Re: ATM Help with University Optics mirror cell

[Adam Perkins <scopeguru@yahoo.com>]

Johnny,

You're correct.  Picture a bolt with a hypothetical
"slop" of 1 degree.  As the bolt gets longer, the
actual distance travelled by its tip is increased. 
For the exact same angular displacement (amount of
"slop"), the bolt-tip moves much further for a long
bolt than a short one (think of the bolt as a lever,
and the bolt-hole as the fulcrum).

However, unless this slop or springiness is severe, I
don't suppose its capable of moving the primary's
optical axis too far in any direction.  

What would really be cause for concern would be slop
that allows the bolt to move in-and-out of its hole
(letting one mirror support move up and down, rather
than side-to-side).  Deflection of the mirror cell in
this manner will tilt the cone of light heading from
your primary to secondary mirror much more severely. 
Once again, due to the large distance between your
primary and focal plane, a small angular displacement
of the primary provides a large axial displacement at
the focal plane.

My 2 cents?  Try things "as is" and see if you have
any collimation problems before you cut up your tube. 
I have screwed up many projects with the goal of
"improving" them (computers are a particular problem
area for me here).  

Good luck,

Adam Perkins
Covington, Louisiana



--- Johnny <takmais@swbell.net> wrote:

> 
> I've got a university optics mirror cell for an 8in
> mirror.  ......(I) was
> unable to reach focus so
> instead of redrilling closer holes i simply extended
> the bolts in the cell
> as far as i could.  
> I feel that this
> arangement is more unstable for the mirror and that
> this would make it loose
> collimation more easily.
> Sorta like a
> short building would
> sway less than a tall building i guess.  



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