Thanks all for the comments. If you think about it the faint part of the image came from seven exposures for only four minutes each at an ISO of 500..
I can easily take narrowband images for 16 to 20 minutes or more. With a decent number to reduce noise all the faint stuff will come up.
Below is an image done last year with the 300mm lens at f/2.8. I hope to go deeper and clearer with the 100ED and 150mm achro.
I will also do it all again with the 300mm lens plus narrowband data.
large image 1.0MB
http://members.optusnet.com.au/~cheekyfish/oriongas.jpg
M42 is just a test,mainly to see if I could get 'natural' colour with narrowband data. The use of EasyHDR will also give me the full dynamic range of the target object visible in the one final image. Next on the list some supernova remnants in Vela when they are high enough.
As usual weather will dictate progress!
Bert