Re: [ATM] RE:anealing

["Bob May" <bobmay@nethere.com>]

Ah, I missed the autocollimation word in the question!  That indeed does
make the paraboloid without a toroid condition.
Now, as to using subdiameter flats, that is going to be a bit difficult but
can be solved by putting an EP near the focus point and locating the flat's
return in the image from the EP.  Note that when you subdiameter a
telescope, the off-axis image ends up producing a large spot of light where
the aperture is in what would be called the star test image. You won't see
the full star test image but only the part that is returned from the mirror
and you can explore the location of that spot in the image and get the spot
into the right location.  How accurate you ucan do so, I don't know but I'd
suspect that you can do this good enough to berify that the surfaces are
right or not.  Needless to say, the bigger the subdiameter flat, the better
it will be as you will quickly be able to see the center hole in the image
and be able to locate the flat more accurately as a result.  For example, a
flat 1/2 the diameter will end up with the central hole showing 1/2 of it's
diameter in the image.
Other than that method, I don't think that it would be possible to
accurately focus a telescope unless you do so against the real world and
then put the flat in the path for the actual testing.
Bob May
bobmay@nethere.com
http://nav.to/bobmay
http://bobmay.astronomy.net

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