Re: ATM Long focal length advice required please,

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

To do the Foucault or other test on that mirror, I'd find somebody that
knows video and have him build an amplifier for the video signal out of a
camera (in the monitor is the best in the circuit after the crt signal comes
out of the control chip) and use that video setup with its additional
contrast to test the mirror.
You may also want to use a webcam although you may run out of contrast as
those are limited to 8 bits of grayscale.  An astrocam of about any kind
with the larger grayscale can be used.
You may need to play with the lens on the camera so that the mirror fills
the screen vertically.  Sinlget lenses are fine if you are using a LED for
the light source as you don't have to worry about color correction.
Once you get this stuff done, you will be able to test the mirror very
nicely.  While I could setup to test a 17' ROC, something like that does
take a substantial sized room to test.  Trying to do it by a naked eye is
going to be an exercise in frustration without good solid bases for the
tester and the mirror stand -you can't do this on the second floor of a
building as even concrete moves a fair bit.  The use of a small telescope
will also help.
Good luck!
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net