That 0.8-0.85x reducer is about $US 249 = $AU 351.
For around two times that price or below, say $600 to $700 (if you're a good wheeler-dealer) you could have a used Canon 6D fullframe camera, which would yield a far cleaner image and give you a much wider field of view. It would be the equivalent of 1/1.6 ~= 0.625x reducer AND you will not have added any additional optics in to the optical path, which can degrade contrast and add abberations.
Using a full-frame 6D without a field-flattener... well, it's not pretty.
The 1100D I use is full-spectrum and cooled, modified by me. Not going to do that to my 6D
But to the point, a simple doublet has a field curvature and that is need to be corrected even for a APS-C size sensor... let alone a 6D full frame.
So the FF/FR has dual function. An Astrograph corrected for full-frame is beyond my $$$
A quick test of the SW FF/FR 0.85x
It works, no distortion in the APS-C DSLR corner. Hope the uploaded pic will show the difference.
I needed to get a 56M TO 48M adapter to attache to the OAG, and have to use the thin OAG to get to focus with on the 80ED. My preferred OAG is the more solid Celestron... have to work on that. Shorten the OTA or buy a 2" helical focuser and make an adapter.
