Optical thin film manufacturing method and optical thin film

An optical thin film manufacturing method for manufacturing an optical thin film having a first thin film portion and a second thin film portion whose film configuration is different from that of the first thin film portion, on a film formation surface of a base member directly or via an intermediate film, the method comprising:

• forming the first thin film portion on a first film formation portion of the film formation surface;
• forming a washing-time removal film on the first thin film portion, the washing-time removal film having at least one of a fluff-like structure, a pyramid group-like structure and a pinholder-like structure, and being at least one of aluminum and an aluminum compound;
• forming the second thin film portion on a second film formation portion, that is different from the first film formation portion of the film formation surface, and on the first film formation portion on which the first thin film portion and the washing-time removal film have been formed;
• and
• removing the washing-time removal film and the second thin film portion thereon by washing.