Optical film and method for production thereof

A resin solution, comprising:

• a solvent comprising 50 parts by weight or more of toluene based on 100 parts by weight of the solvent;
• and
• an ester-based polymer that is dissolved in the solvent and comprises a repeating unit represented by formula (I):
• wherein
• A and B each represent a substituent, a and b represent the number of the substituents A and the number of the substituents B, respectively, each of which is an integer of 0 to 4,
• A and B each independently represent hydrogen, halogen, an alkyl group of 1 to 6 carbon atoms, or a substituted or unsubstituted aryl group,
• D represents a covalent bond or at least one atom or group selected from the group consisting of a CH2 group, a C(CH3)2 group, a C(CZ3)2 group, wherein Z is halogen, a CO group, an O atom, a S atom, a SO2 group, a Si(CH2CH3)2 group, and an N(CH3) group,
• R1 represents a straight-chain or branched alkyl group of 1 to 10 carbon atoms or a substituted or unsubstituted aryl group,
• R2 represents a straight-chain or branched alkyl group of 2 to 10 carbon atoms or a substituted or unsubstituted aryl group,
• p1 represents an integer of 0 to 3, p2 represents an integer of 1 to 3, and
• n represents an integer of 2 or more.