Re: ATM astatic supports

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

Hi,

A classical cell for dobsonian scopes is not very hard to build but is not
always very efficient because of the hysteresis (If only I could spell this
word correctly ;-)) When the OTA is move up and down, the mirror is "unload"
"reload" from the pads of the triangle. This triangle or most of the time
made with metal screw and bolts to enable the "flotaisson movement". Their
is a lot of small room for friction and a most of the time, the mirror will
never be supported the same way. This variations are very small but for a
large thin blank like we can find now in large dobson scope, this begin to
be a big problem to have a good image. By good image, I mean that it's not
because a mirror is large that (if is quality is good, seeing allow it and
good collimation of course) it can't give good images. If the mirror is
great one images the support can easily destroy this good figure. An astatic
mirror cell give it a constant support that don't change and that always
give the same push thanks to the conterweight that carry the good weight to
support the glass. It's of course not very intresting for small or very
thick mirror, but for something around 20 to 24 inc and beyond in 1.5 to 1.6
inc thick, it begin to be interesting. The bigger and thinner the glass, the
more intesting it is. Professionnal has used this cell for a long time and
that's not for no reason. They of course have jumped to new technic, but for
us, that's really intresting. Thanks to the work of some professionnals,
it's is easier to make now because a levers carry 3 points (hybrid system),
before that evolution, a levers carry 1 point, needless to say it was tricky
to use and tune. I have created nothing, I simply try to spread the word.


Frédéric Géa
http://www.astrosurf.com/altaz
-----Message d'origine-----
De : Michael Koch <astro.electronic@t-online.de>
À : geaf@unionfinancieredefrance.fr <geaf@unionfinancieredefrance.fr>
Cc : atm@shore.net <atm@shore.net>
Date : lundi 26 mars 2001 12:50
Objet : ATM astatic supports



Hi Frédéric,

> May be you have seen a pic of an unbelivible thin blank
> http://www.astrosurf.com/altaz/astatic.htm

What is the advantage of an astatic support, compared with a normal 18-point
support (with 6 triangles, 3 bars and 3 adjustment screws, but without
counterweights)?

Michael

*******************************************
ASTRO ELECTRONIC  Dipl.-Ing. Michael Koch
      http://www.astro-electronic.de
*******************************************