Thanks everyone for the advice, I know it is not the dew as that night there was very low humidity and took another 12 shots at M16 before dew showed at all. Merlin, the serial number is 1255 on the genesis...sounds like one of the first batch!!!
Bert, I have a baader uv/ir filter in the camera, I had a look at the graphs for the original canon and the baader filter and the uv cutoff seems very much the same except there is a small peak in the uv at about 320-350nm range.. Also the baader filter has a slightly higher transmission rate the that end.. At the red end I can understand some red abberrations as the baader gets down much more than the canon off cause so we get the hydrogen emmisions and more..and I guess most lenses are not well corrected into IR. I might give a uv block filter a go like suggested by you Merlin and fringe remover by Houghy and see how it goes..
I have put up a pic of 2 shots of stars near m42 (excuse the poor quality of the shots as that was all I could find) left is after modd and the right is before.(bad focus).they are unprocessed except the modded has a slight red custom balance used and the moon was up as well...shows more blue after the modd I think....
..CS Gary