From: "James Lerch" 
To: "ATM List" 
Reply-To: "James Lerch" 


----- Original Message -----
From: "Vladimir Galogaza" 
>
> >I've always had the intuitive suspicion that zone radii errors were
> >Robo-Foucault's Achilles' heel.
> > J. Burrows.
>
> Achilles' heel was fatal fault (for Achilles). Accuracy of the zone
> determination is not fatal (for Robotest , in its JL incarnation).
> It is influencing its accuracy. To what extent, we shall see soon.

Yes, the extent of Robo's accuracy shall soon be publicly known, perhaps as soon
as this time next week.

As a quick reminder, Robo was written to specifically address the problems
associated with testing optics during a weekend 4 hour ATM Class/Workshop.
Robo
had two specific requirements:

#1 Maintain accuracy equal to or better than classic Couder mask, knife edge
testing.

#2 Substantially reduce test time.

Requirement #2 has been meet without question, the other requirement is now in a
'interesting' state, as Couder and Robo strongly disagree (for this size and
F/Ratio optic)

> It seems that I  forgot what has caused RoboFoucault investigation.
> As far as I remember it was observation ( by Robo author) that results are
> sensitive ( depending) on the source ( or image ) intensity.
> But later this aspect was not mentioned any more nor resolved. Instead
> efforts are concentrated on the comparison of the Robo results with
>  " absolute truth" that is to find out absolute accuracy ( and
> repeatability) of
> RoboFoucault test.
> Initial  intensity related problem is forgotten or under a carpet. Why is
> that so?

The solution was public discussed, starting with the post from Mike Peck
(last paragraph):

http://astro.umsystem.edu/atm/ARCHIVES/MAY03/msg00164.html

Specifically, Mike's suggestion of implementing a Slit based source,
eliminated the change in KE readings as a result of changing either the
image source intensity, or the Shade of Gray used for evaluating nulls.  I
do not know why this should be so.

BTW, slit vs. slitless appeared to agree with each other WHEN a bright
image source and low shade of gray were used during the slitless Robo test.

James Lerch

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