If the manufacturer chooses to make a parabalic dish with a diameter
equal to 4 times the focal length he must make the depth equal to the
focal length. That is unless his factory is in a different dimension.
Greg Kunkel
--- Mike Feldman <> wrote:
> 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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