Patent ID: 6881457

Claim:
An optical compensation film comprising a cellulose ester film comprising cellulose ester wherein (a) each of photoelastic coefficient C(md) in a mechanical direction and a photoelastic coefficient C(td) in a transverse direction of the cellulose ester film is 1×10 −9 to 1×10 −13 Pa −1 , and C(md)<C(td); (b) a retardation R 0 within a plane of the cellulose film defined by Formula (I) is 20 to 70 nm; (c) a retardation R t of the cellulose ester film in a thickness direction defined by Formula (II) is 70 to 400 nm; (d) each of a dimensional variation ratio S(md) in the mechanical direction and a dimensional variation ratio S(td) in the transverse direction of the cellulose ester film prior to and after being allowed to stand at ambient conditions of 80° C. and 90 percent relative humidity for 50 hours are −1 to 1 percent, and |S(md)|>|S(td)|; and (e) the cellulose ester simultaneously satisfies Formulas (IV) and (V); R 0 =( nx−ny )× d (I) R t ={( nx+ny )/2 −nz}×d (II) wherein nx is a refractive index in a transverse direction within a plane of the film, ny is a refractive index in a mechanical direction within a plane of the film, nz is a refractive index in a thickness direction of the film, and d is a thickness of the film in nm; and 2.55 ≦X+Y≦ 2.85 (IV) 1.4≦X≦2.85 (V) wherein X is a degree of substitution of an acetyl group and Y is a degree of substitution of a propionyl group or a butyryl group.