The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 18-50mm F2.8-4.5 DC OS HSM and the Canon 17-40mm f4.0L USM 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 17-40mm f4.0L USM is the longer of the two lenses at 97mm. The Sigma 18-50mm F2.8-4.5 DC OS HSM with a length of 89mm, is 8mm shorter. Besides being longer, the Canon 17-40mm f4.0L USM also has a larger diameter of 84mm compared to the Sigma 18-50mm F2.8-4.5 DC OS HSM's 74mm 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 18-50mm F2.8-4.5 DC OS HSM weighs 395g, which means it is 105g (20%) lighter than the Canon 17-40mm f4.0L USM which has a weight of 500g.
Filter Threads
The Sigma 18-50mm F2.8-4.5 DC OS HSM has a filter size of 67mm whereas the Canon 17-40mm f4.0L USM has a 77mm 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 Sigma 18-50mm F2.8-4.5 DC OS HSM:
And these are the 77mm filters that we recommend for the Canon 17-40mm f4.0L USM:
Lens Mounts
Both the Sigma 18-50mm F2.8-4.5 DC OS HSM and the Canon 17-40mm f4.0L USM 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.
Sigma 18-50mm F2.8-4.5 DC OS HSM is also available in Pentax KAF3 , Sony Alpha, Sigma SA and Nikon F (DX) mounts.
Focal Range
Sigma 18-50mm F2.8-4.5 DC OS HSM has a focal range of 18-50mm and
2.8X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
28.8-80mm when used on a APS-C / DX format camera.
On the other hand, the Canon 17-40mm f4.0L USM has a focal range of 17-40mm and 2.4X zoom ratio . When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of 27.2 - 64mm.