Focuser tilt or field curvature?

[that_guy]

Hi guys, just going through my images taken yesterday. I noticed one corner had badly distorted stars. Is this due to field curvature or from tilt of the focuser. The new camera (Qhy9 with 2" filterwheel) is on the heavier side that may have contributed to the tilt. Is there a solution to this without having to resort to a more expensive focuser?

I've uploaded 100% crop of the corner in question and the full image (with IIS compression) for your analysis.

Thanks
Tony

[JA]

Hi Tony,

Maybe- Is there any radial play or axial tilt/rock in the existing focuser and/or camera mount / nose piece? If so, it maybe possible to use shims to counteract the play /deflection for the purpose of testing whether this is the cause, maybe even some sort of makeshift repair or clamp to prop against deflection/movement.

Best
JA

[billdan]

With a 22mm diag chip its unlikely to be field curvature, you would need a larger sensor like a full frame DSLR for that to show up.

If its gravity induced tilt, it should disappear if you pointed the scope straight up. That leaves the focuser thumb screws not aligning the camera properly, so its pointing straight.

[Joshua Bunn]

Hi Tony.

Here is a good way to check if its field curviture or if its focuser tilt.
If you rotate your camera 180 deg without disturbing how the camera is seated... ie. With a rotator...and the effected stars stay in the same place on the image download, then you have camera tilt. If however the effected stars don't follow, then its field curviture or collimation etc.

HTH
Josh.