Sigma has for the first time marketed a true fisheye optic for crop sensors, projecting a circular 180° image onto APS-C sensors. The new lens sports a focal length of 4.5mm and maximum aperture of f/2.8.
The other type of fisheye lens available is the diagonal variety which squeezes a 180° angle of view into a standard rectangular format. This new 10mm F2.8 EX DC Fisheye HSM from Sigma is just such a lens. That said, it captures a true 180° vista only when mounted in front of a Nikon DX sensor - users of Canon and Sigma DSLRs make do with 167° and 154° respectively. A built-in lens hood and HSM focusing are here and the lens will focus down to 1.8cm (0.7 in) from the front surface of the lens giving a reproduction ratio of 1:3.3.