Originally posted by bossa It's not about shallow DOF so much as getting the DOF you want at more civilized apertures. An 31mm F1.8 lens on APS-C cannot compete with an 50mm F2 lens on FF. I know most (if not all) lenses are certainly sharper when stopped down a little so a cheaper longer lens on FF that might cost as little as $400 that can out-perform a $1500 lens on APS-C is welcome...
An example:
31mm @ F/1.8 on APS-C @ 1 meter DOF = 75.89mm
50mm @ F/3.2 on FF @ 1 meter DOF = 76.91
+1 for a point I haven't seen before. If that 50 is an SMC f/1.7 then it's just as sharp as (or sharper than) the 31/1.8 and just as fast, with notably thinner DOF. To match FF 50/1.7 on APS-C would take a 35/1.1, and good luck.
EDIT: I should have added: And yes, for the same DOF, the FF 50 needs only a much slower aperture and will be notably sharper, rendering detail much better. For the same DOF, the fastest APS 35 is at the edge of acceptability, whilst a fast FF 50 is stopped-down to near its sweet spot. So, a cheaper FF lens for better results, or an equal FF lens for MUCH better results -- THAT is the point here.
Last edited by RioRico; 04-23-2012 at 06:10 AM.