The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 14mm F1.8 DG HSM and the Canon 15mm f2.8 Fisheye for their suitability to various photography scenarios:
Size and Weight Comparison
Size of a lens is an important deciding factor when comparing two lenses.Sigma 14mm F1.8 DG HSM is the longer of the two lenses at 126mm. The Canon 15mm f2.8 Fisheye with a length of 62mm is 64mm shorter. Besides being longer, the Sigma 14mm F1.8 DG HSM also has a larger diameter of 95mm compared to Canon 15mm f2.8 Fisheye's 73mm diameter.
Weight of a lens is as important as its external dimensions, especially if you are planning to hand hold your camera and lens combination for longer periods. Canon 15mm f2.8 Fisheye weighs 330g, 71% (840g) lighter than the Sigma 14mm F1.8 DG HSM's weight of 1170g.
Lens Mounts
Both Sigma 14mm F1.8 DG HSM and Canon 15mm f2.8 Fisheye has the same Canon EF lens mount. Some of the latest released cameras that are compatible with the Canon EF lenses are Canon 1D X III, Canon 6D MII and Canon 5D MIV.
Sigma 14mm F1.8 DG HSM is also available in Sigma SA and Nikon F (FX) mounts.
Focal Range
Sigma 14mm F1.8 DG HSM is a prime lens with fixed focal lenght of 14mm. When it is mounted on an APS-C sensor camera with 1.6x crop, it provides an 35mm (FF) equivalent of 22.4mm.
Canon 15mm f2.8 Fisheye is a prime lens with fixed focal lenght of 15mm. When it is mounted on an APS-C sensor camera with 1.6x crop, it provides an 35mm (FF) equivalent of 24mm.