Celestron NexStar 8i Telescope User Manual


 
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Perfect collimation will yield a star image very symmetrical just inside and outside of focus. In addition, perfect
collimation delivers the optimal optical performance specifications that your telescope is built to achieve.
If seeing (i.e., air steadiness) is turbulent, collimation is difficult to judge. Wait until a better night if it is turbulent or
aim to a steadier part of the sky. A steadier part of the sky is judged by steady versus twinkling stars.