Thank you once again.
However, I appear to have missed a trick here. I am now working on a new-build 64Bit Vista box, and while I have calibrated my monitor with a Spyder, the web version of the image is not appearing as it should.
Here is the corrected image...which addresses the background which was too dark, and which brings out the outer arms of M61.
Thanks again
Martin
http://www.martinpughastrophotograph.../M61LRGBv3.jpg