JP2016206223A - Image capturing lens, lens unit, image capturing device, digital still camera, and mobile terminal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image capturing lens which has a reduced chief ray angle of rays focused on a peripheral section of an image sensor and a sufficient distance secured between the image sensor and the image capturing lens, and which is wide angle, well corrected for aberrations, exhibits little deterioration in optical performance, and has a six-lens configuration, and to provide an image capturing device, lens unit, digital still camera, and mobile terminal having the same.SOLUTION: An image capturing lens is for forming an image of an object on an imaging plane of an image sensor and is configured with six lenses comprising, in order from the object side, a first lens, second lens, third lens, fourth lens, fifth lens, and sixth lens, the first lens having negative refractive power, and the first and second lenses having negative composite refractive power. The first lens has a convex meniscus-shaped surface on the object side, and the sixth lens is an aspherical surface on the image side, the aspherical surface being shaped such that an extremum of an aspherical surface sag amount thereof is at a position other than an intersection of the aspherical surface and an optical axis on the optical surface.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a wide-angle imaging lens used in an imaging device, an imaging device including the imaging lens, a digital still camera including the imaging device, and a portable terminal.

  In recent years, digital still cameras and portable terminals equipped with an imaging device using a solid-state imaging device such as a CCD (Charge Coupled Device) type image sensor or a CMOS (Complementary Metal Oxide Semiconductor) type image sensor have become widespread. However, in addition to the convenience and design of these imaging devices, the general user needs to improve the image quality. Therefore, the solid-state imaging device is made smaller and has higher pixels, and the imaging lens Despite being small in size, higher optical performance tends to be required. In addition, in order to enable imaging of a short-distance subject, there is a tendency that a wide-angle imaging lens having a focal length of 28 mm or less in terms of a 35 mm photograph, that is, a field angle of 75 degrees or more is preferred. As an imaging lens for such applications, there is a six-lens imaging lens that can satisfactorily suppress various aberrations that become conspicuous as a result of widening of the angle and can achieve higher performance than imaging lenses with four or five lenses. Proposed.

  As a six-lens imaging lens, a first lens having positive refractive power in order from the object side, a convex surface facing the object side, a second lens having positive refractive power, and a third lens having positive refractive power An imaging lens including a lens, a fourth lens having positive or negative refractive power, a fifth lens having positive refractive power, and a sixth lens having negative refractive power is known (for example, Patent Document 1). ). In addition, a first lens having negative refractive power in order from the object side, a convex surface on the object side and a concave surface on the image side, a second lens having positive refractive power, and a first lens having positive or negative refractive power An imaging lens including three lenses, a fourth lens having a negative refractive power, a fifth lens having a negative refractive power, and a sixth lens having a positive or negative refractive power is known (Patent Document 2). .

US Patent Publication No. 2013/0279021 Chinese Patent No. 202844391

  Here, generally, an optical low-pass filter, an infrared cut filter, and a cover glass that protects the image sensor are often disposed between the image pickup lens and the image sensor. In the disclosed imaging lens, only a thin infrared cut filter of about 0.2 mm is provided. Therefore, in such a configuration of the prior art, the imaging device is not covered with the cover glass. Therefore, in order to prevent foreign matter such as dust from adhering to the imaging surface, the imaging device is assembled in a controlled environment such as a clean room. This must increase the cost. On the other hand, in the case where the image sensor is protected with a cover glass so as to be able to be assembled even in a general environment, the sixth lens and the image sensor closest to the image sensor in the image sensor of Patent Document 1 and Patent Document 2 Since the distance between the two is relatively narrow, there is a problem in that there is no room for the assembly space, and there is a possibility of causing interference between members in consideration of a manufacturing error that may occur in each member. Such a problem of interference tends to become more prominent with a so-called wide-angle lens having a small focal length with respect to the size of the image sensor. On the other hand, it is possible to avoid interference by thinning the parallel flat plate of the optical low-pass filter, infrared cut filter and cover glass, but thinning the parallel flat plate while maintaining high optical performance significantly increases the cost. Will be invited. Therefore, in order to manufacture the imaging device at a low cost, it is preferable to increase the distance between the sixth lens of the imaging lens and the imaging element as much as possible while suppressing the overall length.

  In addition, the imaging lenses disclosed in Patent Literature 1 and Patent Literature 2 have a chief ray angle (CRA) that is focused on the periphery of the imaging device, which is as large as 20 ° or more. There is a problem in that the image quality is lowered due to the occurrence of color unevenness due to a decrease (peripheral light amount decrease) and color mixing characteristics deterioration. Here, in order to suppress the degradation of image quality, a technique for optimizing the microlens arranged on the surface of the image sensor according to the CRA of the imaging lens has been developed, but the degradation of the image quality is completely corrected. Therefore, it is preferable to use an imaging lens with suppressed CRA in order to inexpensively manufacture an imaging device capable of obtaining a high-quality image.

  Further, the imaging lenses disclosed in Patent Document 1 and Patent Document 2 have a focal length of about 24-28 mm in terms of a 35 mm photograph, and meet the demand for a wider-angle imaging lens that has a focal length of 20 mm or less. It can be said that it is difficult to do.

  Further, in recent years, the demand for reliability has been increased, and an imaging lens having a small change in optical performance is preferred even when the temperature changes. However, the imaging lens disclosed in Patent Documents 1 and 2 is a plastic lens. Degradation of performance due to temperature changes is inevitable.

  The present invention has been made in view of the above-described problems, suppresses the chief ray angle of the light beam condensed on the periphery of the image sensor, can secure a sufficient interval between the image sensor and the image pickup lens, and has a wide angle and good aberration. It is an object of the present invention to provide an imaging lens having a six-lens configuration in which the optical performance is less deteriorated and an imaging device including the imaging lens, a lens unit, a digital still camera, and a portable terminal.

  The imaging lens according to claim 1 is an imaging lens for forming a subject image on an imaging surface of an imaging element, and sequentially from the object side, a first lens, a second lens, a third lens, and a fourth lens. , A fifth lens and a sixth lens, the first lens has a negative refractive power, the first lens and the second lens have a negative combined refractive power, The first lens has a meniscus shape convex toward the object side, the image side surface of the sixth lens is an aspheric surface, and an aspheric surface at a position on the optical surface other than the intersection of the aspheric surface and the optical axis. The sag amount has a shape having an extreme value.

  According to the present invention, the first lens has a negative refractive power, and the first lens and the second lens have a negative combined refractive power, so that the focal length with respect to the size of the image sensor is small. A wide-angle lens can be configured as a so-called retrofocus type lens, which increases the back focus, so that the interval between the imaging lens and the imaging surface can be widened. Space can be secured.

  The first lens has a negative refractive power, the first lens and the second lens have a negative combined refractive power, and the first lens has a meniscus shape that is convex toward the object side. It has a divergence action that bends a light beam incident from a large angle in a direction parallel to the optical axis, and it is possible to satisfactorily correct the aberration of the wide-angle lens while ensuring telecentricity.

  In addition, by making the image side surface of the sixth lens an aspherical surface, various aberrations can be favorably corrected over the entire screen. Furthermore, since the aspheric sag amount has an extreme value at a position other than the intersection of the aspheric surface and the optical axis within the effective diameter, the chief ray angle (CRA) at the periphery of the image sensor can be suppressed. . Note that “the aspheric sag amount has an extreme value” means that the height in the direction perpendicular to the optical axis from the optical axis to any point on the aspheric cross section is h, and the reference position (aspherical surface to that point) First-order differential (dX (h) / dh) = 0, where X (h) is the distance in the optical axis direction (aspherical surface sag amount) from the surface apex of A or the point on the optical axis of the aspheric surface) The point represented by.

Here, in the imaging lens of the present invention, various aberrations on the imaging surface must be corrected well. For example, barrel distortion (distortion) that becomes noticeable with a wide-angle lens having a small focal length is suppressed to such an extent that a distortion image can be corrected satisfactorily in the imaging apparatus. At this time, the optical distortion (D) is D ≧ −25% over the entire image height, and more preferably D ≧ −20%. Here, the optical distortion is defined by the following expression, which is a pincushion type when positive and a barrel distortion when negative.
D = y−y ₀ / y ₀ * 100 (%)
However,
y: actual image height y ₀ : ideal image height

  An imaging lens according to a second aspect of the present invention is the imaging lens according to the first aspect, wherein the second lens has a positive refractive power, the third lens has a positive refractive power, and the fourth lens is The fifth lens has a negative refractive power, the fifth lens has a positive refractive power, and the sixth lens has a negative refractive power.

  Of the six-lens configuration in the imaging lens, three lenses are positive lenses (lens having positive refractive power), and three lenses are negative lenses (lens having negative refractive power), so that Petzval sum and chromatic aberration are reduced. Correction can be facilitated, and an imaging lens having good imaging performance up to the periphery can be obtained. Further, a positive refractive power is formed by combining the first lens to the fifth lens, and the sixth lens has a negative refractive power, so that a so-called telephoto type lens configuration can be obtained, and the total length of the imaging lens can be increased. It can be set as the structure advantageous for size reduction.

The imaging lens described in claim 3 is characterized in that, in the invention described in claim 1 or 2, the following conditional expression is satisfied.
fb / f> 0.6 (1)
However,
fb: Back focus (air equivalent distance) (mm)
f: Total focal length (mm) of the entire imaging lens system

Expression (1) is a conditional expression for appropriately setting the back focus in the imaging lens. By satisfying the expression (1), the sixth lens and the imaging surface are not brought too close to each other, and a space for arranging an optical low-pass filter, an infrared cut filter, and a cover glass for protecting the imaging element can be secured. it can. Here, the back focus is a distance on the optical axis between the image-side surface of the sixth lens and the imaging surface, and an optical low-pass filter, an infrared cut filter, a cover glass for protecting the imaging device, and the like are arranged. In such a case, these are calculated as air conversion distances. Moreover, it is more preferable to satisfy the following conditional expressions.
fb / f> 0.7 (1 ′)

The imaging lens of Claim 4 satisfies the following conditional expressions in the invention of any one of Claims 1-3.
d6 / f> 0.5 (2)
However,
d6: Distance between the sixth lens and the imaging surface of the imaging device (air equivalent distance) (mm)
f: Total focal length (mm) of the entire imaging lens system

Expression (2) is a conditional expression for appropriately setting the distance between the imaging lens and the imaging surface. By satisfying the expression (2), the sixth lens and the imaging surface are not brought too close to each other, and a space for arranging an optical low-pass filter, an infrared cut filter, and a cover glass for protecting the imaging element can be secured. it can. Here, d6 is a distance from the position where the aspherical sag amount of the sixth lens is closest to the image side to the imaging surface, and an optical low-pass filter, an infrared cut filter, a cover glass for protecting the imaging element, and the like are arranged. If these are to be calculated, these are calculated as air conversion distances. In addition, from the above viewpoint, the following conditional expressions are more preferable.
d6 / f> 0.6 (2 ′)

  According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, at least two of the first lens to the sixth lens are glass lenses.

  When the imaging lens includes at least two glass lenses, the imaging lens is unlikely to deteriorate when an environmental change such as temperature occurs. In general, an AR coating is applied to the lens. However, since the antireflection effect can be enhanced by using a glass lens, it is preferable because a ghost attributed to the surface reflection of the lens can be suppressed. Further, the glass lens is more preferable because the selectable range of the refractive index and the Abbe number is wider than that of the plastic lens, and the aberration can be corrected well by selecting an appropriate glass material.

  The imaging lens according to a sixth aspect is the invention according to the fifth aspect, wherein the at least two glass lenses have a positive refractive power.

  In order to exhibit the intrinsic performance of the imaging lens that forms an image on the imaging element, the total refractive power from the first lens to the sixth lens must be positive, and therefore the refraction of the positive lens. The absolute value of the force becomes larger than the absolute value of the refractive power of the negative lens. Therefore, from the viewpoint of suppressing the deterioration of the imaging performance when the temperature changes, it is preferable that the positive lens is a glass lens with little refractive index and shape change due to temperature change.

  According to a seventh aspect of the present invention, in the invention of any one of the first to sixth aspects, all surfaces from the first lens to the sixth lens on the object side and the image side are aspherical surfaces. Features.

  By making the surfaces of all the lenses aspherical surfaces, it is possible to suppress the chief ray angle of the light rays condensed on the periphery of the image sensor, correct aberrations well, and reduce the total lens length.

  An imaging lens according to an eighth aspect is characterized in that, in the invention according to any one of the first to seventh aspects, an angle of view is 95 degrees or more.

  In the case of a wide-angle imaging lens having an angle of view of 95 degrees or more, that is, a focal length of 20 mm or less in terms of a 35 mm size photograph, the distance between the image-side surface of the sixth lens and the imaging surface becomes short, and an optical low-pass filter The space for arranging the infrared cut filter and the cover glass for protecting the image pickup device tends to be narrow. However, according to the present invention, since the first lens and the second lens have a negative combined refractive power, the back focus is sufficiently large, and even a wide-angle imaging lens is located on the image side of the sixth lens. Sufficient space can be secured.

An imaging lens according to a ninth aspect is characterized in that, in the invention according to any one of the first to eighth aspects, the following conditional expression is satisfied.
ED1 / 2Y <1 (3)
However,
ED1: Effective diameter (mm) of the object side surface of the first lens
2Y: Diagonal length of the image sensor (mm)

  Expression (3) is a conditional expression for appropriately setting the effective diameter (front lens diameter) of the first lens. The effective diameter (front lens diameter) of the first lens arranged closest to the object side becomes larger as the angle of view is 95 degrees or more, that is, the focal length is 20 mm or less in terms of a 35 mm photograph, and the entire imaging lens becomes larger. The lens weight tends to increase. However, according to the present invention, the first lens can be suppressed to the same size as the image pickup device, the enlargement of the image pickup lens can be avoided, and the weight thereof can be reduced.

  A lens unit according to a tenth aspect is characterized in that the imaging lens according to any one of the first to ninth aspects is assembled to a barrel that holds the imaging lens.

  An image pickup apparatus according to an eleventh aspect includes an image pickup element that photoelectrically converts a subject image and the lens unit according to the tenth aspect.

  A digital still camera according to a twelfth aspect includes the imaging device according to the eleventh aspect.

  According to a thirteenth aspect of the present invention, there is provided a mobile terminal including the imaging device according to the eleventh aspect.

  Since the amount of captured light increases as the pixel size of the image sensor increases, generally, the larger the image sensor size, the higher the quality of the image. Specifically, an image sensor having a size of 1 / 2.3 type (imaging surface diagonal length of about 8 mm) or more is preferable to an image sensor having a size of 1/3 type (image surface diagonal length of about 6 mm) or less. .

  According to the present invention, the principal ray angle of the light beam condensed on the periphery of the image sensor can be suppressed, the distance between the image sensor and the image pickup lens can be sufficiently secured, the aberration is corrected well at a wide angle, and the optical performance is hardly deteriorated. An imaging lens having six lenses, an imaging device including the imaging lens, a lens unit, a digital still camera, and a portable terminal can be provided.

It is a perspective view of imaging device 100 concerning this embodiment. It is a block diagram of imaging device 100 concerning this embodiment. 3 is a cross-sectional view of an imaging lens 101 held by a lens barrel 53. FIG. 3 is a cross-sectional view in the optical axis direction of the imaging lens of Example 1. FIG. FIG. 4 is an aberration diagram of Example 1 (spherical aberration (a), astigmatism (b), distortion (c)). 2 is a graph showing a chief ray angle (CRA) of a light beam with respect to an image height in Example 1, where the horizontal axis is the image height and the vertical axis is the CRA. FIG. 14 is a diagram illustrating the aspherical shape of the fourteenth surface (image side surface of the sixth lens) of Example 1, where the vertical axis represents the height h from the optical axis and the horizontal axis represents the sag amount X. FIG. 6 is a cross-sectional view in the optical axis direction of the imaging lens of Example 2. FIG. 6 is an aberration diagram of Example 2 (spherical aberration (a), astigmatism (b), distortion (c)). FIG. 5 is a graph showing a chief ray angle (CRA) of a light beam with respect to an image height in Example 2, where the horizontal axis is the image height and the vertical axis is the CRA. FIG. 14 is a diagram illustrating the aspherical shape of the fourteenth surface (image side surface of the sixth lens) of Example 2, with the vertical axis representing the height h from the optical axis and the horizontal axis representing the sag amount X.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1A and 1B are perspective views of an imaging apparatus 100 according to the present embodiment, in which FIG. 1A is a front view and FIG. 1B is a rear view. FIG. 2 is a block diagram of the imaging apparatus 100 according to the present embodiment. FIG. 3 is a cross-sectional view of the imaging lens 101 held by the lens barrel 53.

  As illustrated in FIG. 2, the imaging apparatus 100 includes an imaging lens 101, a solid-state imaging device 102, an A / D conversion unit 103, a control unit 104, a timing generation unit 106, an imaging device driving unit 107, and an image. A memory 108, an image processing unit 109, an image compression unit 110, an image recording unit 111, and a monitor LCD 112 are configured. A lens barrel 53 is attached to a camera body 120 that houses these components. As shown in FIG. 1, the imaging lens 101 faces the front, and the monitor LCD 112 is provided on the back side.

  As shown in FIG. 3, the imaging lens 101 arranged in the lens barrel 53 constitutes a lens unit, and in order from the object side, a first lens L1, a second lens L2, an aperture stop S, a third lens L3, It consists of a fourth lens L4, a fifth lens L5, and a sixth lens L6, and the flange portions abut against each other via the spacer SP (and the aperture stop S), thereby maintaining the interaxial distance.

  In FIG. 2, a solid-state image sensor 102 is an image sensor such as a CCD or CMOS, and includes an RGB color filter. The solid-state image sensor 102 photoelectrically converts incident light for each of R, G, and B, and outputs an analog signal. The A / D conversion unit 103 converts an analog signal into digital image data.

  The control unit 104 controls each unit of the imaging device 100. The control unit 104 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), and a ROM (Read Only Memory), and various programs read out from the ROM and expanded in the RAM, and various in cooperation with the CPU. Execute the process.

  The timing generator 106 outputs a timing signal for analog signal output. The image sensor driving unit 107 controls driving of the solid-state image sensor 102.

  The image memory 108 stores image data so as to be readable and writable. The image processing unit 109 performs various image processes on the image data. The image compression unit 110 compresses captured image data by a compression method such as JPEG (Joint Photographic Experts Group). The image recording unit 111 can also record image data on a recording medium such as a memory card set in a slot (not shown).

  The monitor LCD 112 is a color liquid crystal panel or the like, and displays image data after shooting, a through image before shooting, various operation screens, and the like.

  Here, the operation of the imaging apparatus 100 will be described. In subject photographing, subject monitoring (through image display) and image photographing execution are performed. In monitoring, an image of a subject obtained through the imaging lens 101 is formed on the light receiving surface (imaging surface) of the solid-state image sensor 102. An analog as a photoelectric conversion output corresponding to an optical image that is driven by a timing generation unit 106 and an image sensor drive unit 107 and is imaged at a fixed period, while the solid-state image sensor 102 disposed behind the imaging optical axis of the imaging lens 101 is driven. Output the signal for one screen.

  The analog signal is appropriately gain-adjusted for each primary color component of RGB, and then converted into digital data by the A / D conversion unit 103. The digital data is subjected to color process processing including pixel interpolation processing and γ correction processing by the image processing unit 109 to generate a luminance signal Y and color difference signals Cb, Cr (image data) as digital values, and the image memory. 108, the signal is periodically read out, the video signal is generated, and output to the monitor LCD 112. Note that the control unit 104, which is also a white balance adjustment unit, adjusts the white balance of the captured image.

  The monitor LCD 112 functions as an electronic viewfinder in monitoring, and displays captured images almost in real time.

  In such a monitoring state, still image data is photographed when the user operates a release button (not shown) at a timing when still image photographing is desired. In response to an operation of a release button (not shown), one frame of image data stored in the image memory 108 is read and compressed by the image compression unit 110. The compressed image data is recorded on a recording medium by the image recording unit 111.

[Example]
Examples of the imaging lens of the present invention will be shown below. Symbols used in each example are as follows. Unless otherwise indicated, the unit of value for distance is mm.
f: Focal length of the entire imaging lens system fb: Back focus (air conversion distance)
F: F number 2Y: Diagonal length of the imaging surface of the imaging element FOV: Angle of view R: Radius of curvature d: Axial distance Nd: Refractive index νd of lens material with respect to d-line νd: Abbe number of lens material f1: First lens Focal length f2: Focal length of second lens f3: Focal length of third lens f4: Focal length of fourth lens f5: Focal length of fifth lens f6: Focal length of sixth lens f12: First lens and second lens Synthetic focal length d6 of the lens: Distance between the position of the sixth lens closest to the image plane and the image plane (air conversion distance)

  In each embodiment, the surface described with “*” after each surface number is a surface having an aspheric shape, and the shape of the aspheric surface has the vertex of the surface as the origin and the X axis in the optical axis direction. (The image side is plus), and the height in the direction perpendicular to the optical axis is h, and is expressed by the following “Expression 1”.

ただし、
Ａｉ：ｉ次の非球面係数
Ｒ ：曲率半径
Ｋ ：円錐定数

However,
Ai: i-order aspheric coefficient R: radius of curvature K: conic constant

  Regarding the meaning of the paraxial radius of curvature described in the claims and the examples, in the actual lens measurement scene, in the vicinity of the center of the lens (specifically, the central region within 10% of the lens outer diameter) ) Can be regarded as the paraxial curvature radius when fitting the shape measurement value in the least square method. For example, when a secondary aspherical coefficient is used, a radius of curvature that takes into account the secondary aspherical coefficient in the reference curvature radius of the aspherical definition formula can be regarded as the paraxial curvature radius. (For example, refer to P41-42 of “Lens Design Method” written by Yoshiya Matsui (Kyoritsu Publishing Co., Ltd.) as a reference)

Example 1
The specifications of the imaging lens of Example 1 are shown below.
f = 2.95mm
fb = 2.40 mm
F = 2.8
2Y = 7.75mm
FOV = 105 °

The surface data of the imaging lens of Example 1 is shown below.
Surface number R (mm) d (mm) Nd νd Effective radius (mm)
1 ∞ ∞
2 * 1512.557 0.50 1.5305 55.7 2.90
3 * 2.189 1.06 1.85
4 * 2.114 1.00 1.6346 23.9 1.55
5 * 2.555 0.82 1.12
6 (Aperture) ∞ 0.03 0.69
7 * 12.536 1.05 1.5891 61.3 0.71
8 * -2.083 0.41 1.02
9 * -13.851 0.40 1.6346 23.9 1.20
10 * 3.801 0.31 1.47
11 * 222.985 1.56 1.6168 63.9 1.72
12 * -2.120 0.10 2.11
13 * 2.841 0.77 1.5305 55.7 2.66
14 * 1.793 1.27 2.87
15 ∞ 0.30 1.5163 64.1 3.11
16 ∞ 0.20 3.16
17 ∞ 0.50 1.5163 64.1 3.20
18 ∞ 0.40 3.28

  Here, the second and third surfaces are the first lenses, the fourth and fifth surfaces are the second lenses, the seventh and eighth surfaces are the third lenses, and the ninth and tenth surfaces are the fourth lenses. The eleventh and twelfth surfaces represent the fifth lens, and the thirteenth and fourteenth surfaces represent the sixth lens. Both the second surface and the third surface have a convex shape on the object side near the optical axis, and the first lens has a meniscus shape convex on the object side.

The aspheric surface data of Example 1 is shown below.
Second side
K = -1.12478E + 01, A4 = 2.44121E-02, A6 = -3.89921E-03, A8 = 4.91435E-04, A10 = -3.46127E-05, A12 = 1.05262E-06
Third side
K = -1.98831E + 00, A4 = 2.63351E-02, A6 = 6.59298E-03, A8 = -2.11712E-03, A10 = 3.92989E-04, A12 = 3.08010E-05
4th page
K = -5.46683E + 00, A4 = 4.20103E-02, A6 = -1.80717E-02, A8 = 6.80385E-03, A10 = -1.35670E-03
5th page
K = -2.98269E + 00, A4 = 7.47080E-03, A6 = 1.14275E-02, A8 = -1.06292E-02, A10 = 5.12550E-05
7th page
A4 = -4.10278E-02, A6 = -1.97203E-04, A8 = -6.15862E-02, A10 = 3.25569E-02
8th page
A4 = -2.04665E-02, A6 = 1.28742E-03, A8 = -1.44768E-02, A10 = 1.43884E-03
9th page
K = -1.52944E + 01, A4 = -7.96461E-02, A6 = 4.10280E-02, A8 = 1.15994E-03, A10 = -1.07178E-02, A12 = 3.42866E-03
10th page
A4 = -6.79992E-02, A6 = 2.48833E-02, A8 = -6.41630E-04, A10 = -2.08666E-03, A12 = 4.36769E-04
11th page
A4 = 3.52989E-02, A6 = -2.75977E-02, A8 = 1.08377E-02, A10 = -2.17486E-03, A12 = 1.72774E-04
12th page
K = -4.49451E + 00, A4 = -1.18965E-02, A6 = 6.59674E-03, A8 = -2.16225E-03, A10 = 3.60779E-04, A12 = -2.47984E-05
13th page
K = -8.15611E + 00, A4 = -8.38773E-03, A6 = -2.28787E-03, A8 = 9.55820E-04, A10 = -1.42340E-04, A12 = 9.70435E-06, A14 = -2.46429 E-07
14th page
K = -5.60530E + 00, A4 = -2.13233E-02, A6 = 2.78012E-03, A8 = -4.16055E-04, A10 = 5.27933E-05, A12 = -4.33158E-06, A14 = 1.48664E -07

The focal length of each lens is shown below. At this time, since the refractive power is the reciprocal of the focal length, the positive / negative of the refractive power is the same as the positive / negative of the focal length.
f1 = −4.13 mm
f2 = 10.27mm
f3 = 3.11mm
f4 = -4.66mm
f5 = 3.40mm
f6 = -12.28mm
f12 = −6.40 mm

Values corresponding to the conditional expression of the imaging lens of Example 1 are shown below.
(1) Formula: fb / f = 0.81
(2) Formula: d6 / f = 0.68
(3) Formula: ED1 / 2Y = 0.75

  The imaging lens of Example 1 is a wide-angle lens having an angle of view of 105 degrees, which satisfies the conditional expressions (1) to (3). Between the sixth lens and the imaging device, an optical low-pass filter and an infrared ray cut are provided. The space | interval which arrange | positions the cover glass which protects a filter and an image pick-up element is ensured.

  In Example 1, the first lens, the second lens, the fourth lens, and the sixth lens are plastic lenses, and the third lens and the fifth lens are glass mold lenses.

  In the surface data of the imaging lens of Example 1, the shooting distance is infinity, but the shooting distance is not limited to this in the present invention. For example, the imaging lens is provided with a focus mechanism that corrects a deviation in the imaging position due to a change in the shooting distance by changing the distance (d14) between the 14th surface and the 15th surface on the optical axis, thereby reducing the shooting distance range. Can be spread. In Example 1, when the shooting distance is 50 mm (d1 = 50 mm), the distance between the 14th surface and the 15th surface on the optical axis is 1.44 mm.

  FIG. 4 is a cross-sectional view of the image pickup lens of Example 1, which draws on-axis and off-axis rays. In the figure, L1 is a first lens having negative refractive power, L2 is a second lens having positive refractive power, L3 is a third lens having positive refractive power, L4 is a fourth lens having negative refractive power, L5 is a fifth lens having a positive refractive power, L6 is a sixth lens having a negative refractive power, S is an aperture stop, and I is an imaging surface. F is a parallel plate assuming an optical low-pass filter and an infrared cut filter, and CG is a parallel plate assuming a cover glass that protects the image sensor. Note that the combined refractive power of the first lens L1 and the second lens L2 is negative.

  FIG. 5 is an aberration diagram ((a) spherical aberration, (b) astigmatism, (c) distortion) applied to the imaging lens of Example 1. Various aberrations on the image plane are corrected satisfactorily. Here, the barrel-shaped distortion (distortion) that becomes conspicuous in the wide-angle lens is D ≧ −15% in the entire image height, and the distortion image can be corrected well in the imaging apparatus. In the following aberration diagrams, in the astigmatism diagrams, the solid line S represents the sagittal image plane, and the dotted line M represents the meridional image plane.

  FIG. 6 is a graph showing the chief ray angle (CRA) of the light beam with respect to the image height in Example 1. As shown in FIG. 6, since the CRA is 20 ° or less, it is possible to suppress a decrease in image quality due to a decrease in light collection efficiency (a decrease in peripheral light amount) and color unevenness due to a deterioration in color mixing characteristics.

  FIG. 7 is a diagram illustrating the aspherical shape of the fourteenth surface (image side surface of the sixth lens) of Example 1. The 14th surface has an extreme value when the sag amount X is h = 2.09 mm, suppresses the chief ray angle (CRA) at the periphery of the image sensor, and corrects various aberrations well on the entire screen. Yes.

(Example 2)
The specifications of the imaging lens of Example 2 are shown below.
f = 2.95mm
fb = 2.01mm
F = 2.8
2Y = 7.75mm
FOV = 105 °

The surface data of the imaging lens of Example 2 is shown below.
Surface number R (mm) d (mm) Nd νd Effective radius (mm)
1 ∞ ∞
2 * 1784.557 0.50 1.5305 55.7 3.07
3 * 2.259 0.98 1.98
4 * 2.171 1.00 1.6346 23.9 1.69
5 * 2.766 0.98 1.25
6 (Aperture) ∞ 0.03 0.69
7 * 11.670 1.10 1.5891 61.3 0.71
8 * -1.955 0.35 1.03
9 * -21.168 0.42 1.6346 23.9 1.20
10 * 3.453 0.39 1.43
11 * 305.400 1.72 1.6168 63.9 1.70
12 * -2.156 0.10 2.16
13 * 2.805 0.84 1.5305 55.7 2.89
14 * 1.572 0.88 3.10
15 ∞ 0.30 1.5163 64.1 3.20
16 ∞ 0.20 3.24
17 ∞ 0.50 1.5163 64.1 3.27
18 ∞ 0.40 3.33

  Here, the second and third surfaces are the first lenses, the fourth and fifth surfaces are the second lenses, the seventh and eighth surfaces are the third lenses, and the ninth and tenth surfaces are the fourth lenses. The eleventh and twelfth surfaces represent the fifth lens, and the thirteenth and fourteenth surfaces represent the sixth lens. Both the second surface and the third surface have a convex shape on the object side near the optical axis, and the first lens has a meniscus shape convex on the object side.

The aspheric surface data of Example 2 is shown below.
Second side
K = -1.12478E + 01, A4 = 1.91075E-02, A6 = -2.72811E-03, A8 = 2.94986E-04, A10 = -1.88154E-05, A12 = 5.83292E-07
Third side
K = -1.61655E + 00, A4 = 1.50391E-02, A6 = 5.21099E-03, A8 = -1.14061E-03, A10 = 1.22405E-04, A12 = 1.12676E-05
4th page
K = -4.09109E + 00, A4 = 2.34865E-02, A6 = -6.07010E-03, A8 = 2.19518E-03, A10 = -5.57464E-04
5th page
K = -4.26809E + 00, A4 = 1.32643E-02, A6 = 6.02472E-03, A8 = -6.73510E-03, A10 = 3.56029E-04
7th page
A4 = -4.81607E-02, A6 = -1.26742E-03, A8 = -6.20713E-02, A10 = 3.82222E-02
8th page
A4 = -1.46894E-02, A6 = 1.08371E-03, A8 = -1.12208E-02, A10 = 1.22245E-03
9th page
K = -1.52944E + 01, A4 = -6.10796E-02, A6 = 4.38830E-02, A8 = -1.04266E-02, A10 = -1.67126E-03, A12 = 1.14010E-03
10th page
A4 = -5.96694E-02, A6 = 2.69454E-02, A8 = -3.79982E-03, A10 = -8.06670E-04, A12 = 2.56421E-04
11th page
A4 = 2.64559E-02, A6 = -2.32365E-02, A8 = 9.42940E-03, A10 = -1.80724E-03, A12 = 1.41040E-04
12th page
K = -4.27863E + 00, A4 = -7.93420E-03, A6 = 2.49200E-03, A8 = -9.76106E-04, A10 = 2.22202E-04, A12 = -1.45749E-05
13th page
K = -7.30096E + 00, A4 = -1.12823E-02, A6 = -1.64059E-03, A8 = 9.32918E-04, A10 = -1.39555E-04, A12 = 9.28615E-06, A14 = -2.31395 E-07
14th page
K = -4.50400E + 00, A4 = -2.10905E-02, A6 = 2.80918E-03, A8 = -3.89499E-04, A10 = 4.26764E-05, A12 = -3.18303E-06, A14 = 1.07899E -07

The focal length of each lens is shown below. At this time, since the refractive power is the reciprocal of the focal length, the positive / negative of the refractive power is the same as the positive / negative of the focal length.
f1 = −4.26 mm
f2 = 9.62mm
f3 = 2.93mm
f4 = −4.65mm
f5 = 3.47mm
f6 = −8.83 mm
f12 = −7.16 mm

The values corresponding to the conditional expression of the imaging lens of Example 2 are shown below.
(1) Formula: fb / f = 0.68
(2) Formula: d6 / f = 0.51
(3) Formula: ED1 / 2Y = 0.79

  The imaging lens of Example 2 is a wide-angle lens having an angle of view of 105 degrees, which satisfies the conditional expressions (1) to (3). Between the sixth lens and the imaging device, an optical low-pass filter and an infrared ray cut are provided. The space | interval which arrange | positions the cover glass which protects a filter and an image pick-up element is ensured.

  In Example 2, the first lens, the second lens, the fourth lens, and the sixth lens are plastic lenses, and the third lens and the fifth lens are glass mold lenses.

  In the surface data of the imaging lens of Example 2, the shooting distance is infinite, but the shooting distance is not limited to this in the present invention. For example, the imaging lens is provided with a focus mechanism that corrects a deviation in the imaging position due to a change in the shooting distance by changing the distance (d14) between the 14th surface and the 15th surface on the optical axis, thereby reducing the shooting distance range. Can be spread. In Example 2, when the shooting distance is 50 mm (d1 = 50 mm), the distance between the 14th surface and the 15th surface on the optical axis is 1.05 mm.

  FIG. 8 is a cross-sectional view of the image pickup lens of Example 2, in which on-axis and off-axis rays are drawn in an overlapping manner. In the figure, L1 is a first lens having negative refractive power, L2 is a second lens having positive refractive power, L3 is a third lens having positive refractive power, L4 is a fourth lens having negative refractive power, L5 is a fifth lens having a positive refractive power, L6 is a sixth lens having a negative refractive power, S is an aperture stop, and I is an imaging surface. F is a parallel plate assuming an optical low-pass filter and an infrared cut filter, and CG is a parallel plate assuming a cover glass that protects the image sensor. Note that the combined refractive power of the first lens L1 and the second lens L2 is negative.

  FIG. 9 is an aberration diagram ((a) spherical aberration, (b) astigmatism, (c) distortion aberration) applied to the imaging lens of Example 2. Various aberrations on the image plane are corrected satisfactorily. Here, the barrel-shaped distortion (distortion) that becomes conspicuous in the wide-angle lens is D ≧ −15% in the entire image height, and the distortion image can be corrected well in the imaging apparatus.

  FIG. 10 is a graph showing the chief ray angle (CRA) of light with respect to image height in Example 2. As shown in FIG. 11, since the CRA is 20 ° or less, it is possible to suppress a decrease in image quality due to a decrease in light collection efficiency (a decrease in peripheral light amount) and color unevenness due to a deterioration in color mixing characteristics.

  FIG. 11 is a diagram illustrating the aspherical shape of the 14th surface (image side surface of the sixth lens) of Example 2. The 14th surface has an extreme value when the sag amount X is h = 2.26 mm, suppresses the chief ray angle (CRA) at the periphery of the image sensor, and corrects various aberrations well on the entire screen. Yes.

  Further, the present invention is not limited to the embodiments described in the specification, and it is understood that other embodiments and modifications are included in the art from the embodiments and ideas described in the present specification. It is obvious to For example, any of at least two positive lenses among the three positive lenses may be a glass lens. Even when a dummy lens having substantially no refractive power is further provided, it is within the scope of the present invention. Further, although a digital still camera equipped with an imaging device is shown as an example, it can also be installed in a portable terminal.

  The present invention can provide an imaging lens suitable for a portable terminal or a digital still camera.

DESCRIPTION OF SYMBOLS 100 Imaging device 101 Imaging lens 102 Solid-state image sensor 103 Conversion part 104 Control part 106 Timing generation part 107 Imaging element drive part 108 Image memory 109 Image processing part 110 Image compression part 111 Image recording part 112 Monitor LCD
120 Camera body L1-L6 Lens S Aperture stop CG Cover glass F IR cut filter

Claims (13)

  An imaging lens for forming a subject image on an imaging surface of an imaging element, and in order from the object side, a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens The first lens has a negative refractive power, the first lens and the second lens have a negative combined refractive power, and the first lens is convex toward the object side. It is a meniscus shape, the image side surface of the sixth lens is an aspheric surface, and the aspheric sag amount has an extreme value at a position on the optical surface other than the intersection of the aspheric surface and the optical axis. An imaging lens characterized by the above.   The second lens has a positive refractive power, the third lens has a positive refractive power, the fourth lens has a negative refractive power, and the fifth lens has a positive refractive power. The imaging lens according to claim 1, wherein the sixth lens has negative refractive power. The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
fb / f> 0.6 (1)
However,
fb: Back focus (air equivalent distance) (mm)
f: Total focal length (mm) of the entire imaging lens system The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
d6 / f> 0.5 (2)
However,
d6: Distance between the sixth lens and the imaging surface of the imaging device (air equivalent distance) (mm)
f: Total focal length (mm) of the entire imaging lens system   The imaging lens according to claim 1, wherein at least two of the first lens to the sixth lens are glass lenses.   The imaging lens according to claim 5, wherein the at least two glass lenses have a positive refractive power.   The imaging lens according to claim 1, wherein all surfaces from the first lens to the object side and image side of the sixth lens are aspherical surfaces.   The imaging lens according to any one of claims 1 to 7, wherein an angle of view is 95 degrees or more. The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
ED1 / 2Y <1 (3)
However,
ED1: Effective diameter (mm) of the object side surface of the first lens
2Y: Diagonal length of the image sensor (mm)   A lens unit comprising the imaging lens according to any one of claims 1 to 9 assembled to a barrel that holds the imaging lens.   An image pickup apparatus comprising: an image pickup device that photoelectrically converts a subject image; and the lens unit according to claim 10.   A digital still camera comprising the imaging device according to claim 11.   A portable terminal comprising the imaging device according to claim 11.

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