Re: [ATM] Cass mirror separation

[Ric Rokosz <radicell2@yahoo.com>]

> 
> John Sherman wrote:
> > I know that the distance separating the mirrors in
> a Cass-type
> > scope is fairly critical for high-res views,
> unlike in a Newt. So
> > what if you have a pair of mirrors and are unsure
> of the designed
> > separation?

Perhaps you could give us the mirror size and
f/ratio,plus the secondary size and the year this
sytem was made.If it looks like a typical Cass system
say f/4 primary it may be a "stock" layout and using
some Cass software - as in Texerau's book,you could
zero in on a good guess.Also for the secondary,you
might consider making some cardboard templates for
given R values and match up the curve on the
secondary.

A typical backfocus used for a Cass is about 9- 10
inches and using that with the Cass software will zero
in even more.Granted field size is unknown but
secondary size will tell you something.
There use to be an online Windows' Cass calcuator
(based on the one in Texereau) but I cann't find it
anymore.

If your secondary holder assembly has a large travel
distance (as pro's motorize their secondary holders
and focus with it - not at the eyepiece end as atm's
do)you could move the secondary back and forth and
check where the focus at the focuser end is and pick
the middle point of the distance travelled as the best
spot for the secondary and then measure the
seperation.As for field size you could use the full
moon to gauge how much of it appears on a blank card
placed at focus.Lots of work but doable.

Ric


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