Right at the beginning: This is not a duplicate of questions involving blurry images through their eyepieces. I only get blurry images for 2 of my 3 eyepieces so it's not the telescope's fault and in the past, these eyepieces got me some pretty sharp images.

I possess a Celestron NexStar Evolution 8 SC-telescope and got the 2 included eyepieces (40mm and 13mm) and an Omegon Oberon 7mm 1.25" eyepiece. All the magnifications should be below the maximum useful magnification of the telescope. However, I noticed kinda blurry images for the 7mm and 13mm eyepieces; it seems as if I can't really get the images focused through them. The 40mm one works perfectly fine.

I know that when I got them (around a year ago), they weren't as blurry; I even found an image of a nearby spire I took last year with the 7mm eyepiece and I could clearly read the text written there. Today I tried looking at it again and I couldn't even make out any text; I can hardly focus enough to get somewhat sharp edges.

Temperature can only have a minor effect since I took the images last year at about the same time (and therefore similar ambient temperature).

I have no idea what could cause this, I really hope someone can help me because those blurry images are SO annoying!

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    $\begingroup$ It is either the telescope (collimation problem?) and it is not bad enough at low power (with the 40 mm eyepiece) to notice the problem, or the problem is with the 13 mm and 7 mm eyepieces. Have you looked through the eye pieces at a lamp? Are they dirty, moisture, foggy, or other problem? If the eye pieces alone are good, then the problem must be the scope. $\endgroup$
    – JohnHoltz
    Commented May 23, 2022 at 1:35
  • 2
    $\begingroup$ Another possible problem would be FOD (dirt) in the eyepiece socket. The 40 mm eyepiece offset would not be noticeable, but the change in the position of the more powerful eyepieces might limit the focus quality. $\endgroup$ Commented May 23, 2022 at 12:31
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    $\begingroup$ @JohnHoltz Can I somehow check collimation without buying a dedicated laser measurement device? I already tried looking into the telescope without eyepiece attached and I see my eye staring back at me. So it can't be completely off. Or do you have any advice on what collimation device to buy? $\endgroup$
    – 299792458
    Commented May 23, 2022 at 13:48
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    $\begingroup$ @CarlWitthoft That might be it. I'll try cleaning it carefully and next time I got the opportunity to test it (i.e. a clear night) I'll let you know if it helped $\endgroup$
    – 299792458
    Commented May 23, 2022 at 13:49
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    $\begingroup$ @JohnHoltz What would be the procedure to clean the eyepiece if it's foggy / there's moisture or dirt in/on it? $\endgroup$
    – 299792458
    Commented May 23, 2022 at 13:50


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