[tornado33]

Thanks all.
Jeff, I uswed only the red channel as when I first started using the Ha filter, I loked at the other 2 channels and noted they only contain stars and thermal noise/amp glow, no nebusosity (except in very bright ones like M42 where excess light leakes over into the green and blue pixels). Im thinking if I reject those 2 channels I will be keeping only about 1/3 of the thermal noise.

Heres an original (10 mins ISO1600) both full and cropped. The noise is incredible, a cooled DSLR would be better, its incredible how much dark subtraction can remove most of the thermal noise too.

Heres just the green and blue channels, theres no nebulosity, just thermal noise and some amp glow.
Scott