5Dmaniac wrote in post #6560436
I searched the archives, but couldn't find any direct comparisons. I just got the Canon 28mm f/2.8 and I am really disappointed by the (lack of) corner sharpness at the largest aperture. The center of the lens is capable of delivering a sharp image, but the corners are almost unusable - very very blurry. I wanted to use this lens on my 5D for low light photography, but the quality won't do. How does the f/1.8 version compare to the f/2.8. I have read so much about the performance issues of the 1.8 on FF cameras, that I shied away from it, but now I feel that I made a mistake (not a big one, as I only paid $50 for this lens). Thanks for any and all help.
For low light photography, most of the time it is about the centre of the image, so this shouldn't really be a problem in most cases.
However, on a 5D, this lens starts shining at F/5.6, whereas a 28 F/1.8 starts a little sooner. Even with this lens on a 5D you need to stop down to get very sharp corners. However, it is very usable from about F/2.
If you want better performance, you may want to consider the 24L. It is very good at F/1.4, but even here the corners are a little soft at F/1.4 on FF.
With WA lenses there is always some fall-off at the edges and corners, and this will show up more strongly on FF than it will on APS-C, using the same lens of course. Note that the sharpest and best WA lenses often have maximum apertures of F/2.8 or even smaller, and still command quite a premium. It is hard to make a (relatively) fast WA that is qualitatively as good in the corners as it is in the centre, and this is caused entirely by the combination of rectilinear image projection and large AoVs in the first place.
Kind regards, Wim