Optical information recording/reproducing apparatus.

摘要

A condensing optical system for condensing light from a record medium (5) onto a photodetector (7) in such as an optical information recording/reproducing system, comprises a first lens group (L1) and a second lens group (L2), and these first and second lens groups cooperate to correct aberrations, esp. 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.