> Hi,
>
> I have just recently bought an 8" f/6 Discovery dobson. So far I have spent
> 4 nights observing and it was very nice. However, I have 2 problems.
>
> 1. My focuser (2") moves not only in and out of the tube (to focus the
> image), but it also moves up and down (about 1mm). Depending on where the
> focuser is, collimation can be anywhere from okay to way off. I was thinking
> about buying a new focuser but I don't want to spend more that $100 on it.
> Are the Orion focusers any good?
(I have read that the standard DHQ focusers leave a bit to be desired mechanically.)
For $99 + shipping one could get a 2" JMI RCF... http://www.jimsmobile.com/images/rcf_1_b.jpg
> 2. When I collimate the optics it seems that the reflection of the spider in
> the main mirror is not in the center of the main mirror (this could be an
> optical illusion - I'm not sure). I didn't want to mess around with it, so I
> left it alone.
>
I would suggest one pass with a laser to make sure everything is squared up.
Its possible the focuser is not square. Maybe it came loose in shipping.
Fwiw, when I first got my 8" dob I observed with it for a couple months then
discovered the secondary alignment was way off. I'm assuming you dont have
a laser, so the next time you are out somewhere like coe just find someone with
a good laser, preferably the holographic kind.
jeff
