Re: [ATM] Is my mount right?

[Dale Eason <atmpob@yahoo.com>]

No that will not do as a mirror mount.  For that thin
of mirror you will need much better support.  Plop
will help you design a usable cell.

Others on the list have also tried cells similar to
yours with very poor results.

You do not need the spider and secondary mirror to do
a Foucault test.

  As far as testing using Foucault you will also have
trouble because of improper support.  When testing
vertically the mirror is only supported by its edge
and it tends to fold over on itself.  I find a huge
difference in surface measurements when I tilt it back
onto its cell 20 deg and test then.  I am using an 18
point PLOP designed cell for my 16 X 1 F5.  My edge is
supported on two bolts spaced at 90 degrees apart on
the bottom edge.  

I am in the process of documenting this with pictures
and data using a Foucault tester and Interferometer. 
I will post to the list in soon.  Tilting the mirror
makes the Foucault test very difficult to perform if
you don't have the vertical space.  

Others on the list have posted about this problem as
well so you should search the archives.


Dale Eason



--- David  Williams <dwilliams1128@earthlink.net>
wrote:

> Hello
> 
> I am making a 20" telescope and I posted pictures of
> the progress on it at this site 
> 
>
http://www.atmlist.net/contrib/dwilliams1128-at-earthlink-dot-net/
>  
> 
> and then you click on 20"Telescope Stuff and there
> are the pictures.
> 
> On some of the pictures you can see the plywood
> structure that I used as a mount for the primary
> mirror.  I  have used a layer of 3/4" thick weather
> stripping in a circle shape and then as a cross
> shape in the middle.  I was wondering if this is
> orthodox procedure in the atm list.  Probably though
> I should use a floating point mirror cell or Plop,
> but I don't know much or anything about either one
> of these things.  
> 
> Either way I'm about ready to test out the mirror
> optically.  I have the foucaolt tester and have done
> that already.  And a friend of mine Jerry Martinsen
> from Stergis, MI who has made a few mirrors,  said
> that the mirror is probably polished out now.  I
> told him that I can see my reflection in the mirror
> directly over head and he said that isn't the way to
> tell.  He said that the way to tell if it is
> polished is to do the foucaolt test.  So I have the
> two mirrors the primary and the secondary and the
> primary holder, I just need the spider and holder
> for the secondary.  The man who's making that is
> Gary Wolanski.  He lives in Vancouver BC.  
> 
> Well thank you for your help.
> David Williams
> dwilliams1128@earthlink.net
> Bye
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 


__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com 
_______________________________________________
ATM mailing list http://www.atmlist.net/