With a near full Moon tested the stopped down 300mm lens with HA on Carina Neb.
Canon 5DH, Canon 300mm F2.8L at f/3.5. Astronomik 13nm HA filter.
10x(2m, 4m, 8m) at 400ISO, fridge at -5.0C.
Large image 4.8MB
http://members.optusnet.com.au/~cheekyfish/car_ha.jpg
Bert