The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Canon 10-18mm f4.5-5.6 IS STM and the Sigma 8mm F3.5 EX DG Fisheye 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 10-18mm f4.5-5.6 IS STM is the longer of the two lenses at 72mm. The Sigma 8mm F3.5 EX DG Fisheye with a length of 69mm, is 3mm shorter. Besides being longer, the Canon 10-18mm f4.5-5.6 IS STM also has a larger diameter of 75mm compared to the Sigma 8mm F3.5 EX DG Fisheye'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. Canon 10-18mm f4.5-5.6 IS STM weighs 240g, which means it is 160g (40%) lighter than the Sigma 8mm F3.5 EX DG Fisheye which has a weight of 400g.
Lens Mounts
The Canon 10-18mm f4.5-5.6 IS STM has the Canon EF-S lens mount whereas the Sigma 8mm F3.5 EX DG Fisheye 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 Blackmagic URSA 12K LF, Z CAM E2-F6 II 6K and Z CAM E2-S6 II 6K for the Canon EF Mount.
Sigma 8mm F3.5 EX DG Fisheye is also available in Nikon F (FX) and Sigma SA mounts.
Focal Range
Canon 10-18mm f4.5-5.6 IS STM has a focal range of 10-18mm and
1.8X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
16-28.8mm when used on a APS-C / DX format camera.
On the other hand, the Sigma 8mm F3.5 EX DG Fisheye is a prime lens with fixed focal lenght of 8mm. When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of 12.8mm.
