How does an ExpoDisc differ from a gray card?
Gray cards are generally made out of non-durable mat board to reduce unwanted reflections but overtime they become damaged, dirty and their dyes can shift in color. As a result most gray card manufacturers recommend that the card be replaced after a couple of months of use. To use a gray card effectively it needs to occupy at least 15% of the image frame when setting exposure or color balance. Therefore, in many cases the card needs to be large (e.g. 8″ x 10″) which makes it difficult to carry around and store. Finally gray cards need to be used at precise angles to make sure that the light being reflected towards the camera is at the same angle as the light being reflected by the subject. The ExpoDisc, on the other hand, is much better constructed and convenient to use: it is made of durable materials that will last for years; small enough to fit in your shirt pocket or store with your other filters; and, easier to use since it efficiently captures and averages light from a wide angle
