Digital Camera Dilema - Depth of field

[Kenelm Philip]

	Here is the situation with regard to depth of field, quoted from
the _Handbook of Photography_ (Henney & Dudley, 1939):

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Depth of Focus, Including Enlargement of the Print.

It can easily be shwon that if we photograph the same object with two lenses
of different focal lengths and diamters, if we subsequently enlarge the
smaller picture to make it the same size as the larger picture, and if we
insist on equally sharp definition in the two final equal-sized pictures,
then the depths of focus of the two cameras will be proportional solely to
the _diameters_ of the two lenses. Thus an f/2 lens of 2-in. focus and an
f/4 lens of 4-in. focus both have a diameter of 1 in. The 2-in.lens forms
a picture half as large as the 4-in. lens, but after enlargement to make
them equal in size, the depth of focus of each will turn out to be the same.
This property constitutes the real advantage of the miniature camera, in
that it permits the use of a fast lens without the loss of depth of focus.
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It is thus true that digital cameras where the CCD is smaller than a 35mm
film do indeed have a (theoretical) advantage in depth of field--provided
that the resolution of the CCD is high enough to make use of the advan-
tage.

							Ken Philip
fnkwp at uaf.edu




 
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