Sorry to hear about the focus problem.
How could it happen with both cameras? where you on auto focus with both, if so the lack of light may have been the problem. not allowing the auto focus to work properly.
Cleaning lenses George
Well I tend to use my slr lenses "Naked" ie without any filters. A decent filter that doesn't detract from the quality of the lens, can cost up to 60 to 80 pounds.
When I need to clean a lens, I first blow off any dust with a Rocket blower, then gently blow onto the lens and then wipe the lens glass with a Microfibre cloth gently. A small amount of dust etc on a lens is unlikely to show in a picture, a finger mark will. keep a lens cap on when not taking pictures.
Malcolm