Archived posting to the Leica Users Group, 1999/12/01

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Subject: Re: [Leica] RE: 75mm f1.4 DOF
From: "Henning J. Wulff" <henningw@archiphoto.com>
Date: Wed, 1 Dec 1999 20:16:36 -0800

At 7:06 PM -0800 12/1/99, Jacques Bilinski wrote:
>> The 100 APO macro may not be the best example because, if my recollection
>> serves, the focal length shortens as you focus closer
>
>Yes, you are right about this, but I think that both the stated focal length
>and the stated angle of view are for the lens focused at infinity.
>
>On that same brochure the angle of view for the 35mm lens is given as 64
>degrees and that of the 15mm (less than half of the 35mm)  lens is given at
>110 degrees (not 128 plus degrees).
>
>One way to convince yourself that angle of view is not exactly directly
>proportional to focal length is by drawing little scale diagrams. You will
>see that this rule is way off for very wide angle lenses, but a good approx.
>for tele lenses.

I think this is pretty well known by anyone who has used a variety of
lenses or who understands basic trigonometry. Where is this leading us?

   *            Henning J. Wulff
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