Lately, after changing the whole IS and optical system of my EF70-300 IS, i felt my shots look oof even though i'm quite confident that i hv it sharp in the viewfinder. So just now, i did a test.
Slap on the 500d CU filter,undo IS, mount on tripod with cable release, set to manual focussing and adjust to the minimum focussing distance to get the highest magnification. This is what I get at different F-stops, very strange...
No.1 to no.5 is F 5.6, F 8, F 11 F 16, F 22
And from shot 1 thru to shot 5, I've ensured thru the viewfinder that the original focussed line stayed in focus.
It seems that as my F-stop gets higher, the back gets sharper than the original focussed point. I'll be glad if u can tell me it's something wrong.