P3D Re: 2519 - focus

[roberts@xxxxxxxxxxxxxxxxx (John W Roberts)]

>Date: Tue, 20 Jan 1998 06:49:07 -0700
>From: Duncan Waldron <J.Waldron@xxxxxxxxx>
>Subject: P3D Re: 2519 - focus

>Sorry Jim (and others who replied), but the terms "depth of field" and
>"depth of focus" are very clearly defined in photography, and cannot be
>interchanged. 

>Depth of field refers to the distance range in front of and behind the
>subject - the point of focus - which will be rendered acceptably sharp;
>for example, when focusing on an object 5 metres away, the depth of field
>may, with the appropriate aperture, extend from (say) 2 metres to 10
>metres in front of the camera (strictly speaking, in front of the focal
>plane).

>Depth of focus refers to the distance in front of and behind the focal
>plane within which an acceptably sharp image of the subject exists.

I think maybe you need more words to describe the distinction between these
two terms. From what's written above, "depth of focus" sounds like a pretty
useless term - why not discard the current definition and use the term for
something else? In the example you give, is the "depth of focus" 3 meters
(the distance from five meters away to two meters away), or is it 5 meters
(the distance from five meters away to ten meters away)? By "point of focus",
do you mean the same thing as "focal plane"?

>For the width of a scene being photographed, or viewed though a binocular,
>you would refer to the field of view.

Good point.

John R


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