Quote Originally Posted by Russ Young View Post
see Eric Renner's book... he used a one gallon jar. Spray painted interior black then scraped the paint off a small area (the size of a pencil eraser) and placed a brass sheet with a pinhole in it over that spot.

That's a great idea! I'll try that. What worries me most is the exposure time. I guess that the opacity of the sea water will make it longer. I'll have to try over and over again. I'm looking for information on the web for charts or something that helps.