A very articulately written statement, which can be summarized generally as:
"No, I am not wrong. But yes, I admit that in general the world of photography takes a position contradictory to what I have been saying."
Thank you for the kind and civil discussion David.
Hi Sheldon,
I agree with that conclusion, and I add thanks for a daily dose of entertainment. Also thanks to the contributors to this thread who are knowledgeable enough to resist derailing tactics commonly used by trolls. Thank goodness none of those are to be found around here ...
And now for another piece of relevant information; One of the most authoritative sources on optics I've seen on the internet, Paul van Walree, suggests a simple formula for the calculation of the COC "Sharpness criterion" (as always as a function of output magnification and viewing distance) in the
PDF manual with his
VWDOF (Windows) application on page 3 and 4:
A better approach is to determine the required COC value C yourself:
C = V / (1000 * Q * Mp)
Where:
C = Circle of Confusion in millimetres to be used in DOF formulae,
V = Viewing distance in millimetres,
Q = Quality factor, Q=1 for Conventional, Q=2 for Demanding, or Q=3 for Critical sharpness
Mp = Output magnification factor, Output size divided by Sensor array size
This very simple formula holds very well in the daily practice of planning different shooting/presentation scenarios.
Of course for a more tailored answer to the OPs question, we therefore need more input, but failing that let's assume the following scenario (see attachment for a VWDOF output).
Leica S2 with a 70mm lens @ f/2.5, focused at 10 metres distance, versus
Nikon D3x with a 50mm lens @ f/1.6 focused at 10 metres distance.
If their COCs (assuming critical sharpness is required, Q=3) are scaled in proportion (!) to their sensor array diagonals, then they will both have about the same DOF at 10 metres distance, close to 1.27 metres in total. The exact DOF will vary with output magnification, but it will scale in proportion for both camera/lens scenarios, because the COCs have been scaled in anticipation of their required magnification to same size output. However, there are still some differences, e.g. the amount of blur at other distances (e.g. at infinity, or at 1 metre behind the plane of focus). Unfortunately no simple factor can explain it all, but a good DOF calculator is always handy for these sorts of questions (provided one uses the right input).
Of course this also doesn't tell us anything about differences in optical quality nor in handling ease of such different platforms.
Cheers,
Bart