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After an initial collimation, I took my scope (150mm/750mm) out for a star test. While I could see concentric circles when the bright star is at the centre of the video, when the star is on the side of the view, I get an image typical of an uncollimated scope. Please refer the images below. The left image is how it appears when the bright star is at the centre. The right image is how it appears when the star is on the upper portion of the view.

The left image is how it appears when the bright star is at the centre. The right image is how it appears when the star is on the upper portion of the view.

Does my scope require further collimation, or is it fine the way it is now?

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  • $\begingroup$ You're fine. Always collimate in the center. This way you'll eliminate coma, eyepiece aberrations, etc. $\endgroup$ – Florin Andrei Mar 13 '18 at 19:54
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Your scope is f/5. There will always be some coma aberration. Always, the image quality is worse as you get closer to the edge of the field of view (FOV). Personally, given that the fact that you will want to observe your targets at the center of the FOV, this collimation would be acceptable.

Happy photon hunting!

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  • $\begingroup$ In the spirit of a good Stack Exchange answer and for my own curiosity, could you expand a little bit what it is about the information in the question that allows for the conclusion that "this collimation would be acceptable"? I'm not doubting it, but adding a little more explanation, if possible, makes for a better answer. Thanks! $\endgroup$ – uhoh Mar 11 '18 at 9:48
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    $\begingroup$ Hello! He says that the collimation on his scope looks more like the picture on the left, where the circles are concentric. That's an indication that the collimation is not that bad. I would be more sure if I could see another plot describing how the clips, that hold the primary mirror, look like. $\endgroup$ – astromath Mar 12 '18 at 7:12
  • $\begingroup$ I can't see the clips that hold the primary mirror no matter how much I adjust the focuser in or out. Although the primary mirror covers the complete portion of secondary mirror, the reflection of the clips are just outside the visible portion in the secondary mirror. $\endgroup$ – Bijoy Thangaraj Mar 14 '18 at 18:33

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