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Re: [OM] Mind Bender

Subject: Re: [OM] Mind Bender
From: Roger Wesson <roger@xxxxxxxxxxxxxxxxxxxxxxx>
Date: Mon, 25 Nov 2002 14:25:16 +0000
Field of view is proportional to the inverse of the focal length is it not? I think that's true for rectilinear lenses but no doubt someone will correct me if I'm wrong. As John said, you need to define what you mean by 'half way', but if you mean field of view, then the maths is as follows:

By definition:

FOV(halfway) = [ FOV(100) + FOV(200) ] / 2

As FOV is proportional to 1 / focal length, this can be written as

1/FL(halfway) = [ 1/100 + 1/200 ] / 2

so FL(halfway) = 133.3, or 135, near enough.

That's the way I see it anyway.

Roger

AG Schnozz wrote:

150.  I think AG is stirring the war pot again...


Stir, stir, add hot peppers, stir, stir...

Actually, this is quite fascinating because the obvious answer
isn't necessarily the right answer.  J.L. added more questions
to the fire, but...

Take a look at your lens charts and specifically look at
angle-of-view.

AG-Schnozz




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