Had a go at Orion with the 80ED last night just to see what was possible.
Canon 5DH in cam NR on. ISO 1600, 4X1min + 4X6min, LPR filter, Hutech FR/FF, 80ED @ F6.4, stacked with Registar Raw to 16b Tiff. levels and curves in PS.
This is all I managed before the cloud rolled in again!
600K
http://users.bigpond.net.au/avandonk/Orion_sm1.jpg
Bert