An optical system focuses an object upon an image surface of a solid-state image device. The optical system has a master optical system and a condenser lens. The master optical system and the condenser lens both have positive optical power. The focusing optical system fulfills the following conditions: ##EQU1## where a represents the distance between the exit pupil of the master optical system and the image surface;b represents the distance between the exit pupil of the entire optical system and the image surface; andY' represents the maximum image height.