Depth of Field calculation for area arrays ...

[by way of Jeanne Anderson <[EMAIL PROTECTED]>]

Dear Colleagues in the Electronic Imaging Technical Group:

I have been trying to calculate depth of field for certain
close-up situations in my own work.  I am quite familiar
with the standard formulae for determining the bounds of
the depth of field ...

Near Limit :

  Dn =  1/(1 + Dcf/F**2)

Far Limit  :

  Dn = 1/(1 - Dcf/F**2)

where

  D = focused distance,  c = limiting circle of confusion,
  f = f-number of the lens apertue, F = focal length of the lens.

My question relates to the "appropriate" value to use for
the circle of confusion.  Typically, for film, a value of 1/1000
of the focal length of the lens is used (Focal Encycopedia of
Photography).  Alternatively, an absolute value of 1/30 mm is
recommended (Kingslake, R. "Optical System Design").  However,
these figures are based on the limits of human vision when
examining FILM.  (The basis for these values is ... "How big
can a point-image become before it is no longer perceived as
a point?")

Clearly, video systems and CCD sensors introduce another element
to this.  I've made a brief examination of the literature, and
the best discussion I can find is a technical note provided by EG&G
Reticon in their camera handbook (Application Note #127).  In this
paper, the authors use the inter-pixel spacing as the "appropriate"
value for the circle of confusion ("acceptable blur spot").  Can
anyone on this list justify/dispute this for me?  My intuition tells
me this is probably a good "starting point", but my intuition and
reality are often at odds with each other.  The EG&G note simply
states what is done, without justification.  It does not attribute
the note to a particular individual.

Any thoughts, feedback, references, etc. would be helpful.

Regards, and thanks,         

Jim WALTON
Chairman, SPIE Technical Group on High-Speed Photography,
    Videography and Photonics

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