Newtonian Focus and Collimation

[BlueAstra]

I'm currently setting up an AG10 Newtonian imaging system, and would welcome advice and guidance on focus and collimation. In this system it's a classic Newtonian with a 'Wynne corrector' for field flattening, operating at F/3.8. I collimated the system visually using the cat's eye autocollimator, although in the process I accendentally loosened the central locking bolt on the secondary. I tightned this up and the secondary looks circular, and re did the cats eye collimation. I then installed the camera equipment (Wynne corrector, SX FW+OAG+SXV-H16). I noticed in the first couple of images I took that the focal plane did not appear flat. In the image below, the top left quadrant seemed to show significant defocus compared with the rest of the image.

I downloaded a trial copy of CCD Inspector and ran it on the image:

This seemed to show a tilt in the image plane, with the worst tilt in the top left. For the next image I tweeked the secondary using the CCD inspector liveview mode, so I could continuosly monitor the image plane curavature and collimation while adjusting the mirror. This improved the image, but its still not right. I took an image at five points (corners & centre) with a Bahtinov mask on, and I did a through focus star check in the centre of the image:

I also did a close up of a very bright star, Vega:

I can see the four main spikes from the secondary holder, but not sure what the mini spikes near the core are.

I suspect that I have a focal plane tilt in the camera (which can be adjusted on the bench), or that the camera is not at the perfect focus for the Wynne corrector. Tweeking the secondary has probably moved it from its perfect visual collimation in order to compensate for camera tilt, so although I've apparently improved the image the setup is not right.

Prior to removing the camera for further investigation, does anyone have any comments on the above?

[Catanonia]

Having very similar problems with my corrector / reducer and newtonian running from F4 to F2.8

I found that my CCD was not level to the CCD case. I used digital venier calipers and found a 0.5mm difference across the CCD chip.

Also if you have now messed with the secondary, re-cats eye and check the secondary peep hole on the autocolimator (offest) as well as the primary one to ensure you have it spot on.