THIN FILM ND FILTER AND METHOD FOR MANUFACTURING THE SAME

PROBLEM TO BE SOLVED: To provide a thin film type ND filter and a method for manufacturing the filter with superior mass productivity in which flat spectral characteristics of the transmittance can be obtained with good reproducibility. SOLUTION: The thin film type ND filter 30 consists of an optical multilayer body 5 formed on a polymer film substrate 1 with an adhesive layer 2 interposed. The optical multilayered body 5 is formed by alternately depositing an Nb layer 3 and a dielectric layer 4 for two times each, in the total of four layers. Because the film thickness of the Nb layers 3 can be rather easily controlled during forming, variance in the transmittance is decreased. The ND filter 30 can be manufactured by roll coating in a film forming device equipped with two vapor deposition sources. The vapor deposition sources are used for forming the Nb layers 3 and dielectric layers 4. The Nb layers 3 and the dielectric layers 4 are continuously formed on the substrate 1 by sputtering the respective vapor deposition sources while rotating feeding rolls and takeup rolls.