Patent ID: 8021724

Claim:
An optical film having an inner portion exhibiting an N value defined by the following equation smaller than an N value at a surface of the optical film: N =( nx+ny )/2 −nz, wherein nx represents an in-plane refractive index in a slow axis direction of the optical film, ny represents an in-plane refractive index in a fast axis direction of the optical film, and nz represent a refractive index in a thickness direction of the optical film, wherein the N value is calculated from the refractive indices nx, ny, and nz at a depth “a” from the surface of the optical film, wherein nx, ny, and nz at the depth “a” are measured by cutting out a slice of the optical film of the depth range of (a−0.5) μm to (a+0.5) μm using an automatic birefringence meter, provided that, in the case of a≦0.5 μm, a slice of a depth of 1 μm from the surface of the optical film is cut out to measure the refractive indices, wherein the optical film meets the following conditions: N (0)≧ N ( a ); −10 ≦N (0)/ N ( a )<0; and 0 <a≦d/ 2, and wherein a represents a depth from the surface of the optical film; d represents a thickness of the optical film; N(0) represents an N value at a depth 0 from the surface; and N(a) represents an N value at a depth a from the surface.