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Needed help with collimation.

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Recently I've been getting terrible-looking stars despite what looks like perfect collimation. All my stars look elongated. I will post pictures to help answer this question. I use a Cheshire eyepiece. My telescope is a SkyWatcher 250PDS.



Abberation Inspector.png

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This is the best I could do with your image, it's important to include the whole of the edge of the focus tube and I've had to make a judgement call which I am not confident about, so please bear this in mind.

With the above caveat, I see offset, tilt and rotation errors but before doing anything I'd take another shot this time including the whole of the focus tube.




More details at https://astro.catshill.com/collimation-guide/

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Personally, having struggled with trying to collimate my 200p using just a cheshire or DIY pin hole method I purchased a second hand Hotech laser collimator and that made things a hole lot easier.  Since then there have been other brands of laser collimator even own branded for less then £50 (link to suggestions)

Where some fail in the process is getting the collimation sorted is setting up the focuser  and optical axis all square to each other, and a laser helps with that no end.

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