A method of forming an optical film results in a film having a useful central 60% portion with a caliper variation of about 5% or less of an average thickness of the film. The method includes selecting a draw ratio λ in a first in-plane stretch direction, setting an effective draw gap defined by a length L and a width W, and stretching a polymer film at the draw ratio and effective draw gap. The effective draw gap is set such that the stretching step fits into one of two regimes, the first regime referred to as a uniaxial regime and characterized by a β equal to or less than about 1.0; and the second regime referred to as a planar extension regime and characterized by a β equal to or greater than about 10.0. The disclosure also describes an optical film formed by the method.