I hear you regarding a corrected field.
My Tak Mewlon 180 (a Dall-Kirkham Cassegrain design) has a small, on-axis region of sharpest focus where it is very crisp but with an extended object such as the moon, as soon as I move away from that small, central sweet spot the sharpness degrades quite noticeably.
With my Canon DSLR, I can get around this by taking several shots for a mosaic, with the moon placed at different positions in the field of view then I assemble the sharpest region from each of the frames.
However, with the 3.54x2.69 mm ASI120MM chip I am always recording in that sweet spot in the centre.
Cheers
Dennis