| 摘要 |
PROBLEM TO BE SOLVED: To provide an ND filter capable of suppressing unnecessary light reflection occurring when light is made incident on the surface of the ND filter including a transparent region and reducing the occurrence of a ghost. SOLUTION: The ND filter 10 is composed of the transparent region 11 and an ND region 12 which damps light in a prescribed proportion. When the ND filter 10 is fitted to a light amount control diaphragm, the transparent region 11 is located on a part or the whole region of a diaphragm opening part region in an open state. As an opening is driven into a small diaphragm state in accordance with a light amount of an object, the ND region 12 advances into a diaphragm opening according to the driving and the light amount is gradually reduced. An ND film is not deposited on the transparent region 11, but a fine ruggedness periodical structure having a pitch shorter than visible light wavelength is formed on the surface, the fine ruggedness periodical structure becomes an antireflection structure and, therefore, light made incident on the surface of the transparent region 11 is hardly reflected. COPYRIGHT: (C)2008,JPO&INPIT
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