 90D and Canon SL3.
Tamron 18-200mm F3.5-6.3 Di II VC is also available in Nikon F (DX) and Sony Alpha 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 18-200mm F3.5-6.3 Di II VC has a focal range of 18-200mm and 11.1X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 28.8-320mm when used on a APS-C / DX format camera. 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.