Finally began to see something after some helpful advice from a couple of forum members. My error was not setting the white levels etc in relation to the histogram. It's all new to me - except in terms of ordinary photography, so I was in the dark - literally. I now have 'live' images which are essential for alignment and focussing. Conditions were not good, however, with an almost full moon, thin cloud and lots of dew. So I packed in knowing that I was at least on the right road and looking forward to next time.