JP2007127960A - Imaging optical system, imaging lens device and digital equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-definition imaging optical system capable of completely correcting chromatic aberration while achieving complete miniaturization with constitution of three lenses. <P>SOLUTION: The imaging optical system 10 is equipped with: a first lens 11 having positive optical power; a second lens 12 having positive optical power; and a third lens 13 having negative optical power in order from an object side. In the imaging optical system 10, a diffractive surface is formed on at least one lens surface of the lens surfaces 11a and 11b of the first lens 11 and the lens surfaces 12a and 12b of the second lens 12, which are positive lenses. The imaging optical system 10 is constituted to satisfy a conditional expression; 0.2<P<SB>L</SB>/P<2.0 when assuming that power by the refraction of the lens including the diffractive surface is P<SB>L</SB>and power by the refraction and the diffraction of the entire system of the imaging optical system 10 is P. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an imaging optical system composed of a plurality of lenses, and more particularly to an imaging optical system, an imaging lens device, and a digital apparatus equipped with the imaging lens device suitable for downsizing.

  In recent years, mobile phones and personal digital assistants (PDAs) have become widespread, and specifications for incorporating compact digital still camera units and digital video units into these devices have become common. Until now, most image sensors used in mobile phones and the like have a low pixel count of about 100,000 to 350,000 pixels, and such an image sensor is composed of one or two lenses. An imaging optical system was used. However, in recent years, a large number of image sensors that exceed 1 million pixels have been adopted in mobile phones and the like, and such high-pixel image sensors have insufficient correction of chromatic aberration and the like in the above-described image pickup optical system. Thus, the resolution performance could not be improved.

  The number of lenses may be increased in order to increase the correction capability of chromatic aberration, but it is desirable that the number of lenses be as small as possible in order to be incorporated in a small digital device such as a mobile phone. In view of these points, an attempt was made to construct an imaging optical system with three lenses, but chromatic aberration could not be sufficiently corrected with the configuration of three lenses. On the other hand, in an imaging optical system composed of one or two lenses, Patent Documents 1 and 2 disclose an imaging optical system in which chromatic aberration is corrected by forming a diffractive surface on a lens surface. Has been. However, with one or two lens configurations, resolution performance is insufficient even if a diffractive surface is provided.

By the way, Patent Document 3 discloses that a reading optical system applied to an image scanner or the like instead of an imaging optical system has a three-lens configuration and forms a positive diffractive surface on one of its lens surfaces. Has been. However, since the reading optical system has a long optical total length and a narrow angle of view, it is difficult to apply the technique disclosed in Patent Document 3 as it is to a small digital device such as a mobile phone.
Japanese Patent Laid-Open No. 10-104533 JP-A-10-161020 Japanese Patent Laid-Open No. 11-52231

  The present invention has been made in view of the above-described situation, and a high-definition imaging optical system and imaging lens that can sufficiently correct chromatic aberration while achieving sufficient compactness with a three-lens configuration. An object is to provide a device and a digital device.

In order to solve the above technical problem, the present invention provides an imaging optical system, an imaging lens device, and a digital device having the following configurations. Note that the terms used in the following description are defined in the present specification as follows.
(A) A refractive index is a refractive index with respect to the wavelength (587.56 nm) of d line | wire.
(B) Abbe number is determined when the refractive index for d line, F line (486.13 nm) and C line (656.28 nm) is nd, nF, nC and Abbe number is νd, respectively.
νd = (nd−1) / (nF−nC)
The Abbe number νd obtained by the definition formula
(C) The notation regarding the surface shape is a notation based on the paraxial curvature.
(D) When the notation “concave”, “convex” or “meniscus” is used for the lens, these represent the lens shape near the optical axis (near the center of the lens) (based on the paraxial curvature) Notation).

An imaging optical system according to a first aspect of the present invention includes a first lens having a positive optical power, a second lens having a positive optical power, and a negative optical power from the object side to the image side. In an imaging optical system including a third lens having power, a diffractive surface is formed on at least one of the lens surfaces of the first lens and the second lens, and the lens including the diffractive surface is refracted. The power according to the above satisfies the following conditional expression (1).
0.2 <P _L /P<2.0 (1)
Where P _L : power due to refraction of the lens including the diffractive surface
P: Power of refraction and diffraction of the entire system

  According to this configuration, three positive and negative lenses are configured in order from the object side, and at least one lens surface of the positive lenses is an imaging optical system having a diffractive surface. In such a configuration of three positive and negative lenses, chromatic aberration is corrected by a negative lens (third lens) that is generally located closest to the image side. In such an imaging optical system, in order to shorten the total lens length for compactness, it is necessary to increase the power of the positive lens appropriately, but this causes a problem that chromatic aberration is deteriorated. Therefore, in the present invention, at least one lens surface of the positive lenses has a diffractive surface, so that the chromatic aberration can be corrected even in the positive lens, that is, the positive lens including the diffractive surface has an appropriately strong refraction power. The imaging optical system can be made compact.

  And it is required that the power of refraction of the lens including the diffractive surface satisfies the conditional expression (1). If the upper limit of conditional expression (1) is exceeded, it will be difficult to sufficiently correct chromatic aberration with the diffraction surface alone, and if the lower limit is not reached, the total length of the optical system cannot be shortened sufficiently. Therefore, by providing the configuration according to claim 1, it is possible to provide a high-definition imaging optical system that can sufficiently correct chromatic aberration and the like while achieving sufficient compactness with the configuration of three positive and negative lenses. Become.

An imaging optical system according to a second aspect is characterized in that, in the first aspect, the following conditional expressions (2) and (3) are satisfied.
0.0 <P _DOE /P<0.3 (2)
−2.00 <P _N /P<−0.05 (3)
However, P _DOE : Power by diffraction
P _N : Power by refraction of the third lens

  As described above, the chromatic aberration is corrected by the negative lens in the configuration of three positive and negative lenses. Therefore, it is necessary to correct the chromatic aberration by increasing the power of the negative lens having only one lens as the imaging optical system becomes more compact. However, if the power of the negative lens is increased too much, the balance with spherical aberration is lost and various aberrations cannot be corrected well. In the present invention, since the diffractive surface is formed on at least one lens surface of the positive lens, the chromatic aberration is corrected also on the diffractive surface. As a result, the chromatic aberration is reduced without excessively increasing the power of the negative lens. However, by satisfying the requirements of the conditional expressions (2) and (3) in relation to the power of the entire system, the diffractive power of the diffractive surface and the power of refraction of the negative lens, it can be made more compact and highly efficient. It becomes possible to provide an imaging optical system balanced in terms of definition. When the upper limit of conditional expression (2) is exceeded, the tendency of excessive correction of axial chromatic aberration becomes significant. When the lower limit is reached, the diffractive surface does not function as a diffractive optical element. On the other hand, if the upper limit of conditional expression (3) is exceeded, the power of the negative lens (third lens) becomes too small to make it impossible to move the principal point position away from the image plane side, and the overall length is shortened with respect to the focal length. Tend to be difficult. On the other hand, if the lower limit is not reached, the power of the negative lens becomes too large, the eccentricity error sensitivity becomes high, and adjustment between the lenses becomes essential, and the cost tends to increase.

An imaging optical system according to a third aspect of the present invention is the imaging optical system according to the first or second aspect, wherein the imaging optical system includes an optical aperture, the diffractive surface is disposed in the vicinity of the optical aperture, and the maximum field angle passing through the diffractive surface. The principal ray has a height satisfying the following conditional expressions (4) and (5).
| D _DOE | / D _S <0.7 (4)
| H _DOE | / D _DOE <1.2 (5)
Where D _DOE is the distance on the optical axis from the optical aperture to the diffractive surface.
D _S: distance from the optical stop to the image plane
_HDOE : ray height of the chief ray at the maximum angle of view through the diffraction surface

  In general, a diffractive optical element has an Abbe number = −3.45, which is very high in dispersion characteristics as compared with an optical resin or optical glass. In order to correct the longitudinal chromatic aberration, an appropriate diffraction power is required, but the lateral chromatic aberration affects not only the power but also the light beam height. Therefore, by arranging the diffractive surface in the vicinity of the optical aperture (which can reduce the degree of separation of the axial light and the off-axis light in the diffractive surface), the height of the principal ray having the maximum field angle passing through the diffractive surface. The chromatic aberration of magnification can be corrected appropriately by satisfying conditional expressions (4) and (5). When the upper limit of conditional expression (4) and conditional expression (5) is exceeded, the tendency of excessive correction of lateral chromatic aberration becomes remarkable.

  An imaging optical system according to a fourth aspect is the imaging optical system according to any one of the first to third aspects, wherein the imaging optical system includes an optical diaphragm, and the optical diaphragm is disposed between the first lens and the second lens. It is characterized by being.

  In the case of an imaging optical system having three positive and negative lenses in order from the object side, an optical aperture is interposed between the first lens and the second lens so that the first lens and the second lens are symmetrical. Can be arranged. Thereby, there is an advantage that generation of coma, astigmatism, distortion, and the like can be suppressed.

  An imaging optical system according to a fifth aspect is the imaging optical system according to any one of the first to third aspects, wherein the imaging optical system includes an optical diaphragm, and the optical diaphragm is disposed on the object side of the first lens. And

  According to this configuration, since the optical aperture is disposed on the object side of the first lens, the exit pupil position can be separated from the image plane. Thereby, there exists an advantage that telecentricity can be improved.

An imaging optical system according to a sixth aspect is characterized in that, in any one of the first to fifth aspects, the following conditional expression (6) is satisfied.
0.6 <D / f <1.9 (6)
Where D: thickness on the optical axis from the object side surface of the first lens to the image side surface of the third lens
f: Focal length of the entire system

  According to this configuration, it is possible to achieve a balance between compactness of the imaging optical system and aberration correction. Exceeding the upper limit of the conditional expression (6) is advantageous in correcting aberrations, but causes an increase in the total length of the optical system. On the other hand, if the value is below the lower limit, it is advantageous for shortening the total length of the optical system, but aberrations are deteriorated. In particular, when the angle of view is widened, distortion and field curvature deterioration become obvious.

  An imaging optical system according to a seventh aspect is characterized in that in any one of the first to sixth aspects, the imaging optical system has at least one lens made of an optical resin material. According to this configuration, by using a lens made of a resin material, mass production with stable quality is possible, and a significant cost reduction can be achieved.

  An imaging optical system according to an eighth aspect of the present invention is the imaging optical system according to the seventh aspect, wherein the lens having the diffractive surface is a lens made of an optical resin material. Since the diffractive surface has a complicated structure, it is desirable to form the diffractive surface by a molding process using a mold. Therefore, by using an optical resin material for the glass material of the positive lens to which a diffractive surface is added, it becomes possible to produce a positive lens with a diffractive surface by molding, thereby facilitating manufacturing and reducing costs. .

  The imaging optical system according to claim 9 is the lens according to claim 8, wherein the lens made of the optical resin material is a lens molded using a material in which inorganic particles having a maximum length of 30 nanometers or less are dispersed in the resin material. It is characterized by being.

In general, when fine particles are mixed in a transparent resin material, light scattering occurs and the transmittance decreases, so that it is difficult to use as an optical material. However, by making the size of the microparticles smaller than the wavelength of the transmitted light beam, it is possible to substantially prevent scattering. The refractive index of the resin material decreases as the temperature increases, but the refractive index of the inorganic fine particles increases as the temperature increases. Therefore, it is possible to make almost no change in the refractive index by using these temperature dependencies so as to cancel each other. Specifically, by dispersing inorganic particles having a maximum length of 30 nanometers or less in a resin material serving as a base material, a resin material having extremely low temperature dependency of the refractive index can be obtained. For example, by dispersing fine particles of niobium oxide (Nb ₂ O ₅ ) in acrylic, the refractive index change due to temperature change can be reduced. Therefore, by using a resin material in which such inorganic particles are dispersed in at least one lens, it is possible to suppress a back focus shift caused by an environmental temperature change of the entire variable magnification optical system according to the present invention. it can.

  An imaging optical system according to a tenth aspect of the present invention is the imaging optical system according to any one of the first to ninth aspects, wherein the lens having power only by refraction among the first lens and the second lens is a lens made of an optical glass material. And According to this configuration, when only one of the two positive lenses has a diffractive surface, the other positive lens does not have a diffractive surface and has only the power of refraction. By using glass as the glass material, it is possible to minimize the back focus shift due to the environmental temperature change.

  An imaging lens device according to an eleventh aspect includes the imaging optical system according to any one of claims 1 to 10 and an imaging element that converts an optical image into an electrical signal, and the imaging optical system includes the imaging element. An optical image of a subject can be formed on the light receiving surface. According to this configuration, a compact and high-definition imaging lens device that can be mounted on a mobile phone, a portable information terminal, or the like can be realized.

  A digital device according to a twelfth aspect includes the imaging lens device according to the eleventh aspect, and a control unit that causes the imaging lens device and the imaging element to perform at least one of photographing a still image and a moving image. The imaging optical system of the imaging lens device is assembled so that an optical image of a subject can be formed on the light receiving surface of the imaging element. According to this configuration, a digital device such as a mobile phone equipped with a high-definition and compact imaging lens device can be realized.

  According to the present invention, a high-definition imaging optical system, an imaging lens device, and a digital device that can sufficiently correct chromatic aberration and the like with a small number of lenses of a three-lens configuration are inexpensive and sufficiently compact. Can be offered at.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<Description of configuration of imaging optical system>
FIG. 1 is an optical path diagram schematically showing a configuration of an imaging optical system 10 according to the present invention. The imaging optical system 10 forms an optical image of a subject on a light receiving surface 16a (image surface) of an image sensor 16 that converts an optical image into an electrical signal, and is from the object side (subject) to the image side. A first lens 11 having a positive optical power, a second lens 12 having a positive optical power, and a third lens 13 having a negative optical power are provided toward (imaging device 16). An imaging optical system having three positive and negative lenses.

  In FIG. 1, the first lens 11 is composed of a biconvex positive lens, the second lens 12 is composed of a positive meniscus lens convex on the image side, and the third lens 13 is composed of a negative meniscus lens convex on the object side. An example of a configuration is shown. An optical aperture 14 is disposed between the first lens 11 and the second lens 12, and a low-pass filter 15 is disposed between the third lens 13 and the image sensor 16 for removing noise components. Has been. In such a configuration, the optical image of the subject existing on the object side is guided by the imaging optical system 10 along the optical axis AX to the light receiving surface 16a of the imaging device 16, and the optical image of the subject is captured by the imaging device 16. It is what is done.

  In the present invention, in such an imaging optical system 10, at least one of the lens surfaces 11a and 11b of the first lens 11 that is a positive lens and the lens surfaces 12a and 12b of the second lens 12 is provided on the lens surface. A diffraction surface (DOE) is formed. This diffractive surface is a surface that bends the light beam by diffracting action, and since this diffractive surface has a negative Abbe number (−3.45), a combination of positive lenses (first lens 11 and second lens 12). ) Can correct chromatic aberration. The diffractive surface may be formed on any one of the four lens surfaces 11a, 11b, 12a, and 12b, but each of the first lens 11 and the second lens 12 has a diffractive surface. Or diffractive surfaces may be formed on both surfaces of either the first lens 11 or the second lens 12, or diffractive surfaces may be formed on all four lens surfaces.

When the power due to refraction of a lens including such a diffractive surface is P _L and the power due to refraction and diffraction of the entire imaging optical system 10 is P, as shown by the conditional expression (1), P _L / P is
0.2 <P _L /P<2.0
It is configured to satisfy the relationship. Accordingly, it is possible to provide a high-definition imaging optical system 10 that can sufficiently correct chromatic aberration and the like while achieving sufficient compactness with a configuration of three positive and negative lenses.

Here, it is desirable that the relationship P _L / P in the conditional expression (1) satisfies the following conditional expression (1) ′.
0.2 <P _L /P<1.5 (1) ′
If P _L / P exceeds the upper limit of the conditional expression (1) ′, the adjustment between the lenses is inevitably required due to the increased decentration error sensitivity, which increases the manufacturing cost. Get higher.

Since the imaging optical system 10 has a configuration of three positive and negative lenses, the chromatic aberration is corrected by the negative lens (third lens 13). However, if the power of the third lens is excessively increased for such correction. Therefore, the balance with spherical aberration is lost, and various aberrations cannot be corrected satisfactorily. Therefore, when the power due to diffraction is P _DOE and the power due to refraction of the third lens 13 is P _N , as indicated by the conditional expressions (2) and (3), P _DOE / P and P _N / P is
0.0 <P _DOE /P<0.3
−2.00 <P _N /P<−0.05
It is desirable to be configured to satisfy this relationship. With this configuration, it is possible to satisfactorily reduce chromatic aberration without increasing the power of the third lens 13 excessively.

In addition, it is more desirable that the relation between P _DOE / P and P _N / P in the conditional expressions (2) and (3) satisfies the following conditional expressions (2) ′ and (3) ′.
0.01 <P _DOE /P<0.15 (2) ′
−2.00 <P _N /P<−0.2 (3) ′
When P _DOE / P exceeds the upper limit of the conditional expression (2) ′, the pitch of the diffraction grating on the diffractive surface becomes fine and the tendency to increase the manufacturing difficulty becomes remarkable, and the manufacturing cost increases. On the other hand, if the value is below the lower limit, the axial chromatic aberration cannot be sufficiently corrected because the diffraction power is small. On the other hand, if P _N / P exceeds the upper limit of conditional expression (3) ′, the power of the third lens 13 becomes too small to make it difficult to reduce the Petzval sum in the entire imaging optical system 10 and to align the image plane. It becomes difficult. If the lower limit is not reached, there is a disadvantage that the power of the third lens 13 becomes too strong and the sensitivity of manufacturing error increases.

  The imaging optical system 10 is provided with an optical diaphragm 14, which is preferably disposed in the vicinity of the lens surface on which the diffractive surface is formed. In the example of FIG. 1, for example, when the diffractive surface is formed on the lens surface 11b, it is desirable to arrange the optical aperture 14 as close as possible. Thereby, the degree of separation of the axial light and the off-axis light on the diffractive surface can be reduced, and the ray height of the principal ray having the maximum field angle passing through the diffractive surface can be reduced.

Furthermore, the distance on the optical axis from the optical aperture 14 to the diffraction surface (for example, the diffraction surface of the lens surface 11b) is D _DOE , the distance from the optical aperture to the image surface (the light receiving surface 16a of the image sensor 16) is D _S , and diffraction. when the chief ray ray height of the maximum angle of view passing through the plane and _{H DOE,} the conditional expression (4), as indicated by _{(5), | D DOE |} / D S and _{| H} DOE _| / D _DOE
| D _DOE | / D _S <0.7
｜ H _DOE | / D _DOE <1.2
It is desirable to satisfy the relationship. Thereby, it becomes possible to appropriately correct the lateral chromatic aberration.

If conditional expression (4), in _{(5) | D DOE | /} D S and _| H DOE _| a _{/ D DOE} relationship, following (4) ', (5)' to satisfy the conditional expression It is more desirable.
0.01 <| D _DOE | / D _S <0.45 (4) ′
0.3 <| H _DOE | / D _DOE <1.0 (5) ′
| D _{DOE |} when _/ D _S exceeds the upper limit of conditional expression (4) ', the correction effect with respect to the axial chromatic aberration is reduced, and so tend to correction effect for lateral chromatic aberration if the lower limit is less noticeable . Similarly, when | H _DOE | / D _DOE exceeds the upper limit of conditional expression (5) ′, the correction effect for axial chromatic aberration decreases, and when it falls below the lower limit, the correction effect for lateral chromatic aberration tends to decrease. become.

  As described above, it is desirable to arrange the optical diaphragm 14 in the vicinity of the diffractive surface, but it is preferable to arrange the optical diaphragm 14 between the first lens 11 and the second lens 12 as shown in FIG. One of the optical configurations. That is, in the case of the imaging optical system 10 having three positive and negative lenses in order from the object side, the optical diaphragm 14 is interposed between the first lens 11 and the second lens 12 so that both lenses are symmetrical. Therefore, the occurrence of coma, astigmatism, distortion and the like can be suppressed.

  Note that, from the viewpoint of enhancing the telecentricity of the imaging optical system 10, it is desirable that the optical aperture 14 be disposed on the object side (the lens surface 11a side) of the first lens 11. This is because the exit pupil position can be separated from the image plane by disposing the optical aperture 14 on the object side of the first lens 11.

Further, the imaging optical system 10 satisfies the conditional expression (6) when the thickness on the optical axis from the object side surface of the first lens 11 to the image side surface of the third lens 13 is D and the focal length of the entire system is f. As shown, D / f is
0.6 <D / f <1.9
It is desirable to satisfy the relationship. Thereby, the balance between the compactness of the imaging optical system 10 and the aberration correction can be achieved.

Here, it is more desirable that the D / f relationship in the conditional expression (6) satisfies the following conditional expression (6) ′.
0.8 <D / f <1.9 (6) ′
If the lower limit of conditional expression (6) ′ is not reached, it is necessary to increase the power of each lens in order to shorten the overall length of the optical system, resulting in an increase in manufacturing error sensitivity. Due to this, there are many cases in which adjustment between lenses is indispensable, and the manufacturing cost increases.

  Next, regarding the manufacturing method of the imaging optical system 10, there is no particular limitation on the glass material constituting the first to third lenses 11 to 13, and glass materials made of various optical glass materials and optical resin (plastic) materials can be used. it can. However, if an optical resin material is used, it is lightweight and can be mass-produced with an injection mold or the like. Therefore, compared with the case of manufacturing with a glass material, the cost is reduced and the imaging optical system 10 is lightened. Is advantageous. Therefore, it is desirable to provide the imaging optical system 10 with at least one lens made of an optical resin material. Of course, two or more lenses made of an optical resin material may be provided.

  In particular, it is desirable that the first lens 11 and / or the second lens 12 on which the diffractive surface is formed is made of a lens made of an optical resin material. Since the diffractive surface has a complicated structure, it is preferable to form the diffractive surface by a molding process using a mold having a diffractive shape rather than processing the optical glass material. Therefore, by using an optical resin material as a glass material for a positive lens provided with a diffractive surface, a positive lens with a diffractive surface can be mass-produced by injection molding using a mold, etc., facilitating manufacturing and reducing costs. It will be able to plan. It is also possible to form a diffractive surface by molding a predetermined diffractive optical element with an optical resin material and affixing it to a lens made of a glass material.

As such a lens made of a resin material, it is desirable to use a lens molded using a material in which inorganic particles having a maximum length of 30 nanometers or less are dispersed in a resin material. As such an inorganic particle-dispersed resin material, for example, a composite material in which fine particles of niobium oxide (Nb ₂ O ₅ ) are dispersed in acrylic can be exemplified. By using such a lens made of a resin material, it is possible to extremely reduce the refractive index change due to the temperature change of the resin material lens.

  In addition, a lens having a diffractive surface and no power due to refraction (for example, the second lens 12 when the diffractive surface is formed on the first lens 11 and the diffractive surface is not formed on the second lens 12) is It is desirable that the lens is made of an optical glass material. According to this configuration, the back focus shift due to the environmental temperature change can be made as small as possible.

  It is desirable that all the lens surfaces of the first to third lenses 11 to 13 provided in the imaging optical system 10 are aspherical surfaces. This makes it possible to achieve both compactness and high image quality of the imaging optical system 10.

  Further, in the imaging optical system 10, a mechanical shutter having a function of shielding light from the imaging element 16 may be disposed instead of the optical aperture 14. Such a mechanical shutter is effective in preventing smear when, for example, a CCD (Charge Coupled Device) type is used as the image sensor 16.

  The low-pass filter 15 is a parallel plate-shaped optical component that is disposed on the light receiving surface 16a of the image sensor 16 and removes noise components. As the low-pass filter 15, for example, a birefringence low-pass filter made of a crystal whose direction of a predetermined crystal axis is adjusted, a phase-type low-pass filter that realizes a required optical cutoff frequency characteristic by a diffraction effect, and the like Is applicable. Note that the low-pass filter 15 is not necessarily provided, and an infrared cut filter that reduces noise included in the image signal of the image sensor 16 may be used instead. Further, an infrared reflection coating may be applied to the surface of the optical low-pass filter 15 to realize both filter functions by one.

  The image sensor 16 photoelectrically converts R, G, and B component image signals according to the amount of light of the subject image formed by the imaging optical system 10 and outputs it to a predetermined image processing circuit. is there. For example, as the imaging device 16, R (red), G (green), and B (blue) color filters are pasted in a checkered pattern on the surface of each CCD of an area sensor in which the CCD is two-dimensionally arranged. In addition, it is possible to use a so-called Bayer type single-chip color area sensor. In addition to such a CCD image sensor, a CMOS image sensor, a VMIS image sensor, or the like can also be used.

<Description of digital equipment incorporating imaging optical system>
Next, a digital device incorporating the imaging optical system 10 as described above will be described. FIG. 2 is an external configuration diagram of a foldable camera-equipped mobile phone 20 showing an embodiment of a digital device according to the present invention. In the present invention, the digital device includes a digital still camera, a video camera, a digital video unit, a personal digital assistant (PDA), a personal computer, a mobile computer, or peripheral devices (mouse, scanner, printer, etc.). Shall be.

  2A shows an operation surface of the mobile phone 20, and FIG. 2B shows a back surface thereof. The cellular phone 20 has a foldable structure in which a first casing 201 and a second casing 202 are connected by a hinge 203, and the operation surface of the first casing 201 is long in the vertical direction. A rectangular display 21 is provided. The operation surface of the second housing 202 is provided with an image switching button 22, a shutter button 23, and various operation buttons 24 for starting an image shooting mode and switching between still image and moving image shooting. Further, the mobile phone 20 incorporates an imaging lens device 25 constituted by the imaging optical system 10 described above, and the objective lens is exposed on the back surface of the mobile phone 20.

  FIG. 3 is a functional block diagram showing an electrical functional configuration related to imaging of the mobile phone 20. The cellular phone 20 includes an imaging unit 30, an image generation unit 31, an image data buffer 32, an image processing unit 33, a control unit 34, a storage unit 35, and an I / F unit 36 for the imaging function. The

  The imaging unit 30 includes an imaging lens device 25 and an imaging element 16. Light rays from the subject are imaged on the light receiving surface of the image sensor 16 by the imaging optical system 10 and become an optical image of the subject. The imaging device 16 converts the optical image of the subject imaged by the imaging optical system 10 into electrical signals (image signals) of R (red), G (green), and B (blue) color components. , B are output to the image generation unit 31 as image signals of respective colors. The imaging device 16 controls imaging operations such as imaging of either a still image or a moving image or reading of output signals of each pixel (horizontal synchronization, vertical synchronization, transfer) in the imaging device 16 under the control of the control unit 34. Is done.

  The image generation unit 31 performs amplification processing, digital conversion processing, and the like on the analog output signal from the image sensor 16 and determines an appropriate black level, γ correction, and white balance adjustment (WB adjustment) for the entire image. Then, well-known image processing such as contour correction and color unevenness correction is performed to generate image data of each pixel from the image signal. The image data generated by the image generation unit 31 is output to the image data buffer 32.

  The image data buffer 32 is a memory that temporarily stores image data and is used as a work area for performing processing described later on the image data by the image processing unit 33. For example, a RAM (Random Access Memory) is used. Etc.

  The image processing unit 33 is a circuit that performs image processing such as resolution conversion on the image data in the image data buffer 32. Further, the image processing unit 33 can be configured to correct aberrations that could not be corrected by the imaging optical system 10 as necessary.

  The control unit 34 includes, for example, a microprocessor, and controls the operations of the imaging unit 30, the image generation unit 31, the image data buffer 32, the image processing unit 33, the storage unit 35, and the I / F unit 36. . That is, the control unit 34 controls the imaging unit 30 to execute at least one of still image shooting and moving image shooting of the subject.

  The storage unit 35 is a storage circuit that stores image data generated by still image shooting or moving image shooting of a subject, and includes, for example, a ROM (Read Only Memory) and a RAM. That is, the storage unit 35 has a function as a memory for still images and moving images.

  The I / F unit 36 is an interface that transmits / receives image data to / from an external device. For example, the I / F unit 36 is an interface that conforms to a standard such as USB or IEEE1394.

  An imaging operation of the mobile phone 20 configured as described above will be described. When shooting a still image, first, the image switching mode 22 is pressed to activate the image shooting mode. Here, the still image shooting mode is activated by pressing the image switching button 22 once, and the moving image shooting mode is switched by pressing the image switching button 22 again in this state. That is, the control unit 34 of the mobile phone 20 that has received an instruction from the image switching button 22 causes the imaging unit 30 to perform at least one of still image shooting and moving image shooting of the object on the object side.

  When the still image shooting mode is activated, the control unit 34 controls the imaging unit 30 to take a still image. Thereby, an optical image is periodically and repeatedly formed on the light receiving surface of the image sensor 16, converted into image signals of R, G, and B color components, and then output to the image generation unit 31. The image signal is temporarily stored in the image data buffer 32, subjected to image processing by the image processing unit 33, transferred to a display memory (not shown), and guided to the display 21. Then, the photographer can adjust the main subject to fit in a desired position on the screen by looking at the display 21. By pressing the shutter button 23 in this state, a still image can be obtained. That is, the image data is stored in the storage unit 35 as a still image memory.

  Further, when performing moving image shooting, the image switching button 22 is pressed once to activate the still image shooting mode, and then the image switching button 22 is pressed again to switch to the moving image shooting mode. As a result, the control unit 34 controls the imaging unit 30 to capture a moving image. Thereafter, in the same manner as in the case of still image shooting, the photographer looks into the display 21 and adjusts so that the image of the subject obtained through the imaging lens device 25 falls within a desired position in the screen. By pressing the shutter button 23 in this state, moving image shooting is started. The frame image signal of the captured moving image is temporarily stored in the image data buffer 32, subjected to image processing by the image processing unit 33, transferred to the display memory, and guided to the display 21. Here, when the shutter button 23 is pressed again, the moving image shooting is completed. The captured moving image is guided to and stored in the storage unit 35 as a moving image memory.

<Description of More Specific Embodiment of Imaging Optical System>
A specific configuration of the imaging optical system 10 constituting the imaging lens system 25 mounted on the imaging optical system 10 as shown in FIG. 1, that is, the camera-equipped mobile phone 20 as shown in FIG. This will be described with reference to FIG.

  FIG. 4 is a cross-sectional view (optical path diagram) in which the optical axis (AX) is cut longitudinally and shows an arrangement of three lenses in the imaging optical system 10A of the first embodiment. Through this Example 1 and Examples 2 to 16 shown below, these three lenses are arranged in order from the object side (left side in FIG. 4) in the figure, the first lens (L1) having positive optical power, The positive and negative lenses are composed of a second lens (L2) having a negative optical power and a third lens (L3) having a negative optical power. In addition, on the image side of the third lens (L3), a light receiving surface of the imaging element (SR) is arranged via a parallel plate (FT). The parallel plate (FT) corresponds to an optical low-pass filter, an infrared cut filter, a cover glass of an image sensor, or the like. The optical diaphragm (ST) is disposed on either the image side or the object side of the first lens (L1).

  The imaging optical system 10A according to the first exemplary embodiment illustrated in FIG. 4 includes, in order from the object side, a first lens (L1) including a positive meniscus lens convex toward the object side, an optical aperture (ST), and a positive meniscus convex toward the image side. The lens includes a second lens (L2) made of a lens and a third lens (L3) made of a negative meniscus lens concave on the image side. All of the first to third lenses (L1 to L3) are double-sided aspheric lenses, and a diffractive surface is formed on the image-side lens surface of the first lens (L1). The first lens (L1) and the third lens (L3) are resin lenses, and the second lens (L2) is a glass lens. A mechanical shutter may be arranged in place of the optical aperture (ST) (the same applies to the following embodiments).

  In FIG. 4, the numbers ri (i = 1, 2, 3,...) Given to the respective lens surfaces are the i-th lens surfaces when counted from the object side, and “*” marks are given to ri. The attached surface indicates an aspherical surface, and the surface with “#” mark on ri indicates a diffractive surface. The optical diaphragm (ST), both surfaces of the parallel plate (FT), and the light receiving surface of the image sensor (SR) are also handled as one surface. Such a treatment is the same in the optical path diagrams (FIGS. 5 to 19) for other embodiments to be described later, and the meanings of the reference numerals in the drawings are basically the same as those in FIG. However, it does not mean that they are exactly the same. For example, the lens surface closest to the object is denoted by the same reference numeral (r1) throughout the drawings, but these curvatures are the same throughout the embodiments. It does not mean that.

  Under such a configuration, the light beam incident from the object side sequentially passes through the first, second and third lenses (L1, L2, L3) and the parallel plate (FT) along the optical axis AX, and takes an image. An optical image of the object is formed on the light receiving surface of the element (SR). In the image sensor (SR), the optical image corrected by the parallel plate (FT) is converted into an electrical signal. This electric signal is subjected to predetermined digital image processing, image compression processing, and the like as necessary, and is recorded as a digital video signal in a memory of a mobile phone, a portable information terminal, or other digital device by wire or wirelessly Or transmitted to.

  Tables 1 to 3 show construction data of each lens in the imaging optical system 10A of Example 1. Table 49 below shows numerical values obtained when the above-described conditional expressions (1) to (6) are applied to the imaging optical system 10A according to the first embodiment.

  Table 1 shows, in order from the left, the number of each lens surface, the radius of curvature of each surface (unit: mm), the interval between lens surfaces on the optical axis (axis upper surface interval) (unit: mm), each The refractive index of the lens, and the Abbe number. The axial upper surface distance is a distance converted assuming that the medium existing in a region between a pair of opposing surfaces (including an optical surface and an imaging surface) is air. Here, the number i (i = 1, 2, 3,...) Of each lens surface is the i-th optical surface counted from the object side on the optical path, as shown in FIG. The affixed surface is an aspherical surface (aspherical refractive optical surface or a surface having a refractive action equivalent to that of an aspherical surface), and the surface marked with “#” is a diffractive surface. It is shown that it is the surface that is being done. In addition, since each surface of the optical diaphragm (ST), both surfaces of the plane parallel plate (FT), and the light receiving surface of the image sensor (SR) are flat surfaces, their curvature radii are ∞.

Table 2 is a table showing aspheric data of a surface that is an aspheric surface (a surface in which i is marked with * in Table 1). The aspherical shape of the lens surface uses a local orthogonal coordinate system (x, y, z) in which the surface vertex is the origin and the direction from the object toward the imaging device is the positive direction of the z-axis. Define. Table 2 shows the values of the conical coefficient k and the aspherical coefficients A, B, and C based on the definition according to the following expression (7).
Z (h) = (c · h ² ) / [1 + sqrt {1- (1 + k) c ² h ² }]
+ Ah ⁴ + Bh ⁶ + Ch ⁸ + ... (7)
However, Z: displacement in the z-axis direction at the position of height h (based on the surface vertex)
h: Height in the direction perpendicular to the z-axis (h ² = x ² + y ² )
c: Paraxial curvature (= 1 / radius of curvature)
A, B, C: 4th, 6th and 8th order aspheric coefficients
k: Conical coefficient

Table 3 is a table showing diffractive surface data of a surface having a diffractive surface (a surface in which # is added to i in Table 1). The diffraction shape is defined by the following equation (8) representing the phase shape of the pitch of the diffraction surface. In addition, the phase coefficient shown in Table 3 is set so that the design wavelength is 587.56 nm of the d-line and the design order is + 1st order (the optical power ΦD of the diffraction surface is represented by ΦD = −2 · C1). It is a thing.
φ (h) = (2π / λ0) · (C1 · H2 + C2 · H4 + C3 · H6 + ...)
... (8)
Where φ (h): phase function
λ0: Design wavelength
C1, C2, C3 ... Ci: second order, fourth order, sixth order, ... 2i order phase coefficients

  The left side of FIG. 20 shows the spherical aberration (LONGITUDINAL SPHERICAL ABERRATION), astigmatism (ASTIGMATISM), and distortion (DISTORTION) of the imaging optical system 10A in Example 1 under the lens arrangement and configuration as described above. Shown in order. In this figure, the horizontal axis of spherical aberration and astigmatism represents the deviation of the focal position in mm, and the horizontal axis of distortion aberration represents the amount of distortion in percentage (%). The vertical axis of spherical aberration is indicated by a value normalized by the incident height, while the vertical axis of astigmatism and distortion is indicated by the height of the image (image height) (unit: mm).

  Further, the spherical aberration diagram shows red (wavelength 656.28 nm) with a one-dot chain line, yellow (so-called d-line; wavelength 587.56 nm) with a solid line, and blue (wavelength 435.84 nm) with a broken line. The aberrations when using light are shown respectively. In the figure of astigmatism, symbols s and t represent results on the sagittal (radial) plane and the tangential (meridional) plane, respectively. Further, the diagrams of astigmatism and distortion are the results when the yellow line (d line) is used. As can be seen from FIG. 20, the imaging optical system 10A of Example 1 exhibits excellent optical characteristics with distortion within 5%. Further, the focal length (unit: mm) and the F value in the imaging optical system 10A are shown in Table 50 below. From these tables, it can be seen that in the present invention, a bright optical system with a short focal point can be realized.

  FIG. 5 is a cross-sectional view (optical path diagram) in which the optical axis (AX) is cut longitudinally and shows an arrangement of three lenses in the imaging optical system 10B of the second embodiment. The imaging optical system 10B includes, in order from the object side, a first lens (L1) composed of a positive meniscus lens convex to the object side, an optical aperture (ST), and a second lens (L2 composed of a positive meniscus lens convex to the image side). ) And a third lens (L3) composed of a negative meniscus lens concave on the image side. All of the first to third lenses (L1 to L3) are double-sided aspheric lenses, and a diffractive surface is formed on the object-side lens surface of the first lens (L1). The first lens (L1) and the third lens (L3) are resin lenses, and the second lens (L2) is a glass lens. Construction data of each lens in the imaging optical system 10B are shown in Tables 4 to 6.

  FIG. 6 is a cross-sectional view (optical path diagram) in which the optical axis (AX) is cut longitudinally and shows an arrangement of three lenses in the imaging optical system 10C of Example 3. The imaging optical system 10C includes, in order from the object side, a first lens (L1) composed of a biconvex positive lens, an optical aperture (ST), a second lens (L2) composed of a positive meniscus lens convex to the image side, and It is composed of a third lens (L3) composed of a negative meniscus lens concave on the image side. All of the first to third lenses (L1 to L3) are double-sided aspheric lenses, and a diffractive surface is formed on the image-side lens surface of the first lens (L1). The first lens (L1) and the third lens (L3) are resin lenses, and the second lens (L2) is a glass lens. Construction data of each lens in the imaging optical system 10C are shown in Tables 7 to 9.

  FIG. 7 is a cross-sectional view (optical path diagram) in which the optical axis (AX) is cut longitudinally and shows an arrangement of three lenses in the imaging optical system 10D of Example 4. The imaging optical system 10D includes, in order from the object side, a first lens (L1) composed of a positive meniscus lens convex on the object side, an optical aperture (ST), and a second lens (L2 composed of a positive meniscus lens convex on the image side). ) And a third lens (L3) composed of a biconcave negative lens. All of the first to third lenses (L1 to L3) are double-sided aspheric lenses, and a diffractive surface is formed on the image-side lens surface of the first lens (L1). The first lens (L1) and the third lens (L3) are resin lenses, and the second lens (L2) is a glass lens. Construction data of each lens in the imaging optical system 10D are shown in Tables 10 to 12.

  FIG. 8 is a cross-sectional view (optical path diagram) in which the optical axis (AX) is longitudinally shown, showing an arrangement of three lenses in the imaging optical system 10E of Example 5. The imaging optical system 10E includes, in order from the object side, a first lens (L1) composed of a positive meniscus lens convex on the object side, an optical aperture (ST), and a second lens (L2 composed of a positive meniscus lens convex on the image side). ) And a third lens (L3) composed of a negative meniscus lens concave on the image side. All of the first to third lenses (L1 to L3) are double-sided aspheric lenses, and a diffractive surface is formed on the image-side lens surface of the first lens (L1). All of the first to third lenses (L1 to L3) are resin lenses. Construction data of each lens in the imaging optical system 10E are shown in Tables 13 to 15.

  FIG. 9 is a cross-sectional view (optical path diagram) in which the optical axis (AX) is cut longitudinally and shows an arrangement of three lenses in the imaging optical system 10F of Example 6. The imaging optical system 10F includes, in order from the object side, a first lens (L1) composed of a biconvex positive lens, an optical aperture (ST), a second lens (L2) composed of a positive meniscus lens convex to the image side, and It is composed of a third lens (L3) composed of a negative meniscus lens concave on the image side. All of the first to third lenses (L1 to L3) are double-sided aspheric lenses, and diffractive surfaces are formed on the image side of the first lens (L1) and the object side lens surface of the second lens (L2). Has been. All of the first to third lenses (L1 to L3) are resin lenses. The construction data of each lens in the imaging optical system 10F is shown in Tables 16-18.

  FIG. 10 is a cross-sectional view (optical path diagram) in which the optical axis (AX) is cut longitudinally and shows an arrangement of three lenses in the imaging optical system 10G of Example 7. The imaging optical system 10G includes, in order from the object side, a first lens (L1) composed of a biconvex positive lens, an optical aperture (ST), a second lens (L2) composed of a positive meniscus lens convex to the image side, and It is composed of a third lens (L3) composed of a negative meniscus lens concave on the image side. All of the first to third lenses (L1 to L3) are double-sided aspheric lenses, and a diffractive surface is formed on the object-side lens surface of the second lens (L2). The second lens (L2) and the third lens (L3) are resin lenses, and the first lens (L1) is a glass lens. The construction data of each lens in the imaging optical system 10G is shown in Table 19 to Table 21.

  FIG. 11 is a cross-sectional view (optical path diagram) in which the optical axis (AX) is longitudinally shown, showing an arrangement of three lenses in the imaging optical system 10H of Example 8. The imaging optical system 10H includes, in order from the object side, a first lens (L1) composed of a biconvex positive lens, an optical aperture (ST), a second lens (L2) composed of a positive meniscus lens convex to the image side, and It is composed of a third lens (L3) composed of a negative meniscus lens concave on the image side. All of the first to third lenses (L1 to L3) are double-sided aspheric lenses, and a diffractive surface is formed on the image-side lens surface of the second lens (L2). The second lens (L2) and the third lens (L3) are resin lenses, and the first lens (L1) is a glass lens. The construction data of each lens in the imaging optical system 10H is shown in Tables 22-24.

  FIG. 12 is a cross-sectional view (optical path diagram) in which the optical axis (AX) is cut longitudinally and shows an arrangement of three lenses in the imaging optical system 10I of Example 9. The imaging optical system 10I includes, in order from the object side, an optical aperture (ST), a first lens (L1) including a positive meniscus lens convex on the object side, and a second lens (L2) including a positive meniscus lens convex on the image side. ) And a third lens (L3) composed of a negative meniscus lens concave on the image side. All of the first to third lenses (L1 to L3) are double-sided aspheric lenses, and a diffractive surface is formed on the object-side lens surface of the first lens (L1). The first lens (L1) and the third lens (L3) are resin lenses, and the second lens (L2) is a glass lens. Construction data of each lens in the imaging optical system 10I is shown in Tables 25 to 27.

  FIG. 13 is a cross-sectional view (optical path diagram) in which the optical axis (AX) is longitudinally shown, showing an arrangement of three lenses in the imaging optical system 10J of Example 10. The imaging optical system 10J includes, in order from the object side, an optical aperture (ST), a first lens (L1) composed of a positive meniscus lens convex on the object side, and a second lens (L2) composed of a positive meniscus lens convex on the image side. ) And a third lens (L3) composed of a negative meniscus lens concave on the image side. All of the first to third lenses (L1 to L3) are double-sided aspheric lenses, and a diffractive surface is formed on the image-side lens surface of the first lens (L1). The first lens (L1) and the third lens (L3) are resin lenses, and the second lens (L2) is a glass lens. The construction data of each lens in the imaging optical system 10J are shown in Table 28 to Table 30.

  FIG. 14 is a cross-sectional view (optical path diagram) in which the optical axis (AX) is taken longitudinally and shows an arrangement of three lenses in the imaging optical system 10K of Example 11. The imaging optical system 10K includes, in order from the object side, an optical aperture (ST), a first lens (L1) composed of a positive meniscus lens convex on the object side, and a second lens (L2) composed of a positive meniscus lens convex on the image side. ) And a third lens (L3) composed of a negative meniscus lens concave on the image side. All of the first to third lenses (L1 to L3) are double-sided aspheric lenses, and a diffractive surface is formed on the object-side lens surface of the second lens (L2). The second lens (L2) and the third lens (L3) are resin lenses, and the first lens (L1) is a glass lens. Construction data of each lens in the imaging optical system 10K is shown in Tables 31 to 33.

  FIG. 15 is a cross-sectional view (optical path diagram) in which the optical axis (AX) is longitudinally shown, showing an arrangement of three lenses in the imaging optical system 10L of Example 12. The imaging optical system 10L includes, in order from the object side, an optical aperture (ST), a first lens (L1) composed of a biconvex positive lens, a second lens (L2) composed of a positive meniscus lens convex to the image side, and It is composed of a third lens (L3) composed of a negative meniscus lens concave on the image side. All of the first to third lenses (L1 to L3) are double-sided aspheric lenses, and a diffractive surface is formed on the image-side lens surface of the second lens (L2). The second lens (L2) and the third lens (L3) are resin lenses, and the first lens (L1) is a glass lens. Construction data of each lens in the imaging optical system 10L are shown in Table 34 to Table 36.

  FIG. 16 is a cross-sectional view (optical path diagram) in which the optical axis (AX) is longitudinally shown, showing an arrangement of three lenses in the imaging optical system 10M of Example 13. The imaging optical system 10M includes, in order from the object side, an optical aperture (ST), a first lens (L1) composed of a biconvex positive lens, a second lens (L2) composed of a positive meniscus lens convex to the image side, and It is comprised by the 3rd lens (L3) which consists of a biconcave negative lens. All of the first to third lenses (L1 to L3) are double-sided aspheric lenses, and a diffractive surface is formed on the image-side lens surface of the first lens (L1). The first lens (L1) and the third lens (L3) are resin lenses, and the second lens (L2) is a glass lens. The construction data of each lens in the imaging optical system 10M is shown in Table 37 to Table 39.

  FIG. 17 is a cross-sectional view (optical path diagram) in which the optical axis (AX) is longitudinally shown, showing an arrangement of three lenses in the imaging optical system 10N of Example 14. The imaging optical system 10N includes, in order from the object side, an optical aperture (ST), a first lens (L1) composed of a positive meniscus lens convex on the object side, and a second lens (L2) composed of a positive meniscus lens convex on the image side. ) And a third lens (L3) composed of a negative meniscus lens concave on the image side. All of the first to third lenses (L1 to L3) are double-sided aspheric lenses, and a diffractive surface is formed on the image-side lens surface of the first lens (L1). The first lens (L1) and the third lens (L3) are resin lenses, and the second lens (L2) is a glass lens. The construction data of each lens in the imaging optical system 10N are shown in Tables 40 to 42.

  FIG. 18 is a cross-sectional view (optical path diagram) in which the optical axis (AX) is longitudinally shown, showing an arrangement of three lenses in the imaging optical system 10O of Example 15. The imaging optical system 10O includes, in order from the object side, an optical aperture (ST), a first lens (L1) composed of a positive meniscus lens convex on the object side, and a second lens (L2) composed of a positive meniscus lens convex on the image side. ) And a third lens (L3) composed of a negative meniscus lens concave on the image side. All of the first to third lenses (L1 to L3) are double-sided aspheric lenses, and a diffractive surface is formed on the image-side lens surface of the first lens (L1). All of the first to third lenses (L1 to L3) are resin lenses. The construction data of each lens in the imaging optical system 10O are shown in Tables 43 to 45.

  FIG. 19 is a cross-sectional view (optical path diagram) in which the optical axis (AX) is longitudinally shown, showing an arrangement of three lenses in the imaging optical system 10P of Example 16. The imaging optical system 10P includes, in order from the object side, an optical aperture (ST), a first lens (L1) composed of a biconvex positive lens, a second lens (L2) composed of a positive meniscus lens convex to the image side, and It is composed of a third lens (L3) composed of a negative meniscus lens concave on the image side. All of the first to third lenses (L1 to L3) are double-sided aspherical lenses, and a diffractive surface is formed on the image surface of the first lens (L1) and the lens surface on the object side of the second lens (L2). ing. All of the first to third lenses (L1 to L3) are resin lenses. The construction data of each lens in the imaging optical system 10P is shown in Table 46 to Table 48.

  The spherical aberration, astigmatism, and distortion of the imaging optical systems 10B to P shown in Examples 2 to 16 under the lens arrangement and configuration as described above are shown in FIGS. In these diagrams, the spherical aberration diagram shows the aberrations when three light beams having different wavelengths are used, as in FIG. 20, red with a dashed line, yellow with a solid line, and blue with a broken line. . The imaging optical systems 10B to 10P in any of the examples also exhibit excellent optical characteristics with distortion within approximately 5%.

  Table 49 shows numerical values when the above-described conditional expressions (1) to (6) are applied to the imaging optical systems 10B to P of Examples 2 to 16, respectively.

  Further, Table 50 shows F values and focal lengths (unit: mm) in the imaging optical systems 10B to P of Examples 2 to 16. From these tables, it can be seen that, similarly to Example 1, a bright optical system with a short focal point can be realized.

  As described above, according to the imaging optical systems 10A to 10P according to Examples 1 to 16 described above, it is possible to satisfactorily correct various aberrations while achieving compactness with a small number of lenses such as a three-lens configuration. A detailed imaging optical system can be provided.

It is a figure which shows typically the structure of the imaging optical system concerning this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is an external appearance block diagram of the mobile telephone with a camera carrying the imaging optical system based on this invention, Comprising: (a) is an external appearance block diagram which shows the operation surface, (b) is an external appearance block diagram which shows the back surface of an operation surface. It is. It is a functional block diagram which shows the structure of the function part which concerns on the imaging of the mobile telephone as an example of the digital apparatus which comprises the imaging optical system which concerns on this invention. It is sectional drawing which shows the optical path figure of the imaging optical system which concerns on Example 1 of this invention. 6 is a cross-sectional view illustrating an optical path diagram of an imaging optical system according to Example 2. FIG. 6 is a cross-sectional view illustrating an optical path diagram of an imaging optical system according to Example 3. FIG. 10 is a cross-sectional view illustrating an optical path diagram of an imaging optical system according to Example 4. FIG. FIG. 10 is a cross-sectional view illustrating an optical path diagram of an imaging optical system according to Example 5. FIG. 10 is a cross-sectional view illustrating an optical path diagram of an imaging optical system according to Example 6. 10 is a cross-sectional view illustrating an optical path diagram of an imaging optical system according to Example 7. FIG. FIG. 10 is a cross-sectional view illustrating an optical path diagram of an imaging optical system according to Example 8. FIG. 10 is a cross-sectional view illustrating an optical path diagram of an imaging optical system according to Example 9. FIG. 10 is a cross-sectional view illustrating an optical path diagram of an imaging optical system according to Example 10. 14 is a cross-sectional view illustrating an optical path diagram of an imaging optical system according to Example 11. FIG. 14 is a cross-sectional view illustrating an optical path diagram of an imaging optical system according to Example 12. FIG. 14 is a cross-sectional view illustrating an optical path diagram of an imaging optical system according to Example 13. FIG. FIG. 16 is a cross-sectional view illustrating an optical path diagram of an imaging optical system according to Example 14; FIG. 16 is a cross-sectional view illustrating an optical path diagram of an imaging optical system according to Example 15. 22 is a cross-sectional view illustrating an optical path diagram of an imaging optical system according to Example 16. FIG. 3 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion of the imaging optical system in Example 1. FIG. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging optical system in Example 2. FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging optical system in Example 3. FIG. 9 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging optical system in Example 4. FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging optical system in Example 5. FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging optical system in Example 6. FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging optical system in Example 7. FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging optical system in Example 8. 10 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion of the imaging optical system in Example 9. FIG. FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging optical system in Example 10. FIG. 12 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging optical system in Example 11. FIG. 14 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging optical system in Example 12. FIG. 14 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging optical system in Example 13. FIG. 20 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging optical system in Example 14. FIG. 20 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging optical system in Example 15. FIG. 20 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging optical system in Example 16.

Explanation of symbols

10, 10A to 10P Imaging optical system 11, L1 first lens 12, L2 second lens 13, L3 third lens 14, ST optical aperture 15, FT low-pass filter 16, SR imaging element AX optical axis 20 mobile phone (digital equipment) )
25 Imaging lens device

Claims (12)

An imaging optical system comprising a first lens having a positive optical power, a second lens having a positive optical power, and a third lens having a negative optical power from the object side to the image side In
A diffractive surface is formed on at least one of the lens surfaces of the first lens and the second lens, and the power of refraction of the lens including the diffractive surface satisfies the following conditional expression (1). An imaging optical system.
0.2 <P _L /P<2.0 (1)
Where P _L : power due to refraction of the lens including the diffractive surface
P: Power of refraction and diffraction of the entire system The imaging optical system according to claim 1, wherein the following conditional expressions (2) and (3) are satisfied.
0.0 <P _DOE /P<0.3 (2)
−2.00 <P _N /P<−0.05 (3)
However, P _DOE : Power by diffraction
P _N : Power by refraction of the third lens The imaging optical system has an optical diaphragm,
The diffractive surface is disposed in the vicinity of the optical aperture, and the ray height of the principal ray having the maximum field angle passing through the diffractive surface satisfies the following conditional expressions (4) and (5): The imaging optical system according to claim 1 or 2.
| D _DOE | / D _S <0.7 (4)
| H _DOE | / D _DOE <1.2 (5)
Where D _DOE is the distance on the optical axis from the optical aperture to the diffractive surface.
D _S: distance from the optical stop to the image plane
_HDOE : ray height of the chief ray at the maximum angle of view through the diffraction surface   The imaging optical system according to claim 1, wherein the imaging optical system includes an optical diaphragm, and the optical diaphragm is disposed between the first lens and the second lens. .   The imaging optical system according to claim 1, wherein the imaging optical system includes an optical diaphragm, and the optical diaphragm is disposed on the object side of the first lens. The imaging optical system according to claim 1, wherein the following conditional expression (6) is satisfied.
0.6 <D / f <1.9 (6)
Where D: thickness on the optical axis from the object side surface of the first lens to the image side surface of the third lens
f: Focal length of the entire system   The imaging optical system according to claim 1, comprising at least one lens made of an optical resin material.   The imaging optical system according to claim 7, wherein the lens having the diffractive surface is a lens made of an optical resin material.   9. The imaging optical system according to claim 8, wherein the lens made of an optical resin material is a lens molded using a material obtained by dispersing inorganic particles having a maximum length of 30 nanometers or less in a resin material. .   The imaging optical system according to any one of claims 1 to 9, wherein, among the first lens and the second lens, a lens having power only by refraction is a lens made of an optical glass material. An imaging optical system according to any one of claims 1 to 10, and an imaging device that converts an optical image into an electrical signal,
An imaging lens apparatus, wherein the imaging optical system is capable of forming an optical image of a subject on a light receiving surface of the imaging element. An imaging lens device according to claim 11,
A control unit that causes the imaging lens device and the imaging device to perform at least one of still image shooting and moving image shooting of a subject;
A digital apparatus, wherein an imaging optical system of the imaging lens device is assembled so as to form an optical image of a subject on a light receiving surface of the imaging element.

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