Lens caps can be an expensive replacement for some cameras. If you're looking for a cheap solution to keep your lens clean and safe after losing a cap, DIY Photography reader Stu Carlson suggests using the bottom of a soft drink bottle.This isn't going to work on every lens, since sizes vary, but the soft drink bottle works so well on Stu's 10.5mm lens that he hasn't bothered purchasing a replacement. With the variety of different bottle sizes out there, you can probably find a bottle that fits just as snug on your camera lens. Just make sure you clean it out first.
Object of Desire - 10.5mm Lens Cap [DIY Photography]