Try the lens from f/3.2 down to about f/5.6. Wide open at f/1.4 the lens is not especially Sharp in the corners and you can see some optical flaws, but this is pretty par for the course for most regular-grade f/1.4 50s . This lens is not a $5,995 Leica 50, nor is it a $1,200 50, nor is it an $800 lens, and it improves quite a bit from f/1.4 to F 2.8. At f/ 2.8 on a modern high-megapixel sensor the lens is actually quite sharp and careful testing of my 50 revealed that F3 is its sharpest lens opening due to the small size of pixels on the Canon 60D. The lens reached its highest sharpness at a surprisingly wide aperture.... I don't have the figures on hand but if you are shooting on a 5D-II or 6D it is possible I suppose that the maximum sharpness is reached at f/4 or thereabouts. However it's possible that the increased depth of field that a smaller aperture such as F 7.1 gives, might yield a better picture. There is a lot of talk about loss of sharpness due to diffraction but in my experience shooting at a small f stops such as F-16 can yield added depth of field that makes for a sharper- looking picture. I am talking about f/3- f/3.2 for getting the maximum amount of sharpness for flat plane or distance shooting, as in test chart or astrophotography. It is in certain situations like this that diffraction can cut your sharpness and a surprisingly wide-aperture such as F 3.2 might actually be better than a medium aperture such as F / 5.6.