Re: [ATM] Re: Foucault test limitations

["James Lerch" <jlerch1@tampabay.rr.com>]

----- Original Message ----- 
From: "Vladimir Galogaza" <vladimir.galogaza@zg.tel.hr>

> James,
>
> What was amount of primary astigmatism of the Charlie's
> mirror you finaly settled on (before hundred polishing sessions).
> Was it z(4)=0.128; Z(5)=-0.141

Yes, these were the values I feel are pretty close to reality.  If you do all
the math, it worked out to being just shy of 1/2 wave wavefront @ 550nm of
primary astigmatism.

I should also note, that using the star test to reveal the astigmatism was
rather difficult at this level.  If you knew it was there, you could see
something odd happening right as you went thru best focus at the eyepiece.

BTW, I should also add the extreme admiration I have for any optician that can
control ALL the following variables, and end up with a 0.9 or greater Strehl!

    A) No obvious scratches
    B) Excellent Surface polish (as seen by reflected laser / focused Sun
light), its possible to make a great polish worse during figuring!
    C) Surface microripple (seen under knife edge testing)
    D) Optical edge condition (not turned up or down)
    E) Control astigmatism
    F) And still put the right amount of evenly applied correction in it!

> >Robo agrees with the interferometer so long as there is LIMITED astigmatism
>
> Where will you place this limit approximately?

Not certain, I still need to gather more data.  I'm confident that the bounds of
the limits are between 0 and .4 Waves of PA on the wavefront @ 550nm.

> Do you have idea or feeling  at what level of primary astigmatism
> Couder mask Foucault fails?

Nope, but I'm hoping the Mirror Round Robin results may answer some of these
questions.  My results were rather interesting, and I'm eagerly waiting to see
the accumulated Couder Mask results from other test operators.

Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction,testing, and coating site)

"Anything that can happen, will happen" -Stephen Pollock from:
"Particle Physics for Non-Physicists: A Tour of the Microcosmos"

" Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent. "
                                                           Calvin Coolidge


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