PURPOSE: To obtain a dustproof mask which exhibits high light transparent to both (i) rays and (g) ray by consisting the title film of cellulose esters and specifying both the transmissivity of light of 365nm and 436nm wavelengths to 98%.

CONSTITUTION: The film consists of the cellulose esters and both the transmissivity of the light of 365nm and 436nm are specified to ≥98%. The max. effect is obtd. when the cellulose ester is cellulose propionate and the film thickness belongs to any range among 1.45W1.48μm, 2.18W2.21μm, 2.92W2.95μm, 3.65W3.68μm, and 4.39W4.41μm. The film which is usable for both of an (i) ray stepper and (g) ray stepper and is economical is thereby obtd. A photolithography stage is simultaneously facilitated.