I'm now toying with the idea of taking some fairly heavy material (e.g. thick denim), spray it with some sort of water resistant spray (e.g. the silicon aerosol that you can buy to waterproof clothing and shoes), and sewing velcro strips to tighten one end around the front of the lens.
Denim might not be too great an idea - cotton soaks up water like a sponge, and water resistant sprays wear off quite quickly in my experience. A better plan might be to start with water-proof material - cut up a cheap plastic raincoat or something?
S
