The present invention provides an optical unit for high-resolution applications all lenses in which are made of plastics. The optical unit includes lens (1) and (2). The lens (1) is a plastic lens having an Abbe number of 45-60. The lens (2) is a lens injection molded from a polycarbonate material comprising a structure derived from spirobiindan and having a glass transition temperature of 120-150.degree. C.