[ATM] Star testing an uncoated mirror? No luck.

[Bob May]

First off, find focus for the scope by looking at any bright
source or do it in the daytime where you can see something far
away.  6" mirrors do a good job of seeing the hillside about 2
miles away at Peters place so an 8" is even brighter.  Once you
find the focus point, you can then do the str test.  The light
from the bearing must be visible easily for the test to work and
this can be done even in the daylight. with a 3/8" or so
ballbearing without problems.  200-300' is more like a usable
distance to put the artificial star as this is more the minimum
distance to keep from seeing much in the way of spherical
abrration for a typical length scope.  The alignment initially of
the scope isn't critical, just make sur that things look
concentric when looking in the focuser.  A pinhole to center the
eeye is moree than enough for practible results.
You probabbly didn't have a focus and/or pointed in the right
direction so never saw a focused image.  Doint the test in the
daylight is often the better thing as you can see if you are
focused and whether  youare pointed in the right direction.
Eveen just setting it up in the hallway before taking it outdoors
for a real test will be  informative.  Remember that as the star
gets closer, the focus point is further from the primary!
Bob May

rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net