Re: ATM Zero-Obstruction Newtonian

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

Any of the hydrostones should work equally well.  POP is just not good for
doing anything with water around.
The truth of the matter is that the professional opticians usually use a
hard pitch to do blocking of parts if they don't use blocking wax (a real
hard wax with a fairly high melting temp) for the purpose.  Also, they don't
put the material all the way up to the surface of the glass but rather just
enough to hold it securely from moving.
As to testing, the surfaces of the glass is what is important and the need
for reflections from other parts is not needed.  You can see the fringes of
an interfrometer test just fine when you look at several surfaces and you
can tell right away if the parts are moving as the fringes won't be all in a
line from one surface to the next.  The results look just like somebody put
a mask on a larger surface and the holes are all round ones scattered about.
When doing several surfaces at one time, you do want to keep the surface
area up to a fair percentage otherwise the pitch will tend to rise and thus
do turned down edges.  The additional surfaces can be any ol' piece of glass
of about the same consistancy in the holes so that the pitch is kept worked.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net