Re: ATM caustic curve

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

I've heard of a lot of different tests that have been developed.
I understand the Caustic Test as given by Schroeder and consider it to be a
rather complex test.
I understand the Foucault test (that is what I use for testing with a
modified Couder mask set) and it is easy to do.
I understand a Wire Test where you get a ring at the zone of the ROC of that
distance.
Things like the Ronchi test are of a different variety.
The Poor Man's Caustic I don't understand.  I haven't seen a decent
description of how it works.  My understanding of this test is that you look
on one side for the start of darkening of the zone of interest and take the
measurement.  On the other side of the mirror, you find the final darkening
of the same zone and that should be the same distance from the mirror.  If
this is the test, I'd rather not trust it as this is not a good thing to do
without a pinhole of Airy size or a slit of that width.  Anything wider will
spread the bright side away from where it should be.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net