JP2012203234A - Imaging optical system, imaging apparatus and digital instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging optical system composed of five lenses able to correct various aberrations more satisfactorily while achieving a smaller size, and an imaging apparatus and a digital instrument that have the optical system.SOLUTION: An imaging optical system 1 includes, in order from an object side, first to fifth lenses 11 to 15. The first lens 11 is convex on the object side and has positive refractive power, a second lens 12 has negative refractive power, and the fifth lens 15 has negative refractive power and has an aspherical shape that is concave on an image side and has a vertical contact at a position other than the position of an intersection with the center axis. If the focal distance of the entire system is f, the focal distance of the fifth lens 15 is f5, an amount of sag on an object side surface on the principal ray at the maximum field angle is z5o, the thickness of a core is t5, the length of the optical path of an e line on the principal ray at the maximum field angle is p5e, the length of the optical path of a c line on the principal ray on the axis is p5c, the maximum image height is Y, and the entire optical length is TL, the imaging optical system satisfies 0.2<|f5/f|<0.5, 1<|z5o/t5|<4, 2.5<p5e/p5c<5 and 0.63<Y/TL<0.9.

Description

  The present invention relates to an imaging optical system, and more particularly to an imaging optical system suitably applied to a solid-state imaging device such as a CCD image sensor or a CMOS image sensor. The present invention relates to an imaging device including the imaging optical system and a digital device equipped with the imaging device.

  In recent years, imaging devices using solid-state imaging devices such as CCD (Charged Coupled Device) type image sensors and CMOS (Complementary Metal Oxide Semiconductor) type image sensors have become more sophisticated and downsized. Digital devices such as mobile phones and personal digital assistants equipped with image pickup devices using various image pickup devices are becoming widespread. In addition, the imaging optical system (imaging lens) for forming (imaging) an optical image of an object on the light receiving surface of the solid-state imaging device, which is mounted on these imaging devices, is further reduced in size and performance. The demand for is increasing. In such an imaging optical system, a three-element or four-element optical system has been proposed, and moreover, in recent years, higher performance can be achieved. A system has also been proposed.

  Such an imaging optical system is disclosed in Patent Document 1 and Patent Document 2, for example. The imaging lens disclosed in Patent Document 1 includes, in order from the object side, a positive first lens having a convex surface on the object side, a negative meniscus second lens having a concave surface on the image surface side, and an image. A positive meniscus third lens having a convex surface facing the surface, a negative fourth lens having an aspheric surface on both sides and a concave surface on the image surface side in the vicinity of the optical axis, and a positive lens having both surfaces aspheric. Or a negative fifth lens, wherein the Abbe number of the first lens is larger than 50, the Abbe number of the second lens is smaller than 30, and the Abbe number of the fourth lens is smaller than 30. According to Patent Document 1, the imaging lens having such a configuration can obtain a correction effect of axial chromatic aberration and lateral chromatic aberration while corresponding to an increase in the number of pixels, and an image generated due to a positional deviation during manufacturing. Surface variation can be reduced, and manufacturing suitability is excellent (for example, paragraph 0007).

  In addition, the imaging lens disclosed in Patent Document 2 includes, in order from the object side, a first lens composed of a negative meniscus lens having a convex shape on the object side and a second lens composed of a positive lens having a convex surface on the object side. And a diaphragm, a third lens having a convex shape on the image side, a fourth lens having a positive refractive power in the vicinity of the optical axis, and an image side surface having a concave shape on the image side in the vicinity of the optical axis, and an image at the peripheral portion. And a fifth lens having a convex shape on the side. According to Patent Document 2, the imaging lens having such a configuration is a high-performance lens in which various aberrations are well corrected so that it can cope with an increase in the size of an imaging element and a reduction in pixel size associated with an increase in resolution. A simple lens system can be realized (for example, paragraph 0007).

JP 2007-264180 A JP 2007-279282 A

  By the way, in the imaging lens disclosed in Patent Document 1, it cannot be said that correction of spherical aberration and astigmatism is sufficient, and the merit of the five-lens configuration cannot be fully utilized. Further, in the imaging lens disclosed in Patent Document 1, if it is attempted to further shorten the total lens length, it becomes difficult to cope with the increase in the number of pixels of the imaging element due to performance degradation.

  On the other hand, in the imaging lens disclosed in Patent Document 2, since the front group composed of the first lens and the second lens is a spherical system, correction of spherical aberration and coma aberration cannot be said to be sufficient, and good performance is achieved. It is difficult to ensure. Further, since the front group and the rear group of the third to fifth lenses also have a positive refracting power, the imaging lens of the imaging lens can be compared with a so-called telephoto type structure in which the rear group has a negative refracting power. The principal point position becomes the image side, and the back focus becomes long. For this reason, the imaging lens disclosed in Patent Document 2 is disadvantageous for downsizing.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide an imaging optical system having a five-lens configuration that can more appropriately correct various aberrations while achieving further miniaturization. It is to be. And this invention is providing an imaging device provided with this imaging optical system, and a digital apparatus carrying this imaging device.

In order to solve the above technical problem, the present invention provides an imaging optical system, an imaging apparatus, and a digital device having the following configurations. Note that the terms used in the following description are defined as follows in this specification.
(A) A refractive index is a refractive index with respect to the wavelength (587.56 nm) of d line | wire.
(B) Abbe number is nd, nF, nC, and Abbe number is νd for d-line, F-line (wavelength 486.13 nm), C-line (wavelength 656.28 nm), respectively.
νd = (nd−1) / (nF−nC)
The Abbe number νd obtained by the definition formula
(C) 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).
(D) The notation of refractive power (optical power, reciprocal of focal length) in each single lens constituting the cemented lens is power when both sides of the lens surface of the single lens are air.
(E) Since the resin material used for the composite aspherical lens has only an additional function of the substrate glass material, it is not treated as a single optical member, but is treated as if the substrate glass material has an aspherical surface, and the number of lenses Shall be handled as one sheet. The lens refractive index is also the refractive index of the glass material serving as the substrate. The composite aspherical lens is a lens that is aspherical by applying a thin resin material on a glass material to be a substrate.

An imaging optical system according to an aspect of the present invention includes, in order from the object side to the image side, a first lens having a positive refractive power convex toward the object side, a second lens having a negative refractive power, and a predetermined refraction. Third and fourth lenses having a force, negative refractive power, concave on the image side, and from the intersection of the central axes toward the end of the effective area in the contour of the lens cross section along the central axis In this case, the lens includes a fifth lens having an aspherical shape having a perpendicular contact at a position excluding the intersection of the central axes, and satisfies the following conditional expressions (1) to (4).
0.2 <| f5 / f | <0.5 (1)
1 <| z5o / t5 | <4 (2)
2.5 <p5e / p5c <5 (3)
0.63 <Y / TL <0.9 (4)
Where f5 is the focal length of the fifth lens, f is the focal length of the entire imaging optical system, and z5o is the sag amount of the object side surface of the fifth lens at the maximum field angle principal ray. (Displacement from the surface vertex), t5 is the core thickness of the fifth lens, p5e is the e-line optical path length in the fifth lens at the maximum field angle principal ray, and p5c is The e-line optical path length in the fifth lens at the axial principal ray, Y is the maximum image height, and TL is the optical total length of the imaging optical system.

  The imaging optical system having such a configuration is composed of five lenses, each having the above optical characteristics, and by arranging these five lenses in order from the object side to the image side, spherical aberration. It is possible to correct chromatic aberration and secure telecentricity. In particular, since the principal point position can be brought closer to the object side by making the fifth lens an image-side concave shape, the imaging optical system having such a configuration becomes a so-called telephoto type and shortens its overall length. Can be achieved.

  If the upper limit of the conditional expression (1) is exceeded, the movement of the principal point position becomes small, so the positive refractive power of the first lens becomes large, and it becomes difficult to correct spherical aberration and axial chromatic aberration, which is not preferable. . On the other hand, if the lower limit of conditional expression (1) is not reached, correction of distortion becomes difficult, which is not preferable.

  Exceeding the upper limit of conditional expression (2) is not preferable because it becomes difficult to obtain positive refractive power at the peripheral portion (peripheral portion) of the fifth lens, and it becomes difficult to ensure telecentricity. On the other hand, if the lower limit of conditional expression (2) is not reached, it is difficult to correct astigmatism and lateral chromatic aberration in addition to distortion, which is not preferable.

  Exceeding the upper limit of conditional expression (3) is not preferable because it is difficult to obtain positive refractive power at the peripheral portion (peripheral portion) of the fifth lens, and it becomes difficult to ensure telecentricity. On the other hand, if the lower limit of conditional expression (3) is not reached, it is difficult to correct astigmatism and lateral chromatic aberration in addition to distortion, which is not preferable.

  Exceeding the upper limit of the conditional expression (4) is not preferable because the positive refractive power of the first lens becomes large and it becomes difficult to correct spherical aberration and longitudinal chromatic aberration. On the other hand, if the lower limit of conditional expression (4) is not reached, the lens becomes undesirably large.

  Here, in this specification, in this specification, the distance on the optical axis from the lens surface of the most object-side lens to the image-side focal point in the entire imaging optical system is L, and the entire imaging optical system When the focal length is f, it means that L / f <1.4 is satisfied. The image side focal point refers to an image point when a parallel light beam parallel to the optical axis is incident on the imaging optical system. In addition, when a parallel plate member such as an optical low-pass filter, an infrared cut filter, or a seal glass of a fixed imaging device package is disposed between the most image-side surface and the image-side focal point of the imaging optical system. The parallel plate member calculates the above formula as an air conversion distance.

  In addition, the perpendicular contact is a point where the tangent plane is a plane perpendicular to the optical axis of the lens when the tangent plane of the lens surface is set at each point on the contour line of the lens cross section along the optical axis. Mathematically, it refers to the point that gives extreme values to the contour line. The effective area refers to an area set as an area that is optically used as a lens by design.

In another aspect, the imaging optical system described above preferably satisfies the following conditional expression (5).
0.1 <R5r / f <2 (5)
Here, R5r is the radius of curvature of the image side surface in the fifth lens (the image side concave shape is positive (positive)), and f is the focal length of the entire imaging optical system.

  If the upper limit of conditional expression (5) is exceeded, the positive refractive power at the peripheral portion (peripheral portion) of the fifth lens will be weakened, making it difficult to ensure telecentricity. On the other hand, if the lower limit of conditional expression (5) is not reached, correction of distortion is difficult, which is not preferable.

  In another aspect, in the above-described imaging optical system, it is preferable that the second lens has a concave shape on the image side.

  In the imaging optical system having such a configuration, since the second lens has a concave shape on the image side, it is possible to separate a light beam and to favorably correct curvature of field at the third lens.

  In another aspect, the above-described imaging optical system preferably further includes an aperture stop disposed between the first lens and the second lens.

  The imaging optical system having such a configuration can suppress astigmatism and coma because the aperture stop is disposed between the first lens and the second lens.

In another aspect, the imaging optical system described above preferably satisfies the following conditional expression (6).
1.1 <| f2 / f | <1.7 (6)
Here, f2 is the focal length of the second lens, and f is the focal length of the entire imaging optical system.

  Exceeding the upper limit of conditional expression (6) is not preferable because the correction of axial chromatic aberration is insufficient. On the other hand, if the lower limit of conditional expression (6) is not reached, coma increases, which is not preferable.

In another aspect, the imaging optical system described above preferably satisfies the following conditional expression (7).
0.3 <f34 / f <0.7 (7)
Here, f34 is the combined focal length of the third and fourth lenses, and f is the focal length of the entire imaging optical system.

  Exceeding the upper limit of conditional expression (7) is not preferable because correction of field curvature is insufficient. On the other hand, if the lower limit of conditional expression (7) is not reached, correction of lateral chromatic aberration becomes difficult, which is not preferable.

In another aspect, the imaging optical system described above preferably satisfies the following conditional expression (8).
0.8 <f1 / f <1.5 (8)
Here, f1 is the focal length of the first lens, and f is the focal length of the entire imaging optical system.

  If the upper limit of conditional expression (8) is exceeded, the first lens, which is the front lens, is enlarged, which is not preferable. On the other hand, if the lower limit of conditional expression (8) is not reached, it is difficult to correct spherical aberration and axial chromatic aberration, which is not preferable.

In another aspect, the imaging optical system described above preferably satisfies the following conditional expression (9).
0.6 <t23 / t12 <2 (9)
However, t23 is the axial distance in the air between the second lens and the third lens, and t12 is the axial distance in the air between the first lens and the second lens.

  If the upper limit of conditional expression (9) is exceeded, correction of coma becomes difficult, which is not preferable. On the other hand, if the lower limit of conditional expression (9) is not reached, the correction of axial chromatic aberration becomes insufficient, which is not preferable.

  An imaging apparatus according to another aspect of the present invention includes any of the above-described imaging optical systems 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 the object can be formed on the light receiving surface.

  According to this configuration, it is possible to provide an imaging apparatus using an imaging optical system having a five-lens configuration that can correct various aberrations more favorably while reducing the size.

  According to another aspect of the present invention, a digital apparatus includes the above-described imaging device, and a control unit that causes the imaging device to perform at least one of photographing a still image and a moving image of the subject. The imaging optical system is assembled so that an optical image of the subject can be formed on the imaging surface of the imaging device. Preferably, the digital device comprises a mobile terminal.

  According to this configuration, it is possible to provide a digital device or a portable terminal using an imaging optical system having a five-lens configuration that can correct various aberrations while further reducing the size.

  The imaging optical system according to the present invention has a five-lens configuration, and can correct various aberrations better while reducing the size. According to the present invention, it is possible to provide an imaging device and a digital device using such an imaging optical system.

It is a lens sectional view showing the composition typically for explanation of an image pick-up optical system in an embodiment. It is a schematic diagram which shows the definition of the image surface incident angle of a chief ray. It is a block diagram which shows the structure of the digital device in embodiment. It is an external appearance block diagram of the mobile phone with a camera which shows one Embodiment of a digital device. 3 is a cross-sectional view illustrating an arrangement of lens groups in the imaging optical system in Embodiment 1. FIG. 7 is a cross-sectional view illustrating an arrangement of lens groups in an imaging optical system in Embodiment 2. FIG. 6 is a cross-sectional view illustrating an arrangement of lens groups in an imaging optical system in Embodiment 3. FIG. 6 is a cross-sectional view illustrating an arrangement of lens groups in an imaging optical system in Embodiment 4. FIG. 10 is a cross-sectional view illustrating an arrangement of lens groups in an imaging optical system in Embodiment 5. FIG. FIG. 3 is an aberration diagram of the imaging optical system in Example 1. FIG. 6 is an aberration diagram of the image pickup optical system in Example 2. FIG. 6 is an aberration diagram of the image pickup optical system in Example 3. FIG. 6 is an aberration diagram of the image pickup optical system in Example 4. 10 is an aberration diagram of the image pickup optical system in Example 5. FIG.

  Hereinafter, an embodiment according to the present invention will be described with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted suitably. Further, the number of lenses in the cemented lens is not expressed as one for the entire cemented lens, but is represented by the number of single lenses constituting the cemented lens.

<Description of Imaging Optical System of One Embodiment>
FIG. 1 is a lens cross-sectional view schematically illustrating the configuration of an imaging optical system in the embodiment. FIG. 2 is a schematic diagram showing the definition of the image plane incident angle of the chief ray.

  In FIG. 1, the imaging optical system 1 forms an optical image of an object (subject) on the light receiving surface of an image sensor 18 that converts an optical image into an electrical signal. The optical system is composed of five lenses of first to fifth lenses 11 to 15 in order. The image sensor 18 is arranged such that its light receiving surface substantially coincides with the image plane of the imaging optical system 1 (image plane = imaging plane). The imaging optical system 1 illustrated in FIG. 1 has the same configuration as the imaging optical system 1A (FIG. 5) of Example 1 described later.

  In the imaging optical system 1, the fourth and fifth lenses 14 and 15 are fixed with respect to a predetermined image plane, and the first to third lenses 11 to 13 are drawn out and moved in the optical axis direction. Focusing is performed accordingly. However, in the imaging optical system 1, focusing is the method described above, but other than this, it is also possible to adopt a configuration suitable for an overall extension configuration and an inner focus as appropriate.

  Further, the first lens 11 has a positive refractive power convex toward the object side, the second lens 12 is a meniscus lens having a negative negative refractive power toward the image side, and the third lens 13 is a predetermined lens. The fourth lens 14 has a predetermined refractive power, that is, a positive refractive power or a negative refractive power, and a fifth lens. No. 15 has a negative negative refractive power on the image side. More specifically, in the example shown in FIG. 1, the first lens 11 is a biconvex positive lens, the third lens 13 is a meniscus lens having positive refractive power convex toward the image side, The fourth lens 14 is a meniscus lens having positive refractive power convex to the image side, and the fifth lens 15 is a biconcave negative lens. Furthermore, the fifth lens 15 is perpendicular to the position excluding the intersection point of the optical axis AX when moving from the intersection point of the optical axis AX to the end of the effective area on the contour line of the lens cross section along the central axis (optical axis AX). It has an aspherical shape with IP and IP.

  These first to fifth lenses 11 to 15 are aspheric on both sides. These first to fifth lens groups 11 to 15 may be glass mold lenses, for example, or may be lenses made of a resin material such as plastic. In particular, when mounted on a portable terminal, a lens made of a resin material is preferable from the viewpoint of weight reduction. In the example shown in FIG. 1, the first to fifth lenses 11 to 15 are resin material lenses.

In this imaging optical system 1, the focal length of the fifth lens 15 is f5, the focal length of the entire imaging optical system 1 is f, and the sag of the object side surface of the fifth lens 15 at the maximum field angle principal ray is obtained. The amount (displacement from the surface vertex) is z5o, the core thickness of the fifth lens 15 is t5, the e-line optical path length in the fifth lens 15 at the maximum field angle principal ray is p5e, and the axial principal ray is When the c-line optical path length in the fifth lens 15 is p5c, the maximum image height is Y, and the optical total length of the imaging optical system 1 is TL, the following conditions (1) to (4) The expression is satisfied.
0.2 <| f5 / f | <0.5 (1)
1 <| z5o / t5 | <4 (2)
2.5 <p5e / p5c <5 (3)
0.63 <Y / TL <0.9 (4)

  As shown in FIG. 2, the image plane incident angle of the chief ray is an angle (deg, degree) α of the chief ray having the maximum angle of view with respect to the perpendicular to the image plane among the incident rays on the imaging surface. The image plane incident angle α has a principal ray angle when the exit pupil position is on the object side of the image plane as a positive direction.

  In the imaging optical system 1, an optical aperture 16 that is an aperture stop is disposed between the first lens 11 and the second lens 12.

  Further, a filter 17 and an image sensor 18 are disposed on the image side of the imaging optical system 1, that is, on the image side of the fifth lens 15. The filter 17 is a parallel plate-like optical element, and schematically represents various optical filters, a cover glass of the image sensor, and the like. An optical filter such as a low-pass filter or an infrared cut filter can be appropriately arranged depending on the usage, imaging device, camera configuration, and the like. The image sensor 18 photoelectrically converts the image signal of each component of R (red), G (green), and B (blue) in accordance with the amount of light in the optical image of the subject imaged by the imaging optical system 1, and performs predetermined conversion. This is an element that outputs to an image processing circuit (not shown). As a result, an optical image of the object on the object side is guided to the light receiving surface of the image sensor 18 along the optical axis AX by the imaging optical system 1 at a predetermined magnification, and the optical image of the object is captured by the image sensor 18. .

  The imaging optical system 1 having such a configuration includes five first to fifth lenses 11 to 15, each of which has the optical characteristics described above, and the five first to fifth lenses 11. By arranging .about.15 in order from the object side to the image side, it becomes possible to correct spherical aberration and chromatic aberration and to ensure telecentricity. In particular, since the fifth lens 15 has a concave shape on the image side, the principal point position can be brought closer to the object side. Therefore, the imaging optical system 1 having such a configuration is a so-called telephoto type and has a total length. It becomes possible to shorten.

  Conditional expression (1) defines the focal length of the fifth lens 15. If the upper limit of conditional expression (1) is exceeded, the movement of the principal point position becomes small, so that the positive refractive power of the first lens 11 becomes large, and it becomes difficult to correct spherical aberration and axial chromatic aberration. Absent. On the other hand, if the lower limit of conditional expression (1) is not reached, correction of distortion becomes difficult, which is not preferable.

From such a viewpoint, it is more preferable to satisfy the following conditional expression (1 ′).
0.25 <| f5 / f | <0.47 (1 ′)

  Conditional expression (2) defines the shape of the fifth lens. Exceeding the upper limit of conditional expression (2) is not preferable because it becomes difficult to obtain positive refractive power at the peripheral portion (peripheral portion) of the fifth lens 15 and it becomes difficult to ensure telecentricity. On the other hand, if the lower limit of conditional expression (2) is not reached, it is difficult to correct astigmatism and lateral chromatic aberration in addition to distortion, which is not preferable.

From such a viewpoint, it is more preferable to satisfy the following conditional expression (2 ′).
1.2 <| z5o / t5 | <3.8 (2 ')

  Conditional expression (3) defines the shape of the fifth lens. Exceeding the upper limit of conditional expression (3) is not preferable because it becomes difficult to obtain positive refractive power at the peripheral portion (peripheral portion) of the fifth lens 15 and it becomes difficult to ensure telecentricity. On the other hand, if the lower limit of conditional expression (3) is not reached, it is difficult to correct astigmatism and lateral chromatic aberration in addition to distortion, which is not preferable.

From such a viewpoint, it is more preferable to satisfy the following conditional expression (3 ′).
3 <p5e / p5c <4.9 (3 ′)

  Conditional expression (4) defines the compactness of the optical system. Exceeding the upper limit of the conditional expression (4) is not preferable because the positive refractive power of the first lens 11 becomes large and it becomes difficult to correct spherical aberration and axial chromatic aberration. On the other hand, if the lower limit of conditional expression (4) is not reached, the lens becomes undesirably large.

From such a viewpoint, it is more preferable to satisfy the following conditional expression (4 ′).
0.65 <Y / TL <0.8 (4 ′)

  In the imaging optical system 1 described above, the second lens 12 has a concave shape on the image side. For this reason, the imaging optical system 1 of the present embodiment can separate the luminous flux and correct the curvature of field at the third lens 13 satisfactorily.

  In the imaging optical system 1 described above, the aperture stop 16 is disposed between the first lens 11 and the second lens 12. For this reason, the imaging optical system 1 of the present embodiment can suppress astigmatism and coma.

  In the imaging optical system 1 described above, all lens surfaces facing the air are aspherical surfaces. For this reason, this configuration enables both compactness and high image quality.

In the imaging optical system 1 described above, the radius of curvature of the image side surface of the fifth lens 15 (plus the image side concave shape is positive (positive)) is R5r, and the focal length of the entire imaging optical system 1 is In the case of f, it is preferable that the following conditional expression (5) is satisfied.
0.1 <R5r / f <2 (5)

  Conditional expression (5) defines the surface shape of the fifth lens 15 on the image plane side. If the upper limit of conditional expression (5) is exceeded, the positive refractive power at the peripheral part (peripheral part) of the fifth lens 15 is weakened, and it is difficult to ensure telecentricity. On the other hand, if the lower limit of conditional expression (5) is not reached, correction of distortion is difficult, which is not preferable.

From such a viewpoint, it is more preferable to satisfy the following conditional expression (5 ′).
0.2 <R5r / f <1 (5 ′)

In the imaging optical system 1 described above, when the focal length of the second lens 12 is f2, and the focal length of the entire imaging optical system 1 is f, it is preferable that the following conditional expression (6) is satisfied. .
1.1 <| f2 / f | <1.7 (6)

  Conditional expression (6) defines the focal length of the second lens. Exceeding the upper limit of conditional expression (6) is not preferable because the correction of axial chromatic aberration is insufficient. On the other hand, if the lower limit of conditional expression (6) is not reached, coma increases, which is not preferable.

From such a viewpoint, it is more preferable to satisfy the following conditional expression (6 ′).
1.2 <| f2 / f | <1.6 (6 ′)

In the imaging optical system 1 described above, when the combined focal length of the third and fourth lenses 13 and 14 is f34 and the focal length of the entire imaging optical system 1 is f, the following condition (7) It is preferable to satisfy the formula.
0.3 <f34 / f <0.7 (7)

  Conditional expression (7) defines the combined focal length of the third lens and the fourth lens. Exceeding the upper limit of conditional expression (7) is not preferable because of insufficient correction of curvature of field. On the other hand, if the lower limit of conditional expression (7) is not reached, correction of lateral chromatic aberration becomes difficult, which is not preferable.

From such a viewpoint, it is more preferable to satisfy the following conditional expression (7 ′).
0.4 <f34 / f <0.6 (7 ′)

In the imaging optical system 1 described above, when the focal length of the first lens 11 is f1, and the focal length of the entire imaging optical system 1 is f, it is preferable that the following conditional expression (8) is satisfied. .
0.8 <f1 / f <1.5 (8)

  Conditional expression (8) defines the focal length of the first lens 11. If the upper limit of the conditional expression (8) is exceeded, the first lens 11 that is the front lens is enlarged, which is not preferable. On the other hand, if the lower limit of conditional expression (8) is not reached, it is difficult to correct spherical aberration and axial chromatic aberration, which is not preferable.

From such a viewpoint, it is more preferable to satisfy the following conditional expression (8 ′).
0.81 <f1 / f <1.3 (8 ′)

In the above-described imaging optical system 1, the on-axis distance between the second lens 12 and the third lens 13 is t23, and the air axis between the first lens 11 and the second lens 12 is t23. When the upper interval is t12, it is preferable to satisfy the following conditional expression (9).
0.6 <t23 / t12 <2 (9)

  Conditional expression (9) defines the arrangement of the first to third lenses. Exceeding the upper limit of conditional expression (9) is not preferable because correction of coma becomes difficult. On the other hand, if the lower limit of conditional expression (9) is not reached, the correction of axial chromatic aberration becomes insufficient, which is not preferable.

From such a viewpoint, it is more preferable to satisfy the following conditional expression (9 ′).
0.7 <t23 / t12 <1.5 (9 ′)

  In the above-described imaging optical system 1, a cam, a stepping motor, or the like may be used for driving the first to third lenses 11 to 13 to be extended and moved, or a piezoelectric actuator may be used. May be used. In the case of using the piezoelectric actuator, it is possible to drive each group independently while suppressing an increase in the volume and power consumption of the driving device, and the imaging device can be further downsized.

  In the above-described imaging optical system 1, when a glass lens having an aspheric surface is used, the aspheric glass lens is a glass molded aspheric lens, a ground aspheric glass lens, a composite aspheric lens ( It is also possible to form aspherical resin on a spherical glass lens. Glass molded aspherical lenses are suitable for mass production, and composite aspherical lenses have a high degree of design freedom because there are many types of glass materials that can serve as substrates. In particular, an aspherical lens using a high refractive index material is not easy to mold, so a composite aspherical lens is preferable. In the case of a single-sided aspherical surface, the advantages of the composite aspherical lens can be fully utilized.

  In the above-described imaging optical system 1, when a plastic lens (resin material lens) is used, molding is performed using a material in which particles having a maximum length of 30 nanometers or less are dispersed in plastic (resin material). A lens is preferred.

In general, mixing fine particles with a transparent resin material scatters light and reduces the transmittance, making it difficult to use as an optical material. However, the size of the fine particles should be smaller than the wavelength of the transmitted light beam. The light is not substantially scattered. And although a resin material will have a refractive index falling with a temperature rise, an inorganic particle will raise a refractive index with a temperature rise conversely. For this reason, it is possible to make the refractive index change hardly occur with respect to the temperature change by acting so as to cancel each other by utilizing such temperature dependency. More specifically, by dispersing inorganic fine particles having a maximum length of 30 nanometers or less in a resin material as a base material, a resin material with reduced temperature dependency of the refractive index is obtained. For example, fine particles of niobium oxide (Nb ₂ O ₅ ) are dispersed in acrylic. In the above-described imaging optical system 1, lenses having relatively large refractive power (for example, the first and third lenses 11 and 13 in the example shown in FIG. 1) or all the lenses (first through first in the example shown in FIG. 1). By using a plastic material in which such inorganic particles are dispersed in the five lenses 11 to 15), it is possible to suppress the image point position fluctuation when the temperature of the entire imaging lens system changes.

  Such a lens made of a plastic material in which inorganic fine particles are dispersed is preferably molded as follows.

The temperature change n (T) of the refractive index is expressed by the formula Fa by differentiating the refractive index n with respect to the temperature T based on the Lorentz-Lorentz equation.
n (T) = ((n ² +2) × (n ² −1)) / 6n × (−3α + (1 / [R]) × (∂ [R] / ∂T)) (Fa)
Where α is a linear expansion coefficient and [R] is molecular refraction.

In the case of a resin material, in general, the contribution of the refractive index to the temperature dependence is smaller in the second term than in the first term in the formula Fa, and can be almost ignored. For example, in the case of PMMA resin, the linear expansion coefficient α is 7 × 10 ⁻⁵ , and when it is substituted into the formula Fa, it becomes n (T) = − 12 × 10 ⁻⁵ (/ ° C.), which is approximately the actual measurement value. Match.

Specifically, the temperature change n (T) of the refractive index, which was conventionally about −12 × 10 ⁻⁵ [/ ° C.], can be suppressed to an absolute value of less than 8 × 10 ⁻⁵ [/ ° C.]. preferable. More preferably, the absolute value is less than 6 × 10 ⁻⁵ [/ ° C.].

Therefore, as such a resin material, a polyolefin resin material, a polycarbonate resin material, or a polyester resin material is preferable. In the polyolefin resin material, the refractive index temperature change n (T) is about −11 × 10 ⁻⁵ (/ ° C.), and in the polycarbonate resin material, the refractive index temperature change n (T) is about −14 × 10 ⁻⁵ (/ ° C.), and in the case of a polyester-based resin material, the temperature change n (T) of the refractive index is about −13 × 10 ⁻⁵ (/ ° C.).

  In the above-described imaging optical system 1, when the lens is a resin material lens, an energy curable resin may be used as the resin material.

  In recent years, as a method for mounting an image pickup apparatus at a low cost and in large quantities, a reflow process (heating process) is performed on a substrate on which a solder has been potted in advance, with an IC chip and other electronic components and optical elements placed on the board. A technique has been proposed in which an electronic component and an optical element are simultaneously mounted on a substrate by melting the substrate.

  In order to perform mounting using such a reflow process, it is necessary to heat the optical element together with the electronic components to about 200 to 260 degrees. Under such a high temperature, a lens using a thermoplastic resin is thermally deformed or discolored, and its optical performance is degraded.

  Therefore, it is preferable to use an energy curable resin as the lens material. Compared to lenses using thermoplastic resins such as polycarbonates and polyolefins, this reduces the decrease in optical performance when energy curable resins are exposed to high temperatures, so energy curable resins are suitable for reflow treatment. This is because it is effective. Furthermore, the lens of the energy curable resin is easier to manufacture than the glass mold lens and is inexpensive, and it is possible to achieve both cost reduction and mass productivity in the imaging apparatus incorporating the imaging optical system 1. Here, the energy curable resin includes both a thermosetting resin and an ultraviolet curable resin.

  An example of such an energy curable resin is Shin-Nakamura Chemical Co., Ltd., NK ester DCP (tricyclodecane dimethanol dimethacrylate) made by Nippon Oil & Fats, 1 wt% of perbutyl O as a polymerization initiator, and 150 ° C. Examples include those cured for 10 minutes.

<Description of digital equipment incorporating imaging optical system>
Next, a digital device in which the above-described imaging optical system 1 is incorporated will be described.

  FIG. 3 is a block diagram illustrating a configuration of a digital device according to the embodiment. The digital device 3 includes an imaging unit 30, an image generation unit 31, an image data buffer 32, an image processing unit 33, a driving unit 34, a control unit 35, a storage unit 36, and an I / F unit 37 for the imaging function. Composed. Examples of the digital device 3 include a digital still camera, a video camera, a surveillance camera (monitor camera), a portable terminal such as a mobile phone or a personal digital assistant (PDA), a personal computer, and a mobile computer. Equipment (eg, a mouse, scanner, printer, etc.) may be included. In particular, the imaging optical system 1 of the present embodiment is sufficiently compact when mounted on a mobile terminal such as a mobile phone or a personal digital assistant (PDA), and is preferably mounted on this mobile terminal.

  The imaging unit 30 includes an imaging device 21 and an imaging element 18. The imaging device 21 includes an imaging optical system 1 as shown in FIG. 1 that functions as an imaging lens, a lens driving device (not shown), etc., for performing focusing by driving a lens for focusing in the optical axis direction. It is prepared for. Light rays from the subject are imaged on the light receiving surface of the image sensor 18 by the imaging optical system 1 and become an optical image of the subject.

  As described above, the image sensor 18 converts the optical image of the subject imaged by the imaging optical system 1 into an electrical signal (image signal) of R, G, B color components, and each of the R, G, B colors. It outputs to the image generation part 31 as an image signal. The imaging device 18 is controlled by the control unit 35 for imaging operations such as imaging of either a still image or a moving image, or reading of output signals of each pixel in the imaging device 18 (horizontal synchronization, vertical synchronization, transfer). . Note that the image sensor 18 may be a back-illuminated solid-state image sensor. As a result, the light receiving unit that performs photoelectric conversion is disposed on the imaging optical system 1 side with respect to the wiring layer, so that the substantial light amount reaching the light receiving unit increases from the viewpoint of shading correction described later, and low luminance sensitivity is achieved. It is possible to extremely effectively suppress the peripheral light amount drop due to the improvement and the oblique incidence.

  The image generation unit 31 performs amplification processing, digital conversion processing, and the like on the analog output signal from the image sensor 18 and determines an appropriate black level, γ correction, and white balance adjustment (WB adjustment) for the entire image. Then, known image processing such as contour correction and color unevenness correction is performed to generate image data 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, the image data buffer 32 is a volatile storage element. It is composed of a RAM (Random Access Memory).

  The image processing unit 33 is a circuit that performs predetermined image processing such as resolution conversion on the image data in the image data buffer 32.

  Further, if necessary, the image processing unit 33 could not be corrected by the imaging optical system 1 such as a known distortion correction process for correcting distortion in the optical image of the subject formed on the light receiving surface of the imaging element 18. It may be configured to correct aberrations. In the distortion correction, an image distorted by aberration is corrected to a natural image having a similar shape similar to a sight seen with the naked eye and having substantially no distortion. With this configuration, even if the optical image of the subject guided to the image sensor 18 by the imaging optical system 1 is distorted, it is possible to generate a natural image with substantially no distortion. Further, in the configuration in which such distortion is corrected by image processing by information processing, in particular, only other aberrations other than distortion aberration need to be considered, so that the degree of freedom in designing the imaging optical system 1 is increased and the design is improved. It becomes easier. In addition, in the configuration in which such distortion is corrected by image processing based on information processing, the aberration burden due to the lens close to the image plane is reduced, so that the exit pupil position can be easily controlled, and the lens shape is easy to process. It can be shaped.

  Further, the image processing unit 33 may include a known peripheral illuminance decrease correction process for correcting a peripheral illuminance decrease in an optical image of a subject formed on the light receiving surface of the image sensor 18 as necessary. The peripheral illuminance drop correction (shading correction) is executed by storing correction data for performing the peripheral illuminance drop correction in advance and multiplying the image (pixel) after photographing by the correction data. Since the decrease in ambient illuminance mainly occurs due to the incident angle dependency of the sensitivity in the image sensor 18, the vignetting of the lens, the cosine fourth law, etc., the correction data has a predetermined value that corrects the decrease in illuminance caused by these factors. Is set. With such a configuration, even if the peripheral illuminance drops in the optical image of the subject guided to the image sensor 18 by the imaging optical system 1, it is possible to generate an image having sufficient illuminance to the periphery. It becomes.

  In the present embodiment, the shading correction is performed by setting the pitch of the arrangement of the color filters and the on-chip microlens array slightly smaller than the pixel pitch on the imaging surface of the imaging device 18 so as to reduce the shading. It may be done. In such a configuration, by setting the pitch to be slightly smaller, a color filter or an on-chip microlens array is placed on the optical axis side of the imaging optical system 1 for each pixel toward the periphery of the imaging surface of the imaging element 18. Therefore, the obliquely incident light beam can be efficiently guided to the light receiving portion of each pixel. As a result, shading generated in the image sensor 18 can be kept small.

  The driving unit 34 drives the lens for focusing in the imaging optical system 1 so as to perform desired focusing by operating the lens driving device (not shown) based on a control signal output from the control unit 35. To do.

  The control unit 35 includes, for example, a microprocessor and its peripheral circuits, and includes an imaging unit 30, an image generation unit 31, an image data buffer 32, an image processing unit 33, a drive unit 34, a storage unit 36, and an I / F unit. The operation of each part 37 is controlled according to its function. In other words, the imaging device 21 is controlled by the control unit 35 to execute at least one of the still image shooting and the moving image shooting of the subject.

  The storage unit 36 is a storage circuit that stores image data generated by still image shooting or moving image shooting of a subject. For example, a ROM (Read Only Memory) that is a nonvolatile storage element or a rewritable nonvolatile memory It comprises an EEPROM (Electrically Erasable Programmable Read Only Memory) that is a storage element, a RAM, and the like. That is, the storage unit 36 has a function as a still image memory and a moving image memory.

  The I / F unit 37 is an interface that transmits / receives image data to / from an external device. For example, the I / F unit 37 is an interface that conforms to a standard such as USB or IEEE1394.

  Next, the imaging operation of the digital device 3 having such a configuration will be described.

  When shooting a still image, the control unit 35 controls the imaging device 21 to shoot a still image and operates the lens driving device (not shown) of the imaging device 21 via the driving unit 34. Then, focusing is performed by moving the second lens group 12. As a result, the focused optical image is periodically and repeatedly formed on the light receiving surface of the image sensor 18, converted into image signals of R, G, and B color components, and then output to the image generator 31. . The image signal is temporarily stored in the image data buffer 32, and after image processing is performed by the image processing unit 33, an image based on the image signal is displayed on a display (not shown). The photographer can adjust the main subject so as to be within a desired position on the screen by referring to the display. When a so-called shutter button (not shown) is pressed in this state, image data is stored in the storage unit 36 as a still image memory, and a still image is obtained.

  In addition, when performing moving image shooting, the control unit 35 controls the imaging device 21 to perform moving image shooting. After that, as in the case of still image shooting, the photographer refers to the display (not shown) so that the image of the subject obtained through the imaging device 21 is placed at a desired position on the screen. Can be adjusted. When a shutter button (not shown) is pressed, moving image shooting is started. At the time of moving image shooting, the control unit 35 controls the imaging device 21 to shoot a moving image and operates the lens driving device (not shown) of the imaging device 21 via the driving unit 34 to perform focusing. Do. As a result, a focused optical image is periodically and repeatedly formed on the light receiving surface of the image sensor 18, converted into R, G, and B color component image signals, and then output to the image generation unit 31. . The image signal is temporarily stored in the image data buffer 32, and after image processing is performed by the image processing unit 33, an image based on the image signal is displayed on a display (not shown). Then, when the shutter button (not shown) is pressed again, the moving image shooting is completed. The captured moving image is guided to and stored in the storage unit 36 as a moving image memory.

  With such a configuration, there are provided the imaging device 21 and the digital device 3 using the imaging optical system 1 having a five-lens configuration capable of more appropriately correcting various aberrations while further reducing the size. In particular, since the imaging optical system 1 is reduced in size and performance, it is possible to employ the imaging element 18 having a high pixel while reducing the size (compacting). In particular, since the imaging optical system 1 is small and can be applied to a high-pixel imaging device, the imaging optical system 1 is suitable for a mobile terminal that is increasing in pixel count and functionality. As an example, a case where the imaging device 21 is mounted on a mobile phone will be described below.

  FIG. 4 is an external configuration diagram of a camera-equipped mobile phone showing an embodiment of a digital device. 4A shows an operation surface of the mobile phone, and FIG. 4B shows a back surface of the operation surface, that is, a back surface.

  In FIG. 4, the mobile phone 5 is provided with an antenna 51 at the top, and on its operation surface, as shown in FIG. 4A, a rectangular display 52, activation of image shooting mode, still image shooting and moving image An image shooting button 53 for switching to shooting, a shutter button 55, and a dial button 56 are provided.

  The cellular phone 5 incorporates a circuit for realizing a telephone function using a cellular phone network, and includes the above-described imaging unit 30, image generating unit 31, image data buffer 32, image processing unit 33, and driving unit. 34, the control part 35, and the memory | storage part 36 are incorporated, and the imaging device 21 of the imaging part 30 faces the back.

  When the image shooting button 53 is operated, a control signal indicating the operation content is output to the control unit 35, and the control unit 35 performs the activation and execution of the still image shooting mode and the activation and execution of the moving image shooting mode. Execute the action according to the operation content. When the shutter button 55 is operated, a control signal indicating the operation content is output to the control unit 35, and the control unit 35 executes an operation corresponding to the operation content such as still image shooting or moving image shooting. .

<Description of More Specific Embodiment of Imaging Optical System>
Hereinafter, the specific configuration of the imaging optical system 1 as shown in FIG. 1, that is, the imaging optical system 1 provided in the imaging device 21 mounted in the digital device 3 as shown in FIG. 3 will be described with reference to the drawings. I will explain.

  FIG. 5 is a cross-sectional view illustrating the arrangement of lenses in the imaging optical system according to the first embodiment. FIG. 9 is an aberration diagram of the image pickup optical system according to the first embodiment. FIG. 9 shows the case at infinity. The same applies to Examples 2 to 5 described later (FIGS. 10 to 14).

  As shown in FIG. 5, in the imaging optical system 1A of Embodiment 1, the first to fifth lenses L1 to L5 are arranged in order from the object side to the image side. The fifth lenses L4 and L5 are fixed with respect to a predetermined image plane, and the first to third lenses L1 to L3 are extended integrally to move in the optical axis direction.

  More specifically, in the imaging optical system 1A according to the first exemplary embodiment, the first to fifth lenses L1 to L5 are configured as follows in order from the object side to the image side.

  The first lens L1 is a biconvex positive lens that has a positive refractive power that is convex toward the object side and has a convex surface, and the second lens L2 is a negative lens that has a negative negative refractive power on the image side. The third lens L3 is a positive meniscus lens having a positive refractive power convex toward the image side, and the fourth lens L4 is a positive meniscus lens having a positive refractive power convex toward the image side. The fifth lens L5 is a biconcave negative lens that is concave on the image side and has a concave surface. Further, the fifth lens L5 is perpendicular to the position excluding the intersection point of the optical axis AX when it goes from the intersection point of the optical axis AX to the end of the effective area on the contour line of the lens cross section along the central axis (optical axis AX). IPA, having an aspherical shape with IPA, and having a region having a positive refractive power on a cross section including the optical axis AX in a peripheral region radially away from the optical axis AX by a predetermined distance ing. That is, the fifth lens L5 is a biconcave lens having a negative refractive power having a concave shape on the image side and a concave surface facing the image side within a range from the optical axis AX to a predetermined distance (within a circular area). The negative lens is a positive lens having a positive refractive power within the range from the predetermined distance to the end of the effective region (in the cross-sectional ring-shaped region). The fourth lens L4 is disposed close to the fifth lens L5 so that the convex portion on the image side enters the concave portion on the object side of the fifth lens L5. These first to fifth lenses L1 to L5 are aspherical on both surfaces and are made of a resin material.

  The optical aperture stop ST is disposed between the first lens L1 and the second lens L2. The optical diaphragm ST may be an aperture diaphragm, a mechanical shutter, or a variable diaphragm in the case of Example 2 and Example 3 described later.

  Then, on the image side of the fifth lens L5, the light receiving surface of the image sensor SR is disposed via a parallel plate FT as a filter. The parallel plate FT is a cover glass or the like of various optical filters or the image sensor SR.

  In FIG. 5, the number ri (i = 1, 2, 3,...) Given to each lens surface is the i-th lens surface when counted from the object side (however, the cemented surface of the lens is 1). It is assumed that a surface marked with “*” in ri is an aspherical surface. In addition, both surfaces of the parallel plate FT and the light receiving surface of the image sensor SR are handled as one surface, and the optical aperture stop ST is also handled as one surface. The meaning of such handling and symbols is the same for Examples 2 to 5 described later (FIGS. 6 to 9). However, it does not mean that they are exactly the same. For example, in each of FIGS. 5 to 9 of the first to fifth embodiments, the lens surface arranged closest to the object side has the same symbol (r1). Although attached, it does not mean that these curvatures are the same throughout the first to fifth embodiments.

  Under such a configuration, a light beam incident from the object side sequentially has a first lens L1, an optical aperture stop ST, a second lens L2, a third lens L3, a fourth lens L4, and a fifth lens along the optical axis AX. An optical image of the object is formed on the light receiving surface of the image sensor SR through the lens L5 and the parallel plate FT. In the image sensor SR, the optical image is converted into an electrical signal. This electric signal is subjected to predetermined digital image processing as necessary, and is recorded as a digital video signal in a memory of a digital device such as a digital camera, or other digital signal is transmitted by wired or wireless communication via an interface. Or transmitted to the device.

  The construction data of each lens in the imaging optical system 1A of Example 1 is shown below.

Numerical example 1
Unit mm
Surface data surface number r d nd νd
Object ∞ ∞
1 * 1.987 0.502 1.54470 56.15
2 * -662.161 0.100
3 (Aperture) ∞ 0.150
4 * 7.077 0.183 1.63200 23.41
5 * 2.455 0.359
6 * -11.944 0.713 1.54470 56.15
7 * -2.762 Variable 8 * -2.567 0.825 1.54470 56.15
9 * -1.143 0.416
10 * -1.923 0.504 1.54470 56.15
11 * 2.814 0.600
12 ∞ 0.300 1.51633 64.14
13 ∞ 0.100
Image plane ∞
Aspherical data first surface K = 1.0018e-002, A4 = -2.2545e-003, A6 = -1.1382e-003, A8 = 4.2548e-004, A10 = -2.8106e-003, A12 = 1.4111e-003 , A14 = -3.9776e-003
Second surface K = 2.000e + 002, A4 = 1.8654e-003, A6 = 7.8510e-003, A8 = -1.6648e-002, A10 = -1.3356e-003, A12 = -2.5634e-003, A14 = 4.0137e-003
4th surface K = -1.7915e + 001, A4 = -2.1802e-002, A6 = 5.4398e-002, A8 = -8.4677e-002, A10 = 4.1091e-002, A12 = -9.5315e-003, A14 = -2.1289e-003
Fifth surface K = -2.8863e + 000, A4 = 8.4837e-003, A6 = 5.0146e-002, A8 = -2.2757e-002, A10 = -2.3635e-002, A12 = 3.1893e-002, A14 = -1.2372e-002, A16 = -2.1417e-004
6th surface K = -3.3315e + 001, A4 = -2.3752e-002, A6 = 5.2773e-003, A8 = 1.8787e-002, A10 = 6.3762e-003, A12 = 2.5602e-003, A14 =- 4.3879e-003
7th surface K = 1.4566e + 000, A4 = -1.2393e-002, A6 = 1.9844e-002, A8 = -1.5397e-002, A10 = 7.6824e-003, A12 = 2.6704e-003, A14 =- 8.8074e-004
8th surface K = 4.0403e-001, A4 = -5.4281e-002, A6 = 3.8150e-002, A8 = -6.1761e-003, A10 = -1.0280e-003, A12 = 7.0418e-004, A14 = -9.8832e-005
9th surface K = -3.2233e + 000, A4 = -8.1613e-002, A6 = 3.0868e-002, A8 = -2.1344e-003, A10 = -1.3325e-005, A12 = -8.1672e-005, A14 = 1.1326e-005
10th surface K = -1.2911e + 001, A4 = -4.3622e-002, A6 = 9.6785e-003, A8 = -7.1345e-005, A10 = -1.5455e-004, A12 = 1.6766e-005, A14 = -5.6815e-007
11th surface K = -6.7848e + 000, A4 = -2.8511e-002, A6 = 4.8746e-003, A8 = -7.2599e-004, A10 = 8.0232e-005, A12 = -6.2087e-006, A14 = 2.3630e-007
Various data focal length (Fl) 4.447 (mm)
F number 2.805
Angle of view (half angle of view) W 38.980 (deg)
Image height (Y) 3.658 (mm)
Total lens length (TL) 5.437 (mm)
Back focus (BF) 0.901
Focal length of each lens (mm)
First lens L1 3.639
Second lens L2 -6.039
Third lens L3 6.421
Fourth lens L4 3.140
5th lens L5 -2.021

  In the above surface data, the surface number corresponds to the number i of the symbol ri (i = 1, 2, 3,...) Given to each lens surface shown in FIG. The surface marked with * in the number i indicates an aspherical surface (aspherical refractive optical surface or a surface having a refractive action equivalent to an aspherical surface).

  Also, “r” is the radius of curvature of each surface (unit is mm), “d” is the distance between the lens surfaces on the optical axis in the infinite focus state (axis upper surface distance), and “nd” is The refractive index “νd” of each lens with respect to the d-line (wavelength 587.56 nm) indicates the Abbe number. Since each surface of the optical aperture stop ST, both surfaces of the parallel flat plate FT, and the light receiving surface of the image sensor SR is a flat surface, the radius of curvature thereof is ∞ (infinite).

In each embodiment, the shape of the aspherical surface is defined by the following equation when the surface vertex is the origin, the X axis is taken in the optical axis direction, and the height in the direction perpendicular to the optical axis is h.
X = (h ² / R) / [1+ (1− (1 + K) h ² / R ² ) ^1/2 ] + ΣA _i · h ⁱ
Where Ai is an i-th order aspheric coefficient, R is a reference radius of curvature, and K is a conic constant.

  Note that the paraxial radius of curvature (r) described in the claims, embodiments, and examples is in the vicinity of the center of the lens (more specifically, within 10% of the lens outer diameter) in the actual lens measurement scene. The approximate curvature radius when the shape measurement value in the center region of the curve is fitted by the least square method can be regarded as the paraxial curvature radius. For example, when a secondary aspherical coefficient is used, a curvature radius that takes into account the secondary aspherical coefficient in the reference curvature radius of the aspherical definition formula can be regarded as a paraxial curvature radius (for example, reference literature). (See P41-P42 of “Lens Design Method” by K. Matsui, Kyoritsu Publishing Co., Ltd.).

  In the aspheric data, “en” means “10 to the power of n”. For example, “e + 001” means “10 to the power of +1”, and “e-003” means “10 to the power of −3”.

  Each aberration in the imaging lens 1A of Example 1 under the lens arrangement and configuration as described above is shown in FIG. FIGS. 10A, 10B, and 10C show spherical aberration (sine condition) (LONGITUDINAL SPHERICAL ABERRATION), astigmatism (ASTIGMATISM FIELD CURVER), and distortion aberration (DISTORTION), respectively, in this order. The abscissa of the spherical aberration represents the focal position shift in mm, and the ordinate represents the value normalized by the maximum incident height. The horizontal axis of astigmatism represents the focal position shift in mm, and the vertical axis represents the image height in mm. The horizontal axis of the distortion aberration represents the actual image height as a percentage (%) with respect to the ideal image height, and the vertical axis represents the image height in mm. Moreover, in the figure of astigmatism, the broken line represents the result on the tangential (meridional) surface, and the solid line represents the result on the sagittal (radial) surface.

  In the spherical aberration diagram, three light aberrations are shown: a solid line d line (wavelength 587.56 nm), a broken line g line (wavelength 435.84 nm), and a dashed line C line (wavelength 656.28 nm). is there. The diagrams of astigmatism and distortion are the results when the d-line (wavelength 587.56 nm) is used.

  The above-described treatment is the same in the construction data according to Examples 2 to 5 and FIGS. 11 to 14 showing the respective aberrations.

  FIG. 6 is a cross-sectional view illustrating the arrangement of lenses in the imaging optical system according to the second embodiment. FIG. 11 is an aberration diagram of the image pickup optical system according to the second embodiment.

  As shown in FIG. 6, the imaging optical system 1B according to the second embodiment includes first to fifth lenses L1 to L5 arranged in order from the object side to the image side. The fifth lenses L4 and L5 are fixed with respect to a predetermined image plane, and the first to third lenses L1 to L3 are extended integrally to move in the optical axis direction.

  More specifically, in the imaging optical system 1B of the second embodiment, the first to fifth lenses L1 to L5 are configured as follows in order from the object side to the image side.

  The first lens L1 is a positive meniscus lens having a positive refractive power that is convex toward the object side and has a convex surface facing the object side, and the second lens L2 is negative refractive that is concave toward the image side. The third lens L3 is a positive meniscus lens having a positive refractive power convex toward the image side, and the fourth lens L4 is a positive meniscus lens having a positive refractive power convex toward the image side. The fifth lens L5 is a meniscus lens, and is a biconcave negative lens having a concave shape on the image side and having a concave surface directed. Further, the fifth lens L5 is perpendicular to the position excluding the intersection point of the optical axis AX when it goes from the intersection point of the optical axis AX to the end of the effective area on the contour line of the lens cross section along the central axis (optical axis AX). IPB, has an aspheric shape with IPB, and has a region having a positive refractive power on a cross-section including the optical axis AX in a peripheral region radially away from the optical axis AX by a predetermined distance ing. The fourth lens L4 is disposed close to the fifth lens L5 so that the convex portion on the image side enters the concave portion on the object side of the fifth lens L5. These first to fifth lenses L1 to L5 are aspherical on both surfaces and are made of a resin material. The optical aperture stop ST is disposed between the first lens L1 and the second lens L2. Then, on the image side of the fifth lens L5, the light receiving surface of the image sensor SR is disposed via a parallel plate FT as a filter.

  Under such a configuration, a light beam incident from the object side sequentially has a first lens L1, an optical aperture stop ST, a second lens L2, a third lens L3, a fourth lens L4, and a fifth lens along the optical axis AX. An optical image of the object is formed on the light receiving surface of the image sensor SR through the lens L5 and the parallel plate FT. In the image sensor SR, the optical image is converted into an electrical signal, and this electrical signal is appropriately processed as in the first embodiment.

  The construction data of each lens in the imaging optical system 1B of Example 2 is shown below.

Numerical example 2
Unit mm
Surface data surface number r d nd νd
Object ∞ ∞
1 * 2.256 0.580 1.54470 56.15
2 * 85.922 0.100
3 (Aperture) ∞ 0.150
4 * 5.238 0.300 1.63200 23.41
5 * 2.239 0.290
6 * -28.744 0.639 1.54470 56.15
7 * -2.649 Variable 8 * -2.762 0.913 1.54470 56.15
9 * -1.045 0.362
10 * -2.862 0.300 1.54470 56.15
11 * 1.550 0.600
12 ∞ 0.300 1.51633 64.14
13 ∞ 0.210
Image plane ∞
Aspherical data first surface K = -5.5196e-002, A4 = -3.9020e-003, A6 = -9.4896e-005, A8 = -1.5672e-003, A10 = -2.4317e-003, A12 = 3.0294e -003, A14 = -2.7363e-003
Second surface K = -2.0000e + 002, A4 = -1.5750e-002, A6 = 1.0718e-002, A8 = -8.2950e-003, A10 = -2.7385e-003, A12 = -6.4496e-003, A14 = 4.8470e-003
4th surface K = -5.8697e + 001, A4 = -3.4478e-002, A6 = 3.3542e-002, A8 = -6.3869e-002, A10 = 4.0310e-002, A12 = -9.5319e-003, A14 = -2.1290e-003
5th surface K = -6.1068e + 000, A4 = -2.3813e-003, A6 = 4.5090e-002, A8 = -2.1074e-002, A10 = -2.1426e-002, A12 = 2.7588e-002, A14 = -8.7929e-003, A16 = -2.1411e-004
6th surface K = 2.3961e + 001, A4 = -2.5352e-002, A6 = 6.5023e-003, A8 = 1.6722e-002, A10 = 4.8452e-003, A12 = 1.6567e-003, A14 = -3.0333 e-003
7th surface K = 1.5028e + 000, A4 = -2.2072e-002, A6 = 1.7676e-002, A8 = -1.4579e-002, A10 = 5.77065e-003, A12 = 1.9502e-003, A14 = 5.4302 e-004
8th surface K = 6.5978e-001, A4 = -6.0721e-002, A6 = 3.8714e-002, A8 = -7.1908e-003, A10 = -1.2013e-003, A12 = 7.4111e-004, A14 = -9.8964e-005
9th surface K = -3.4574e + 000, A4 = -7.5959e-002, A6 = 2.9136e-002, A8 = -2.3224e-003, A10 = -2.6804e-005, A12 = -8.1038e-005, A14 = 1.2919e-005
10th surface K = -2.4507e + 001, A4 = -4.7317e-002, A6 = 9.6746e-003, A8 = -6.0653e-005, A10 = -1.5348e-004, A12 = 1.6745e-005, A14 = -5.6620e-007
11th surface K = −9.1209e + 000, A4 = −2.6350e-002, A6 = 4.4494e-003, A8 = −7.3730e-004, A10 = 8.2386e-005, A12 = −6.0683e-006, A14 = 2.3541e-007
Various data focal length (Fl) 4.318 (mm)
F number 2.807
Angle of view (half angle of view) W 39.790 (deg)
Image height (Y) 3.658 (mm)
Total lens length (TL) 5.437 (mm)
Back focus (BF) 1.010
Focal length of each lens (mm)
First lens L1 4.243
Second lens L2 -6.437
Third lens L3 5.310
4th lens L4 2.600
5th lens L5 -1.802

  FIG. 11 shows spherical aberration (sine condition), astigmatism, and distortion in the imaging optical system 1B of Example 2 under the lens arrangement and configuration as described above.

  FIG. 7 is a cross-sectional view illustrating the arrangement of lenses in the imaging optical system according to the third embodiment. FIG. 12 is an aberration diagram of the image pickup optical system according to the third embodiment.

  As shown in FIG. 7, the imaging optical system 1C according to the third embodiment includes first to fifth lenses L1 to L5 arranged in order from the object side to the image side. The fifth lenses L4 and L5 are fixed with respect to a predetermined image plane, and the first to third lenses L1 to L3 are extended integrally to move in the optical axis direction.

  More specifically, in the imaging optical system 1C according to the third embodiment, the first to fifth lenses L1 to L5 are configured as follows in order from the object side to the image side.

  The first lens L1 is a positive meniscus lens having a positive refractive power that is convex toward the object side and has a convex surface facing the object side, and the second lens L2 is negative refractive that is concave toward the image side. A negative meniscus lens having power, the third lens L3 is a biconvex positive lens having positive refractive power, and the fourth lens L4 is a positive meniscus lens having convex positive refractive power on the image side. The fifth lens L5 is a biconcave negative lens that has a concave shape on the image side and faces the concave surface. Further, the fifth lens L5 is perpendicular to the position excluding the intersection point of the optical axis AX when it goes from the intersection point of the optical axis AX to the end of the effective area on the contour line of the lens cross section along the central axis (optical axis AX). IPC, having an aspherical shape with IPC, and having a region having a positive refractive power on a cross-section including the optical axis AX in a peripheral region radially away from the optical axis AX by a predetermined distance ing. The fourth lens L4 is disposed close to the fifth lens L5 so that the convex portion on the image side enters the concave portion on the object side of the fifth lens L5. These first to fifth lenses L1 to L5 are aspherical on both surfaces and are made of a resin material. The optical aperture stop ST is disposed between the first lens L1 and the second lens L2. Then, on the image side of the fifth lens L5, the light receiving surface of the image sensor SR is disposed via a parallel plate FT as a filter.

  Under such a configuration, a light beam incident from the object side sequentially has a first lens L1, an optical aperture stop ST, a second lens L2, a third lens L3, a fourth lens L4, and a fifth lens along the optical axis AX. An optical image of the object is formed on the light receiving surface of the image sensor SR through the lens L5 and the parallel plate FT. In the image sensor SR, the optical image is converted into an electrical signal, and this electrical signal is appropriately processed as in the first embodiment.

  The construction data of each lens in the imaging optical system 1C of Example 3 is shown below.

Numerical Example 3
Unit mm
Surface data surface number r d nd νd
Object ∞ ∞
1 * 2.249 0.565 1.54470 56.15
2 * 20.827 0.105
3 (Aperture) ∞ 0.150
4 * 5.950 0.300 1.63200 23.41
5 * 2.312 0.273
6 * 11.796 0.752 1.54470 56.15
7 * -2.898 Variable 8 * -2.945 0.793 1.54470 56.15
9 * -1.043 0.196
10 * -2.812 0.545 1.54470 56.15
11 * 1.435 0.600
12 ∞ 0.300 1.51633 64.14
13 ∞ 0.100
Image plane ∞
Aspherical data first surface K = -1.3904e-001, A4 = -5.0951e-003, A6 = -4.8601e-004, A8 = -2.1052e-003, A10 = -2.1626e-003, A12 = 3.3772e -003, A14 = -2.7617e-003
Second surface K = -2.0000e + 002, A4 = -3.3072e-002, A6 = 1.9291e-002, A8 = -4.4768e-003, A10 = -4.7340e-003, A12 = -1.1427e-002, A14 = 8.5770e-003
Fourth surface K = -1.2303e + 002, A4 = -6.2515e-002, A6 = 2.9221e-002, A8 = -9.3553e-003, A10 = 8.8444e-003, A12 = -9.5319e-003, A14 = -2.1290e-003
5th surface K = -9.9659e + 000, A4 = -1.0816e-002, A6 = 4.9989e-002, A8 = -1.5215e-002, A10 = -2.2622e-002, A12 = 2.2819e-002, A14 = -6.0890e-003, A16 = -2.1411e-004
6th surface K = 2.1422e + 001, A4 = -2.0245e-002, A6 = 9.2255e-003, A8 = 7.5511e-003, A10 = -1.8692e-003, A12 = -7.9787e-004, A14 = 2.9551e-004
7th surface K = 1.2953e + 000, A4 = -1.5370e-002, A6 = 1.1667e-002, A8 = -1.1284e-002, A10 = 4.9178e-003, A12 = 1.0355e-004, A14 = 6.6195 e-005
8th surface K = 9.1755e-001, A4 = -6.4739e-002, A6 = 3.4622e-002, A8 = -6.8981e-003, A10 = -1.1224e-003, A12 = 7.3036e-004, A14 = -1.1521e-004
9th surface K = -3.5511e + 000, A4 = -7.3798e-002, A6 = 2.67677e-002, A8 = -2.4511e-003, A10 = -2.8452e-005, A12 = -7.7798e-005, A14 = 1.3865e-005
10th surface K = -1.8068e + 001, A4 = -4.9726e-002, A6 = 9.7177e-003, A8 = -4.2858e-005, A10 = -1.5254e-004, A12 = 1.6726e-005, A14 = -5.4561e-007
11th surface K = -8.0016e + 000, A4 = -2.3635e-002, A6 = 4.7273e-003, A8 = -7.4075e-004, A10 = 7.9828e-005, A12 = -6.2352e-006, A14 = 2.4094e-007
Various data focal length (Fl) 4.248 (mm)
F number 2.805
Angle of view (half angle of view) W 40.288 (deg)
Image height (Y) 3.658 (mm)
Total lens length (TL) 5.452 (mm)
Back focus (BF) 0.898
Focal length of each lens (mm)
1st lens L1 4.580
Second lens L2 -6.179
Third lens L3 4.349
4th lens L4 2.584
5th lens L5 -1.669

  FIG. 12 shows spherical aberration (sine condition), astigmatism, and distortion in the imaging optical system 1C of Example 3 under the lens arrangement and configuration as described above.

  FIG. 8 is a cross-sectional view illustrating the arrangement of lenses in the imaging optical system according to the fourth embodiment. FIG. 13 is an aberration diagram of the image pickup optical system according to the fourth embodiment.

  As shown in FIG. 8, the imaging optical system 1D of Embodiment 4 includes first to fifth lenses L1 to L5 arranged in order from the object side to the image side. The fifth lenses L4 and L5 are fixed with respect to a predetermined image plane, and the first to third lenses L1 to L3 are extended integrally to move in the optical axis direction.

  More specifically, in the imaging optical system 1D of Example 4, the first to fifth lenses L1 to L5 are configured in order from the object side to the image side as follows.

  The first lens L1 is a positive meniscus lens having a positive refractive power that is convex toward the object side and has a convex surface facing the object side, and the second lens L2 is negative refractive that is concave toward the image side. A negative meniscus lens having power, the third lens L3 is a biconvex positive lens having positive refractive power, and the fourth lens L4 is a positive meniscus lens having convex positive refractive power on the image side. The fifth lens L5 is a biconcave negative lens that has a concave shape on the image side and faces the concave surface. Further, the fifth lens L5 is perpendicular to the position excluding the intersection point of the optical axis AX when it goes from the intersection point of the optical axis AX to the end of the effective area on the contour line of the lens cross section along the central axis (optical axis AX). It has an aspherical shape having IPD and IPD, and has a region having a positive refractive power on a cross section including the optical axis AX in a peripheral region radially away from the optical axis AX by a predetermined distance. ing. The fourth lens L4 is disposed close to the fifth lens L5 so that the convex portion on the image side enters the concave portion on the object side of the fifth lens L5. These first to fifth lenses L1 to L5 are aspherical on both surfaces and are made of a resin material. The optical aperture stop ST is disposed between the first lens L1 and the second lens L2. Then, on the image side of the fifth lens L5, the light receiving surface of the image sensor SR is disposed via a parallel plate FT as a filter.

  Under such a configuration, a light beam incident from the object side sequentially has a first lens L1, an optical aperture stop ST, a second lens L2, a third lens L3, a fourth lens L4, and a fifth lens along the optical axis AX. An optical image of the object is formed on the light receiving surface of the image sensor SR through the lens L5 and the parallel plate FT. In the image sensor SR, the optical image is converted into an electrical signal, and this electrical signal is appropriately processed as in the first embodiment.

  The construction data of each lens in the imaging optical system 1D of Example 4 is shown below.

Numerical Example 4
Unit mm
Surface data surface number r d nd νd
Object ∞ ∞
1 * 2.356 0.533 1.54470 56.15
2 * 17.146 0.105
3 (Aperture) ∞ 0.150
4 * 5.113 0.300 1.63200 23.41
5 * 2.230 0.219
6 * 11.303 0.770 1.54470 56.15
7 * -2.496 Variable 8 * -4.350 0.754 1.54470 56.15
9 * -1.016 0.203
10 * -1.751 0.300 1.54470 56.15
11 * 1.451 0.600
12 ∞ 0.300 1.51633 64.14
13 ∞ 0.100
Image plane ∞
Aspherical data first surface K = -3.3975e-001, A4 = -8.0710e-003, A6 = -4.5206e-004, A8 = -3.0556e-003, A10 = -6.7339e-004, A12 = 4.1125e -003, A14 = -3.9526e-003
Second surface K = -1.8562e + 002, A4 = -4.5197e-002, A6 = 2.6837e-002, A8 = 7.0199e-004, A10 = -8.9397e-003, A12 = -2.0373e-002, A14 = 1.4308e-002
4th surface K = -1.0295e + 002, A4 = -7.7704e-002, A6 = 2.2556e-002, A8 = -8.7057e-004, A10 = 1.0426e-002, A12 = -9.5319e-003, A14 = -2.1290e-003
5th surface K = -1.1142e + 001, A4 = -2.0122e-002, A6 = 5.0666e-002, A8 = -1.0902e-002, A10 = -2.5674e-002, A12 = 1.8082e-002, A14 = -1.8686e-003, A16 = -2.1411e-004
6th surface K = -2.3920e + 001, A4 = -2.1024e-002, A6 = 1.9440e-002, A8 = 9.7586e-003, A10 = -3.1907e-003, A12 = -2.6916e-003, A14 = 1.2810e-003
7th surface K = 1.1237e + 000, A4 = -1.5128e-002, A6 = 1.625e-002, A8 = -8.8343e-003, A10 = 4.6876e-003, A12 = -2.5871e-004, A14 = 7.9000e-004
8th surface K = 1.2744e + 000, A4 = -8.2734e-002, A6 = 3.3559e-002, A8 = -6.3643e-003, A10 = -1.2614e-003, A12 = 6.7771e-004, A14 = -1.5198e-004
9th surface K = -4.2066e + 000, A4 = -7.8037e-002, A6 = 2.7347e-002, A8 = -2.6016e-003, A10 = -9.9851e-005, A12 = -9.4276e-005, A14 = 1.4092e-005
10th surface K = −8.0123e + 000, A4 = −6.6292e-002, A6 = 9.0513e-003, A8 = 4.6582e-005, A10 = −1.2470e-004, A12 = 2.0201e-005, A14 = -6.9807e-007
11th surface K = -1.1073e + 001, A4 = -2.6837e-002, A6 = 4.8630e-003, A8 = -7.7766e-004, A10 = 7.4539e-005, A12 = -6.3817e-006, A14 = 3.4234e-007
Various data focal length (Fl) 4.080 (mm)
F number 2.806
Angle of view (half angle of view) W 41.648 (deg)
Image height (Y) 3.658 (mm)
Total lens length (TL) 5.171 (mm)
Back focus (BF) 0.898
Focal length of each lens (mm)
First lens L1 4.952
Second lens L2 -6.522
Third lens L3 3.829
Fourth lens L4 2.254
5th lens L5 -1.410

  FIG. 13 shows spherical aberration (sine condition), astigmatism and distortion in the imaging optical system 1D of Example 4 under the lens arrangement and configuration as described above.

  FIG. 9 is a cross-sectional view illustrating the arrangement of lenses in the imaging optical system according to the fifth embodiment. FIG. 14 is an aberration diagram of the image pickup optical system according to the fifth embodiment.

  As shown in FIG. 9, the imaging optical system 1E of Example 5 includes first to fifth lenses L1 to L5 arranged in order from the object side to the image side. The fifth lenses L4 and L5 are fixed with respect to a predetermined image plane, and the first to third lenses L1 to L3 are extended integrally to move in the optical axis direction.

  More specifically, in the imaging optical system 1E of Example 5, the first to fifth lenses L1 to L5 are configured as follows in order from the object side to the image side.

  The first lens L1 is a positive meniscus lens having a positive refractive power that is convex toward the object side and has a convex surface facing the object side, and the second lens L2 is negative refractive that is concave toward the image side. A negative meniscus lens having power, the third lens L3 is a biconvex positive lens having positive refractive power, and the fourth lens L4 is a positive meniscus lens having convex positive refractive power on the image side. The fifth lens L5 is a biconcave negative lens that has a concave shape on the image side and faces the concave surface. Further, the fifth lens L5 is perpendicular to the position excluding the intersection point of the optical axis AX when it goes from the intersection point of the optical axis AX to the end of the effective area on the contour line of the lens cross section along the central axis (optical axis AX). IPE, has an aspheric shape with IPE, and has a region having a positive refractive power on a cross-section including the optical axis AX in a peripheral region radially away from the optical axis AX by a predetermined distance ing. The fourth lens L4 is disposed close to the fifth lens L5 so that the convex portion on the image side enters the concave portion on the object side of the fifth lens L5. These first to fifth lenses L1 to L5 are aspherical on both surfaces and are made of a resin material. The optical aperture stop ST is disposed between the first lens L1 and the second lens L2. Then, on the image side of the fifth lens L5, the light receiving surface of the image sensor SR is disposed via a parallel plate FT as a filter.

  Under such a configuration, a light beam incident from the object side sequentially has a first lens L1, an optical aperture stop ST, a second lens L2, a third lens L3, a fourth lens L4, and a fifth lens along the optical axis AX. An optical image of the object is formed on the light receiving surface of the image sensor SR through the lens L5 and the parallel plate FT. In the image sensor SR, the optical image is converted into an electrical signal, and this electrical signal is appropriately processed as in the first embodiment.

  The construction data of each lens in the imaging optical system 1E of Example 5 is shown below.

Numerical Example 5
Unit mm
Surface data surface number r d nd νd
Object ∞ ∞
1 * 1.944 0.313 1.54470 56.15
2 * 7.697 0.140
3 (Aperture) ∞ 0.150
4 * 4.736 0.233 1.63200 23.41
5 * 2.133 0.253
6 * 12.714 0.708 1.54470 56.15
7 * -2.549 Variable 8 * -4.690 0.672 1.54470 56.15
9 * -0.945 0.187
10 * -1.558 0.332 1.54470 56.15
11 * 1.402 0.600
12 ∞ 0.300 1.51633 64.14
13 ∞ 0.100
Image plane ∞
Aspherical data first surface K = 3.99797e-004, A4 = −2.7293e-003, A6 = 7.1174e-003, A8 = −1.1611e-004, A10 = 5.8533e-003, A12 = 1.0141e-002, A14 = -8.0323e-003
Second surface K = 5.8354e + 000, A4 = -3.7434e-002, A6 = 2.8551e-002, A8 = 7.8731e-003, A10 = -7.7008e-004, A12 = -1.8181e-002, A14 = 9.1211e-003
4th surface K = -9.8549e + 001, A4 = -9.6661e-002, A6 = 1.7448e-002, A8 = 1.4824e-002, A10 = -7.4353e-004, A12 = -9.5317e-003, A14 = -2.1290e-003
Fifth surface K = -1.1882e + 001, A4 = -2.0953e-002, A6 = 5.6183e-002, A8 = -6.9163e-003, A10 = -2.8739e-002, A12 = 1.2738e-002, A14 = 3.8297e-003, A16 = -2.1413e-004
6th surface K = 1.3778e + 001, A4 = -1.7785e-002, A6 = 1.7964e-002, A8 = 9.2277e-003, A10 = -2.6895e-003, A12 = -2.4118e-003, A14 = 1.1988e-003
7th surface K = 1.1693e + 000, A4 = -1.6238e-002, A6 = 1.0699e-002, A8 = -8.4334e-003, A10 = 4.9182e-003, A12 = -1.3302e-004, A14 = 1.0244e-003
Eighth surface K = 5.7321e-001, A4 = -7.9532e-002, A6 = 3.0924e-002, A8 = -6.2707e-003, A10 = -1.2499e-003, A12 = 6.5619e-004, A14 = -1.7383e-004
9th surface K = −4.1331e + 000, A4 = −7.5389e−002, A6 = 2.6391e−002, A8 = −2.88843e−003, A10 = −1.3616e−004, A12 = −1.0940e−004, A14 = 1.0527e-005
10th surface K = -8.1224e + 000, A4 = -6.9352e-002, A6 = 7.1221e-003, A8 = -1.7924e-004, A10 = -1.3262e-004, A12 = 2.2797e-005, A14 = 1.2593e-006
11th surface K = -1.1488e + 001, A4 = -2.7864e-002, A6 = 4.9094e-003, A8 = -7.9815e-004, A10 = 7.3742e-005, A12 = -6.3899e-006, A14 = 3.6542e-007
Various data focal length (Fl) 3.956 (mm)
F number 2.806
Angle of view (half angle of view) W 42.394 (deg)
Image height (Y) 3.658 (mm)
Total lens length (TL) 4.872 (mm)
Back focus (BF) 0.898
Focal length of each lens (mm)
First lens L1 4.686
Second lens L2 -6.363
Third lens L3 3.963
Fourth lens L4 2.043
5th lens L5 -1.303

  FIG. 14 shows spherical aberration (sine condition), astigmatism, and distortion in the imaging optical system 1E of Example 5 under the above lens arrangement and configuration.

  Table 1 shows numerical values when the above-described conditional expressions (1) to (9) are applied to the imaging optical systems 1A to 1E of Examples 1 to 5 listed above.

  As described above, the imaging optical systems 1A to 1E in the first to fifth embodiments have a five-lens configuration and satisfy the above-described conditions. As a result, the imaging optical systems 1A to 1E are smaller than the conventional optical system. Various aberrations can be corrected more satisfactorily. The imaging optical systems 1A to 1E according to the first to fifth embodiments are sufficiently reduced in size when mounted on the imaging device 21 and the digital device 3, particularly when mounted on the portable terminal 5. A pixel imaging device 18 can be employed.

  For example, a high-pixel image sensor 18 of a class (grade) of about 8M to 16M pixels such as 8M pixel, 10M pixel, and 16M pixel has a short pixel pitch when the size of the image sensor 18 is constant (pixel The imaging optical systems 1A to 1E need a resolution corresponding to the pixel pitch, and are defined by, for example, specifications when the imaging optical system 1 is evaluated with the required resolution, for example, with MTF. Although it is necessary to suppress various aberrations within a predetermined range, in the imaging optical systems 1A to 1E in Examples 1 to 5, various aberrations are suppressed within the predetermined range as shown in the respective aberration diagrams. Therefore, since the imaging optical systems 1A to 1E in Examples 1 to 5 correct various aberrations satisfactorily, the imaging optical systems 1A to 1E are preferably used for the imaging element 18 of the class of 5M to 8M pixels, for example.

  In order to express the present invention, the present invention has been properly and fully described through the embodiments with reference to the drawings. However, those skilled in the art can easily change and / or improve the above-described embodiments. It should be recognized that this is possible. Therefore, unless the modifications or improvements implemented by those skilled in the art are at a level that departs from the scope of the claims recited in the claims, the modifications or improvements are not covered by the claims. To be construed as inclusive.

AX Optical axis 1, 1 </ b> A to 1 </ b> E Imaging optical system 3 Digital device 5 Mobile phone 11, L1 first lens 12, L2 second lens 13, L3 third lens 14, L4 fourth lens 15, L5 fifth lens 18, SR Image sensor 21 Imaging device

Claims (11)

From the object side to the image side,
A first lens having positive refractive power convex toward the object side;
A second lens having negative refractive power;
Third and fourth lenses having a predetermined refractive power;
A position having negative refractive power, concave on the image side, and excluding the intersection position of the central axis when moving from the intersection point of the central axis toward the end of the effective area in the contour of the lens cross section along the central axis An imaging optical system comprising a fifth lens having an aspherical shape with a perpendicular contact and satisfying the following conditional expressions (1) to (4).
0.2 <| f5 / f | <0.5 (1)
1 <| z5o / t5 | <4 (2)
2.5 <p5e / p5c <5 (3)
0.63 <Y / TL <0.9 (4)
However,
f5: focal length of the fifth lens f: focal length of the entire imaging optical system z5o: sag amount of the object side surface in the fifth lens at the maximum field angle principal ray (amount of displacement from the surface vertex)
t5: Core thickness of the fifth lens p5e: e-line optical path length in the fifth lens at the maximum field angle principal ray p5c: c-line optical path length in the fifth lens at the axial principal ray Y: Maximum image height TL: Optical total length of imaging optical system The imaging optical system according to claim 1, wherein the following conditional expression (5) is satisfied.
0.1 <R5r / f <2 (5)
However,
R5r: radius of curvature of the image side surface of the fifth lens (the image side concave shape is positive (positive))
f: Focal length of the entire imaging optical system The imaging optical system according to claim 1, wherein the second lens has a concave shape on the image side. The imaging optical system according to any one of claims 1 to 3, further comprising an aperture stop disposed between the first lens and the second lens. The imaging optical system according to claim 1, wherein the following conditional expression (6) is satisfied.
1.1 <| f2 / f | <1.7 (6)
However,
f2: Focal length of the second lens f: Focal length of the entire imaging optical system The imaging optical system according to claim 1, wherein the following conditional expression (7) is satisfied.
0.3 <f34 / f <0.7 (7)
However,
f34: Composite focal length of the third and fourth lenses f: Focal length of the entire imaging optical system The imaging optical system according to claim 6, wherein the following conditional expression (8) is satisfied.
0.8 <f1 / f <1.5 (8)
However,
f1: Focal length of the first lens f: Focal length of the entire imaging optical system The imaging optical system according to claim 1, wherein the following conditional expression (9) is satisfied.
0.6t23 / t12 <2 (9)
However,
t23: On-axis distance in air between the second lens and the third lens t12: On-axis distance in air between the first lens and the second lens The imaging optical system according to any one of claims 1 to 7,
An image sensor that converts an optical image into an electrical signal,
An image pickup apparatus, wherein the image pickup optical system is capable of forming an optical image of an object on a light receiving surface of the image pickup element. An imaging device according to claim 9,
A controller that causes 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 apparatus is assembled on an imaging surface of the imaging element so that an optical image of the subject can be formed. The digital device according to claim 10, comprising a mobile terminal.

Images