Just getting back to AP after a hiatus of a few years, wondering if I can canvas an opinion or two?
I am using an Orion eon72 refractor and im showing heaps of field curvature, as I expected I suppose (shown in first image). I bought an astro-tech 2" Field flattener (no reducer) and popped it on my Canon 1000D direct to t-ring as instructed for my 55mm back focus and I got what you will see in the second image. An improvement forsure, but not what I was hoping for.Still elongated stars in the corners.
After some reading, I have come to believe that a much bigger backfocus may be necessary for this setup, which I tried last night. looks better from a distance, but now the corner stars appear pinched,
Does this just mean the backfocus is still a way short and needs to be played with? Or is it actually a worse situation than having elongated stars?
All images are 120secs single subs, guided, Orion eon72 refractor and a modded canon 1000D. Only basic stretch with PixInsight has been performed. Dont know how much you'll see after the compression etc but anyway. Perhaps I should post stacked versions to astrobin and leave the links here?
