Just to update - I've actually just fitted a "Deeproof" 67mm lens adaptor ordered from www.divervision.com ( only place I could find it!) and I am really quite impressed with the adaptor. Also impressed with www.divervision.com in that I ordered it last Wednesday and it arrrived on Monday....not bad from the US! It is very robust and is a swing-away design that allows you to flip (or unflip) a macro or wide angle lens over the lens. The metal rim attaches to the canon lens housing with a couple of tiny grub screws (only 1/4 turn past contact)...I've just fitted a piece of the Inon 'clear water' film to the inside of the housing in front of the flash - this blocks visible light but allows sufficient infra-red through to fire the flash (so absolutely no backscatter issues). I'm off to the Philippines this July where I hope to give the new rig a major workout.