I've posted on this before, so I'll say it briefly: Run
the output of a laser pointer into a 10x microscope objective
and you get a diffraction-limited point source. Set your
scope far enough away so that the fan-shaped beam from the
source more than covers the scope and you have a near-perfect
star.
mam
-----Original Message-----
From: Rob Hawley
To: The Astronomy Connection
Sent: 1/20/2003 6:27 PM
Subject: RE: [TAC] RE: Artifical Star
The concerns cited by Dennis were also echoed on the LX200GPS list. I am
in
no way recommending that vendor. I paid by credit card and am prepared
to
also stop payment if the device has not shipped. I am crossing my
fingers
that will not be necessary. I should note that I contacted the BBB
serving
Kansas and their report does not reflect the level of bad experiences I
have
heard on the newsgroups.
The problem of creating a good star is harder then it seems. The light
source for a 10" SCT needs to appear no larger than .45 arcseconds or
the
scope will resolve it as a non-point source. I leave to the reader to
compute the tradeoff of distance vs hole size to get that value. I was
quite
surprised when I did the math. You need a very small round hole and a
very
bright light source. The advantage of the Eztelescope unit was they
claim to
have a very small hole.
If you don't want to take the hassle (risk) with eztelescope.com you can
try
building it yourself. The light source you can get a radio shack (or
elsewhere). The small hole is more of a problem (see the discussion on
http://groups.yahoo.com/group/LX200GPS concerning the 25 micron orifices
available through smallparts.com). That is certainly my plan B.
Rob Hawley
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