ATM Supplement to Foucault Follies

[Roger Ceragioli <rogerc@dakotacom.net>]

Earlier today I posted a message about some experiences with knife edge
testing a 6" f/4 mirror.  I should also note the following data concerning
an 8" f/4 mirror:

Optical Dia.: 7.96"
RC: 63.75"

Couder Mask Data:
Inner edge of zone 1: 0.00"
Outer edge of zone 1: 0.89"
Outer edge of zone 2: 1.84"
"  "  "  "  " zone 3: 2.56"
"  "  "  "  " zone 4: 3.11"
"  "  "  "  " zone 5: 3.58"
"  "  "  "  " zone 6: 3.98"

Readings:
zone 1: -.173
zone 2: -.162
zone 3: -.143
zone 4: -.120
zone 5: -.095
zone 6: -.072

Again TEX and ADMIR will calculate the mirror as being undercorrected
(about 1/5 wave PV).  This one hasn't been star tested yet, but I had the
opportunity to examine it by autocollimation against a 10" aluminized flat,
which had a hole cored in it.  The flat is known to be of good quality over
the inner 8".  Using a Ronchi tester, I and Dean Ketelsen saw the bands to
be quite straight across the whole diameter of my 8" f/4.  Earlier we
examined my 6" f/4 and saw the same thing.

What all this stuff that I've posted perhaps means is just that the
idiosyncrasies of my particular tester combined with my testing
predilections tend to make my tests underestimate the amount of correction
that I've put into my mirrors.  Small errors matter a whole lot more with
an f/4 mirror than with an f/6 or f/8.

Roger Ceragioli