Condensing optical system with corrected chromatic aberration, and information recording/reproducing apparatus using this optical system

摘要

A condensing optical system for condensing light from a record medium onto a photodetector in such as an optical information recording/reproducing system, comprises a first lens group and a second lens group, and these first and second lens groups cooperate to correct aberrations, especially a chromatic aberration, in the system with respect to plural wavelengths of lights esp. by making Abbe's numbers of those first and second lens groups different from each other.