JP5449459B2 - Optical system, interchangeable lens, and imaging apparatus having the same - Google Patents

Description

  The present invention relates to an optical system and an image pickup apparatus having the optical system, and is suitable for a silver salt film camera, a digital still camera, a video camera, and the like.

  Optical elements such as lenses and filters made of resins such as acrylic resins and polycarbonate resins are often used in optical systems used in recent imaging devices such as digital cameras and video cameras.

  An optical element made of a resin has features such that it can be easily manufactured by molding and has a high degree of freedom in shape. Adhesion is facilitated by using properties such as thermoplasticity and ultraviolet curing. In addition, there are features such as easy transfer of the fine structure. Therefore, an optical element made of a resin is used in an optical system as a plastic mold lens, an adhesive on a bonding optical surface, a diffractive optical element, a focus plate, a microlens for an image sensor, and a color filter.

  On the other hand, the optical surfaces of the optical elements constituting the optical system are often provided with an antireflection structure for preventing reflection.

  It is technically difficult to deposit an antireflection film made of a dielectric on the optical surface of an optical element made of resin. Therefore, in recent years, an antireflection effect can be obtained by providing a fine irregular periodic structure (irregularities) shorter than the visible light wavelength on the optical surface of an optical element made of resin instead of the dielectric antireflection multilayer film. (Patent Documents 1 and 2).

  Patent Document 1 discloses an optical element in which a plurality of fine irregularities having a fine periodic structure are formed on an optical surface to prevent reflection.

  On the other hand, Patent Document 2 discloses an antireflection element that performs antireflection by arranging a plurality of fine convex portions or concave portions in a staggered manner or arranging the openings in a hexagonal shape in plan view.

JP 2005-157119 A JP 2006-10831 A

  In general, since a resin is made of a polymer having a covalent bond of carbon atoms, it undergoes physical and chemical changes when a large amount of ultraviolet light is incident. This is because the bonds in the polymer are broken by the energy of the irradiated ultraviolet light. Further, the binding energy of the resin is determined for each bond, and the wavelength of ultraviolet light corresponding to the bond energy is determined.

  For example, the binding energy of the C—C bond is 346 kJ / mol, and the wavelength of the ultraviolet light corresponding to this is λ = 347.2 nm.

  Similarly, the bond energy of C = C bond is 340 kJ / mol and the wavelength is λ = 353.3 nm. The binding energy of the C—O bond is 386 kJ / mol and the wavelength is λ = 311.2 nm. The bond energy of C═O bond is 374 kJ / mol and the wavelength is λ = 321.2 nm.

  When the resin is irradiated with light having a shorter wavelength, each bond may be broken. The influence of these bonds by the ultraviolet light having a wavelength of 300 nm to 400 nm is a cause of deterioration of optical performance when an optical element made of resin is used.

  S (sulfur) element is used to increase the refractive index of the resin. The bond energy of this C—S bond is as low as 269 kJ / mol. Therefore, the C—S bond is easily broken, and the resin may be yellowed by the influence of the S element.

  Generally, a glass material used for a lens has a high absorption rate of ultraviolet light. Further, a general multilayer film for visible light has a low transmittance of ultraviolet light. Therefore, the transmittance of ultraviolet light is low in a general lens system (optical system).

  For this reason, the irradiation light quantity of the ultraviolet light to the optical member which consists of resin arrange | positioned at the image side of a lens system becomes comparatively low. For this reason, there is almost no influence by ultraviolet light by entering the optical element made of resin.

  However, when ultraviolet light is concentrated and incident on an optical element made of resin, the influence of ultraviolet light cannot be ignored.

  On the other hand, the antireflection multilayer film used in the lens system has high antireflection characteristics with respect to visible light. However, it acts as an increased reflection film for ultraviolet light.

  FIG. 13 is an explanatory diagram of spectral characteristics of a general antireflection film. As shown in FIG. 13, when a general antireflection film is optimized and designed to suppress the reflectance over the entire visible light range, the reflectance increases in the wavelength region of ultraviolet light and infrared light. In the anti-reflection multilayer film, the low-refractive-index dielectric L layer and the high-refractive-index dielectric H layer are laminated in such a thickness that the optical path length is about ¼ wavelength, and the interference is canceled by interference. It is configured to meet.

  However, in the case of ultraviolet light or infrared light, reflections are strengthened by interference.

  FIG. 7 and FIG. 8 are cross-sectional views of main parts when an imaging apparatus as a reference example of the imaging apparatus of the present invention to be described later and a general optical system used therefor are schematically shown.

  An optical system 1 is composed of an interchangeable lens (photographing system). Reference numeral 2 denotes a single-lens reflex camera, to which the optical system 1 is detachably attached. i indicates a lens number counted from the object side (light incident side), and Gi is an i-th lens constituting the optical system 1.

  Reference numerals 3 and 4 denote optical surfaces on the object side and the image side of the first lens G1.

  Reference numerals 5 and 6 denote object-side and image-side optical surfaces of the second lens G2.

  Reference numerals 7 and 8 denote optical surfaces on the object side and the image side of the third lens G3.

  The fourth lens G4 is composed of a composite aspherical lens, and an aspherical layer (optical element) 9a formed by molding a plastic resin (resin) is formed on the optical surface 9 on the object side. The lens element 9b made of the optical surfaces 9 and 10 is made of a normal glass glass material. The optical surfaces 9 and 10 are spherical surfaces.

  Reference numeral 11 denotes an image sensor arranged on the optical axis of the optical system 1 in the single-lens reflex camera 2. Reference numeral 12 denotes a light source. Reference numeral 13 denotes a viewfinder.

  In FIG. 7, ultraviolet light from a strong point light source 12 such as the sun passes through the optical surfaces 3 and 4 of the first lens G1, and passes through the optical surfaces 5 and 6 of the second lens G2. Then, the light is reflected by the antireflection multilayer film on the optical surface 7 of the third lens G3 and the optical surface 6 of the second lens G2, and as a result, a surface reflection ghost is formed on the optical element 9a made of resin. is there.

  Further, as shown in FIG. 8, when a part of the lens element of the optical system 1 moves by zooming or focusing and is in a specific position, the ultraviolet light from the light source 12 outside the field of view becomes a ghost and becomes the imaging element 11. In some cases, an image is formed.

  In Patent Document 1, a structure in which fine uneven portions are repeatedly arranged at a regular periodic pitch is used. For this reason, even if the reflected light is sufficiently small with respect to the visible light, a lot of diffracted light is generated with respect to the ultraviolet light.

  For example, as shown in FIG. 9, even if the light source 12 is outside the field of view, the incident light is greatly diffracted by the fine uneven periodic structure formed on the optical surface 6, and is imaged on the image sensor 11 by the subsequent optical system. May be.

  In the example of Patent Document 1, the fine uneven periodic structure is two-dimensional and squarely arranged at the lens interface. Therefore, the diffracted light tends to concentrate in the grating direction.

  As in the case of Patent Document 1, the antireflection element of Patent Document 2 generates diffracted light with a regular periodic pitch. Unlike the square arrangement, the two-dimensional spread of diffracted light is oblique or six directions every 60 degrees, but the number of separation is not changed. For this reason, the effect of dispersing the energy of the light beam is not improved. Accordingly, in this case as well, ghosts may be generated due to strong diffraction in a specific direction.

  Even if the amount of ultraviolet light irradiated to the entire optical element made of resin is small, the optical element is partially degraded when the ultraviolet light is condensed.

  When an optical element made of resin is used in the optical path, the present invention reduces the concentration of ultraviolet light on this optical element, prevents deterioration of the optical characteristics of the optical element made of resin, and provides good optical performance. It is an object of the present invention to provide an optical system and an imaging apparatus having the same.

The optical system of the present invention is an optical system including an optical element made of resin in an optical path, and has at least two optical surfaces on the light incident side of the optical element made of resin with a wavelength of visible light or less. Are formed with no repeating structure, or with a random arrangement interval,
The effective refractive index of the concavo-convex portion decreases as the distance from the optical surface on which the concavo-convex portion is formed,
The concavo-convex part has a scattering rate of Sa with a wavelength of 360 nm,
Scattering rate of Sb with respect to a wavelength of 550 nm,
Rb reflectivity for a wavelength of 550 nm,
When Sa> 1%
Sb <1%
Rb <5%
Satisfies the conditional expression
When A2 is the effective diameter of the optical surface closer to the optical element made of the resin among the two optical surfaces, and D12 is the distance between the two optical surfaces,
0 <A2 / D12 <2.0
It is characterized by satisfying the following conditional expression.

  According to the present invention, when an optical element made of a resin is used in the optical path, it is possible to reduce the concentration of ultraviolet light on the optical element and to prevent deterioration of the optical characteristics of the optical element made of resin. An optical system capable of obtaining optical performance and an image pickup apparatus having the optical system are obtained.

FIG. 1 is a configuration diagram of the main part of an optical system according to Example 1 of the present invention. FIG. 2 is a configuration diagram of the main part of another embodiment of the optical system according to the first embodiment of the present invention. FIG. 3 is a main part configuration diagram of an optical system according to a second embodiment of the present invention. FIG. 6 is a main part configuration diagram of another implementation state of the optical system according to the second embodiment of the present invention. FIG. 5 is a main part configuration diagram of an optical system according to a third embodiment of the present invention. Schematic diagram showing the refractive index in the cross-sectional direction of a fine uneven structure below the wavelength Schematic diagram showing ghost in the optical system of the conventional example Schematic diagram showing ghost in the optical system of the conventional example Schematic diagram showing ghost in the optical system of the conventional example SEM photograph from the interface of fine uneven structure below the wavelength SEM photograph of fine uneven structure below wavelength from the cross-sectional direction SEM photograph from the interface of the uneven structure of fine structure below the wavelength Graph showing the spectral reflectance characteristics of a reflective film made of a dielectric multilayer film Graph showing spectral reflectance characteristics of fine uneven structure below wavelength Graph showing spectral scattering rate characteristics of fine uneven structure below wavelength Graph showing spectral reflectance characteristics of fine uneven structure below wavelength Graph showing spectral scattering rate characteristics of fine uneven structure below wavelength Schematic diagram showing the refractive index in the cross-sectional direction of a fine uneven structure below the wavelength Schematic diagram for explaining conditional expression (4)

  The optical system of the present invention includes at least one optical element made of resin in the optical path. The resin is a material having a C—S bond between a carbon atom and a sulfur atom. The optical element made of resin is, for example, at least one of a plastic mold lens, an adhesive for a cemented lens, a color filter, and a polarizing plate.

  On at least one of the optical surfaces on the light incident side (object side) of the optical element made of resin in the optical path, a plurality of concavo-convex portions (concave / convex structures) having a size equal to or smaller than the wavelength of visible light have a repetitive structure. It is formed with no or a random arrangement interval.

  Here, the concavo-convex part scatters ultraviolet light and has an antireflection effect on visible light.

Specifically, the operation of the uneven portion is as follows.
Sa is a scattering rate with respect to a wavelength λa = 360 nm.
Let Sb be the scattering rate for the wavelength λb = 550 nm.
Let Rb be the reflectance for wavelength λb = 550 nm.

At this time, Sa> 1% (1)
Sb <1% (2)
Rb <5% (3)
The following conditional expression is satisfied.

  Here, the scattering rate S refers to the ratio of the intensity of all light beams that spreads in directions other than the incident direction with respect to the intensity of the incident light beam when the incident light beam is irradiated onto the uneven portion.

  The reflectance R is the ratio of the intensity of the reflected light beam to the incident light beam incident on the uneven portion.

  Conditional expression (1) indicates the lower limit of the degree of ultraviolet light scattering. If the scattering rate Sa in light with a wavelength of 360 nm is smaller than the conditional expression (1), it becomes difficult to effectively prevent ghosts based on ultraviolet light.

  Conditional expressions (2) and (3) indicate transmission performance for visible light having a wavelength of 550 nm. If the upper limit of conditional expression (2) is exceeded and the scattering rate Sb increases, the effect of visible light scattering on the image increases, which is not good.

  If the reflectance Rb increases beyond the upper limit of the conditional expression (3), that is, if the reflectance at the concavo-convex portion increases, it becomes difficult to effectively reduce ghost against visible light.

  The concavo-convex portion formed on the optical surface of this embodiment reduces the generation of ghosts due to surface reflection of ultraviolet light while ensuring high transmittance for visible light.

  In particular, for light from a strong point light source such as sunlight, regardless of the incident angle of the light beam and the zooming or focus state of the optical member, the occurrence of ghosts due to surface reflection is reduced and the light beam is prevented from being collected. I can do it. As a result, it is possible to minimize the deterioration of the optical element made of resin in the optical system.

  Embodiments of the present invention will be described below with reference to the drawings.

[Example 1]
FIG. 1 is a schematic view of the essential part schematically showing the configuration of Embodiment 1 of the optical system of the present invention.

  FIG. 2 shows a modification of a part of the first embodiment shown in FIG. FIG. 2 corresponds to a case where some optical members (lenses) are moved in the optical axis direction for focusing and zooming in the optical system 1 of FIG.

  In the figure, reference numeral 1 denotes an optical system, which includes an interchangeable lens (photographing system). Reference numeral 2 denotes a single-lens reflex camera (camera body) to which the optical system 1 is detachably attached.

  i indicates a lens number counted from the object side (light incident side), and Gi is an i-th lens constituting the optical system 1.

  In the embodiment of FIG. 1, the optical system 1 is composed of four lenses, the first lens G1 to the fourth lens G4. However, the number of lenses of the optical system 1 is not limited to four, and any number is possible. good.

  Reference numerals 3 and 4 denote optical surfaces on the object side and the image side of the first lens G1. Reference numerals 5 and 6 denote object-side and image-side optical surfaces of the second lens G2. Reference numerals 7 and 8 denote optical surfaces on the object side and the image side of the third lens G3.

  The fourth lens G4 is composed of a composite aspherical lens, and an aspherical layer (optical element) 9a formed by molding a plastic resin (resin) is formed on the optical surface 9 on the object side.

  The object-side surface of the optical element 9a has an aspheric shape. The lens element 9b including the optical surfaces 9 and 10 is made of a normal glass glass material. The optical surfaces 9 and 10 are spherical. Reference numeral 11 denotes an image sensor that receives an image disposed on the optical axis of the optical system 1 in the single-lens reflex camera 2. Reference numeral 12 denotes a light source. Reference numeral 13 denotes a viewfinder.

  In Example 1, the two optical surfaces 6 and 8 constituting the optical system 1 are provided with concave and convex portions having a fine structure having a wavelength of visible light (wavelength 400 nm to 700 nm) or less.

  In this embodiment, the optical surface on which the concavo-convex portion is formed is located on the image side from the second optical surface as counted from the light incident side. An antireflection film made of a thin film is formed on the first optical surface.

  In FIG. 1, the light beam from the light source 12 is transmitted and refracted through the optical surfaces 3, 4, and 5 and reaches the optical surface 6. The optical surface 6 has a concavo-convex portion (fine concavo-convex structure).

  FIG. 11 is a SEM (scanning electron microscope) photograph of a cross section of a fine concavo-convex structure. FIG. 12 is an SEM photograph of a fine uneven structure observed from above the surface. The uneven portion of this fine structure is a petal-like crystal deposited, and the vicinity of the substrate interface is the densest, and becomes sparse as the distance from the interface increases.

  Since the uneven portion of this fine structure is sufficiently small with respect to visible light, it can be considered as a thin film having an equivalent refractive index (effective refractive index). FIG. 6 is an explanatory diagram schematically showing the effective refractive index of the cross section of FIG.

  In FIG. 6, the horizontal axis is the effective refractive index Ns. The vertical axis represents the distance D from the optical surface. Since the medium in the vicinity of the interface Da with the optical surface 6 is dense, the effective refractive index Ns is also high.

On the other hand, the effective refractive index Ns decreases as the distance from the interface increases, and the effective refractive index 1 is almost equal to that of air at the upper end of the structure. That is, the effective refractive index of the concavo-convex portion is lowered as the distance from the optical surface on which the concavo-convex portion is formed is decreased. For this reason, visible light (wavelength 400 nm to 700 nm) has a good antireflection structure as shown in the graph of spectral reflectance shown in FIG.

  On the other hand, with respect to ultraviolet light (wavelength to 400 nm), the scattering rate increases as shown in the graph of the spectral scattering rate shown in FIG. Further, the scattered light direction at this time is not concentrated in a specific direction because the pitch of the concavo-convex portions is irregular.

  Therefore, the ultraviolet light from the light source 12 is transmitted through the optical surfaces 3, 4, 5, then scattered by the optical surface 6, and diffused in all directions (within a solid angle of 4π and in the entire space). Most of the diffused light is absorbed by the wall in the lens barrel.

  Some rays pass through the optical surface 7 on the image side from the optical surface 6 and reach the optical surface 8. Since the optical surface 8 is also provided with the concave and convex portions having the fine structure shown in FIGS. 11 and 12, scattering occurs here.

  For this reason, in the optical system of FIG. 1, only a small amount of ultraviolet scattered light is incident on the aspherical layer 9a made of resin disposed on the optical surface 9, and the ultraviolet light rays are collected. Absent.

  Similarly, in the optical system of FIG. 2, the scattered light of the ultraviolet light is only slightly incident on the image sensor 11 and the ultraviolet light is not collected on the surface of the image sensor 11.

  In Example 1, the scattered lights Sa and Sb and the reflectance Rb due to the uneven portions of the fine structure arranged on the optical surfaces 6 and 8 are as shown in the graphs of FIGS.

That is,
Sa = 1.5%
Sb = 0.1%
Rb = 0.4%
It is. This satisfies the conditional expressions (1), (2), and (3) described above.

  In the present embodiment, the concavo-convex portions are formed on at least two optical surfaces 6 and 8 among the optical surfaces on the light incident side (light incident side, object side) of the optical element 9a made of resin.

  In this embodiment, A2 is the effective diameter of the optical surface (optical surface 8) closer to the optical element 9a made of resin, out of the two optical surfaces.

Let D12 be the distance between the two optical surfaces 6 and 8 in the optical axis direction.
At this time,
0 <A2 / D12 <2.0 (4)
The following conditional expression is satisfied.

  FIG. 19 is a schematic diagram for explaining the technical contents of conditional expression (4).

  Conditional expression (4) defines the ratio between the distance between two optical surfaces that scatter ultraviolet light and the effective diameter of the optical surface on the image side of the two optical surfaces. In particular, the ratio of light rays reaching the optical surface 8 serving as the second scattering surface out of the ultraviolet light scattered by the optical surface 6 serving as the first scattering surface is limited.

  Assuming that light rays incident parallel to the optical axis are completely scattered by the first optical surface 6, it is considered that they are uniformly scattered in the direction of a hemisphere centered on the first optical surface 6. The ratio of light rays reaching the second optical surface 8 is indicated by the ratio of the solid angle of the second optical surface 8 viewed from the first optical surface 6 to the hemisphere.

  In Example 1 of FIG. 1, the value of conditional expression (4) is A2 / D12 = about 1 / 1.5, which satisfies conditional expression (4). Also in FIG. 2, A2 / D12 = about 1, which satisfies the conditional expression (4).

[Example 2]
FIG. 3 is a schematic view of the essential part schematically showing the configuration of Embodiment 2 of the optical system according to Embodiment 2 of the present invention.

  FIG. 4 shows a modification of a part of the second embodiment shown in FIG. 3 and 4, the same members as those in FIG.

  In Example 2, the concave and convex portions are formed on at least three optical surfaces among the optical surfaces on the light incident side of the optical element 9a made of resin.

  In FIG. 3, as in FIG. 1, 1 is an interchangeable lens. Reference numeral 2 denotes a single-lens reflex camera. In the interchangeable lens 1, 3 and 4 are optical surfaces of the first lens G1 in order from the incident side.

  Similarly, 5 and 6 are optical surfaces of the second lens G2. Reference numerals 7 and 8 denote optical surfaces of the third lens G3. The fourth lens G4 is a compound aspheric lens. An aspherical layer (optical element) 9a is formed on the incident side of the fourth lens G4 by molding a plastic resin.

  The object side surface of the optical element 9a has an aspherical shape. The lens element 9b including the optical surfaces 9 and 10 is made of a normal glass glass material. The optical surfaces 9 and 10 are spherical. Reference numeral 11 denotes an image sensor arranged on the optical axis of the optical system 1 in the single-lens reflex camera 2.

  In Example 2, fine irregularities having a wavelength of visible light or less are formed on the optical surface 6, the optical surface 7, and the optical surface 8.

  In FIG. 3, the light beam from the light source 12 is refracted through the optical surfaces 3, 4, 5 and reaches the optical surface 6. As in the first embodiment, the optical surface 6 is provided with the uneven portions (fine uneven structures) shown in FIGS. 11 and 12.

  The fine structure irregularities are petal-like crystals deposited in the same manner as in Example 1, with the vicinity of the substrate interface being the most dense and becoming sparse as the distance from the interface is increased. Since the uneven portion of this fine structure is sufficiently small with respect to visible light, it can be considered as a thin film having an equivalent refractive index (effective refractive index). The effective refractive index of the cross section is the same as in FIG.

  Since the medium is dense near the interface with the optical surface, the effective refractive index is also high. On the other hand, the effective refractive index decreases as the distance from the interface increases, and the effective refractive index is substantially equal to that of air at the upper end of the structure. Therefore, the visible light has a good antireflection structure as in the spectral reflectance graph shown in FIG.

  On the other hand, as for the ultraviolet light, the scattering rate is increased like the spectral scattering rate shown in FIG. In addition, the scattered light direction at this time is not concentrated in a specific direction because the arrangement interval of the uneven portions is irregular.

  Therefore, the ultraviolet light from the light source 12 passes through the optical surfaces 3, 4, and 5, then is scattered by the optical surface 6 and diffused in all directions. Most of the diffused light is absorbed by the wall in the lens barrel.

  Some rays reach the optical surface 7. Since this optical surface 7 is also formed with uneven portions having the same fine structure as the optical surface 6, the same scattering occurs on the optical surface 7. A part of the light beam scattered by the optical surface 7 reaches the optical surface 8. Since the optical surface 8 is also provided with uneven portions having the same fine structure as the optical surface 6, the same scattering occurs on the optical surface 8.

  Therefore, in Example 2 of FIG. 3, the scattered light of ultraviolet light only slightly enters the aspherical layer 9a disposed on the optical surface 9, and the ultraviolet light is not collected.

  Similarly, in the optical system of FIG. 4, only the scattered light of the ultraviolet light is incident on the image sensor 11, and the ultraviolet light is not collected.

  As a result, the second embodiment has the same effect as the first embodiment.

[Example 3]
FIG. 5 is a schematic view of the essential part schematically showing the configuration of the optical system according to Example 3 of the present invention.

  In Example 3, the concavo-convex portions are formed on at least three optical surfaces on the light incident side of the optical element 9a made of resin.

  In FIG. 5, the same members as those in FIG.

  In FIG. 5, as in FIG. 1, 1 is an interchangeable lens. Reference numeral 2 denotes a single-lens reflex camera. In the interchangeable lens 1, 3 and 4 are optical surfaces of the first lens G1 in order from the incident side.

  Similarly, 5 and 6 are optical surfaces of the second lens G2. Reference numerals 7 and 8 denote optical surfaces of the third lens G3. The fourth lens G4 is a compound aspheric lens. An aspherical layer (optical element) 9a is formed on the incident side of the fourth lens G4 by molding a plastic resin.

  The object side surface of the optical element 9a has an aspherical shape. The lens element 9b including the optical surfaces 9 and 10 is made of a normal glass glass material. The optical surfaces 9 and 10 are spherical. Reference numeral 11 denotes an image sensor arranged on the optical axis of the optical system 1 in the single-lens reflex camera 2.

  In Example 3, fine uneven portions having a wavelength equal to or less than the wavelength of visible light are formed on the optical surface 6, the optical surface 8, and the optical surface 9c on the light incident side of the optical element 9a.

  In FIG. 5, the light from the light source 12 passes through the optical surfaces 3, 4, and 5 and reaches the optical surface 6. As in the first embodiment, the optical surface 6 is provided with the uneven portions (fine uneven structures) shown in FIGS. 11 and 12.

  The fine structure irregularities are petal-like crystals deposited in the same manner as in Example 1, with the vicinity of the substrate interface being the most dense and becoming sparse as the distance from the interface is increased. Since the uneven portion of this fine structure is sufficiently small with respect to visible light, it can be considered as a thin film having an equivalent refractive index (effective refractive index). The effective refractive index of the cross section is the same as in FIG.

  Since the medium is dense near the interface with the optical surface, the effective refractive index is also high. On the other hand, the effective refractive index decreases as the distance from the interface increases, and the effective refractive index is substantially equal to that of air at the upper end of the structure. Therefore, the visible light has a good antireflection structure as in the spectral reflectance graph shown in FIG.

  On the other hand, as for the ultraviolet light, the scattering rate is increased like the spectral scattering rate shown in FIG. Further, the scattered light does not concentrate in a specific direction because the uneven pitch is irregular.

  Therefore, the ultraviolet light from the light source 12 is transmitted through the optical surfaces 3, 4, and 5, then scattered by the optical surface 6 and diffused in all directions. Most of the diffused light is absorbed by the wall in the lens barrel.

Some rays reach the optical surface 7. The light beam that has passed through the optical surface 7 reaches the same optical surface 8 as the optical surface 6. Concave and convex portions having the same fine structure as the optical surface 6 are also formed on the optical surface 8. For this reason, similar scattering occurs here. A part of the light beam scattered by the optical surface 8 reaches the optical surface 9c. The optical surface 9c is provided with a concavo-convex portion having a fine structure shown in FIG.
For this reason, scattering also occurs on the optical surface 9c.

  FIG. 10 is an SEM photograph of the structure of the concavo-convex portion of the optical surface 9c observed from above the surface. The concave and convex portions of this fine structure are concave or convex shapes arranged at random. The vicinity of the substrate interface is the densest and becomes sparse as the distance from the interface increases. Since this fine structure is sufficiently small with respect to visible light, it can be considered as a thin film having an equivalent refractive index (effective refractive index).

  18 is an explanatory diagram schematically showing the effective refractive index of the cross section of the structure shown in FIG. 10 in the same manner as FIG. Since the medium is dense near the interface with the optical surface 9c, the effective refractive index Ns is also high.

  On the other hand, the effective refractive index decreases as the distance from the interface increases, and the minimum effective refractive index is obtained at the upper end of the structure. Therefore, the visible light has a good antireflection structure as shown in the graph of spectral reflectance shown in FIG.

  On the other hand, with respect to ultraviolet light, the scattering rate increases as shown in the graph of the spectral scattering rate shown in FIG. Further, the scattered light direction at this time is not concentrated in a specific direction because the pitch of the concavo-convex portions is irregular.

  Therefore, in FIG. 5, only the scattered light of the ultraviolet light is incident on the image sensor 11, and the ultraviolet light is not condensed.

  As a result, Example 3 achieves the same effect as Example 1.

  In each embodiment, the optical element made of resin may be a microlens, a focus plate, or the like. Moreover, the lens which comprises a finder may be sufficient.

  According to each embodiment, for an optical element using a plastic mold lens as a part of an optical system, an adhesive on a bonding surface, a DOE element, a focus plate, a micro lens for an image sensor, a resin such as a color filter, etc. , The influence of ultraviolet light can be reduced.

  As a result, it is possible to obtain an optical system and an image pickup apparatus having the optical system in which favorable optical characteristics are obtained with little change in optical characteristics due to deterioration of the optical elements.

1: Interchangeable lens 2: Single-lens reflex camera 3: First optical surface of the first lens G1 4: Second optical surface of the first lens G1 5: First optical surface of the second lens G2 6: Of the second lens G2 Second optical surface 7: First optical surface of third lens G3 8: Second optical surface of third lens G3 9: First optical surface of fourth lens G4 10: Second optical surface of fourth lens G4 11: Image sensor 12: Light source (sun)
13: Finder 14: The shaded part of the sphere

Claims (8)

In an optical system including an optical element made of resin in an optical path, a plurality of irregularities having a size equal to or smaller than the wavelength of visible light on at least two optical surfaces of the light incident side of the optical element made of resin The part is formed without a repeating structure, or is formed with a random arrangement interval,
The effective refractive index of the concavo-convex portion decreases as the distance from the optical surface on which the concavo-convex portion is formed,
The concavo-convex part has a scattering rate of Sa with a wavelength of 360 nm,
Scattering rate of Sb with respect to a wavelength of 550 nm,
Rb reflectivity for a wavelength of 550 nm,
When Sa> 1%
Sb <1%
Rb <5%
Satisfies the conditional expression
When A2 is the effective diameter of the optical surface closer to the optical element made of the resin among the two optical surfaces, and D12 is the distance between the two optical surfaces,
0 <A2 / D12 <2.0
An optical system characterized by satisfying the following conditional expression:   2. The optical system according to claim 1, wherein the concavo-convex portion is formed on at least three optical surfaces among optical surfaces on a light incident side of the optical element made of the resin.   The optical system according to claim 1, wherein the optical element made of the resin is at least one of a plastic mold lens, an adhesive for a cemented lens, a color filter, and a polarizing plate.   The optical system according to claim 1, wherein the resin is a material having a C—S bond between a carbon atom and a sulfur atom.   The optical surface on which the concavo-convex portion is formed is an optical surface located on the image side from the second optical surface counting from the light incident side, and an antireflection film made of a thin film is formed on the first optical surface. The optical system according to claim 1, wherein the optical system is formed.   An imaging apparatus comprising: the optical system according to any one of claims 1 to 5; and an imaging element that receives an image formed by the optical system. In an interchangeable lens having an optical system that is detachable from the camera body and includes an optical element made of resin in the optical path,
A plurality of concave and convex portions having a size equal to or smaller than the wavelength of visible light are formed without having a repetitive structure on at least two of the optical surfaces on the object side of the optical element made of the resin, or are random. Formed with an array interval,
The uneven portion is
The effective refractive index of the concavo-convex portion decreases as the distance from the optical surface on which the concavo-convex portion is formed,
Sc is a scattering rate for a wavelength of 360 nm,
Scattering rate of Sb with respect to a wavelength of 550 nm,
Rb reflectivity for a wavelength of 550 nm,
When Sa> 1%
Sb <1%
Rb <5%
Satisfies the conditional expression
When A2 is the effective diameter of the optical surface closer to the optical element made of the resin among the two optical surfaces, and D12 is the distance between the two optical surfaces,
0 <A2 / D12 <2.0
An interchangeable lens characterized by satisfying the following conditional expression: An imaging apparatus comprising: the interchangeable lens according to claim 7; and an imaging element that receives an image formed by the interchangeable lens.