With the trend to compactness and light weight in the digital era, the market in mirrorless interchangeable lens cameras produced by removing a mirror box and pentaprism from digital single-lens reflex (DSLR) cameras is increasing.
Since a mirrorless interchangeable lens camera does not include a mirror box, a phase-difference autofocus method used in a DSLR camera cannot be used. Accordingly, the mirrorless interchangeable lens camera usually uses a contrast autofocus method. The mirrorless interchangeable lens camera includes an image sensor. The image sensor is a device that converts an optical image signal into an electrical image signal. Recently, demands for applying the phase-difference autofocus method to mirrorless interchangeable lens camera systems has increased.