the ultimate refrierator

John K Clark (
Sun, 21 Dec 1997 22:43:48 -0800 (PST)


On Sun, 21 Dec 1997 Hara Ra <> Wrote:

>At the focus of the telescope, with a really low f-ratio, the sky
>will be seen to be mostly the black hole.

The lower the f-ratio the shallower the depth of focus, that is, the more
nonlinear it becomes. This fact is of some importance when dealing with real
light sources that are not mathematical points.

>Imagine a an ellipsoid, with the radiaitor at one focus and the
>black hole at the other. The radiator will see the full sky as the
>black hole. All of the radiation from the radiator will go to the
>black hole.

I haven't worked out the calculation but my intuition tells me that you'd do
better to forget about the huge ellipsoid and just make your heat radiator
bigger. It's true that a light beam passing through one focus of an ellipsoid
will pass through the other focus too, but it's not necessarily true that a
light beam that passes near one focus will pass near the other one too.

It's a little off the subject but this reminds me of something I read a few
years ago about a man who made elliptical pool tables rather than the more
traditional rectangular ones. They were not very popular. The trouble was
that skilled professional players were not much better than rank amateurs at
the game. Chaos took over and nobody had any idea where the billiard balls
would end up when a shot was made. Skill plays no part when a elliptical
table is used, it turns the game into one of chance.

John K Clark

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