P3D DOF and Hyperfocal distance - part I

["Dr. George A. Themelis" <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

I posted this in the RBTS1 list and I think it might be useful
to be posted here... for those unfamiliar with these concepts.
All this info is in the "DrT Tutorial" in our newletter
(reprints available for sale) and also in my Realist book
(to be released in two weeks):

- Depth of Field = range of "acceptable sharpness" in front and 
  behind the plane of focus.  

  For example, for the Realist (and any camera with 35 mm lenses), 
  the Depth of field with the camera focused at 10 feet and an aperture 
  of f8 is 6 feet to 29 feet.  Note that the DOF is asymmetrically 
  distributed, i.e. there is less in front (6 to 10 feet) and more
  in the back (10 to 20 feet).

  The definition of "acceptable sharpness" is based on a constant, known 
  as "circle of confusion".  In simple words, this is how much a point is 
  allowed to get out of focus and become a circle, and still perceived as 
  a point by the eyes.  For 35 mm film, it is generally accepted that the
  "circle of confusion" is 1/750 in. or 0.03 mm.  (Note: in earlier
  Realist literature, a more conservative value of 1/1000 in. was used)

- As you focus further and further, there will be a point when the
  DOF extends to infinity.  The closest focusing distance for which
  DOF extends to infinity is known as the "hyperfocal distance".
  This is important for stereo because focusing at the hyperfocal
  distance gives you the maximum depth of field.  

To be continued.... -- George Themelis


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