I am a big fan of the ExpoDisc, that comes in basically the same sizes as UV filters, albeit, it is thicker. I got mine over-sized for my Canon telephoto lenses – it”s easy just to hold it over the end of the lens, rather than screw it on. Turn off the auto-focus and shoot an image lit as the camera will see the subject i.e. fire the strobes if strobes are in use. The resulting image is a neutral gray (18% gray) that may then be used with any DSLR that allows setting custom white balance based on an in-camera image.
“The ExpoDisc Professional Digital White Balance Filter (patent pending) is a custom white balance filter that allows digital photographers to quickly and easily set an accurate custom white balance. Consistently producing excellent results in natural, artificial, and studio lighting, the versatile ExpoDisc even excels in difficult mixed lighting environments.”
Both the design and packaging are excellent!
One note: I found out that using an image to set a custom white balance doesn”t actually alter any particular settings in the camera, it is used as a reference as other images are shot. In other words, don”t delete the image used to set the custom white balance until after all images in that particular light are taken.