The present invention discloses an optical film comprising: a reflective polarizer having a pass axis; and a stretched polyethylene terephthalate film having an x-axis in the direction of greatest stretch; a Z-axis which is perpendicular to the plane of the stretched polyethylene terephthalate film; and a y-axis, which is perpendicular to the both the x-axis and z-axis. The stretched polyethylene terephthalate film is laminated to the reflective polarizer. The refractive indices nx along the x-axis, the refractive index ny along the y-axis and the refractive index nz along the z-axis of said stretched polyethylene terephthalate film enables the stretched polyethylene terephthalate film to have a refractive index symmetry point given Theta(sf) in the follow fomula. However, no solution with respect to Theta(sa) exists in the following formula.