Re: ATM Fixed vs Moving source

["Bob May" <bobmay@nethere.com>]

Actually Andrew, when you really sit down to look at the shadows, you will
find that even the moving source tester can be easily measured (I use a
cheap ($14 at regular price) dial indicator that reads to .001")  better
than you can see the shadows on the mirror.  I am just able to see about
.002"-.003" at best for determining the location of the ROC of a particular
zone on most mirrors.  This is quite good enough to get some decent results
out of TEX when the mirror is indeed good.  Since errors tend to stay on the
same side of the error band when testing (you tend to mistake the equal
brightness the same way every time more than bouncing around) the error is
mostly taken out by the way that the equations work (you end up thinking you
have a ROC of a few thousandths of an inch more than you actually do!) and
thus the results are very close to reality.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net