The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 18-35mm F1.8 DC HSM and the Canon 28-135mm f3.5-5.6 IS 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. Sigma 18-35mm F1.8 DC HSM is the longer of the two lenses at 121mm. The Canon 28-135mm f3.5-5.6 IS USM with a length of 97mm, is 24mm shorter. On the other hand, there is no difference between the max diameters of these lenses, both coming at 78mm.
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 28-135mm f3.5-5.6 IS USM weighs 540g, 33% (270g) lighter than the Sigma 18-35mm F1.8 DC HSM's weight of 810g.
Below you can find the dimension and weight table of the Standard Zoom Lenses in Canon EF Mount for size comparison purposes.
Standard Lenses in Canon EF Mount for Size Comparison
Filter Threads
Both the Sigma 18-35mm F1.8 DC HSM and the Canon 28-135mm f3.5-5.6 IS USM have the same Filter thread size of 72mm.
Below are links to the 72mm filters that we recommend you to consider for these lenses:
Lens Mounts
Both the Sigma 18-35mm F1.8 DC HSM and the Canon 28-135mm f3.5-5.6 IS 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 18-35mm F1.8 DC HSM is also available in Pentax KAF , Sony Alpha, Sigma SA and Nikon F (DX) mounts.
Focal Range
Sigma 18-35mm F1.8 DC HSM has a focal range of 18-35mm and
1.9X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
28.8-56mm when used on a APS-C / DX format camera.
On the other hand, the Canon 28-135mm f3.5-5.6 IS USM has a focal range of 28-135mm and 4.8X zoom ratio . When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of 44.8 - 216mm.