Re: ATM Star test collimation dilemma

[Mike Reed <mreed@eai.com>]

Bob King wrote:
> 
> Hello all,
> 
> Everyone has been so helpful in the past so I put this question to you. I have
> 10" f/4 system which I first collimated with a simple sight tube. Then I tried a
> star test at a relatively high power. However I found that when the shadow of the
> secondary was centered in the bright disk of the primary on one side of focus it
> was off center on the other side of focus. If I tried to center everything up on
> that side of focus then the other side was off. It has been impossible for me to
> rack in and out and see the secondary centered on both sides of focus. Does
> anyone know what gives here?
> I thought at first it might be the focuser tube jiggling but that seems to be OK.
> Even when I try to jiggle it it doesn't seem to affect the secondary position in a
> star test.

I'm kind of new at this myself, but it sounds to me like the optical
axis of the focuser isn't parallel and coincident with the reflected
optical axis of the primary. Make sure your focuser is square to the
tube and that the diagonal is exactly centered under the focuser.

-Mike