Big black circle in view field

[Burke Family]

Hi! We upgraded to a SCT - Meade LX200 - and we cannot solve what We think should be an easy fix. When we get a target object in view, there is a black circle in the center of the image - the white around the circle is equidistant, so it is not off center. We understand this to be the shadow of the secondary mirror and an indication that we are not adequately in focus. But we don’t seem to be able to bring the object into focus at all. This include using course manual focus and the fine motorized micro focuser. Have also tried different magnification eyepieces on the off chance it would help. A sample image is attached. Ignore the horizontal line - that’s a scratch in my phone lens. Would appreciate any advice. Thanks!

[Pikaia]

Your scope is a long way out of focus but this is normal for a new scope (my SCT was similar when I got it). Point it at a bright star or planet with low magnification and turn the focus so that the donut shape gets smaller. This will take many turns, but you will see it change size after a few turns.

[Piet Le Roux]

Try using it without the secondary focuser and only a eyepiece and see if you can achieve focus then. Is this a new or used LX200? what size LX200 is it?

[John Baars]

A SCT has a huge focus range. Do you see a change in the size of the donut as you turn? An SCT needs a lot of turning. Try 20 gently turns clockwise or more until it stops, or then 40 X counterclockwise or more with the motor completely disconnected.

You may be able to keep on turning endlessly without the mirror reacting. In that case, the worm and the rack somehow have become separated from each other. Then try the entire above procedure again with the telescope pointing straight up. You then let gravity do the work in the hope that the worm and rack engage. If that doesn't work, repeat with the telescope pointing towards the ground. Even if they engage, the telescope will need servicing and maintenance.

When it is a new one.You enter the warranty danger zone with the following: if it doesn't work either, you can still try to disassemble and reassemble the shaft on which the focus button is attached. Push it gently back in, in most cases you feel it engage. Or disassemble the entire rear to see what is wrong. In most cases, the mirror must also be removed after disassembly because otherwise you cannot reach the focussing mechanism.

[Burke Family]

Thanks everyone. This is a 12” scope. Curiously, we did not see the disc while looking at the moon later in the evening, but the disc is back again as we look at Mars tonight. Seeing conditions are not optimal (clear skies but less than ideal atmospheric conditions). And it’s cold - below zero. I thought I’d eliminated the disc with a careful focus on low magnification, but when moving to a higher power eye piece the disc came back. I will try the procedures mentioned above and see if they help. Thanks! This was a used LX200 we picked up from a private owner - scope checked out fine when we were looking at the purchase. I feel this must be a beginner’s learning curve thing, and and that I am missing something simple. I’m also wondering about the microfocuser and whether it’s working the way it should. I would like to bring this indoors where it’s warm and I can comfortably get familiar with it, but have heard that might be a bad idea b/c of condensation. ? Planning to re-read the manual as well.

[Pikaia]

When you change to a different eyepiece you will have to refocus as eyepieces all have a different focal plane. Did you actually get it in sharp focus with anything?

[gregl]

This sounds like a focal plane issue. How about putting up a close-up photo of the back end of the scope with the eyepiece and assorted fixings attached so we can see how you have it set up?

[John Baars]

So, if I understand well, you can focus on a star or planet and see this circle as an addendum in the field of view?
If so, I might suggest it looks like a reflection near the focal plane, like gregl already suggests. The Moon is too bright to see it.
It is a matter of systematically removing and adding parts near the focal plane to determine which combination of eyepieces and other parts causes the least complaints.
I have also seen pictures of reflections coming from the corrector, which were from neighboring lights under certain grazing light conditions.
All in all quite difficult to find the cause. If you look into the telescope from the front in daylight, is everything pitch black? If not, that's what you can tackle first.

[gregl]

...
I have also seen pictures of reflections coming from the corrector, which were from neighboring lights under certain grazing light conditions.
...

Good point. Be sure you are using a dew shield (photographers call it a lens hood) over the outboard end of your scope.