Re: ATM astigamatism

["Frédéric Géa" <geaf@unionfinancieredefrance.fr>]

Furniture pads are good but don't use too thick pads that could go slowly
down under the weight of the mirror:
Yes, teflon can be glued but after a special process. If I'm not wrong it is
"etched" Teflon, available for thin thickness (about 2 mm thick) at "Weber",
a shop in Paris where it's possible to find a lot of diffrent stuff. I have
bought some to put on a cell and it seems to be good. The face that receive
the glue is brown and the other is the same as standard teflon. Also, their
is easy to cut teflon like plastic, often blue, which is used to move eavy
furniture. It's far less expensive than real etched teflon (at least in
France) and seems to be good enough for the back of a primary. Adjust the
tension of the sling in order to have the primary center in the cell. Many
times,  problems come from the sling's support/attachement to the cell. They
must be SOLID ROCK because a mirror is not really light. If not, the mirror
will not keept is position while observing low in the sky. Safety belt car
are very strong. I have used one before piano wire lateral support for an
eavy 22" and the sling didnt stretch too much. The sling can sometime move
and some people put some velcro on the edge of the blank and on the sling to
keep it on position. It's really hard to drill the sling and dangerous
because it turns on itself. It's much better to use a metal point heated
with fire. try to have some possible adjustement because it's really hard to
know what will be the real position with the mass of the optic. Collimation
is not tricky. In case you move the scope, try to find a system to keep in
position because it will no longer be glued to the cell and will be able to
move in the mirror box. Also, clip will be intresting to keep it in the box
in case their is none currently.

hope this help.



Frédéric Géa
http://www.astrosurf.com/altaz

>I think I will cut all 18 blobs with which the primary is mounted this
>weekend and make a sling. My (Krige/Berry type) tailgate is prepared for a
>sling, so this must be no problem. I'll make the sling from a safety belt
of
>an old car. Kriege and Berry advise to use furniture pads as support point
>for the primary. I also read soewhere that teflon can be used, but this
>cannot be glued. Which kind of stuff can be recommended?
>
>Another question: when using a sling, how can be decided whether it is the
>primary or secondary mirror that must be collimated or if the sling must be
>adjusted?
>
>Jan
>http://www.geocities.com/janvangastel/
>
>