I've got an AT72EDII, DSLR, and Orion field flattener. It's much better than no flattener, but still isn't perfect in the corners. I've read about fine tuning flatteners by adjusting the spacing, but that doesn't appear to work. I tried adding spacers between the flattener and T-ring from no spacer up to a 5mm spacer, and the stars in the corners look unchanged. Am I misunderstanding how to fine tune it? I've attached crops of the corners of a couple images. The first with no spacer, the second with a 5mm spacer.
Edited by ajreynolds, 17 October 2020 - 10:35 PM.