From: "CSC" 
To: "Atm" 
Reply-To: "CSC" 


650 feet is about far enough.  Your scope will show it to be overcorrected.
To keep it within 1/4 wave wavefront error, Suiter's table 5-2 suggests it
needs to be about 70 times the 6' focal length or about 400-500'  Further
is better, of course.

A 1/4" ball bearing will not likely be enough.  I use 2" and
3" colored Christmas tree balls on various tree lines. early a.m.
tests are best. Red balls are dramatic. showing the minima very clearly.
Our Meade 16" f/4.5 tests out overcorrected on stars and the sun test
about equally. Most nights it is a great scope.

Observing a close star means racking out the focus further, and your
diagonal may not be big enough.  Watch out for this!

Colin

-----Original Message-----
From: owner-atm{at}shore.net [mailto:owner-atm{at}shore.net]On Behalf Of Jerry
B. Hillman
Sent: Monday, June 30, 2003 5:42 PM To: atm{at}shore.net
Subject: ATM daytime star testing with sun



Hi all,
Is it feasible to use the reflected image of the sun off of a ball bearing
to do daytime star testing?
My property is large enough that I can place the ball bearing up to 650
feet away. If so, would a 1/4" ball bearing be big enough? If I could
do this then it would give me many more opportunities to star test. (It is
cloudy today or I would already be trying it.) Clear skies, Jerry

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