[Leica] Depth of field vs. depth of focus

["Oliver Bryk" <oliverbryk@attbi.com>]

Dante Stella wrote:
"Can someone point me to a formula for calculating depth of focus for a
given focal length and aperture?  This is NOT depth of field, but rather
the focus zone on and around the film plane."

fCalc and similar calculators derive depth of field, not depth of focus.
According to John Williams's "Image Clarity: High Resolution Photography",
depth-of-field calculators assume that the image cone is geometrically
exact. The depth of focus is in part a function of lens design errors,
diffraction, and construction defects. I haven't found any references to
methods for calculating it. I'm way out of my field here; Erwin Puts to the
rescue!
Oliver Bryk




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