The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Tokina 16.5-135mm f3.5-5.6 DX and the Sigma 18-200mm F3.5-6.3 DC for their suitability to various photography scenarios:
Size and Weight Comparison
The weight of a lens is equally significant as its external dimensions, particularly if you intend to handhold your camera and lens combination for extended periods. Sigma 18-200mm F3.5-6.3 DC weighs 405g, 33% (205g) lighter than the Tokina 16.5-135mm f3.5-5.6 DX's weight of 610g.
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
Filter Threads
The Tokina 16.5-135mm f3.5-5.6 DX has a filter size of 77mm whereas the Sigma 18-200mm F3.5-6.3 DC has a 62mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 77mm filters that we recommend you to consider for the Tokina 16.5-135mm f3.5-5.6 DX:
And these are the 62mm filters that we recommend for the Sigma 18-200mm F3.5-6.3 DC:
Lens Mounts
Both the Tokina 16.5-135mm f3.5-5.6 DX and the Sigma 18-200mm F3.5-6.3 DC 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.
Tokina 16.5-135mm f3.5-5.6 DX is also available in Nikon F (DX) mount.
Sigma 18-200mm F3.5-6.3 DC is also available in Nikon F (DX) , Pentax KAF, Sony Alpha and Sigma SA mounts.
Focal Range
Tokina 16.5-135mm f3.5-5.6 DX has a focal range of 17-135mm and
7.9X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
27.2-216mm when used on a APS-C / DX format camera.
On the other hand, the Sigma 18-200mm F3.5-6.3 DC 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.