Takashi

Sorry, CCD inspector? Delrin spacers? Yes I agree, the problem looks a little like "Spacing too close" in your picture.

Thanks for fast response. Those two screws adjust a compression ring, and no matter how much I adjust these, the result looks the same.

Hi! I have the following setup: 1. William Optics Zenithstar 71 2. P-FLAT-F6 3. Standard T2 ring to Canon adapter 4. Canon 600D It looks like the attached picture (except for camera) According to this website: https://agenaastro.com/william-optics-2-0-8x-apo-reducer-field-flattener-6-p-flat-f6.html It says the distance from flattener to sensor should be 55-57mm. The canon 600D has 44mm flange to sensor distance. The T2 ring is the normal common one which I think has around 12mm, so I should get around 56mm distance. But whatever I do, the picture looks horrible in the corner with a APS-C sensor. See this image for example: https://www.nineplanets.se/imageViewer_dark.asp?ID=97 Look at the corners... 😞 What am I doing wrong? Anyone else has experience with this combination? This is the second WO telescope + flattener I have the more or less same problem with... so I guess I'm missing something?