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From: jbm@eos.arc.nasa.gov (Jeffrey Mulligan)
Newsgroups: comp.graphics
Subject: lenses (was Re: Lunar Distortions)
Keywords: projection, perspective, distortion
Message-ID: <7622@eos.arc.nasa.gov>
Date: 27 Nov 90 23:28:47 GMT
References: <27332@cs.yale.edu> <1097@shakti.ncst.ernet.in> <9236@pasteur.Berkeley.EDU>
Organization: NASA Ames Research Center, California
Lines: 28

ph@miro.Berkeley.EDU (Paul Heckbert) writes:

>Related question: is there a formula relating camera lens
>focal length and angle of view?  (I would guess that such a relationship
>would not be theoretical, but would be based on praticalities,
>and would vary from manufacturer to manufacturer)

Focal length and angular field are independent.
For example, you can have a 50mm focal length lens
which is a "standard" lens for 35mm photography, or a 50mm wide
angle lens for a larger film format.
There are some applications (enlarging?) where it is sometimes
recommended to use a wide angle lens from a larger film
format in place of a standard lens to assure better
field uniformity.

For a family of lenses designed for a given film size, then
of course there will be a relationship between focal length
and field of view, since economics dictate that the field
of view should be no larger than necessary.  Note that the
field does not have a sharply defined size, but that the intensity
drops off continuously at the margins of the field (vignetting).

-- 

	Jeff Mulligan (jbm@eos.arc.nasa.gov)
	NASA/Ames Research Ctr., Mail Stop 262-2, Moffett Field CA, 94035
	(415) 604-3745