[ATM] testing flats with a green laser
princenorman at bellsouth.net
Sat Dec 1 15:14:56 JST 2007
That sounds like grand fun!!!...wish there were just one cat aroud who
wanted to play with atm stuff that I could confer with...consider yourself
most fortunate to find the company of other enthusiasts....as i work in a
vacum...learn by my experience only...it is a tedious venture, but not
without its rewards in terms of understanding...
Good luck in all your projects...as always ..too all on the list... even if
my cavelier atitude, and mouth sometimes obvuscate such notions...i never
mean any offence...
word!...,and HEARD!...oh and forgive my crappy spelling too!!!!...hheeh
----- Original Message -----
From: "Guy Brandenburg" <gfbrandenburg at yahoo.com>
To: <atm at atmlist.net>
Sent: Friday, November 30, 2007 23:23 PM
Subject: [ATM] testing flats with a green laser
> This evening at the NCA-CCCC telescope making workshop, as usual, Jim
> McPherson brought in an interesting project. He had purchased a roughly 10
> inch quartz opitcal window that was supposed to be 1/10 wave (or something
> like that) and was wondering if we had a way of testing that claim. Well,
> I had received a gift from some folks at NASA-Goddard of a heliostat
> complete with a 12 inch flat mirror. But I didn't know how flat that was,
> either. In any case the 12 inch flat had a deteriorated aluminum coating,
> and we couldn't see any lines when we put one on the other. Plus, I had
> neglected to bring in the monochromatic light box that I had made - it's
> in my garage. The aluminum coating on the 12 inch flat swamps any
> interference fringes.
> So, I decided to kill a couple of birds with one stone, as it were. I used
> some paper towels and our trusty mixture of CuSo4 and HCl to strip off the
> aluminum coating, then we washed the known flat, and Jim happened to have
> a GREEN laser pointer. We found a couple of small Korean-War era lens
> blanks that one side frosted, shone the laser through the frosted blanks,
> putting all of this into a darkened room, and the interference fringes
> showed up well. Not as good as in my little monocrhomatic light box, but
> well enough for everybody to see them. And they were straight!
> Jim also had another piece of glass that was supposed to be flat by about
> a wave or two every inch, which is not all that flat, frankly, by optical
> standards. It was quite fun to watch it when we made a stack of all three
> of these pieces of glass. I began to see Moire' patterns!
> Bottom line - if you don't have a mnochromatic light box, and you want to
> test flats, you can use some double-frosted glass and a green laser
> Guy Brandenburg, Washington, DC
> My home page on astronomy, mathematics, education:
> or else
> "Education isn't rocket science. It's much, much harder."
> (Author unknown)
> ATM mailing list http://www.atmlist.net/
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