US Patent 7436451 Image sensing apparatus and its control method

An image sensing apparatus in which time required before the apparatus becomes in an image-sensing possible status is reduced. The image sensing apparatus has a constituent element comprising a first image sensing unit as a main unit and a constituent element comprising a second image sensing unit as a sub unit, having a structure more simple than that of the first image sensing device. An aperture amount in an initial stage of an aperture unit when the first image sensing unit is enabled to perform image sensing is determined based on a light amount detected by a light amount detector in the second image sensing unit and an F value of the first image sensing unit.