From: "Tom Krajci" 
To: 
Reply-To: "Tom Krajci" 


From: hermit 

>When possible, you should drop that part and do final figuring using
the >star test any how.

I fail to see the utility in taking your nearly-finished mirror out of the
controlled testing environment of your basement/workshop/garage (where you
are in control of all the variables in a small, manageable space)...and
take it outside, where many variables are outside your control (weather,
adding a secondary mirror...have you checked its surface
figure?...atmospheric problems with real stars or across fields with
artificial stars...collimation errors, etc., etc.)

You call this an improvement?

I call it the abandonment of a controlled testing environment for a far
more dubious testing environment.

I recommend using the star test as a means to verify/certify/calibrate your
indoor test results.  But you can only do that when you carefully control
the variables in the great, wild outdoors.  (So if you're gonna sweat
bullets to control parameters in the outdoors...move indoors where it's
easier to control everything.  Work smarter, not harder.)

I'll ask an obvious question here:  how many major optics manufacturers
(small and large volume) use star testing regularly as part of their
figuring process?  Zambuto?  Pegasus?  And the list goes on and on. (Some
do, but that's a minority.)

Why do people have problems with indoor testing?  Simple.  They have not
taken a methodical approach to their testing theory and technique.

Why is Robo-Foucalt going through such long growing pains?  A lack of
methodical approach to testing theory and technique.  (Lots of enthusiasm,
but....)  Check out the article Suiter wrote a few years ago on foucalt
testing with electronic cameras, software, etc.  Thank him profusely for
laying down a solid theoretical basis...you only have to perfect your
technique because Suiter did the first half of the job for you.

How did I make 20 mirrors with reasonably good figures...without resorting
to star testing at any phase of their work?  Simple.  I was methodical
about testing theory and technique.

Mirror testing is like computer programming - garbage in...garbage out.


If you insist on mirror testing without a solid basis in theory and
technique...you test mirrors at your own peril.

You have been warned.

Tom Krajci
Tashkent, Uzbekistan


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