Re: [ATM] first light on a Lurie-Houghton

[David Weinshenker <daze39@earthlink.net>]

Guy Brandenburg wrote:
> If the problem is, in fact, the tilt of
> the corrector plate - which I am not sure of - 
> then fixing that would be very, very difficult.
> How many of you can say that you can
> align ANYTHING to within 1/10 of a degree?

This probably a totally naive suggestion, since
I am totally unfamiliar with the "Lurie-Houghton"
configuration... but is there any way the "corrector
plate" could be installed on an adjustable mount?
I note that H. R. Suiter [1] gives a figure of 1.8 - 3
arcminutes for the tolerance of the tilt of the
primary mirror of an f/4.5 reflecting telescope -
which is 1/20 - 1/33 of a degree, or as least as
tight a tolerance as appears to be indicated here.

If the mechanical design of the corrector plate
allows for it, having it on a "three-screw" adjustable
mount might permit attempting to tune out the aberration
visually... at least it might be a troubleshooting
technique: if the coma refuses to null out, or seems
to be minimal at a clearly off-center adjustment, then
you have a clue that something else is to blame, but
it sounds like the corrector plate angle might be finicky
enough (according to the figures given here) that it
needs a "test and adjust" process to go from the
initial "installed by measurement" alignment to the
optically optimum setting (as does the primary mirror
of a fast reflector).

-dave w

[1] "Star Testing Astronomical Telescopes", p. 105
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