[ATM] what did I do wrong???

[mikell at optonline.net (Michael Lindner)]

On Wednesday 28 January 2004 09:16 pm, c f wrote:
> ...nothing, nada, zippo!!!  I could just make out a single dot on the
> mirror...

You *did remember to put the foucault tests at the center of curvature, not 
the focal plane of the mirror (88.8" away)....

If you've done that, then you probably mismeasured the focal length, and you 
need to find out where the real center of curvature is. Take a flashlight, 
hold it next to your head (actually, if you have a head mounted flashlight so 
much the better).  Stand where the foucault tester was, and find the return 
beam from the flashlight with your eye. move your head. Does the reflection 
move the same way? If so, then move back a little. If it moves the opposite 
way move forward a little. You will get to a point where the flashlight beam 
fills the mirror and is *very* sensistive to movement. That means you are 
close to the center of curvature.

Now set up your foucault tester at this point and try again. It may take some 
small movements towards or away from the mirror to find the exact center of 
curvature, but it *will* happen.

Good luck, and clear skies. Let us know how it goes!
-- 
Michael Lindner
http://www.starastronomy.org *** http://home.att.net/~mikel
http://www.atmsite.org *** http://www.atmlist.net