Focusing a Celestron Nexstar 6SE

[Pollyanna24]

I know this is an old thread but here goes...  I seem to be having the same problem with my 6".  I've viewed Saturn and Jupiter before with beautiful images but now it's as if the planet is huge with a big black circle in the center.  I f I remove the eyepiece and look into the diagonal I see the same thing but I can look from the side and see what I think is the acutal planet behind the black circle.  The black circle is in the middle so I don't think I have a collumation issue.  I can start to make the ring of light around the black circle smaller by focussing closer but I get to the stopping point.  Backing the focus know all the way to infinity (I'm too scared to go all the way back for fear the knob will come all the way off) does not help.  I'm inclined to believe the device may have been jostled and the focal point has somehow shifted but I'm hoping you guys have seen this before.  Any advice would be greatly appreciated.  Jupiter is as close as it's gonna be for awhile and I sure would like to see it!

[Ben the Ignorant]

The knob won't fall off, turn it till the image is sharp. The large disk of light is the massively unfocused planet, and the black circle is the shadow of the round secondary mirror's housing. We all see that in our scopes when they're largely defocused, don't be surprised if it takes an enormous number of turns, my C5's knob makes 37 turns from infinity focus to closest focus (at 2.5 meters).

That's necessary to make the focus accurate, and to allow the Schmidt-Cassegrain telescopes to be used as long-range microscopes and macrophoto objectives. I've taken pictures of bumblebees from 3 meters and birds from a few tens of meters when using my Celestron as a telephoto/macrophoto lens.

[Jim Rand]

Make sure nothing has condensation on it.  Spent a good hour after a couple beers struggling with that!