Patent ID: 7948591

Claim:
A uniaxial retardation film having an optical axis in plane and where extraordinary ray refraction index>ordinary ray refraction index, wherein the retardation film satisfies the following equations (1) to (4): 118 nm≦ Rxy (550)≦160 nm (1) −10 nm≦ Ryz (550)≦10 nm (2) 0.75 ≦Rxy (450)/ Rxy (550)≦0.97 (3) 1.03 ≦Rxy (650)/ Rxy (550)≦1.25 (4), in equations (1) to (4), Rxy(λ), Ryz(λ) represent the retardation Rxy, Ryz of the retardation film at wavelength λnm respectively, and are defined as Rxy=(nx−ny)×d, Ryz=(ny−nz)×d where nx, ny (nx>ny) are the principal refraction indexes in the in plane direction, nz is the principal refraction index in the out of plane direction, and d is the thickness in the retardation film.