Patent ID: 7336330

Claim:
An optical film comprising an achromatic retardation film having an in-plane refractive index nx showing the maximum refractive index, a refractive index of ny in the direction perpendicular to the direction described just before, and a refractive index of nz in the thickness direction wherein nx>ny and nz>ny, and wherein Δna=nx−ny and da is a thickness of the film, Δna·da is 100 to 400 nm at a wavelength of 550 nm, the difference between a retardation obtained in an ideal achromatic film and an actually obtained retardation is −50 to 50 nm at the wavelength shorter than 550 nm, and the difference is −80 to 80 nm at the wavelength longer than 550 nm, and a polarizing element, said achromatic retardation film and said polarizing element being laminated so that the maximum refractive index direction of said achromatic retardation film coincides with the direction of an absorption axis of the polarizing element.