Doggone it Moose, you beat me to it!
The interaction of focal length with frame size (on film) and print
enlargement is something I had to learn and recalibrate my feel for when I
first started using a medium format 645 . . . the need to stop it down by
about a half-stop to full-stop more if I want the same DOF for the same
composition (including same angular field of view) because the lens focal
length to do it is longer. It's compensated for some by less magnification
being needed for the same size print, but not completely. I'd have to walk
through the DOF equations in gory detail to demonstrate how it all works
and that's more lengthy than I want to tackle here (so I'll spare you all
from it too).
-- John Lind
At 10:23 PM 5/30/2005, Moose wrote:
>Exactly! However, to get the same size print or other display size, the
>image has to be enlarged about twice as much, which changes the DOF.
>Remember, DOF is inherently subjective and, no matter what it looks
>like, DOF tables have always been calculated back from the acceptable
>fuzziness to the human eye at a given display size. So if one is happy
>with a half size print, DOF is the same, otherwise, it is less.
>
>Moose
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