Fixed lenses are easier to design than zoom lenses. The designer might optimize the project for only one focal lenght and does not need to worry about correcting distortions in several different focal lenghts. So, one could expect that Canon might produce a fixed lens wider than the 11mm, as it happened in the past, when we had the 16-35mm (and 17-40mm), but also the 14mm. However, today the widest Canon lens is the 11-24 (and also the widest rectilinear wide angle lens - hooray Canon). Why can´t we have an 8mm, a 9mm or a 10mm rectilinear lens? Is there a theoretical limit for wide angle lenses on DSLRs due to, for example, register distance or mirror clearance distance?