Quote:
Originally Posted by ghammer
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.
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I hope you meant
c=1/30mm (approx 0.03333)
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The simpler formula I posted gives 6.4mm DoF for either focal length, so the difference between the two formulas is negligible here.
But a 1/30 mm CoC for 35mm equipment dates from the 1920s and 30s . Modern lenses, films and sensors are capable of much better performance and it's often appropriate to work from a much smaller CoC - especially with a "cropped" sensor like the M8's. At 1/50mm CoC and 1:2 magnification and f/16, total DoF is less than 4mm.
I'll leave it to someone else to calculate the effect of the lens extension on f/stop on DoF!