Re: ATM Interference Testing Technique and a D-K Secondary

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

Dwight, you don't need good phase info with the test as the local phase of
the incoming is compared to the reflected phase being bounced back up.  You
aren't measuring inches of distance but rather microinches and the biggest
thing is to get the bandwidth of the colors down so that the phase is the
nearly the same for all of the colors.  Having several color will make the
resulting interference bands happen at a different rate across the surfaces
under test as the phase angle will be different for each color.
I might also note that if the rings are down to 20 then you have a 10 wave
difference between the two surfaces and this is correctable with nothing
more than a bit of polishing, trying to get rid of the radius differences
like yo would do if you were grinding.
If you want to, you can do some of the changing of radius with the test tool
but only if you don't have the exact radius that you should have in the
first place.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net