A developing unit has first and second partition walls and which divide the inside of a developer reservoir into first to third chambers parallel to the developing roller, and first to third mixers which are disposed in the first to third chambers. A first thermally-conductive container stores a metal hydride while a second thermally-conductive container stores a metal alloy that is capable of absorbing hydrogen atoms at a pressure that is less than the storage pressure of the metal hydride. The bulb comprises gaseous material with metal halides andor light emitters that, when powered, substantially stays in an arc shape state. By such arrangements, the optical lens assembly with a filter member for image taking can have good chromatic aberration correction and reduce the total length for applications to electronic products such as cameras and mobile phones requiring high resolution.