I've had some difficulty getting sharp images across all focal lengths on my 28-135 zoom, and some frustrations as well with my new 100mm f2.8 Macro. I've just read a long review of the 50D where it referred to something called DLA which causes a loss of sharpness due to a difraction angle on fstops smaller than 7.9? This article suggests a reduced image size to allow smaller aperature use without this blurring effect.


Any comments on this?


Also what may appear to be a basic photographic question - but one I frankly don't know the answer to. When a lens is focused at infinity, does fstop impact depth of field? I find myself angling towards smaller fstops to ensure DOF, but if it's not a concern at infinity, as suggested by someone who will for now remain nameless, that would make my air show photographyfar easier.... I do know it is less of an issue at non - macro distances, but this person is suggesting it is a non-issue when focusing on objects that are at infinity. Your comments would be appreciated.