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


----- Original Message -----
From: "Tom Krajci" 

> I'm still looking for objective analysis of Robo Foucalt's methods and
> theoretical performance.  Until I find that sort of info...the jury is
> out on how good or bad the approach is.  (However, the flood of opinions
> on the ATM list will not abate! ;-)
>

Hi Tom,

As the author of Robo-Foucault, I'd love to see an independent analysis
done!  In the mean time I'll try to stick to 'just the facts' used to
satisfy myself the dang thing worked :)

#1 I have used Robo to test and document 29 mirrors to date (over a 13 month
period)

#2 Sizes range from a 3" F/8 to a 20" F/5, most being 8 - 12" F/4-6

#3 Most of the mirrors are student mirrors from our ATM Class.

#4 Six of the mirrors have been critically tested using:
    A) Classic Couder mask/Foucault testing
    B) Star Testing using a 33% obstruction
    C) Ronchi-Star tested using a 240lpi Ronchi screen
    D) The six mirrors were in the range of 8-11" F/5-8
    D) All three tests strongly indicate Robo works

#5 I've sent digital Foucault images to list members for independent
analysis.  Of course this only tests that the zone radius being nulled is
accurate (which it was), but still leaves accurate longitudinal readings
unverified. (BTW, I have nearly 1gig of  Foucault images recorded to date
:)

#6 Three of the mirrors tested have been commercial mirrors brought to use
by dissatisfied owners.  All three mirrors tested as 'unacceptable' by our
criteria (actually James Burrows' criteria).  Here's a case in point, the
20" F/5
    A) 64 measurements tested over 8 zones across two diameters with a
sample standard deviation (n-1) of < 0.001"
    B) Measured Longitudinal correction from Z1 (r=2.9") to Z8 (r=9.6") was
0.183" +/- 0.001"
    C) Calculated Longitudinal correction for above should have been 0.211"
    D) Sixtests reports this mirror as having a 0.4 Strehl & 41nm RMS
surface error
    E) Figure45 reports this mirror as almost 1/2wave PV, 1/6wave RMS, 0.3
Strehl
    F) Reported observations of the scope during normal use in focus were
"Soft images"
    G) Possible testing error include pinching on the test stand, and
thermal stabilization.  Efforts were made to avoid these errors, but they
could persist.
    F) BTW, we haven't seen the scope in the field since bench testing, so
no chance to do Star or Ronchi-Star testing :(

In summary, I've made my best effort to ensure that Robo can sort the
"good" from the "Not so good" mirrors.  Myself, our
local group of ATM students and instructors, and my Beta Testers all
concur.  Of course, time will be the final arbiter on this matter.  For the
moment, I wait :)

Take Care,
James Lerch
http://lerch.no-ip.com/atm (My Telescope Construction, Testing, and Coating site)

--- BBBS/NT v4.00 MP