The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Nikon AF-S Fisheye 8-15mm F3.5-4.5 and the Sigma 8-16mm F4.5-5.6 DC HSM for their suitability to various photography scenarios:
Size and Weight Comparison
The size of a lens is an important deciding factor when comparing two lenses. Sigma 8-16mm F4.5-5.6 DC HSM is the longer of the two lenses at 106mm. The Nikon AF-S Fisheye 8-15mm F3.5-4.5 with a length of 83mm, is 23mm shorter. On the other hand, the Nikon AF-S Fisheye 8-15mm F3.5-4.5 has a larger diameter of 78mm compared to the Sigma 8-16mm F4.5-5.6 DC HSM's 75mm diameter.
The 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. Nikon AF-S Fisheye 8-15mm F3.5-4.5 weighs 485g, which means it is 70g (12%) lighter than the Sigma 8-16mm F4.5-5.6 DC HSM which has a weight of 555g.
Lens Mounts
The Nikon AF-S Fisheye 8-15mm F3.5-4.5 has the Nikon F (FX) lens mount whereas the Sigma 8-16mm F4.5-5.6 DC HSM has the Nikon F (DX) lens mount. Some of the latest released cameras that are compatible with these mounts are Nikon D6, Nikon D780 and Nikon D3500 for the Nikon F (FX) Mount and Nikon D3500, Nikon D7500 and Nikon D5600 for the Nikon F (DX) Mount.
Sigma 8-16mm F4.5-5.6 DC HSM is also available in Canon EF , Pentax KAF3, Sony Alpha and Sigma SA mounts.
Focal Range
Nikon AF-S Fisheye 8-15mm F3.5-4.5 has a focal range of 8-15mm and 1.9X zoom ratio . When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of 12 - 22.5mm.
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 12-24mm when used on a APS-C / DX format camera.