Quote:
Originally Posted by giordano
The (Ilford) Manual of Photography gives this formula for depth of field at near distances: Total Depth = 2*c*N*(m+1)/m^2
where c is circle of confusion, N is the numerical f/stop and m is the magnification ratio. Focal length isn't a factor. |
This is an approximation. The exact expression is:
2*c*N*(m+1)/(m^2-(c*N/f)^2)
with
f the focal length. So there is really a difference for all ratios m (Luigi is right), but the difference is very small for c approaching 1. For Luigis case: c=0.33, m=0.5, and N=16 it is 6.403mm versus 6.400mm.