Archived posting to the Leica Users Group, 1999/08/31

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Subject: Re: [Leica] Depth of field... (more than you wanted to know)
From: "Jacques Bilinski" <jbilin@axionet.com>
Date: Tue, 31 Aug 1999 17:40:12 -0700

>
> So, my question is:  What is the scientific justification for this "rule
of
> thirds"?  Empirically it doesn't seem to exist.
>
>
Some of these rules are useful approximations which work over a certain
range of values, but break down outside this range. Take the 'rule' which
states 'double the focal length and you will get half the angle of view'.
This rule works fine for longer focal lengths but breaks down for short
ones. A 2mm theoretical lens for example will cover just under 180 degrees,
but a 1mm lens won't cover 360 degrees.