With a near full Moon tested the stopped down 300mm lens with HA.
Canon 5DH, Canon 300mm F2.8L at f/3.5. Astronomik 13nm HA filter.
5x(4m, 8m, 16m) at 400ISO, fridge at -5.0C.
Full res image 2,4MB
http://members.optusnet.com.au/~fmlee/ngc6334%20(2).jpg
The use of the 86mm aperture really makes this lens perform. The stars are very good over the whole field and the size of the stars are exactly the same whether HA or colour.
bert