On 2014-11-24 20:57:12 +0000, Alfred Molon said:

I was browsing photozone.de and couldn't find any full-frame rectilinear
12mm lens. The widest was 14mm. Why is that the case?

I own a full frame rectilinear 12mm lens, the first of its kind. The
Voigtlander Heliar 12mm f/5.6 Aspherical. It's a rangefinder (Leica
screw mount) lens which won't work on an SLR though. Looks like
Photozone needs to get with the program - I bought it a decade ago!

["https://www.cameraquest.com/voigtlen.htm"]

In the APS-C world there is the Sigma 8-16, which has an equivalent FF
focal length of 12mm. A bit strange that for APS-C there are wider
rectilinear lenses than for FF.

Not really because with the APS-C format you can design the rear
element of a lens closer to the image plane, which turns out to be
pretty crucial with super-wide lenses. A full frame SLR's mirror would
probably smash itself into pieces against the Sigma lens you mention.