Originally posted by beholder3 Maybe you want to look at the vignetting results of this cheapo point-and-shoot lens for reference (check those grey pictures under "falloff"):
Canon 85mm f/1.2 L II
Wouldn't want one of these. Obviously too weak and too badly vignetting to be called a FF lens.
If you compare that to the DA40XS "crop" lens, well...
OK. Now there's a real test with 40 xs on a 5d mk3 from ricehigh. Does the corner look good enough to you? If it's normal to you, congratulations.
http://img.photobucket.com/albums/v313/RiceHigh/5Ds/40mm_Pancake/IMG_1039.jpg Look at the lower right corner. Notice that this is taken at about f5,6 (manually fixed aperture).
This is not acceptable for a modern lens. You are wrong, corner sharpness of an 85 1,2 @ 1,2 and 1,4 is not expected to be perfect. But a normal prime f2,8-5,6 should perform flawlessly. Again, you are wrong. It's too bad in the corners to be used on FF without cropping. And you'd need to crop down the image to about APS-C for the corners to be good. :-)
That ken rockwell test shows that the 85 1,2 got much better corners at 1,2 than the xs 40 got at f5,6...
http://www.kenrockwell.com/canon/lenses/images/85mm-f12/sharpness/12-corner-IMG_9498.jpg f1,2 in the right corner. :-)