Re: [ATM] Secondary Offset

["Stephen Koehler" <s.c.koehler@gmail.com>]

Mitchell,

>      Hm Okay. Normally I sort of just eye ball it, there is no way for me to
> truly center it under the focuser so I just adjust it till it looks centered
> under the focuser, hopefully that is offsetting it enough.

A typical site tube consists of a 4 to 5 inch tube inserted in the
focuser with a cap containing a centered peep hole of about 1/8 inch
diameter.  The peep hole keeps your eye centered in the focuser when
you look through it.  You compare the inside edge of the far end of
the site tube with the circular outline of the secondary.  Once they
are concentric, the secondary is centered.  This is "eye balling" the
centering of the secondary, but it's plenty accurate.  It's much
harder to judge the placement of the secondary without a site tube to
keep your eye on the center line.

As far as offsetting goes, if you have centered the secondary as
described, you have also offsetted it toward the primary.  If,
instead, you were to perfectly align the center of the secondary with
the optical axis of the focuser, the secondary would not look centered
in the site tube.

I apologize if I'm repeating things you already know.  It sounded like
you had not used a site tube.

-- 
Steve Koehler
_______________________________________________
ATM mailing list http://www.atmlist.net/