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Reflection reducing film, optical member and optical system

Title: Reflection reducing film, optical member and optical system.
Abstract: A reflection reducing film is provided on a surface of an optical substrate, and is sequentially provided with a buffer layer and a reflection reducing layer. The reflection reducing layer includes first to eighth layers sequentially laminated from the side of the buffer layer. The first and sixth layers are made of a low-refractive index material having a refractive index in the range of 1.35 to 1.50 at the d-line, the third, fifth and seventh layers are made of an intermediate-refractive index material having a refractive index in the range of 1.55 to 1.85 at the d-line, and the second, fourth and eighth layers are made of a high-refractive index material having a refractive index in the range of 1.70 to 2.50 at the d-line. ...

USPTO Applicaton #: #20120276350 - Class: 428212 (USPTO) -
Inventors: Etsuo Terayama

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The Patent Description & Claims data below is from USPTO Patent Application 20120276350, Reflection reducing film, optical member and optical system.


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This application is a Divisional of co-pending U.S. application Ser. No. 12/470,216 filed on May 21, 2009, which claims priority under 35 USC 119 from Japanese Patent Application No. 2008-134224 filed May 22, 2008 and Japanese Patent Application No. 2008-134225 filed May 22, 2008; the entire contents of which are incorporated herein by reference.


1. Technical Field

The present invention relates to a reflection reducing film which is formed on one face of an optical member such as a lens, a filter and the like to exhibit a reflection reducing effect with respect to light having a predetermined wavelength band, and an optical member and an optical system which have the reflection reducing film.

2. Related Art

Generally, an image pickup apparatus such as a photographic camera or a TV broadcasting camera has a number of optical members such as lenses, prisms, filters and the like disposed on an optical path thereof. When light is incident on surfaces of the respective optical members, a portion of the light becomes reflection light. Herein, when the number of the optical members increases, a total amount of the reflection light increases and thus defects, for example, flare and ghost occur in images of a broadcasting camera. In addition, since reflectances on the surfaces of the optical members have distribution with respect to a wavelength of the incident light and wavelength dependences of various reflectances are shown in accordance with constituent materials for the respective optical member, a chromaticity balance deteriorates, and thus it is necessary to adjust a white balance in an entire image pickup apparatus.

Accordingly, a surface of each optical member may be provided with a reflection reducing film (also referred to as the antireflection film). The reflection reducing film is a multilayer film in which dielectric films having different refractive indices are combined, and a configuration thereof is disclosed in, for example, the following Non-Patent Document 1. In the Non-Patent Document 1 (“Light•Thin Film Manual”, The Optronics Co., Ltd, Oct. 9, 1989, P 246-247), an antireflection film having a 5-layer structure is disclosed and an attempt has been made to achieve a low reflectance over a wider band.

In addition to the Non-Patent Document 1, Patent Document 1 (JP-A-2002-267801) discloses an antireflection film having a 9-layer structure.

For example, the antireflection film disclosed in the above Non-Patent Document 1 exhibits relatively excellent low reflectance characteristics when being provided on an optical substrate having a refractive index lower than 1.70 at the d-line. However, it is found that there is a tendency in which flatness in reflectance distribution is lost as described later and a reflectance is thus increased at a specific wavelength when the antireflection film is provided on an optical substrate having a high refractive index higher than 1.75.

Tables 1 and 2 show basic data (constituent materials, refractive indices and optical film thicknesses) of antireflection films (Related examples 1 and 2) having a laminate structure corresponding to the antireflection film disclosed in Non-Patent Document 1. And FIG. 45 shows reflectance distributions of the antireflection films having the basic data of Tables 1 and 2.

TABLE 1 OPTICAL FILM RELATED CONSTITUENT REFRACTIVE THICKNESS EXAMPLE 1 MATERIAL INDEX N INDEX Nxd OPTICAL BK-7 1.51 — SUBSTRATE 1st LAYER SUB-M1 1.67 0.25 λ 0 2nd LAYER ZrO2 2.05 0.50 λ 0 3rd LAYER Al2O3 1.62 0.50 λ 0 4th LAYER SUB-H4 2.05 0.50 λ 0 5th LAYER MgF2 1.39 0.25 λ 0 AIR — 1.00 —

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