I had this idea about two days ago — make a lens cap out of the same material used for an ExpoDisc and you can leave it on all the time.
Turns out it has already been done. [via dps]
Rather begs a DIY version though doesn’t it? I have a cheap 3rd party extra lens cap (bought at great expense in Venice just down from the Rialto when I thought I’d lost my original Nikon cap), which I could merge with a Pringles can lid with or without a coffee filter.
I prefer this approach:
http://photography-on-the.net/forum/showthread.php?t=396330
Get a sheet of acrylic diffuser material, and you could slide it in the Cokin Filter System. I’ve only tried to hold a sheet in front of the lens, and used it to measure WB on my old D70. Worked fine!
Sounds like another good idea! Thanks for sharing.
I used a 1.5 inch hole saw to cut out the center of a lens cap and glued a cut out from a heavy duty styrafoam plate on the outside. On a densitomiter it read perfectly neutral. Tested this out worked perfectly, ended up making about one hundred of them for the company I work for, hard use in the field no issues so far, tested better than some of the ones we purchased.