ATM Re: PLanets viewed through a 10" dob??

["Bob May" <bobmay@nethere.com>]

The Ronchi test is basically the same as that done on the bench at the focal
length when you use a flat mirror to bounce the light back to the mirror.
It differs in that the image produced is a one pass image.  Thus straight
lines are produced when the mirror is a perfect parabola.
If you see curving lines, then the parabola isn't perfect and you are
measuring it's error directly rather than looking at the curved lines from
the ROC and figuring out how far they are from what they should be.  As a
result of the test and looking at what the results are, you can figure out
whether you are not there yet with a parabolic mirror.  Zones also stand out
nicely with the Ronchi test on a star in addition.
The SCTs (both Meade) show lines that are diverging and you make your
adjustments to make the lines parallel - inside of focus goes one way and
outside of focus goes the other way with the secondary adjustment (no other
adjustments available on those scopes).
Bob May
My new web space address is http://webu.wigloo.com/bobmay/ or
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and my new email address is bobmay@nethere.com
Bob May