From: "Jack Schmidling" 
To: 
Reply-To: "Jack Schmidling" 


From: "Ross Sackett" 

> The focuser need not be square to anything.  The
> important thing is that it points directly at the
> optical center of the secondary (that is, where the
> optical axis hits the secondary, not its physical
> center).  You can check this using the sight tube you
> use to collimate your scope.  Some focusers have four
> screws on the base for making this adjustment,
> otherwise just shim the attachment bolts with bits of
> sheet metal or scrap plastic.....

Looking through the sight tube, how do I know where the optical center of
the secondary is?

Wouldn't moving the secondary have the same effect as shimming the focuser
for this purpose?

js

>

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