Digital Camera Dilema - Depth of field

[Clay Taylor]

All -

    Kenelm is absolutely right, but note that in his example that the image
of the subject taken through the shorter focal length / faster lens (the 2
inch f/2.0) must be MAGNIFIED (in this case 2x) to the same size as the 4"
lens image to find that the Depths-of-field are in fact identical.   Had
that example used the 2" lens at f/4 (to match the f-stop of the 4" lens)
and then magnified the image 2x, the depth of field would have been GREATER.
Excellent, right?

    The problem here (especially with digital cameras) is that you are using
less pixels to cover the subject, and when the image is enlarged to a
workable size, the image quality suffers - you are in effect doing the
"digital zoom" that is such a horrible marketing gimmick in the camcorder
and digital-still camera  world.

Clay Taylor
Moodus, CT
ctaylor at att.net
----- Original Message -----
From: "Kenelm Philip" <fnkwp at aurora.alaska.edu>
To: <leps-l at lists.yale.edu>
Sent: Friday, September 28, 2001 4:45 PM
Subject: Re: Digital Camera Dilema - Depth of field


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