JP2010048896A - Optical system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical system with excellent reliability, which has reflection preventive structure composed of fine uneven structure, thus has high reflection preventive properties, and also free from deterioration of performance such as the clouding of a lens even in use at high temperature or for a long period. <P>SOLUTION: In the optical system comprising: a lens with reflection preventive structure composed of a plurality of fine uneven structure with the average pitch of ≤400 nm; and a lens barrel holding the lens, a coating film comprising fluorine is formed on part or the whole of the surface of the lens barrel. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical system, and more particularly to an optical system having an antireflection structure having a fine concavo-convex structure.

  Conventionally, in a lens using a translucent medium (translucent member) such as glass or plastic, a surface treatment such as providing an antireflection film on the light incident / exit surface in order to reduce loss of transmitted light due to surface reflection Has been given. For example, as an antireflection film for visible light, a multilayer film in which a plurality of dielectric thin films are stacked is known. This multilayer film is formed by depositing a metal oxide or the like on the surface of a light-transmitting substrate by vacuum deposition.

  In recent years, optical systems such as lenses for digital cameras are required to have high optical performance and to be small and light as a whole. In response to this, a lens having a large aperture or a lens having a surface with a small curvature radius has been used.

  When such a lens is used in an optical system, light rays are incident at a large angle around the lens. For this reason, an antireflection film in which dielectric thin films are laminated in a multilayer manner has a wide incident angle, so that reflection cannot be sufficiently suppressed, causing harmful light such as ghosts and flares.

In view of such a situation, in Patent Document 1, at least one or more optical surfaces of an optical element are configured to have a fine uneven periodic structure having a period shorter than the visible light wavelength.
JP 2005-157119 A

  In the prior art disclosed in Patent Document 1 described above, the anti-reflection effect is obtained with respect to a wide light incident angle by providing the fine concavo-convex structure. However, the fine concavo-convex structure having a cycle shorter than the visible light wavelength has a feature that the surface area is very large compared to a normal lens surface. For this reason, for example, the moisture adsorbed on the inner surface of the lens barrel is released due to, for example, use at a high temperature or long-term storage (leaving), and the clouding occurs due to adsorption to the fine uneven structure. Had.

  Accordingly, an object of the present invention is to have an antireflection structure having a fine concavo-convex structure, to have high antireflection characteristics, and to deteriorate performance such as a lens becoming cloudy even when used under high temperature or stored for a long time. It is an object to provide an optical system with no reliability and excellent reliability.

  In order to achieve the above object, the present invention provides an optical system having a lens having an antireflection structure composed of a plurality of fine concavo-convex structures having an average pitch of 400 nm or less, and a lens barrel holding the lens. A feature is that a coating film containing fluorine is formed on part or all of the surface of the lens barrel.

  According to the present invention, by using a lens having an antireflection structure composed of a fine concavo-convex structure, a high antireflection function is realized, and there is no performance deterioration such as clouding even when used under high temperature or stored for a long time. An optical system with excellent reliability can be provided.

  Next, details of the present invention will be described in accordance with the description of the embodiments.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  The optical system of the present invention is an optical system having a lens having an antireflection structure composed of a plurality of fine concavo-convex structures having an average pitch of 400 nm or less, and a lens barrel that holds the lens. Part or all of the film is formed by forming a coating film containing fluorine.

  The antireflection structure comprising a plurality of fine concavo-convex structures having an average pitch of 400 nm or less according to the present invention may be produced by any method.

  For example, a method can be used in which a film is formed by applying a solution containing aluminum on the lens surface, and the film is subjected to warm water treatment to form a fine relief structure. Alternatively, a method may be used in which pores formed when anodizing aluminum or an aluminum alloy are formed on the mold surface, and the pores are transferred to the lens surface by a replica method or a molding method. If these methods are used, it is possible to form a fine uneven structure having an average pitch equal to or less than the operating wavelength on a lens surface having a large area at low cost.

  In addition, it may be formed by using a photolithography method, an interference exposure method, an etching method, an array pattern of fine particles, or the like.

FIG. 2 shows a schematic cross-sectional view of the antireflection structure A1 used in Example 1 of the present invention. An average of fine concavo-convex structures 23 made of a material containing aluminum oxide on a substrate (lens) 22 having a refractive index (n _d ) of 1.96880 and a refractive index dispersion (v _d ) of 55.5 and having an average pitch of 400 nm or less. It was formed to have a height of 270 nm. The reason why the average pitch is set to 400 nm or less is that if an average pitch larger than that is used, visible light is diffracted and harmful light is generated.

  FIGS. 3A and 3B show the reflectance at an incident angle of 0 ° and the reflectance at an incident angle of 60 ° of the substrate (lens) 21 on which the antireflection structure is formed. Anti-reflective structures consisting of fine concavo-convex structures with an average pitch below the working wavelength have excellent incident angle characteristics, so that the reflectance is 0.3% or less over the entire visible region at an incident angle of 0 °, and the entire visible region even at an incident angle of 60 ° And achieved high performance of less than 2.0% reflectivity.

  FIG. 1 is a cross-sectional view of the first embodiment of the present invention.

  In FIG. 1, reference numeral 1 denotes an imaging optical system. In this optical system, an antireflection structure A1 having a fine concavo-convex structure with an average pitch of 400 nm or less is formed on the concave surface of the lens 2.

  Further, a coating film 5 containing fluorine is formed on the inner surface of the resin lens barrel 4 to prevent the gas tube inner surface from adsorbing gas components such as moisture. Therefore, even when used at high temperatures or for long periods of time, gas components such as moisture do not desorb from the inner surface of the lens barrel, and the antireflection structure A1 having a fine concavo-convex structure is clouded. The occurrence is prevented.

  In the present invention, a case where a coating film made of fluorine is formed on a part of the lens barrel is shown, but the present invention is not limited to this, and a coating film containing fluorine is formed on the entire surface of the lens barrel. Also good. Furthermore, although the case where the lens barrel is made of resin is shown, the same effect can be obtained when the lens barrel is metal.

  Further, if the surface of the fine concavo-convex structure is subjected to the same treatment for preventing the adsorption of moisture and gas, a higher-performance antireflection structure can be provided.

  In this embodiment, the optical system is an imaging optical system, but the present invention is not limited to this, and may be used for an observation optical system such as binoculars or a scanning optical system.

Sectional drawing of the optical system of Example 1 of this invention Schematic sectional view of an antireflection structure having a fine concavo-convex structure with an average pitch equal to or less than the operating wavelength Reflectivity characteristics of antireflection structure ((a) Incident angle: 0 °, (b) Incident angle: 60 °)

Explanation of symbols

A1 Antireflection structure with fine concavo-convex structure whose average pitch is less than the operating wavelength
1 Optical system
2-3 lenses
4 Lens tube
5 Coating film containing fluorine
21 Substrate (lens) on which antireflection structure A1 is formed
22 Substrate (lens)
23 Fine uneven structure with an average pitch below the operating wavelength

Claims (8)

A lens having an antireflection structure composed of a plurality of fine concavo-convex structures having an average pitch of 400 nm or less;
In an optical system having a lens barrel that holds the lens,
An optical system characterized in that a coating film containing fluorine is formed on part or all of the surface of the lens barrel. The optical system according to claim 1, wherein the fine uneven structure is a structure containing aluminum or aluminum oxide.   The optical system according to claim 1, wherein the lens barrel is made of resin or metal. The surface on which the coating film containing fluorine of the lens barrel is formed,
The optical system according to any one of claims 1 to 3, wherein the contact angle of water is 60 degrees or more.   The optical system according to claim 1, wherein the optical liquid is an imaging optical system.   The optical system according to claim 1, wherein the optical system is an observation optical system.   The optical system according to claim 1, wherein the optical system is a scanning optical system.   An optical apparatus having the optical system according to claim 5.

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