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Date: Mon, 18 Sep 1995 15:43:07 -0400 (EDT)
From: Ernie Wright <[e-mail]>
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Subject: Re: 3.2 Zoom Factor In Camera Menu ?
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John Crane wrote:

> I can see what it is doing, but why does the camera use 3.2 as a default
> factor. What exactly does it mean ? Is it representing a specific type
> of lens ?

Zoom factor is related to the focal length of the (imaginary) lens, but
not in an obvious way.  In 3D jargon, the zoom factor is really the eye
distance from the viewplane.  Since the height of the viewport is fixed
at 2.0, the *vertical* field of view is

   fov = 2 * atan( 1 / zoom )

A zoom of 1.0 gives you a vertical field of view of 90 degrees.

It's obvious from playing with it that the zoom factor can make things
look closer or farther from the camera, like a zoom lens.  But it's
better to think of it as controlling the amount of perspective fore-
shortening.  3.2 gives you cool but somewhat exaggerated perspective.
Settings between 4.0 and 6.0 usually look more natural.

- Ernie

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