The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Canon 18-135mm F3.5-5.6 IS and the Sigma 17-70mm F2.8-4 DC OS HSM C for their suitability to various photography scenarios:
Size and Weight Comparison
The size of a lens is a crucial factor to consider when comparing two lenses. Canon 18-135mm F3.5-5.6 IS is the longer of the two lenses at 96mm. The Sigma 17-70mm F2.8-4 DC OS HSM C with a length of 82mm, is 14mm shorter. On the other hand, the Sigma 17-70mm F2.8-4 DC OS HSM C has a larger diameter of 79mm compared to the Canon 18-135mm F3.5-5.6 IS's 77mm diameter.
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 17-70mm F2.8-4 DC OS HSM C weighs 465g, 9% (50g) lighter than the Canon 18-135mm F3.5-5.6 IS's weight of 515g.
Filter Threads
The Canon 18-135mm F3.5-5.6 IS has a filter size of 67mm whereas the Sigma 17-70mm F2.8-4 DC OS HSM C has a 72mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 67mm filters that we recommend you to consider for the Canon 18-135mm F3.5-5.6 IS:
And these are the 72mm filters that we recommend for the Sigma 17-70mm F2.8-4 DC OS HSM C:
Lens Mounts
The Canon 18-135mm F3.5-5.6 IS has the Canon EF-S lens mount whereas the Sigma 17-70mm F2.8-4 DC OS HSM C has the Canon EF lens mount. Some of the latest released cameras that are compatible with these mounts are Canon T8i, Canon 90D and Canon SL3 for the Canon EF-S Mount and Canon T8i, Canon 90D and Canon SL3 for the Canon EF Mount.
Canon 18-135mm F3.5-5.6 IS is also available in the Canon EF-S mount.
Sigma 17-70mm F2.8-4 DC OS HSM C is also available in Pentax KAF3 , Sony Alpha, Sigma SA and Nikon F (DX) mounts.
Focal Range
Canon 18-135mm F3.5-5.6 IS has a focal range of 18-135mm and
7.5X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
28.8-216mm when used on a APS-C / DX format camera.
On the other hand, the Sigma 17-70mm F2.8-4 DC OS HSM C has a focal range of 17-70mm and 4.1X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 27.2-112mm when used on a APS-C / DX format camera.
