Retardation film and optical device employing it

A retardation film which is a retardation film comprised of a single polycarbonate oriented film, wherein the retardation at wavelengths of 450 nm and 550 nm satisfies the following formula (1):

• R(450)/R(550)<1 (1)
• where R(450) and R(550) represent the in-plane retardation of the oriented polymer film at wavelengths of 450 nm and 550 nm, respectively, and R(550) is at least 50 nm.

A reflective liquid crystal display device provided with a polarizing plate, a λ/4 plate and a liquid crystal cell containing a liquid crystal layer between two substrates each with an electrode with at least one of the electrodes being a transparent electrode in that order, the reflective liquid crystal display device employing as the λ/4 plate a retardation film comprising a single oriented polycarbonate film, wherein the retardation at wavelengths of 450 nm and 550 nm satisfies the following formula (1):

• R(450)/R(550)<1
• where R(450) and R(550) represent the in-plane retardation of the oriented polymer film at wavelengths of 450 nm and 550 nm, respectively, and R(550) is 100-180 nm.