The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Irix 11mm F4 and the Sigma 10mm F2.8 EX DC HSM 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. Irix 11mm F4 is the longer of the two lenses at 118mm. The Sigma 10mm F2.8 EX DC HSM Fisheye with a length of 83mm, is 35mm shorter. Besides being longer, the Irix 11mm F4 also has a larger diameter of 103mm compared to the Sigma 10mm F2.8 EX DC HSM Fisheye's 76mm 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. Sigma 10mm F2.8 EX DC HSM Fisheye weighs 475g, 39% (315g) lighter than the Irix 11mm F4's weight of 790g.
Lens Mounts
The Irix 11mm F4 has the Nikon F (FX) lens mount whereas the Sigma 10mm F2.8 EX DC HSM Fisheye 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.
Irix 11mm F4 is also available in Canon EF and Pentax KAF3 mounts.
Sigma 10mm F2.8 EX DC HSM Fisheye is also available in Canon EF and Sigma SA mounts.
Focal Range
Irix 11mm F4 is a prime lens with fixed focal lenght of 11mm.
On the other hand, the Sigma 10mm F2.8 EX DC HSM Fisheye is a prime lens with fixed focal lenght of 10mm which has an effective (full-frame 35mm equivalent) focal range of 15mm when used on a APS-C / DX format camera.