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Re: Edmund Parabolic Reflectors

Subject: Re: Edmund Parabolic Reflectors
From: Mike Feldman <>
Date: Wed, 04 Aug 2004 13:20:28 -0500
Gregory Kunkel wrote:

>   The math of parabolas states that the width of a parabola at the
> level of the focal point is 4 times the focal point. So each of the
> parabolic dishes have a depth equal to its focal length.

That's true given the assumption that the design happens make the
depth of the dish equal to focal length, but there's nothing
mathematical forcing the manufacturer to this constraint.

> So the 18" has a depth of 4.5" and the 24 inch has a depth of 6".

That being said, the Edmund dishes are in fact as deep as their
focal length, and my 24" diameter dish measures 6" deep.  It seems
to me that there was some discussion here or on a related list
about the Telinga dishes being deeper than their focal length,
and that's important for sound reflectors more so than for
optical reflectors.

-- Mike


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