Carl Weese has an article today about using the ExpoDisc for digital white balance with some interesting history: it was used in 35mm film photography, before it found new life in digital.
ExpoDiscs are basically neutral translucent white filters or caps that allow you to take a white balance or exposure meter reading of the incident light, a couple are slightly cool colored which will shift your your photo to a more pleasing warmer color for skin tones. Sounds fancy, huh? They cost $60-$180.
Another solution is to stick a Pringles lid in front of your lens and set the custom white balance. One problem is that Pringles lids are now clear so some have switched to tennis ball cans.
The cheap plastic end-cap that came with my 50mm Æ’1.8 lens is translucent white. Next time I go out, Iâ€™m going to see how that works and save myself a Benjamin.