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I bought a Matsukov Cassegrain many years ago and now wanted to dust it off and use it. I had two young kids at the time so couldn't really find the time. Last night Jupiter and Saturn were both visible. But both just looked like dark featureless balls when I finally found them. I am sure I had them in sight because they moved out of the field as would be expected, but they looked almost like their shadows i.e. not bright and certainly no colours. What am I doing wrong? used a 10mm and 25 mm eyepiece. Does this mean my telescope is actually not working?

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    $\begingroup$ "dark" compared to what? the night sky is almost black, so planets should appear bright compared to the sky. You should see rings on saturn at least (but you won't see many features on its surface) and the moons and banding should be visible on Jupiter. Is it possible that your telescope is very far out of focus? Try focussing on a distant object during the day. The focus won't be different for planets or stars at night. $\endgroup$
    – James K
    Sep 10, 2023 at 7:58
  • $\begingroup$ To make sure you're in (or near) focus, start with terrestrial objects first, or the moon. $\endgroup$ Sep 12, 2023 at 19:58

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Have a look at the images in these questions and the answers there as well:

Most likely you are simply way out of focus, so the central obstruction of your secondary mirror makes a shadow.

Examples of images from those questions (click for full size if necessary):

out of focus Cassegrain image from https://astronomy.stackexchange.com/q/25914/7982 out of focus Cassegrain image from https://astronomy.stackexchange.com/q/34900/7982

From https://astronomy.stackexchange.com/a/28941/7982 examples of secondary mirror in front that will cause shadows when out of focus (click images for full size if necessary):

"mirror lens" showing secondary mirror "mirror lens" showing secondary mirror


Try these:

  1. Look at a planet (or even just a distant light out a window without going outside) and recreate the effect. Now have someone (or figure out how to do yourself) move their hand or some object in front of the telescope. I expect you'll see its dark shadow appear next to the central one.
  2. While observing the dark shadow phenomenon, slightly move the telescope - almost certainly the dark shadow will remain stubbornly in the center of the field of view but when the planet or star moves far away, the image just goes dark without moving.

Assuming its way out of focus, the next step is to figure out why.

  1. You do have an eyepiece in place, that's a good sign!
  2. Do you have an extra extension tube that doesn't need to be there, or something that does need to be there, like a right angle image erector that's not there? I would guess you need to get the eyepiece many centimeters further from, or closer to the telescope than wherever it is right now.

If you upload a photo to your question of your system (with eyepiece in place) and any other optical components that come with it, that might be helpful.

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