From: Dale Eason 
To: atm{at}shore.net
Reply-To: Dale Eason 



Tom was asking for robo test experience and data points. Here is mine.

I have figured only one mirror (twice) an 8" f7.5.  I used the
standard manual Foucault test both times. The second time when the mirror
needed recoating I tested it again manually and decided to figure it
better.  I got it to what I thought was 1/10 wave as computed by Tex.  I
also star tested it before coating using Suiter's methods.  My star was the
glint off of a dark power pole insolator.  I tried many times but there was
always too much turbulance so I gave up and sent the mirror out to be
coated.

After placing it in the scope I was finally able to star test it on a real
star.  At 1/10 wave I was not expecting to see much difference from inside
focus to outside focus in the images of the rings but I did. After testing
on several occasions and making sure the mirror was cooled and stable I
still could see difference between inside and outsid of focus.  I was not
concerned at the time in trying to quantify the results.  I just wanted to
know if the mirror matched my Foucault readings and expected star test
images. It did not.

I decided to build a tester like James' Robo.  I wrote the software myself
with help from James.  I tested the mirror with it.  I used 10 zones as
compared with my 5 manual zones.  The reduction of the data after many runs
(more than 50) showed the mirror to be about 1/6.5 wave using Figure45xp. 
Also using Figure45xp I had it generate star test images for my scope and
tested mirror.  Those images match   what I saw for
the real star test.

My conclusion is that Robo like testers give results that match the star
test at least for my 8" F7.5 mirror.

Why was my manual test off?  I think it was because the mirror has zonal
error that the 5 zone mask did not catch.  At least that is what the
Figure45xp results show.

Dale Eason

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