TECHNOLOGY FOCUS - CERAMICS AND GLASS - Preferred Component: The support is glass substrate.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (Disclosed): The polyimide is obtained by dehydration ring closure of polyamic acid by thermal method. Preferred Composition: The organic solvent contains amide-type solvent, ketone solvent, ester solvent and/or ether solvent.    TECHNOLOGY FOCUS - POLYMERS - Preferred Process: One portion of polyamic acid is imidated. The polyimide membrane is obtained by coating the polyimide solution or polyamic acid solution to support. Preferred Properties: The polyimide membrane has light transmittance of 70% or more at wavelength of 400 nm, when polyimide membrane has film thickness of 10 mu m, and glass transition temperature of 250 degrees C or more. The difference in maximum in-plane refractive index (nx) and minimum in-plane refractive index (ny) among in-plane refractive indexes of polyimide membrane is less than 0.0002. The refractive index (nz) along thickness direction of polyimide membrane, and maximum in-plane refractive index (nx) and minimum in-plane refractive index (ny) of polyimide membrane satisfy relation: (nx+ny)/2-nz less than 0.005. Preferred Definitions:    x=0.3 to less than 1;and    A=divalent organic group derived from 4,4'-diamino diphenyl ether, 3,4'-diamino diphenylether, 2,2-bis(4-aminophenoxyphenyl)propane, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene or 4,4'-bis(4-aminophenoxy)biphenyl.    EXAMPLE - 9,9-Bis(3-methyl-4-aminophenyl)fluorene (14.4 g) and dimethylformamide (70 g) were stirred, 1,2,4,5-cyclohexane tetracarboxylic dianhydride (12.3 g) was added, stirred, 4,4'-diamino diphenylether (3.3 g) was added, stirred, polyamic acid was obtained, diamine compound and tetracarboxylic dianhydride were added to resultant reaction solution, pyridine (8.6 g), acetic anhydride (13.4 g), dimethylformamide (100 g) and imidation catalyst were added to obtained solution, stirred, 2-propyl alcohol was added, polyimide solution (1 L) was dripped to obtain polyimide powder, obtained polyimide powder was washed using isopropyl alcohol, and vacuum-dried, to obtain polyimide having molecular weight of 73000.