Re: ATM Compliant Focuser

["Peter D. Brooks" <pdbrooks@pacbell.net>]

andrew barrett wrote:
> instead he suggests using a sliding unit.
> 
> "motion is parallel to the optical axis, ie. along the tube. the secondary
> mirror
> is carried along with the focuser so that the focal surface moves relative
> to
> the 'fixed' eyepiece mounting. it is very low profile and can be very
> strong
> making it ideal for astrophotography. I am by no means the first to suggest
> this design"

I mentioned this design to Crazy Ed Erber a year and change ago, and
he immediately pointed out the weakness of the design; your secondary
has to move with the focusser, and you lose a bunch of rigidity
when you depart from the 4-point or optical window mount secondary.
My idea was to have the secondary partially supported on a couple
of vanes of the spider, with sliding contact along a rod to cover
the moving EP.  However, the big concern is a slip/stick motion of the
mirror.

For me, when I get to it, I'll go with a classical Crayford design.

Pete Brooks


--
Peter D. Brooks   
pdbrooks@pacbell.net
$INCLUDE "Witty saying"