When the first APS-C digital cameras were introduced, there weren't wide-angle built exclusively for this format, so it was impossible to get a real wide: even a 14mm on APS gives the equivalent of 21mm. Nikon was the first to introduce an wide lens created exclusively for APS - the Nikkor 12-24 f/4 - and in the next years all other manufacturer have announced their APS-C wide angles. These lenses cover exclusively the APS-C format, if you mount them on fullframe cameras you will get a small image with large black corners, but they allow to get a real wide angle: 10mm, that is the equivalent of 15mm on fullframe. In this article, I have compared five of the most popular APS-C wide angles!
 
Specifications (compared with similar lenses)