The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 17-50mm F2.8 EX DC OS HSM and the Canon 18-135mm f3.5-5.6 IS STM 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 STM is the longer of the two lenses at 96mm. The Sigma 17-50mm F2.8 EX DC OS HSM with a length of 92mm, is 4mm shorter. On the other hand, the Sigma 17-50mm F2.8 EX DC OS HSM has a larger diameter of 84mm compared to the Canon 18-135mm f3.5-5.6 IS STM'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. Canon 18-135mm f3.5-5.6 IS STM weighs 480g, 15% (85g) lighter than the Sigma 17-50mm F2.8 EX DC OS HSM's weight of 565g.
Filter Threads
The Sigma 17-50mm F2.8 EX DC OS HSM has a filter size of 77mm whereas the Canon 18-135mm f3.5-5.6 IS STM has a 67mm 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 Sigma 17-50mm F2.8 EX DC OS HSM:
And these are the 67mm filters that we recommend for the Canon 18-135mm f3.5-5.6 IS STM:
Lens Mounts
The Sigma 17-50mm F2.8 EX DC OS HSM has the Canon EF lens mount whereas the Canon 18-135mm f3.5-5.6 IS STM has the Canon EF-S 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 Mount and Canon T8i, Canon 90D and Canon SL3 for the Canon EF-S Mount.
Sigma 17-50mm F2.8 EX DC OS HSM is also available in the Pentax KAF3 , Sony Alpha, Sigma SA and Nikon F (DX) mounts.
Focal Range
Sigma 17-50mm F2.8 EX DC OS HSM has a focal range of 17-50mm and
2.9X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
27.2-80mm when used on a APS-C / DX format camera.
On the other hand, the Canon 18-135mm f3.5-5.6 IS STM 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.
