Re: ATM astigamatism

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

Well, strange, some problem on the atm list may be. I have posted this mail
few days ago and it is published today !

Fun


Frédéric Géa
http://www.astrosurf.com/altaz
-----Message d'origine-----
De : Frédéric Géa <geaf@unionfinancieredefrance.fr>
À : Jan van Gastel <jhm.vangastel@wanadoo.nl>; 'ATM' <atm@shore.net>
Date : vendredi 9 mars 2001 13:02
Objet : Re: ATM astigamatism


>
>
>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/
>>
>>
>
>