09-06-2011, 08:19 PM
[quote name='Klaus' timestamp='1315339679' post='11350']
Well, the Sigma 12-24mm images at 12mm are reasonably sharp in the corners when choosing a focus distances that is closer to the HFD. At infinity focus the corners are very smeared in the foreground.
The HFD is invariant of field curvature as you mentioned, yes, but in practical terms it is more useful with ultra-wides where a negative field curvature (the corners of the focus field are "pushed" towards infinity) is actually more common (to a varying degree) than a flat one.
[/quote]
Ah.. thanks for expanding on that, Klaus. Yes, makes sense for the corners in such a case. I never put too much attention to the corners myself, so my "focus" is more on the main subject(s) and therefore I appreciate "Merklingers approach" myself.
Well, the Sigma 12-24mm images at 12mm are reasonably sharp in the corners when choosing a focus distances that is closer to the HFD. At infinity focus the corners are very smeared in the foreground.
The HFD is invariant of field curvature as you mentioned, yes, but in practical terms it is more useful with ultra-wides where a negative field curvature (the corners of the focus field are "pushed" towards infinity) is actually more common (to a varying degree) than a flat one.
[/quote]
Ah.. thanks for expanding on that, Klaus. Yes, makes sense for the corners in such a case. I never put too much attention to the corners myself, so my "focus" is more on the main subject(s) and therefore I appreciate "Merklingers approach" myself.