Have you ever tried to get good white balance from your camera, but the consistency was never good? I am sure that you tried some of those preset balance settings, but they did not always work as well as you expected them to. This is where the ExpoDisc comes in.
Sure you can always use a light meter to get your correct readings. Once you have learned how to use it, you can get very accurate readings. The downside is that it takes time to learn and time to set up to get everything correct. Also you don't always have time to get everything just right. With ExpoDisc, getting the proper exposure is as easy as snapping on the disc.
Just what is an ExpoDisc? Invented by George A. Wallace, the original ExpoDisc was an incident exposure and printing tool for use with the 35mm SLR cameras. Generally it comes as a disc although there is square/rectangular version available for large lenses and video mattebox systems. The disc snaps onto the lens of your camera and it allows you then use the camera to set a proper custom white balance that is accurate.
By using the ExpoDisc, you are able to eliminate the need, or certainly reduce the amount of post-processing color adjustment work that needs to be done to your RAW and/or JPEG files. It is much easier to use than a light meter or gray, white, or color calibration cards.
You use the ExpoDisc by snapping it over your camera lens. The ExpoDisc comes in different sizes for different lenses (available sizes are listed at the end of this article). If you have a lot of lenses of differing sizes, get one for the largest size and you can hold it over the smaller lenses when calibrating them.
Since the specific steps are different for each camera, I will just give an overview of the steps to calibrate. You first place the ExpoDisc over the lens. You then take a picture of the light source. For the image of the pony below, I was outside and so I took a shot of the sky behind me, the sun being the source of the light. If you were doing a portrait you would take it of the lighting system. For strobe flash, you would need to trigger your flash system. This shot to look at is nothing more than a gray image, like taking a shot of a gray card, for your camera to use to create a custom white balance.