Is this out of square focuser/camera??

[Rustysplit]

Hi,

Had a first go at getting some subs with the quattro last night. SW coma corrector fitted and dslr.

this is one sub, they are all the same though.

Stars all seem to "flare" downwards but away from centre at the top, then swing round to towards centre at the bottom.

Could this be caused by out of square focuser??

[IanL]

Take one exposure, then rotate the camera in the focusser by 90 degrees and take another exposure.

If the elongated stars are pointing towards the ground in both directions, then the cause is likely to be flex somewhere in the imaging train causing things to droop due to gravity. E.g. the focusser drawtube sagging or a loose connection somewhere between the scope and camera.

If the elongated stars point to the right or left in the second image, then the sensor is not parallel with the focal plane of the scope. Cause could be misalingment of the sensor and camera body (unlikely) or more likely something out of true in the rest of the imaging plane.

[IanL]

Another thought along the same lines, if possible try rotating the corrector to different 90 degree orientations whilst keeping the camera in one orientation and compare the results. That should help you work out if the corrector is the cause (e.g. not parallel/centred with the camera sensor).

[Rustysplit]

Thanks for the ideas. I know it is not an issue between the camera and corrector as exactly the same set up works perfectly on the 200p.

It appears that the SW corrector may not work perfectly with the quattro, but I would still expect the coma to be more regular. So I think it is out of square somewhere.

[Rustysplit]

Problem solved! The roller guides on the focuser needed tightening down a touch. They were allowing the draw tube to sag a tiny bit one way.

Thanks for your help IanL