Thanks all for your thoughts. I had forgotten about the magenta cast issue - damn! However, a couple of mighty fine suggestions there for how to deal with the screw in filters. I'll keep researching

And Graeme (old dog), I wish I had just dropped/lost the filter on land, but it went straight to the bottom of a duck pond

And Sir Rattus, the only time I'm up even vaguely near sunrise is when I play golf. Hmmm, maybe I need to take the camera with me and entertain myself whilst waiting at the inevitable pile up at the tee of the Par 3s

Thanks for all of your thoughts, cheers Deb