1. An imaging apparatus comprising: an optical system configured to generate an optical image of a subject, the optical system including a focus lens; an imaging device configured to convert the optical image to an image signal; a focus unit configured to drive the focus lens in an optical axis direction and focus the optical image on the imaging device; an extracting unit configured to extract a characteristic area including a predetermined characteristic from an image which is based on the image signal; an aperture correction unit configured to perform an aperture correction based on an aperture correction characteristic determined for each of predetermined positions on the image based on the image signal; and a controller configured to determine the aperture correction characteristic based on a position of the characteristic area on the image based on the image signal.