The ExpoDisc™ is a filter for calibrating digital cameras and checking exposure.
Consisting of a white diffusion plastic combined with a lenticular diffuser in a filter assembly, the ExpoDiscT is attached to the camera lens and used like an incident light meter to set the neutral balance. This requires the camera to be pointed back toward the photographer's shooting position. This can be problematic for studio photography with large format cameras mounted on heavy tripods or camera stands.
As shown in the following spectrum, the ExpoDiscT does not have a uniform spectral response. The higher transmittance in the 450-530 nm region combined with the slight drop in transmittance in the 550-700 nm range results in a slightly cyan color to the transmitted light. This cyan appearance will result in a slightly warm cast (reddish) to the images taken with an ExpoDiscT balanced image.
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