Bert,
Heres my version of your Eta Carinae. Pretty basic processing, basically gradient correction and exagerated the red channel a little (because thats the way we like our nebula
) The exif seems to have been lost from the jpeg, so I don't know what the exposure, ISO is. There is a bigger version at:
http://www.pbase.com/terrylovejoy/image/54204797
Have you thought about the 300mm f2.8 + 2x converter? You would get better edge performance for sure.
Terry