The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 8-16mm F4.5-5.6 DC HSM and the Rokinon 8mm f3.5 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. Sigma 8-16mm F4.5-5.6 DC HSM is the longer of the two lenses at 106mm. The Rokinon 8mm f3.5 Fisheye with a length of 77mm, is 29mm shorter. On the other hand, there is no difference between the max diameters of these lenses, both coming at 75mm.
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. Rokinon 8mm f3.5 Fisheye weighs 443g, 20% (112g) lighter than the Sigma 8-16mm F4.5-5.6 DC HSM's weight of 555g.
Lens Mounts
The Sigma 8-16mm F4.5-5.6 DC HSM has the Canon EF lens mount whereas the Rokinon 8mm f3.5 Fisheye has the Sony Alpha 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 Sony A68, Sony A77 II and Sony A58 for the Sony Alpha Mount.
Sigma 8-16mm F4.5-5.6 DC HSM is also available in Pentax KAF3 , Sony Alpha, Sigma SA and Nikon F (DX) mounts.
Rokinon 8mm f3.5 Fisheye is also available in Canon EF , Nikon F (FX), Four Thirds, Pentax KAF and Samsung NX mounts.
Focal Range
Sigma 8-16mm F4.5-5.6 DC HSM has a focal range of 8-16mm and
2.0X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
12.8-25.6mm when used on a APS-C / DX format camera.
On the other hand, the Rokinon 8mm f3.5 Fisheye is a prime lens with fixed focal lenght of 8mm which has an effective (full-frame 35mm equivalent) focal range of 12mm when used on a APS-C / DX format camera.