Polyester carbonate copolymers and optical lenses for optical lenses

An object of the present invention, the refractive index and high transparency is that the birefringence provides an optical lens using polyester carbonate copolymer and it was suitable for a small number of optical lenses optically distortion low. The present invention contains a unit represented by 67-95 mol% of the formula (I) in units and 33 to 5 mol% of the formula is expressed (II), specific viscosity from 0.12 to 0. a polyester carbonate copolymer for the optical lens 30. (Formula (II) Medium Y is a phenylene group or a naphthalene-diyl group.)