JP2010078803A - Optical element and optical system having it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical element having a good antireflection function in a wide wavelength region and a wide incident angle range and generating less flare and ghost when used in an optical system, and an optical system having the same.
An optical element having an antireflection function in a use wavelength region including a visible region, wherein the use wavelength region is a range in which a longest wavelength λH is twice or more than a shortest wavelength λL. The element includes an antireflection structure configured such that a fine uneven structure having an average pitch of the shortest wavelength λL or less is an outermost layer on at least one of the light incident / exit surfaces of the substrate. The pitch P, the refractive index n1 of the material forming the fine concavo-convex structure, the average height h of the fine concavo-convex structure, the incident angle θ of the light beam incident on the fine concavo-convex structure from the air side, etc. are appropriately set. .
[Selection] Figure 1

Description

  The present invention relates to an optical element and an optical system having the same. For example, the present invention relates to an optical element in which an antireflection structure (antireflection layer) having a fine concavo-convex structure having an antireflection function is provided on the surface (light incident / exit surface) of a lens surface (optical member) to effectively prevent reflection. Is.

  Conventionally, in a lens (optical material) using a light-transmitting medium (light-transmitting member) such as glass or plastic, an antireflection structure is provided on the light incident / exit surface in order to reduce loss of transmitted light due to surface reflection. Is provided.

  For example, a dielectric multilayer film is known as an antireflection structure for visible light. This multilayer film is formed by forming a thin film of metal oxide or the like on the surface of a light-transmitting substrate, for example, by vacuum deposition.

  A general antireflection film formed on an optical member is designed to have an excellent antireflection effect in a wavelength range in which a light incident angle is 0 degree and a wavelength range to be used is relatively narrow. On the other hand, in recent years, an optical system used in a wide wavelength region and an optical system in which a light incident angle to an optical element is increased have been used.

  For example, in an optical system such as a digital camera or a video camera, a lens having a large aperture or a lens having a surface with a small curvature radius has been increasingly used.

  When such a lens is used in an optical system, a light beam may be incident at a large angle around the lens.

  In general, when the incident angle of the light flux on the lens surface is wide, it is difficult to sufficiently suppress reflection in a wide wavelength region, which causes generation of harmful light such as ghost and flare.

  For this reason, an antireflection structure having an excellent antireflection function for a wide wavelength region and good incident angle characteristics of a light beam is desired.

As an antireflection structure having a wide wavelength region and good incident angle characteristics, a fine concavo-convex structure having a pitch shorter than the wavelength of visible light is known (Patent Documents 1 and 2).
JP 2005-157119 A JP 2006-10831 A

When the fine concavo-convex structure is formed on the lens surface, it becomes easy to obtain antireflection characteristics with good incident angle characteristics in a relatively wide wavelength range.

  However, in order to obtain a good antireflection function (wavelength band characteristics) in a wide wavelength range and a good antireflection function (incidence angle characteristics) in a wide incident angle range, the structure of the fine concavo-convex structure is appropriately set. Setting is important.

  For example, it is important to appropriately set the pitch and shape (height) of the concavo-convex structure, the refractive index of the material, etc. in consideration of the incident condition of the light beam.

  If the structure of the fine concavo-convex structure is inappropriate, a good antireflection function cannot be obtained in a wide wavelength range and a wide incident angle range, and a lot of flare and ghost are generated when used in an optical system. It becomes difficult to obtain an image of image quality.

  An object of the present invention is to provide an optical element having a good antireflection function in a wide wavelength region and a wide incident angle range and generating less flare and ghost when used in an optical system, and an optical system having the optical element. And

The optical element of the present invention is an optical element having an antireflection function in a used wavelength region including a visible region,
The use wavelength region is a range in which the longest wavelength λH in the use wavelength region is twice or more than the shortest wavelength λL in the use wavelength region,
The optical element includes an antireflection structure configured such that a fine concavo-convex structure having an average pitch of the shortest wavelength λL or less is an outermost layer on at least one of the light incident / exit surfaces of the substrate,
P is the average pitch of the fine concavo-convex structure, n1 is the refractive index of the material forming the fine concavo-convex structure, h is the average height of the fine concavo-convex structure, and θ is the light beam incident on the fine concavo-convex structure from the air side. When the incident angle is
P <λL / (n1 + Sinθ)
0.2λL ≦ h ≦ 0.8λH
It is characterized by satisfying the following conditions.

  According to the present invention, an optical element having a good antireflection function in a wide wavelength region and a wide incident angle range and generating less flare and ghost when used in an optical system, and an optical system having the optical element can be obtained. .

  Hereinafter, the optical element of the present invention and the optical system having the same will be described with reference to the drawings.

  The optical element (lens, prism, parallel plate, filter, etc.) of the present invention has an antireflection function in the used wavelength region including the visible region (wavelength 40 nm to wavelength 700 nm).

  The use wavelength region is a range in which the longest wavelength λH in the use wavelength region is twice or more than the shortest wavelength λL in the use wavelength region.

  The optical element has an antireflection structure (antireflection film) formed on at least one surface (lens surface) of the light incident / exit surface of the substrate. The antireflection structure is configured such that a fine concavo-convex structure having an average pitch of the shortest wavelength λL or less is the outermost layer.

  The antireflection structure described above may be provided on both the light incident / exit surfaces of the optical element.

  FIG. 1 is a schematic configuration diagram of Example 1 of an optical element having the antireflection structure of the present invention. In the optical element 1 shown in FIG. 1, an antireflection structure (antireflection film) 201 is formed on a substrate 11 made of a transparent member (optical member). Reference numeral 14 denotes a fine concavo-convex structure, and the average pitch of the concavo-convex shape (including a conical shape, a polygonal pyramid shape, and the like) is equal to or less than the use wavelength.

  Here, the operating wavelength refers to a wavelength range of 400 nm to 1100 nm including a visible region (wavelength 400 nm to wavelength 700 nm), for example.

  12 and 13 are homogeneous layers (homogeneous films) made of thin films. 301 is air (air layer). da represents the film thickness direction (thickness direction) of the optical element 1.

  The fine concavo-convex structure 14 is provided on the substrate 11 so as to be a film closest to the light incident medium (air).

  FIG. 2 is an explanatory diagram (schematic diagram) of a refractive index structure showing the refractive index n of the material in the film thickness direction da of each member constituting the optical element 1 of FIG.

  2, n21 corresponds to the refractive index of the substrate 11, n22 corresponds to the refractive index of the homogeneous layer 12, n23 corresponds to the refractive index of the homogeneous layer 13, and n24 corresponds to the refractive index of the structure 14. In this case, the apparent refractive index (equivalent refractive index) of the fine concavo-convex structure 14 continuously changes in the film thickness direction da as indicated by the refractive index n24 in FIG.

  The fine concavo-convex structure 14 has a tapered structure from the homogeneous layer 13 side to the air side. Therefore, the refractive index structure is such that the refractive index gradually decreases (decreases) gradually from the homogeneous layer side (substrate side) 13 toward the air 301 side.

  In the optical element 1 of FIG. 1, two homogeneous layers 12 and 13 made of a material different from the fine concavo-convex structure 14 are sandwiched between the base material 11 and the structural layer 14, but one or more homogeneous layers are formed. For example, three or more layers may be used. Moreover, there may be no homogeneous layer.

  It is desirable that the antireflection structure constituting the optical element does not generate diffraction / scattering with respect to incident light. In order to prevent diffraction / scattering from occurring in the fine concavo-convex structure 14, the pitch of the concavo-convex structure is preferably configured as follows.

  Let P be the average pitch of the fine concavo-convex structure 14 (the average of the intervals between the convex portions or the concave portions). The refractive index of the material is n1, the incident angle when light is incident on the structure 14 from the air 301 is θ, and the shortest wavelength of the use region wavelength is λL.

At this time,
P <λL / (n1 + Sinθ) (1)
It is configured to satisfy

  At this time, the fine concavo-convex structure 14 can be handled as a film (layer) whose refractive index continuously changes.

Here, the value of θ is 0 ° ≦ θ <90
Range.

  The refractive index structure of the fine uneven structure 14 changes in the film thickness direction da. For this reason, the height (average height) h of the fine concavo-convex structure 14 is set to the shortest wavelength λL in the use wavelength region and the longest wavelength λH in the use wavelength region.

At this time 0.2λL ≦ h ≦ 0.8λH (2)
It is desirable to set the range.

  In particular, it is effective to use the longest wavelength λH in the infrared range and at a wavelength of 800 nm or more.

Further, the height h of the fine concavo-convex structure 14 is 0.4λL ≦ h ≦ 0.6λH (2a)
In this range, it is particularly effective to prevent reflection at a wide wavelength range and a wide incident angle.

  By setting within such a favorable range, innumerable reflected light with a small amplitude is generated in the fine concavo-convex structure 14 and cancels out by interference, so that an excellent antireflection performance (reflection) in a wide wavelength range. Prevention effect).

  When the height h of the fine concavo-convex structure 14 is 0.2 or less of the shortest wavelength λL in the use wavelength region exceeding the lower limit of the conditional expression (2), the antireflection band becomes narrow.

  Further, when the height h of the fine concavo-convex structure 14 exceeds the upper limit and becomes 0.8 or more of the longest wavelength λH in the use wavelength region, a ripple occurs in the antireflection band. Furthermore, it becomes a factor of scattering, and it becomes difficult to obtain good antireflection performance.

  The antireflection structure according to this example has a configuration in which a wavelength region in which the reflectance is 3% or less at an incident angle of 60 degrees is present in the use wavelength region by 1/2 or more.

  Any method may be used for producing the homogeneous layers 12 and 13 constituting a part of the optical element 1. For example, a dry method (vacuum film forming method) such as a sputtering method or an evaporation method, a dipping method using a sol-gel coating liquid, a wet method (wet film forming method) such as a spin coating method, or the like can be applied.

  By forming a homogeneous layer in advance by these methods, the fine concavo-convex structure 14 is produced. Any method may be used for producing the fine concavo-convex structure 14. For example, a method of applying a film in which fine particles having a particle size of a wavelength or less are dispersed, a method of forming a petal-like alumina fine concavo-convex structure using a sol-gel method, and the like can be applied.

  At least one of the homogeneous layers in the optical element of the present embodiment preferably contains at least one of zirconia, silica, titania, and zinc oxide. Moreover, it is preferable that the fine concavo-convex structure body 14 is mainly composed of alumina such as aluminum or aluminum oxide.

  Hereinafter, although each Example demonstrates by the method of producing a homogeneous layer and a fine concavo-convex structure by a spin coat method, this invention is not limited to the thing manufactured by this method.

  Next, a specific configuration of the optical element of Example 1 will be described.

  In Example 1, the antireflection structure 201 on the transparent member 11 is provided with two homogeneous layers 12 and 13 between the transparent substrate 11 and the fine concavo-convex structure 14, and has three layers as a whole.

  In Example 1, the wavelength region having the antireflection effect, that is, the used wavelength region was a wide wavelength region from 400 nm to 1000 nm. As the transparent member 11, a glass substrate having a d-line refractive index n21 of 1.805 was used.

  As is apparent from FIG. 2, the refractive indexes n22 and n23 of the two homogeneous layers 12 and 13 formed from the transparent member (substrate) 11 side are the same as the refractive index n24a of the fine concavo-convex structure 14 on the substrate 11 side. The substrate 11 has a refractive index n21.

The homogeneous layers 12 and 13 are adjusted by adjusting the refractive index by changing the mixing ratio of the SiO ₂ —TiO ₂ coating solution, and are applied by spin coating, followed by heating and drying. Formed.

  The homogeneous layers 12 and 13 are formed from the substrate 11 side to the first layer 12 with a refractive index n22 of 1.696 and a physical film thickness of 79 nm, and the second layer 13 has a refractive index n23 of 1.504 and a physical film thickness. A uniform layer of 74 nm was formed.

  The fine concavo-convex structure 14 disposed on the most air side was formed by applying a sol-gel coating solution containing alumina by a spin coating method to form a gel film. By immersing it in warm water, a plate-like crystal containing alumina as a main component was precipitated, and a fine uneven structure on the outermost surface (air side) was formed.

  As shown in FIG. 2, the fine concavo-convex structure 14 thus formed has a refractive index that continuously changes from the glass substrate 11 side toward the air 301 with a gentle inclination.

  At this time, the refractive index of the fine concavo-convex structure 14 on the substrate 11 side is approximately 1.4 and continuously changes to the refractive index of air of 1.0. The average height h of the fine uneven structure 14 is 266 nm.

  FIG. 3 is an explanatory diagram of the spectral characteristics of the reflectance of the optical element 1 of the first embodiment. As shown in the spectral characteristics of FIG. 3, in a wide wavelength region from a wavelength of 400 nm to a wavelength of 1000 nm, when the incident angle of light is 0 degree, a high-performance antireflection effect of 0.2% or less is obtained. Furthermore, even at a light incident angle of 60 degrees, an antireflection effect having a good performance of 3% or less can be obtained.

  FIG. 4 is a schematic configuration diagram of Example 2 of an optical element having the antireflection structure of the present invention.

  In the optical element 2 shown in FIG. 4, an antireflection structure 202 is formed on a substrate 31 made of a transparent member.

  The antireflection structure (antireflection film) 202 includes one homogeneous layer 32 between the substrate 31 and the fine concavo-convex structure 33, and is composed of two layers as a whole.

  FIG. 5 is an explanatory diagram (schematic diagram) of the refractive index structure showing the refractive index n of the material in the film thickness direction da of each member constituting the optical element 2 of FIG.

  In FIG. 5, n41 corresponds to the refractive index of the substrate 31, n42 corresponds to the refractive index of the homogeneous layer 32, and n43 corresponds to the refractive index of the fine concavo-convex structure 33.

  The fine concavo-convex structure 33 has a concavo-convex structure in which the average pitch is equal to or less than the use wavelength region. The apparent refractive index (equivalent refractive index) of the fine concavo-convex structure 33 changes in the film thickness direction da as shown in FIG.

  Since the concavo-convex structure of the fine concavo-convex structure 33 is tapered from the homogeneous layer 32 side, the refractive index structure is such that the refractive index gradually decreases from the homogeneous layer 32 side toward the air 302 side. It becomes.

  In this embodiment, the wavelength used is a wide wavelength region from a wavelength of 400 nm to a wavelength of 1000 nm. A glass substrate having a d-line refractive index of 1.516 was used as the transparent member substrate 31. The antireflection film 202 on the substrate 31 has a two-layer structure. One layer from the substrate 31 side is a homogeneous layer 32, and the range of the refractive index n42 is configured within the range of the refractive index n43a on the substrate 11 side of the structure 33 and the refractive index n41 of the base material 11.

The homogeneous layer 32 was formed by applying a SiO ₂ —TiO ₂ coating solution by spin coating, followed by heating and drying to form a thin film layer. The homogeneous layer 32 has a refractive index of 1.465 and a physical film thickness of 79 nm.

  The fine concavo-convex structure 33 was formed by applying a sol-gel coating solution containing alumina onto the homogeneous layer 32 by a spin coating method to form a gel film. By immersing it in warm water, a plate-like crystal containing alumina as a main component was deposited to form a fine uneven structure on the outermost surface (outermost layer).

  The fine concavo-convex structure 33 formed in this way has a refractive index continuously changing with a gentle inclination from the glass substrate 31 side toward the air 302.

  At this time, the refractive index of the fine concavo-convex structure 33 on the substrate 31 side is approximately 1.4 and continuously changes to the refractive index of air 1.0, and the height d of the fine portion 33a of the structure 33 is 362 nm. It is.

  FIG. 6 is an explanatory diagram of the spectral characteristics of the reflectance of the optical element 2 of the second embodiment.

  From the spectral characteristics shown in FIG. 6, a high-performance antireflection effect of 0.2% or less can be obtained when the light incident angle is 0 degree in a wide wavelength range from 400 nm to 1000 nm. Furthermore, even at a light incident angle of 60 degrees, an antireflection effect having a good performance of 2.3% or less can be obtained.

  FIG. 7 is a schematic configuration diagram of Example 3 of an optical element having the antireflection structure of the present invention.

  As shown in FIG. 7, in the optical element 3, a fine concavo-convex structure 52 is directly formed as an antireflection film on a substrate 51 made of a transparent member. The fine concavo-convex structure 52 has a fine concavo-convex structure whose average pitch is equal to or less than the use wavelength. The fine concavo-convex structure 52 has a refractive index continuously changing with a gentle inclination in the film thickness direction da.

  FIG. 8 is an explanatory diagram (schematic diagram) of a refractive index structure showing the refractive index n of the material in the film thickness direction da of each member constituting the optical element 3 of FIG.

  In FIG. 8, n61 is the refractive index of the substrate 51. n62 corresponds to the refractive index of the fine relief structure 52.

  As shown in FIG. 8, the apparent refractive index n62 of the fine concavo-convex structure 52 changes in the film thickness direction da.

  Since the concavo-convex structure of the fine concavo-convex structure 52 has a tapered shape from the substrate 51 side made of a transparent member, the refractive index gradually decreases from the substrate 51 side toward the air 402 side in terms of refractive index structure. It becomes the composition.

  In this example, the wavelength used was a wide wavelength region from 400 nm to 1000 nm. As the substrate 51 made of a transparent member, a glass substrate having a d-line refractive index of 1.439 was used. The fine concavo-convex structure 52 was formed by applying a sol-gel coating solution containing alumina on the substrate 51 by a spin coating method to form a gel film.

  By immersing it in warm water, a plate-like crystal containing alumina as a main component was deposited to form a fine uneven structure on the outermost surface. The fine concavo-convex structure 52 formed in this way has a refractive index continuously changing with a gentle inclination from the glass substrate 51 side toward the air 402.

  At this time, the refractive index of the fine concavo-convex structure 52 on the substrate 51 side is approximately 1.4 and continuously changes to the refractive index of air of 1.0. The height d of the fine concavo-convex structure 52 is 493 nm.

  FIG. 9 is an explanatory diagram of the spectral characteristics of the reflectance of the optical element 3 of the third embodiment.

  As shown in FIG. 9, in a wide wavelength range from 400 nm to 1000 nm, when the light incident angle is 0 degree, a high-performance antireflection effect of 0.2% or less is obtained. Further, even when the light incident angle is 60 degrees, an antireflection effect having a good performance of 1% or less can be obtained.

  The optical element of Example 4 has an antireflection function in two wavelength regions of the first and second wavelength regions having different wavelength regions.

  The optical element has an antireflection function formed on at least one of the light incident / exit sides of the substrate.

  The antireflection structure is configured such that a fine concavo-convex structure having an average pitch equal to or shorter than the shortest wavelength in the two wavelength regions is the outermost layer.

  The wavelength on the long wavelength side in the first wavelength region is λa.

Let λb be the wavelength on the short wavelength side in the second wavelength region on the longer wavelength side than the first wavelength region. And the wavelength λc is changed to λc = (λa + λb) / 2
far. Let h be the average height of the fine relief structure. At this time, λa <λb (3)
0.44 <h / λc <0.56 (4)
Is satisfied.

  FIG. 10 is a spectral characteristic diagram of the antireflection structure according to the optical element of Example 4 of the present invention. The antireflection structure according to Example 4 has a configuration in which the fine uneven structure according to any of Examples 1 to 3 is formed on a glass substrate having a refractive index of 1.52. The height of the fine concavo-convex structure is 400 nm.

  In this embodiment, when used in two different use wavelength regions, a first wavelength region in the visible region (wavelength 400 nm to wavelength 700 nm) and a second wavelength region in the near infrared region (wavelength 900 nm to wavelength 1100 nm). It has a suitable antireflection function.

  The wavelength λa on the long wavelength side of the first wavelength region is 700 nm, and the wavelength λb on the short wavelength side of the second wavelength region, which is longer than the first wavelength region, is 900 nm.

  At this time, the wavelength λc related to the conditional expression (4) is 800 nm, and the reflection ripple is located near the wavelength of 800 nm as shown in FIG.

  When the height h of the fine concavo-convex structure is lowered to 350 nm or less exceeding the lower limit value of the conditional expression (4), a ripple position with high reflection characteristics is located in the first used wavelength band region. If the height h of the fine concavo-convex structure exceeds 450 nm beyond the upper limit value of conditional expression (4), the ripple position with high reflection characteristics is located in the second used wavelength band region, and good characteristics cannot be obtained. End up.

  In this embodiment, the height of the fine concavo-convex structure is 400 nm. A ripple position with high reflection characteristics is a wavelength that is not used between a wavelength of 800 nm and a short wavelength of the first wavelength region to be used (400 nm to 700 nm) and a long wavelength and a second wavelength region to be used (800 nm to 1100 nm). Arranged to be in the region. This makes it possible to obtain good antireflection characteristics within the wavelength used.

  Next, an example of an optical system having any one of the optical elements of Examples 1 to 4 will be described.

  The optical system of the present invention is used in optical devices such as video cameras, digital cameras, and TV cameras. The optical system of the present invention has the optical elements of the above-described embodiments.

  The effective diameter on the light incident side of the optical element closest to the object side is defined as Da. Let f be the focal length of the optical system (the focal length at the wide-angle end when the optical system is a zoom lens).

At this time, 3 ≦ Da / f (5)
Is satisfied.

When the optical system is a zoom lens having a zoom unit, the zoom ratio is Z. At this time,
15 ≦ Z (6)
Is satisfied.

  Next, each example of the optical system of the present invention will be described.

  FIG. 11 is an optical sectional view of an optical system according to Example 4 of the present invention. In FIG. 11, an optical system 702 is a so-called four-group zoom lens having a large aperture and a high zoom ratio (high zoom ratio) used in a TV camera system or the like. The four-group zoom lens 702 is as follows in order from the object side to the image side.

  A first group (front lens group) 71 that is a positive refractive power for focusing, a second group (variator group) 72 that is a negative refractive power for zooming, and an image plane that varies with zooming. A third group (compensator group) 73 having positive refractive power for correction is provided.

  Further, it has an aperture stop 78 and a fourth group (relay lens group) 74 having positive refractive power for image formation, and is composed of four lens groups as a whole. Reference numeral 79 denotes a glass block equivalent to the color separation optical system.

  Next, Numerical Example 4 of the zoom lens according to Example 4 will be described. In Numerical Example 4, i indicates the order of the surfaces from the object side, ri is the radius of curvature of each surface (unit is mm), and di is the thickness of the member between the i-th surface and the (i + 1) -th surface. Air spacing, ni and νi indicate the refractive index and Abbe number with respect to the d-line, respectively. BF is a back focus.

  The intervals d12, d21, and d33 in the numerical examples indicate the focal length and the change in the interval according to zooming.

  In this embodiment, the focal length of the wide end of the optical system 702 is 10 mm, the effective diameter of the first lens surface of the front lens 77 is 200 mm, and the distance 703 for zooming is 245.65 mm. .

  In the fourth group zoom lens 702, the variator group 72 and the compensator group 73 have an interval 703 corresponding to the amount of movement for zooming. The zoom ratio 66 is obtained by changing the distances d12, d21, and d33 to the numerical values in the numerical value example 4, respectively.

In a large-aperture optical system as in this embodiment or a zoom lens with a high zoom ratio, the change in the incident height of the off-axis light beam and its focal length tends to be relatively large. In an optical system that satisfies the conditional expression (5), that is, an optical system having a large aperture whose so-called front lens effective diameter exceeds three times the focal length at the wide-angle end of the entire lens system, the light beam reaching the screen center and the screen periphery In the optical system having a high zoom ratio (high zoom ratio) such that the zoom ratio exceeds 15 times, Z ≧ 15 of conditional expression (6) The light incident angle varies greatly between the off-axis ray at the end and the off-axis ray at the telephoto end.

  The antireflection film using the interference film changes the reflection characteristic due to the change in the incident angle, that is, the angle characteristic.

  As described above, the interference film has a high reflectance when the incident light angle is large, even if good characteristics are obtained when the light incident angle is 0 degree. That is, the spectral transmittance of light rays that reach the vicinity of the center of the screen is close to the theoretical value, but the spectral transmittance of light rays that reach the periphery of the screen greatly deviates from the theoretical value. In addition, the amount of deviation varies greatly depending on the focal length, making it difficult to obtain a desired spectral sensitivity.

  Therefore, in this embodiment, an antireflection structure having a fine concavo-convex structure having a wavelength equal to or smaller than the wavelength is formed on all surfaces of the lens base material constituting the optical system 702.

  FIG. 12 is a theoretical value of the spectral transmittance of the antireflection structure at this time. FIG. 12 shows that the spectral transmittance does not deteriorate significantly not only in the visible range of wavelength 400 to 700 nm but also in the vicinity of wavelength 1000 nm.

  For this reason, an optical system with a high zoom ratio as in the fourth embodiment may be used as an imaging system for the monitoring system. According to this, good image sensitivity can be obtained not only in the visible region but also in the infrared region.

  Here, in Example 5, an antireflection film having a fine concavo-convex structure of a wavelength or less is formed on all lens base materials, but the invention is not limited to this, and it is formed only on a certain lens base material. You may do it. In particular, an interference film may be formed according to the required spectral sensitivity.

[Numerical Example 4]
Unit mm

Surface data
Surface number r d nd νd Effective diameter object surface ∞ ∞
1 582.07650 19.311540 1.496999 81.5 200.000
2 -699.74045 1.000000 199.595
3 -699.74045 5.000000 1.799516 42.2 199.263
4 353.86996 2.008270 198.029
5 396.57864 24.119760 1.433870 95.1 198.213
6 -616.99056 18.747970 198.607
7 280.42746 22.678280 1.433870 95.1 199.530
8 -3987.32808 0.250000 198.871
9 245.22782 20.610710 1.433870 95.1 191.906
10 2602.16223 0.250000 190.552
11 179.56192 11.346810 1.496999 81.5 175.977
12 279.31416 Variable 174.152
13 268.94376 2.000000 1.816000 46.6 50.835
14 58.66295 6.777960 45.433
15 -167.96170 1.900000 1.754998 52.3 44.613
16 124.30386 5.427620 43.528
17 -87.28290 1.900000 1.816000 46.6 43.623
18 73.00824 10.047180 1.922864 21.3 46.162
19 -79.58126 1.088500 46.834
20 -75.79780 2.200000 1.882997 40.8 46.739
21 295.86708 Variable 48.444
22 300.54608 10.258750 1.592400 68.3 69.574
23 -129.39003 0.200000 70.568
24 213.99531 10.658420 1.487490 70.2 71.719
25 -157.02634 3.036230 71.659
26 -99.89310 2.500000 1.720467 34.7 71.512
27 -126.73511 0.200000 72.185
28 118.08827 2.500000 1.846658 23.9 70.770
29 62.49306 0.124430 68.207
30 61.01371 14.102380 1.496999 81.5 68.444
31 -6767.69006 0.200000 67.870
32 127.09849 6.949960 1.487490 70.2 66.681
33 -9031.17452 Variable 65.838
34 (Aperture) 0.00000 4.500000 30.823
35 76.20626 1.800000 1.816000 46.6 29.191
36 57.32932 0.200000 28.697
37 37.53246 5.701980 1.808095 22.8 29.021
38 143.61187 4.970950 28.188
39 -56.40817 2.000000 1.882997 40.8 27.482
40 91.61848 30.039530 1.805181 25.4 27.933
41 -451.77947 5.501890 31.132
42 -778.12061 6.392490 1.620411 60.3 31.951
43 -82.19234 0.200000 32.482
44 -385.98744 2.100000 1.834000 37.2 32.619
45 52.98048 8.308930 1.620411 60.3 33.072
46 -48.78398 0.200000 33.586
47 228.66065 8.777300 1.487490 70.2 33.041
48 -38.13259 2.100000 1.834000 37.2 32.381
49 -104.87405 0.200000 32.662
50 82.71105 6.216970 1.620411 60.3 32.206
51 -1012.77697 2.000000 31.107
52 0.00000 55.500000 1.516330 64.2 60.000
53 0.00000 9.599750 60.000
Image plane 0.00000

Various data
Zoom ratio 66.0

Wide angle Medium telephoto focal length 10.0000 66.6827 660.0000
F number 1.8 1.8 3.3
Angle of view 57.6216 9.4302 0.9549
Image height 5.5 5.5 5.5
Total lens length 547.86 547.86 547.86
BF 48.15 48.15 48.15
Exit pupil position 964.4156 964.4156 964.4156
d12 2.1022 117.1022 159.6507
d21 245.6526 107.5670 3.2865
d33 3.5000 26.5856 88.3176

  FIG. 13 is an optical sectional view of an optical system according to Example 5 of the present invention. In FIG. 13, an optical system 802 is a so-called four-group zoom lens having a large aperture and a high zoom ratio (high zoom ratio) used in a TV camera system or the like.

  The four-group zoom lens 802 is as follows in order from the object side to the image side.

  A first group (front lens group) 81 that is a positive refractive power for focusing, a second group (variator group) 82 that is a negative refractive power for zooming, and an image plane that varies with zooming. A third group (compensator group) 83 having negative refractive power for correction is included. Further, it has an aperture stop 88 and a fourth group (relay lens group) 74 having positive refractive power for image formation, and is composed of four lens groups as a whole. 89 is a glass block equivalent to the color separation optical system.

  Numerical Example 5 of Example 5 is shown in the same manner as Numerical Example 4 of Example 4. The intervals d16, d26, and d29 in Numerical Example 5 indicate the focal length and the change in the interval according to zooming.

  In this embodiment, the focal length of the wide end of the optical system 802 is 30 mm, the effective diameter of the first lens surface of the front lens 87 is 90 mm, and the interval of 803 for zooming is 61.41 mm. Yes.

  In the fourth group zoom lens 802, the variator group 82 and the compensator group 83 have an interval 703 corresponding to the amount of movement for zooming. The zoom ratio 15 is obtained by changing the distances d16, d26, and d29 to the numerical values in the numerical value example 5, respectively.

  In the large-aperture optical system as in this embodiment or the zoom lens with a high zoom ratio, the change in the incident height of the off-axis light beam and its focal length tends to be relatively large.

  In an optical system that satisfies the conditional expression (5), that is, an optical system having a large aperture whose so-called front lens effective diameter exceeds three times the focal length at the wide-angle end of the entire lens system, the light beam reaching the screen center and the screen periphery The angle at which the light beam reaching the lens enters the lens system changes greatly.

  In an optical system having a high zoom ratio (high zoom ratio) such that Z ≧ 15 in conditional expression (6), that is, the zoom ratio exceeds 15, the off-axis light beam at the wide-angle end and the off-axis light beam at the telephoto end. The incident angle of light changes greatly.

  The antireflection film using the interference film changes the reflection characteristic due to the change in the incident angle, that is, the angle characteristic.

  As described above, the interference film has a high reflectance when the incident light angle is large, even if good characteristics are obtained when the light incident angle is 0 degree.

  That is, the spectral transmittance of light rays that reach the vicinity of the center of the screen is close to the theoretical value, but the spectral transmittance of light rays that reach the periphery of the screen greatly deviates from the theoretical value. In addition, the amount of deviation varies greatly depending on the focal length, making it difficult to obtain a desired spectral sensitivity.

  Therefore, in this embodiment, an antireflection structure including a fine concavo-convex structure having an average pitch equal to or less than the wavelength is formed on all surfaces of the lens base material constituting the optical system 802.

  FIG. 14 is a theoretical value of the spectral transmittance of the antireflection structure at this time. FIG. 14 shows that the spectral transmittance does not deteriorate significantly not only in the visible range of wavelength 400 to 700 nm but also in the vicinity of wavelength 1000 nm.

  For this reason, an optical system with a high zoom ratio as in the fifth embodiment may be used as the photographing system of the monitoring system. This makes it possible to obtain good image sensitivity not only in the visible region but also in the infrared region.

  Here, in Example 6, the antireflection film having the fine portions of the fine irregularities of the wavelength or less is formed on all the lens base materials, but the invention is not limited to this, and only on a certain lens substrate. It may be formed. In particular, an interference film may be formed according to the required spectral sensitivity.

[Numerical Example 5]

Unit mm

Surface data
Surface number r d nd νd Effective diameter object surface ∞ ∞
1 124.08843 8.07277 1.48749 70.23 90
2 429.75611 0.15 89.506
3 120.49748 4 1.720467 34.7 87.845
4 85.11712 0 84.506
5 85.11712 12.88861 1.43875 94.99 84.506
6 -7623.63418 9.99782 83.951
7 114.60868 6.92112 1.43387 95.1 75.19
8 483.19677 0.42209 74.029
9 128.41882 7.8054 1.496999 81.54 70.892
10 -935.21739 0 69.34
11 -935.21739 2.5 1.720467 34.7 69.34
12 284.64103 7.7722 66.298
13 -7557.21355 4.81999 1.808095 22.76 61.137
14 -232.091 0 59.789
15 -232.091 2.2 1.720467 34.7 59.789
16 185.4863 Variable 56.646
17 24.28535 1 1.882997 40.76 21.482
18 16.73433 3.18699 19.822
19 198.22097 3.64678 1.808095 22.76 19.721
20 -26.57301 0 19.167
21 -26.57301 0.9 1.882997 40.76 19.167
22 40.79971 0.16833 18.068
23 21.11233 6.12039 1.808095 22.76 17.946
24 25.63884 5.7005 15.599
25 -25.62263 0.9 1.882997 40.76 14.632
26 -64.46006 Variable 14.838
27 -43.5266 0.9 1.717004 47.92 21.886
28 78.00486 2.35438 1.84666 23.78 23.021
29 -9430.13591 Variable Variable 23.484
30 (Aperture) 0 0.73867 28.839
31 79.10065 6.22448 1.603112 60.64 30.129
32 -48.91201 0.15 30.591
33 88.16009 3.4451 1.620411 60.29 30.295
34 -1822.03777 0.15 29.922
35 65.66024 6.20192 1.48749 70.23 29.351
36 -51.88183 1 1.800999 34.97 28.445
37 -150.4514 9.17259 28.016
38 -41.21179 1 1.755199 27.51 23.989
39 -290.75654 38 23.983
40 180.86498 3.81221 1.48749 70.23 21.641
41 -35.73546 3.00612 21.699
42 47.35527 6.01246 1.496999 81.54 20.126
43 -27.94143 0.8 1.882997 40.76 19.065
44 -859.13139 2.50345 18.825
45 -76.54563 0.8 1.834807 42.72 18.41
46 34.01174 2.04025 1.48749 70.23 18.407
47 57.73819 1.5 18.61
48 42.00885 4.52013 1.698947 30.13 19.296
49 -28.28528 1 1.806098 40.92 19.316
50 -54.44837 5 19.415
51 0.00000 33 1.60859 46.44 40
52 0.00000 13.2 1.5168 64.17 40
53 0.00000 7.5093 40
Image plane 0.00000

Various data
Zoom ratio 15.0

Wide angle Medium Telephoto focal length 30.000 119.400 450.000
F number 2.8 2.8 5
Angle of View 20.7777 5.2748 1.4005
Image height 5.5 5.5 5.5
Total lens length 256.13 256.13 256.13
BF 41.68 41.68 41.68
Exit pupil position -523.739 -523.739 -523.739
d16 1.1452 41.8900 59.4426
d26 61.4124 10.8569 10.7124
d29 9.0675 18.8781 1.4700

  The optical system of the present invention can be used as an optical system of optical equipment such as a video camera, a digital camera, a projector, and a telescope.

  Next, a comparative example for the antireflection structure of the present invention and its spectral characteristics will be described.

[Comparative Example 1]
In Comparative Example 1, in order to make a comparison with the antireflection characteristics of Example 1, a thin layer of an inorganic coating is formed on a glass substrate having a refractive index of d-line of 1.805 as a transparent member substrate. A multilayer antireflection film. This multilayer antireflection film was formed by vapor deposition. The multilayer antireflection film has a good antireflection performance in a wide wavelength region. Table 1 shows the structure of the obtained multilayer antireflection film.

  In Table 1, the layer number is a number counted from the glass substrate. FIG. 15 is an explanatory diagram of the spectral characteristics of Comparative Example 1. With the configuration of Table 1, as shown in FIG. 15, in a wide wavelength region from wavelength 400 nm to wavelength 1000 nm, the reflectance is as high as 3.0% or less even when the light incident angle is 0 degree.

  Further, when the light incident angle is 60 degrees, it is about 9.0%. Compared with this, the reflectance of Example 1 of the present invention is low overall, and the antireflection performance is good.

[Comparative Example 2]
Comparative Example 2 is a multilayer reflection in which an inorganic coating is laminated on a glass substrate having a refractive index of d2 of 1.52 which is a substrate of a transparent member for comparison with the antireflection characteristics of Example 2. It is a prevention film. This antireflection film was formed by vapor deposition. The multilayer antireflection film has a good antireflection performance in a wide wavelength region. Table 2 shows the structure of the obtained multilayer antireflection film.

  FIG. 16 is an explanatory diagram of the spectral characteristics of Comparative Example 2.

  With the configuration in Table 2, as shown in FIG. 16, in a wide wavelength region from 400 nm to 1000 nm, even when the light incident angle is 0 degree, the reflectance is as high as 5.0% or less. Further, when the light incident angle is 60 degrees, it is about 10%. Compared to this, Example 2 of the present invention has good antireflection performance.

Schematic structure of antireflection film according to Example 1 of optical element of the present invention Refractive index structure of schematic configuration of antireflection film according to Example 1 of optical element of the present invention FIG. 5 is a characteristic diagram showing an example of an antireflection film according to Example 1 of the optical element of the present invention. Schematic structure of antireflection film according to Example 2 of optical element of the present invention Refractive index structure of schematic configuration of antireflection film according to Example 2 of optical element of the present invention The characteristic view which shows an example of the anti-reflective film which concerns on Example 2 of the optical element of this invention Schematic configuration of antireflection film according to Example 3 of optical element of the present invention Refractive index structure of schematic configuration of antireflection film according to Example 3 of optical element of the present invention The characteristic view which shows an example of the anti-reflective film which concerns on Example 3 of the optical element of this invention FIG. 6 is a characteristic diagram of an optical system according to Example 4 of the present invention. Optical sectional view of an optical system according to Example 4 of the present invention FIG. 6 is a characteristic diagram of an optical system according to Example 4 of the present invention. Optical sectional view of an optical system according to Example 5 of the present invention. Optical system characteristic diagram according to Example 5 of the present invention The characteristic view which shows the comparative example of the antireflection film which concerns on Example 1 of the optical element of this invention The characteristic view which shows the comparative example of the anti-reflective film which concerns on Example 2 of the optical element of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Transparent member 12 Homogeneous layer 13 Homogeneous layer 14 Fine uneven structure 21 Transparent member 31 Transparent member 32 Homogeneous layer 33 Fine uneven structure 51 Transparent member 52 Antireflection structure 71 Lens group 72 Lens group 73 Lens group 74 Lens group 77 Lens 78 Diaphragm 79 Dummy glass 81 Lens group 82 Lens group 83 Lens group 84 Lens group 87 Lens 88 Diaphragm 89 Glass block 201 Antireflection structure 301 Incident medium (air)
202 Antireflection structure 302 Incident medium (air)
402 Incident medium (air)
702 Optical system 703 Lens spacing 802 Optical system 803 Lens spacing

Claims (10)

An optical element having an antireflection function in a used wavelength region including a visible region,
The use wavelength region is a range in which the longest wavelength λH in the use wavelength region is twice or more than the shortest wavelength λL in the use wavelength region,
The optical element includes an antireflection structure configured such that a fine concavo-convex structure having an average pitch of the shortest wavelength λL or less is an outermost layer on at least one of the light incident / exit surfaces of the substrate,
P is the average pitch of the fine concavo-convex structure, n1 is the refractive index of the material forming the fine concavo-convex structure, h is the average height of the fine concavo-convex structure, and θ is the light beam incident on the fine concavo-convex structure from the air side. When the incident angle is
P <λL / (n1 + Sinθ)
0.2λL ≦ h ≦ 0.8λH
An optical element that satisfies the following conditions:   2. The antireflection structure has a configuration in which a wavelength region having a reflectance of 3% or less at an incident angle of 60 degrees is present in a half or more in the use wavelength region. An optical element according to 1.   The optical element according to claim 1, wherein the fine concavo-convex structure has a shape such that an equivalent refractive index continuously decreases from the substrate side.   The optical element according to claim 1, wherein the fine concavo-convex structure includes aluminum or aluminum oxide.   The fine concavo-convex structure is formed directly on one surface of the substrate, or between the fine concavo-convex structure and the substrate, one or more homogeneous layers different in material from the fine concavo-convex structure are provided. The optical element according to claim 1, wherein the optical element is formed.   The optical system according to claim 5, wherein at least one of the homogeneous layers includes one of zirconia, silica, titania, and zinc oxide. An optical element having an antireflection function in two wavelength regions of the first and second wavelength regions having different wavelength regions,
The optical element includes an antireflection structure configured such that a fine concavo-convex structure having an average pitch equal to or shorter than the shortest wavelength in the two wavelength regions is an outermost layer on at least one surface on the light incident / exit side of the substrate. ,
The wavelength on the long wavelength side in the first wavelength region is λa,
The wavelength on the short wavelength side in the second wavelength region longer than the first wavelength region is λb,
λc = (λa + λb) / 2
And when the height of the fine part is h, λa <λb
0.44 <h / λc <0.56
An optical element that satisfies the following conditions: An optical system in which the optical element according to any one of claims 1 to 7 is arranged, wherein Da is an effective diameter on the light incident side of the optical element closest to the object side, and a focal length of the optical system (optical system) When the zoom lens is a zoom lens, the focal length at the wide-angle end is set to f.
An optical system characterized by satisfying the following conditions. The optical system has a zoom unit, and when the zoom ratio of the optical system is Z,
15 ≦ Z
The optical system according to claim 8, wherein the following condition is satisfied.   An optical apparatus comprising the optical system according to claim 8 or 9.