Patent ID: 8221855

Claim:
A cellulose derivative film comprising a cellulose derivative having a substituent, the substituent having a polarizability anisotropy Δα of 2.5×10 −24 cm 3 or more, the polarizability anisotropy Δα being represented by equation: Δα=α x −(α y+αz )/2 wherein Δα is the largest of the eigenvalues obtained by diagonalization of a polarizability tensor; ay is the second largest of the eigenvalues obtained by diagonalization of a polarizability tensor; and az is the smallest of the eigenvalues obtained by diagonalization of a polarizability tensor, and the cellulose derivative film having an Re and an Rth satisfying the respective inequalities: | Rth (589)|≦25 nm | Re (589)|≦10 nm wherein Rth(λ) is a retardation in the thickness direction at a wavelength λ nm; and Re(λ) is an in-plane retardation at a wavelength λ nm.