The 67mm ExpoDisc is a filter used to calibrate your digital camera's or digital camcorder's white balance for true color caption. Simply read and set white balance with the ExpoDisc in place before shooting.The ExpoDisco is a neutral diffusion filter that gathers ambient light and passively transmits 18 percent of it to your camera's/video's light meter, effectively producing a "gray frame." You then set a custom white balance using the gray frame that results in accurate color in most lighting conditions.Features:Fine-tune your color at point of capture Works in mixed, or difficult lighting Replaces your gray cards and white cards