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Fuzzy bright stars with my Celestron CPC 1100 XLT

When looking at the brighter stars I cannot focus them to a sharp image. They appear fuzzy. Image of a star test on Vega attached (taken with a Watec 120N webcam). Diffraction rings are sparse and mottled. Does not really indicate that scope needs collimation. Can you help please.?


Mike Brightmore

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  • Anonymous Dec 20, 2008


    All objects seem out of focus no matter how I adjust the focus knob.

    The images of stars look similar to your picturs. The moon's craters can be seen, but they do not have the sharp definition I was used to with other telescopes I have used. I was told that this could be an issue of the telescope needing to be collimated (sp?) correctly. I noticed that the stars are slightly tear drop shaped which leads me to believe that the optics are misaligned. How is this done? I had a reflector and the process was easy. How is it done on a Celestron Schmidt-Cassegrain?



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The image shows that the optics are not centered properly. The secondary may be tilted slightly to the 2 o'clock position. When not centered, a focused star will have an astigmatic shape, and not come to a full focus. Also check the mirror and corrector plate for dewing, that will also affect the views.

Posted on Nov 08, 2008

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I have had the same problem, but when I got used to the collimation process and which way to turn the adjuster screws life has been much easier for photographing, usung a 7.5mm eye piece for adjusting the perfice circle.

Posted on Aug 20, 2010


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When using telescope for the first time (looking at venus) it would not focus, also the cross at the front of the tube was most prominent.

Do stars appear as small pinpoints in your scope? If not then it sounds like you have not adjusted the focus properly. I recommend you take your telescope outside in the daytime and point it toward a building or tree or hilltop that is somewhat distant from you. The exact distance is not important, but it should a block or more.

With the telescope pointed at the distant object, focus the telescope until the object is sharp and clear. The object might appear upside down -- that's normal for many astronomical telescopes. When you have achieved a sharp focus, leave the focus control alone until you are outside at night under the stars.

The focus should now be fairly close for viewing stars and planets. Small adjustments of the focus control may still be necessary for the sharpest view.

Venus is sometimes a difficult object. It is often fairly low in the sky where the atmosphere is most likely to blur the view. Find a bright star and focus it to a pinpoint, then swing your scope toward Venus.

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If the rings are not concentric, shown in the bottom row, the scope needs collimation. These scopes were not meant to be collimated by the user, being glued together, so you will probably have to send it to Meade.
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