I've been reading a lot of the technical literature about a camera I have (Canon 7D) and there's a point I've got to where I'm confused. I wonder if anyone else could help me out?
I really don't want someone's interpretation of a Google search, I can do that myself. If someone could shed some light on the subject then please could you help me with this:
IF a certain lens, (any lens, say), is sharpest at (say) f/8, and Canon say the camera's DLA is at f/6.8, then what aperture should one be aiming at, given the ideal conditions to go for the sharpest shot?
Simply put, if I dial in f/8 in Av, (aiming for the sharp aperture), but the DLA says fall-off starts around f/6.8, then is f/8 still accepted as the sharpest aperture?
Another camera I own is the 1D4 and DLA fall-off is at f/9.1! Same question applies....
Footnote; I knew nothing of DLA until I read this literature, so I'm quite interested in knowing more.
From the website's definition:
DLA (Diffraction Limited Aperture) is the result of a mathematical formula that approximates the aperture where diffraction begins to visibly affect image sharpness at the pixel level. Diffraction at the DLA is only barely visible when viewed at full-size (100%, 1 pixel = 1 pixel) on a display or output to a very large print. As sensor pixel density increases, the narrowest aperture we can use to get perfectly pixel sharp images gets wider.
DLA does not mean that narrower apertures should not be used - it is simply the point where image sharpness begins to be compromised for increased DOF and longer exposures. And, higher resolution sensors generally continue to deliver more detail well beyond the DLA than lower resolution sensors - until the "Diffraction Cutoff Frequency" is reached (a much narrower aperture). The progression from sharp the soft is not an abrupt one - and the change from immediately prior models to new models is usually not dramatic. Check out this specific diffraction comparison example using the ISO 12233 chart comparison tool. The mouseover feature will show you the degradation at f/11 compared to f/5.6.
[Edited 2011-02-06 08:10:16]