The optical path of the light having spread at each point of an object to be shot is limited by an iris unit of a density filter. Since the density filter unit has a desired transmittance characteristic, the amount of the light passing through the density filter unit continuously changes from the center of the luminous flux toward the periphery. After the luminous flux forms an image on the image forming surface, it spreads toward the light-receptive surface of an image sensor, and becomes an image spreading on the light-receptive surface in a predetermined range.