RE: ATM "matching ronchi" help!

["Mel Bartels" <mbartels@efn.org>]

Rodney, your matching ronchigrams at

http://www.geocities.com/rd1113/6in53.html?1003021799705

look quite nice.

They are smooth without obvious zonal irregularities.  Yes, there is s
small turned edge of 1/8 inch extent, but if mine, I would mask it and
ignore it.  It's not worth destroying the smoothness of the rest of the
surface.  In general, you may have a tad more parabolization in the 80+%
zones and not quite enough in the middle zones.  However, based on my
experience with 6 inch mirrors, this amount is a very small fraction of
a wavelength.  So, at this point, if my mirror, I would star test or run
it through a mirror test program that provides numbers.  What you want
to know is how close the mirror is to 100% parabolization.  The mirror
may be slightly overcorrected based on the ronchigrams.  A star test
will show this instantly (though let the mirror cool for 45 minutes as
these smaller mirrors can show significant overcorrection while
cooling).

Mel Bartels