JP5904208B2 - Imaging lens, imaging optical device, and digital device - Google Patents

Description

  The present invention relates to an imaging lens. More specifically, an imaging optical device that captures an image of a subject with an imaging device (for example, a solid-state imaging device such as a CCD (Charge Coupled Device) type image sensor, a CMOS (Complementary Metal-Oxide Semiconductor) type image sensor), and the like are mounted. The present invention relates to a digital apparatus with an image input function and a small imaging lens that forms an optical image of a subject on a light receiving surface of an imaging element.

  In recent years, imaging optical devices using a solid-state imaging device such as a CCD type image sensor or a CMOS type image sensor have been mounted on mobile terminals, and with the widespread use of the mobile terminals, higher quality images have been obtained. As a result, a device equipped with an image pickup optical device using an image pickup device having a high number of pixels has been supplied to the market. Although the image pickup device having the high number of pixels has been accompanied by an increase in size, in recent years, an increase in the size of pixels has progressed, and the image pickup device has been reduced in size. An imaging lens used in such a highly thinned image sensor is required to have a high resolving power in order to cope with a highly thinned pixel.

  The resolving power of the lens is limited by the F value, and a bright lens with a small F value can obtain a high resolving power, so that a sufficient performance cannot be obtained with an F value of about F2.8 as in the past. Yes. Accordingly, there has been a demand for a bright imaging lens of about F2, which is suitable for an imaging device with a high pixel size, a high resolution, and a small size. As an imaging lens for such an application, an imaging lens having a five-lens configuration has been proposed because a large aperture ratio and high performance can be achieved as compared with a lens having three or four lenses.

  The five-lens imaging lens includes, in order from the object side, a front lens group, an aperture stop, and a rear lens group. The front lens has a first lens having a positive or negative refractive power and a second lens having a positive refractive power. And an imaging lens in which the rear group includes a third lens having a negative refractive power, a fourth lens having a positive refractive power, and a fifth lens having a negative or positive refractive power. 1 and Patent Document 2. The four-lens imaging lens includes, in order from the object side, a front lens group, an aperture stop, and a rear lens group. The front lens group includes a first lens having a negative refractive power and a second lens having a positive refractive power. Patent Document 3 discloses an imaging lens that includes a third lens having a negative refractive power and a fourth lens having a positive refractive power.

JP 2007-279282 A JP 2006-293042 A JP 2007-322844 A

  However, since the imaging lens described in Patent Document 1 has a spherical front system, if the lens is brightened to about F2, correction of spherical aberration and coma becomes insufficient, and good performance cannot be ensured. In addition, since the front group and the rear group have a positive refracting power, the principal point position of the optical system is on the image side and the back side of the rear group has a negative refracting power. The focus becomes longer. For this reason, it is a disadvantageous type for downsizing.

  The imaging lens described in Patent Document 2 has a brightness of about F2, but the first lens and the second lens arranged on the object side of the aperture stop have a positive refractive power. For this reason, the color correction in the front group is insufficient. Further, like the one described in Patent Document 1, both the front group and the rear group have a positive refractive power, and the final lens is also a positive lens, which is disadvantageous for downsizing.

  Furthermore, although the imaging lens described in Patent Document 3 has a brightness of about F2, the aberration correction is insufficient because of the four-lens configuration. Therefore, it cannot be said that the imaging lens is suitable for increasing the number of pixels.

  The present invention has been made in view of such problems, and an object of the present invention is to capture a bright five-lens structure of about F2.0 in which various aberrations are well corrected while being smaller than the conventional type. To provide a lens.

In order to achieve the above object, an imaging lens of a first invention is an imaging lens for forming a subject image on an imaging surface of an image sensor, and is a positive lens with a convex surface facing the object side in order from the object side. The first lens, an aperture stop, a positive second lens having a convex surface facing the image side , a negative third lens, a positive fourth lens, and a negative fifth lens, Conditional expressions (1) and (4) are satisfied.
0 <f1 / f2 <1.26 (1)
1.41 ≦ f1 / f <3.0 (4)
However,
f1: focal length of the first lens,
f2: focal length of the second lens,
f: focal length of the entire imaging lens system,
It is.

The imaging lens of the second invention is characterized in that, in the first invention, the following conditional expression (2) is satisfied.
-4.0 <f3 / f <-1.1 (2)
However,
f3: focal length of the third lens,
f: focal length of the entire imaging lens system,
It is.

According to a third aspect of the present invention, there is provided the imaging lens according to the first or second aspect , wherein the third lens has a concave surface facing the image side.

An imaging lens of a fourth invention is characterized in that, in any one of the first to third inventions, the following conditional expression (3) is satisfied.
1.41 <f2 / f <10.0 (3)
However,
f2: focal length of the second lens,
f: focal length of the entire imaging lens system,
It is.

An imaging lens according to a fifth invention is characterized in that, in any one of the first to fourth inventions, the following conditional expression (5) is satisfied.
15 <νd3 <31 (5)
However,
νd3: Abbe number of the third lens with respect to the d-line,
It is.

The imaging lens of a sixth invention is the imaging lens of any one of the first to fifth inventions, wherein the image side surface of the fifth lens has an aspherical shape, has a negative refractive power at the center thereof, The negative refracting power becomes weaker as it goes, has an inflection point, and satisfies the following conditional expression (6).
0.05 <T5 / f <0.2 (6)
However,
f: focal length of the entire imaging lens system,
T5: thickness of the fifth lens on the optical axis,
It is.

An imaging lens of a seventh invention is characterized in that, in any one of the first to sixth inventions, the lens is entirely made of a plastic material.

The imaging optical apparatus of the eighth invention, the imaging lens according to the first to seventh any one invention, an imaging element for converting into an electrical signal an optical image formed on the imaging surface, the And the imaging lens is provided so that an optical image of a subject is formed on the imaging surface of the imaging device.

According to a ninth aspect of the present invention, there is provided a digital apparatus including the imaging optical device according to the eighth aspect , to which at least one function of still image shooting and moving image shooting of a subject is added.

A digital device according to a tenth aspect of the present invention is the portable device according to the ninth aspect.

  By adopting the configuration of the present invention, it is possible to realize an imaging lens having a bright five-lens configuration of about F2.0 and variously corrected for various aberrations while being smaller than the conventional type, and an imaging optical device including the imaging lens. can do. By using the imaging optical device according to the present invention in a digital device such as a mobile phone or a portable information terminal, a high-performance image input function can be added to the digital device in a compact manner.

The optical block diagram of 1st Embodiment (Example 1). FIG. 6 is an aberration diagram of Example 1. The optical block diagram of 2nd Embodiment (Example 2). FIG. 6 is an aberration diagram of Example 2. The optical block diagram of 3rd Embodiment (Example 3). FIG. 6 is an aberration diagram of Example 3. The optical block diagram of 4th Embodiment (Example 4). FIG. 6 is an aberration diagram of Example 4. The optical block diagram of 5th Embodiment (Example 5). FIG. 6 is an aberration diagram of Example 5. The optical block diagram of 6th Embodiment (Example 6). FIG. 10 is an aberration diagram of Example 6. The optical block diagram of 7th Embodiment (Example 7). FIG. 10 is an aberration diagram of Example 7. The schematic diagram which shows the schematic structural example of the digital apparatus carrying an imaging lens.

The imaging lens and the like according to the present invention will be described below. An imaging lens according to the present invention is an imaging lens for forming a subject image on an imaging surface of an imaging element (for example, a photoelectric conversion unit of a solid-state imaging element), and has a convex surface directed toward the object side in order from the object side. A positive first lens, an aperture stop, a positive second lens having a convex surface facing the image side , a negative third lens, a positive fourth lens, and a negative fifth lens, and so on. The following conditional expressions (1) and (4) are satisfied.
0 <f1 / f2 <1.26 (1)
1.41 ≦ f1 / f <3.0 (4)
However,
f1: focal length of the first lens,
f2: focal length of the second lens,
f: focal length of the entire imaging lens system,
It is.

In order to obtain an imaging lens that is small and bright and has an excellent aberration, the basic configuration of the present invention includes a positive first lens, an aperture stop, a positive second lens, and a negative third lens. It consists of a positive fourth lens and a negative fifth lens. In this lens configuration, in order from the object side, a positive lens group including a first lens, an aperture stop, a second lens, a third lens, and a fourth lens, and a negative fifth lens are arranged in a so-called telephoto type arrangement. Therefore, this configuration is advantageous for reducing the overall length of the imaging lens. Furthermore, by using two negative lenses in the five-lens configuration, it is easy to correct the Petzval sum by increasing the diverging surfaces, and an imaging lens that secures good imaging performance to the periphery of the screen is obtained. It becomes possible. In addition, by arranging the aperture stop between the first lens and the second lens, it is possible to ensure the telecentricity of the image-side light beam, and to suppress the occurrence of lateral chromatic aberration and distortion. . Furthermore, by making the object side surface of the first lens convex, and the image side surface of the second lens convex, it is possible to ensure symmetry before and after the stop, and appropriately correct lateral chromatic aberration and distortion. Is possible.

Conditional expression (1) optimizes the power arrangement before and after the aperture by setting the focal length of the first lens and the second lens to an appropriate range (power: an amount defined by the reciprocal of the focal length), and the total length Is a conditional expression for appropriately achieving the shortening of the lens and the correction of aberration. By exceeding the lower limit of conditional expression (1), it is possible to prevent the focal length of the first lens from becoming too short relative to the focal length of the second lens, and to maintain symmetry before and after the aperture, thereby reducing the image plane. It is possible to prevent the curvature from falling greatly under and the distortion aberration from becoming significantly negative (barrel type). On the other hand, by falling below the upper limit of conditional expression (1), it is possible to prevent the focal length of the first lens from becoming too long relative to the focal length of the second lens, and to maintain symmetry before and after the aperture. It is possible to prevent the field curvature from being excessively overturned and the distortion aberration from being greatly plus (cushion type). Furthermore, shortening of the overall lens length can be achieved.
Conditional expression (4) is a conditional expression for shortening the entire length of the imaging lens and achieving appropriate aberration correction by setting the focal length of the first lens in an appropriate range. By falling below the upper limit of conditional expression (4), the positive power of the first lens can be prevented from becoming too small, and the composite principal point of the first lens to the fourth lens can be arranged closer to the object side. Shortening of the overall length of the imaging lens can be achieved. On the other hand, by exceeding the lower limit of the conditional expression (4), higher-order spherical aberration and coma generated in the first lens can be suppressed.

It is desirable to satisfy the conditional expression below (2).
-4.0 <f3 / f <-1.1 (2)
However,
f3: focal length of the third lens,
f: focal length of the entire imaging lens system,
It is.

  Conditional expression (2) is a conditional expression for achieving shortening of the overall length of the imaging lens and good aberration correction by setting the focal length of the third lens in an appropriate range. If the upper limit of conditional expression (2) is exceeded, the negative power of the third lens becomes too strong, making it difficult to shorten the entire length of the imaging lens. Further, higher-order spherical aberration and coma aberration are generated in the third lens. If the lower limit of conditional expression (2) is not reached, the negative power of the third lens becomes too weak, making it difficult to correct the Petzval sum, and the imaging performance at the periphery of the screen will deteriorate.

According to the above characteristic configuration of the present invention , it is possible to realize an imaging lens having a bright five-lens configuration of about F2.0 and an imaging optical device including the same, in which various aberrations are well corrected while being smaller than the conventional type. It is possible. If the imaging optical device is used in a digital device such as a mobile phone or a portable information terminal, it is possible to add a high-performance image input function to the digital device in a compact manner. It can contribute to functionalization. The conditions for achieving such effects in a well-balanced manner and achieving higher optical performance, downsizing, etc. will be described below.

It is more desirable to satisfy the following conditional expression (1a).
0.3 <f1 / f2 <1.1 (1a)
The conditional expression (1a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (1). Therefore, the above effect can be further enhanced preferably by satisfying conditional expression (1a).
It is more desirable to satisfy the following conditional expression (4a).
1.41 ≦ f1 / f <2.5 (4a)
The conditional expression (4a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (4). Therefore, the above effect can be further increased preferably by satisfying conditional expression (4a).

It is more desirable to satisfy the following conditional expression (2a).
−3.0 <f3 / f <−1.3 (2a)
This conditional expression (2a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (2). Therefore, the above effect can be further increased preferably by satisfying conditional expression (2a).

  It is desirable that the third lens has a concave surface facing the image side. By making the image side surface of the third lens concave, it is possible to easily correct lateral chromatic aberration and Petzval sum.

It is desirable to satisfy the following conditional expression (3).
1.41 <f2 / f <10.0 (3)
However,
f2: focal length of the second lens,
f: focal length of the entire imaging lens system,
It is.

  Conditional expression (3) is a conditional expression for shortening the entire length of the imaging lens and achieving appropriate aberration correction by setting the focal length of the second lens in an appropriate range. By falling below the upper limit of conditional expression (3), it is possible to prevent the positive power of the second lens from becoming too small, and the composite principal point of the first lens to the fourth lens can be arranged closer to the object side. Shortening of the overall length of the imaging lens can be achieved. On the other hand, exceeding the lower limit of the conditional expression (3) can suppress higher-order spherical aberration and coma generated in the second lens.

It is more desirable to satisfy the following conditional expression (3a).
1.5 <f2 / f <6.0 (3a)
This conditional expression (3a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (3). Therefore, the above effect can be further increased preferably by satisfying conditional expression (3a).

It is desirable to satisfy the following conditional expression (5).
15 <νd3 <31 (5)
However,
νd3: Abbe number of the third lens with respect to the d-line,
It is.

  Conditional expression (5) is a conditional expression for appropriately correcting axial chromatic aberration and lateral chromatic aberration by setting the dispersion of the third lens within an appropriate range. When the lower limit of conditional expression (5) is not reached, the longitudinal chromatic aberration can be sufficiently corrected, but the lateral chromatic aberration generated by the peripheral luminous flux becomes large and difficult to correct. On the other hand, if the upper limit of conditional expression (5) is exceeded, the lateral chromatic aberration of the peripheral light beam can be suppressed, but the axial chromatic aberration cannot be corrected.

It is more desirable to satisfy the following conditional expression (5a).
17 <νd3 <27 (5a)
This conditional expression (5a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (5). Therefore, the above effect can be further increased preferably by satisfying conditional expression (5a).

The image side surface of the fifth lens has an aspherical shape, has a negative refractive power at the center thereof, becomes weaker toward the periphery, has an inflection point, and has the following conditional expression (6 ) Is desirable.
0.05 <T5 / f <0.2 (6)
However,
f: focal length of the entire imaging lens system,
T5: thickness of the fifth lens on the optical axis,
It is.

  By making the image side surface of the fifth lens the aspherical shape having an inflection point, the negative refracting power becomes weaker as it goes from the optical axis to the periphery, and it becomes easy to ensure the telecentric characteristics of the image side light beam. Further, the image side surface of the fourth lens does not need to excessively weaken the negative refractive power at the periphery of the lens, and the off-axis aberration can be corrected well. Here, the “inflection point” is a point on the aspheric surface where the tangent plane of the aspherical vertex is a plane perpendicular to the optical axis in the curve of the lens cross-sectional shape within the effective radius.

  Conditional expression (6) is a conditional expression for appropriately achieving the image plane property of the imaging lens by setting the axial thickness of the fifth lens in an appropriate range. In the fifth lens, the refractive power in the vicinity of the optical axis and the refractive power in the vicinity of the fifth lens are greatly different from those of the other lenses, so that the influence of the axial thickness on the field curvature is large. By falling below the upper limit of conditional expression (6), it is possible to prevent the field curvature from falling to the over side. On the other hand, by exceeding the lower limit of conditional expression (6), it is possible to prevent the field curvature from falling to the under side. Therefore, by satisfying conditional expression (6), it is possible to prevent the image plane property of the imaging lens from falling too much toward the over side or the under side.

It is more desirable to satisfy the following conditional expression (6a).
0.07 <T5 / f <0.18 (6a)
The conditional expression (6a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (6). Therefore, the above effect can be further enhanced preferably by satisfying conditional expression (6a).

  It is desirable that all the lenses are made of a plastic material. That is, it is desirable that the imaging lens has only a plastic lens as a lens. In recent years, for the purpose of downsizing the entire imaging optical apparatus including a solid-state imaging device, even a solid-state imaging device having the same number of pixels has been developed with a small pixel pitch and consequently a small imaging surface size. In such an imaging lens for a solid-state imaging device having a small imaging surface size, it is necessary to relatively shorten the focal length of the entire system, so that the curvature radius and the outer diameter of each lens are considerably reduced. Therefore, compared to glass lenses manufactured by time-consuming polishing, all lenses are made of plastic lenses manufactured by injection molding, so that even lenses with small radii of curvature and outer diameters are inexpensive. Mass production is possible. In addition, since the plastic lens can lower the press temperature, it is possible to suppress the wear of the molding die, and as a result, the number of replacements and maintenance times of the molding die can be reduced, and the cost can be reduced.

  The imaging lens according to the present invention is suitable for use as an imaging lens for a digital device with an image input function (for example, a portable terminal). By combining this with an imaging device or the like, an image of a subject is optically captured. An imaging optical device that outputs an electrical signal can be configured. The imaging optical device is an optical device that constitutes a main component of a camera used for still image shooting and moving image shooting of a subject, for example, an imaging lens that forms an optical image of an object in order from the object (that is, subject) side, And an imaging device that converts an optical image formed by the imaging lens into an electrical signal. Then, the imaging lens having the above-described characteristic configuration is arranged so that an optical image of the subject is formed on the light receiving surface (that is, the imaging surface) of the imaging device, and thus has high performance at a small size, low cost. An imaging optical device and a digital device including the imaging optical device can be realized.

  Examples of digital devices with an image input function include cameras such as digital cameras, video cameras, surveillance cameras, in-vehicle cameras, videophone cameras, etc., and personal computers, mobile terminals (for example, mobile phones, mobile computers, etc.) Small and portable information device terminals), peripheral devices (scanners, printers, etc.), cameras incorporated in or external to other digital devices, and the like. As can be seen from these examples, it is possible not only to configure a camera by using an imaging optical device, but also to add a camera function by mounting the imaging optical device on various devices. For example, a digital device with an image input function such as a mobile phone with a camera can be configured.

  FIG. 15 is a schematic cross-sectional view showing a schematic configuration example of a digital device DU as an example of a digital device with an image input function. The imaging optical device LU mounted in the digital device DU shown in FIG. 15 includes an imaging lens LN (AX: optical axis) that forms an optical image (image plane) IM of an object in order from the object (that is, subject) side, A parallel plate PT (cover glass of the image sensor SR; corresponding to an optical filter such as an optical low-pass filter and an infrared cut filter disposed as necessary) and a light receiving surface (imaging surface) SS by the imaging lens LN. And an imaging element SR that converts the optical image IM formed thereon into an electrical signal. When a digital device DU with an image input function is constituted by this imaging optical device LU, the imaging optical device LU is usually arranged inside the body, but when necessary to realize the camera function, a form as necessary is adopted. Is possible. For example, the unitized imaging optical device LU can be configured to be detachable or rotatable with respect to the main body of the digital device DU.

  As described above, the imaging lens LN has a single-focus five-lens configuration including the first to fifth lenses L1 to L5 in order from the object side, and forms the optical image IM on the light receiving surface SS of the imaging element SR. It has become. As the image sensor SR, for example, a solid-state image sensor such as a CCD image sensor or a CMOS image sensor having a plurality of pixels is used. Since the imaging lens LN is provided so that the optical image IM of the subject is formed on the light receiving surface SS which is a photoelectric conversion unit of the imaging element SR, the optical image IM formed by the imaging lens LN is the imaging element. It is converted into an electric signal by SR.

  The digital device DU includes a signal processing unit 1, a control unit 2, a memory 3, an operation unit 4, a display unit 5 and the like in addition to the imaging optical device LU. The signal generated by the image sensor SR is subjected to predetermined digital image processing, image compression processing, and the like as required by the signal processing unit 1 and recorded as a digital video signal in the memory 3 (semiconductor memory, optical disk, etc.) In some cases, it is transmitted to other devices via a cable or converted into an infrared signal or the like (for example, a communication function of a mobile phone). The control unit 2 is composed of a microcomputer, and controls functions such as a photographing function (still image photographing function, moving image photographing function, etc.), an image reproduction function, etc .; and a lens moving mechanism for focusing, etc. For example, the control unit 2 controls the imaging optical device LU so as to perform at least one of still image shooting and moving image shooting of a subject. The display unit 5 includes a display such as a liquid crystal monitor, and displays an image using an image signal converted by the image sensor SR or image information recorded in the memory 3. The operation unit 4 is a part including operation members such as an operation button (for example, a release button) and an operation dial (for example, a shooting mode dial), and transmits information input by the operator to the control unit 2.

  Next, the specific optical configuration of the imaging lens LN will be described in more detail with reference to the first to seventh embodiments. 1, 3, 5, 7, 9, 11, and 13 show first to seventh embodiments of the imaging lens LN in an infinitely focused state in optical cross sections, respectively. The j-th lens Lj is a lens located at the j-th from the object side, and the parallel plate PT disposed on the image side of the imaging lens LN includes an optical low-pass filter, an IR cut filter, a seal glass of a solid-state imaging device, and the like. It is assumed. All the lens surfaces constituting the imaging lens LN are aspheric surfaces, and all the lenses are assumed to be made of a plastic material as an optical material. In addition, it is assumed that the entire focus is performed by moving the first lens L1 to the fifth lens L5 as a single unit for the focus position adjustment in the auto focus, the macro switching function, or the like.

  In the imaging lenses LN of the first to seventh embodiments, from the object side, the positive first lens L1, the aperture stop ST, the positive second lens L2, the negative third lens L3, and the positive fourth lens L4. And the negative fifth lens L5 in this order. In either case, the first lens L1 has a convex surface facing the object side, the second lens L2 has a convex surface facing the image side, and the third lens L3 has a concave surface facing the image side. The image side surface of the fifth lens is an aspheric surface having an inflection point at a position other than the intersection with the optical axis AX.

  By the way, the plastic material has a large refractive index change at the time of temperature change, so if all lenses are made of plastic lenses, the image point position of the entire imaging lens system will fluctuate when the ambient temperature changes. It will be held. Recently, however, it has been found that mixing inorganic fine particles in a plastic material can reduce the effect of temperature changes on the plastic material. More specifically, mixing fine particles with a transparent plastic material generally causes scattering of light and lowers the transmittance, making it difficult to use as an optical material. If the wavelength is smaller than this wavelength, scattering can be substantially prevented from occurring.

In addition, the refractive index of the plastic material decreases as the temperature increases, but the refractive index of the inorganic particles increases as the temperature increases. Therefore, it is possible to make almost no change in the refractive index by using these temperature dependencies so as to cancel each other. Specifically, by dispersing inorganic particles having a maximum length of 20 nanometers or less in a plastic material as a base material, a plastic material with extremely low temperature dependency of the refractive index can be obtained. For example, by dispersing fine particles of niobium oxide (Nb ₂ O ₅ ) in an acrylic resin, a change in refractive index due to a temperature change can be reduced.

  In the imaging lens LN according to the present invention, such a positive lens having a relatively large refractive power (for example, the first lens L1 and the fourth lens L4) or all the lenses (the first to fifth lenses L1 to L5) can be configured as described above. By using a plastic material in which various inorganic particles are dispersed, it is possible to suppress the image point position fluctuation at the time of temperature change of the entire imaging lens LN system.

  In each of the above-described embodiments and each example to be described later, the principal ray incident angle of the light beam incident on the imaging surface of the solid-state imaging device is not necessarily designed to be sufficiently small in the periphery of the imaging surface. However, with recent technology, shading can be reduced by reviewing the arrangement of the color filters of the solid-state imaging device and the on-chip microlens array. Specifically, if the pitch of the arrangement of the color filters and the on-chip microlens array is set slightly smaller than the pixel pitch of the image pickup surface of the image pickup device, the color filter for each pixel becomes closer to the periphery of the image pickup surface. Since the on-chip microlens array is shifted to the optical axis side of the imaging lens, the obliquely incident light beam can be efficiently guided to the light receiving portion of each pixel. Thereby, the shading which generate | occur | produces with a solid-state image sensor can be restrained small. In each embodiment to be described later, a design example aiming at further miniaturization is provided for the portion in which the requirement is relaxed.

Hereinafter, the configuration and the like of the imaging lens embodying the present invention will be described more specifically with reference to the construction data of the examples. Examples 1 to 7 (EX1 to 7) listed here are numerical examples corresponding to the first to seventh embodiments, respectively, and are optical configuration diagrams showing the first to seventh embodiments. (FIGS. 1, 3, 5, 7, 9, 11, and 13) show the lens configurations of the corresponding Examples 1 to 7, respectively. Example 7 is an example not belonging to the present invention.

In the construction data of each embodiment, as surface data, in order from the left column, the surface number, the radius of curvature r (mm), the axial top surface distance d (mm), the refractive index nd with respect to the d line (wavelength: 587.56 nm), An Abbe number vd and an effective radius (mm) regarding the d line are shown. A surface with * in the surface number is an aspheric surface, and the surface shape is defined by the following expression (AS) using a local orthogonal coordinate system (X, Y, Z) with the surface vertex as the origin. . As aspheric data, an aspheric coefficient or the like is shown. It should be noted that the coefficient of the term not described in the aspherical data of each example is 0, and E−n = × 10 ⁻ⁿ for all data.

…（ＡＳ）

... (AS)

However,
h: height in the direction perpendicular to the X axis (optical axis AX) (h ² = Y ² + Z ² ),
X: sag amount in the direction of the optical axis AX at the position of height h (based on the surface vertex),
R: Reference radius of curvature (corresponding to the radius of curvature r),
K: conic constant,
Ai: i-th order aspheric coefficient,
It is.

  As various data, the focal length (f, mm), back focus (fB, mm), F number (F), diagonal length of the imaging surface SS of the imaging element SR (2Y ′, mm; Y ′) The maximum image height), the total lens length (TL, mm), and the half angle of view (ω, °) are shown, and the focal length (mm) of each lens is shown as single lens data. However, the back focus fB used here is the distance from the image side surface of the parallel plate PT to the image plane IM, and the total lens length TL is the distance from the front lens surface to the image plane IM. Table 1 shows values corresponding to the conditional expressions of the respective examples.

  2, 4, 6, 8, 10, 12, and 14 are aberration diagrams of Examples 1 to 7 (EX 1 to 7), where (A) is spherical aberration (mm), (B ) Shows astigmatism (mm), and (C) shows distortion (%). In the spherical aberration diagram (A), the solid line shows the spherical aberration amount for the d-line (wavelength 587.56 nm), the broken line shows the spherical aberration amount for the g-line (wavelength 435.84 nm), and the optical axis AX direction from the paraxial image plane, respectively. The vertical axis represents the F value. In the astigmatism diagram (B), the broken line M represents the meridional image plane with respect to the d-line, and the solid line S represents the sagittal image plane with respect to the d-line by the amount of deviation in the optical axis AX direction from the paraxial image plane. The axis represents the image height Y ′ (mm). In the distortion diagram (C), the horizontal axis represents the distortion with respect to the d-line, and the vertical axis represents the image height Y ′ (mm). Note that the maximum image height Y ′ corresponds to half the diagonal length of the imaging surface SS of the imaging element SR.

  The imaging lens LN (FIG. 1) of Example 1 includes, in order from the object side, a positive first lens L1, a positive second lens L2, a negative third lens L3, and a positive fourth lens L4. The negative fifth lens L5 is composed of an aspherical lens surface, and an aperture stop ST is disposed between the first lens L1 and the second lens L2. When viewing each lens with a paraxial surface shape, the first lens L1 is a positive meniscus lens convex toward the object side, the second lens L2 is a positive meniscus lens convex toward the image side, and the third lens L3 is The fourth lens L4 is a positive meniscus lens convex to the image side, and the fifth lens L5 is a negative meniscus lens concave to the image side.

  The imaging lens LN (FIG. 3) of Example 2 includes, in order from the object side, a positive first lens L1, a positive second lens L2, a negative third lens L3, and a positive fourth lens L4. The negative fifth lens L5 is composed of an aspherical lens surface, and an aperture stop ST is disposed between the first lens L1 and the second lens L2. When each lens is viewed with a paraxial surface shape, the first lens L1 is a positive meniscus lens convex on the object side, the second lens L2 is a biconvex positive lens, and the third lens L3 is biconcave. The fourth lens L4 is a negative meniscus lens convex to the image side, and the fifth lens L5 is a negative meniscus lens concave to the image side.

  The imaging lens LN (FIG. 5) of Example 3 includes, in order from the object side, a positive first lens L1, a positive second lens L2, a negative third lens L3, and a positive fourth lens L4. The negative fifth lens L5 is composed of an aspherical lens surface, and an aperture stop ST is disposed between the first lens L1 and the second lens L2. When each lens is viewed with a paraxial surface shape, the first lens L1 is a positive meniscus lens convex on the object side, the second lens L2 is a biconvex positive lens, and the third lens L3 is biconcave. The fourth lens L4 is a negative meniscus lens convex to the image side, and the fifth lens L5 is a negative meniscus lens concave to the image side.

  The imaging lens LN (FIG. 7) of Example 4 includes, in order from the object side, a positive first lens L1, a positive second lens L2, a negative third lens L3, a positive fourth lens L4, The negative fifth lens L5 is composed of an aspherical lens surface, and an aperture stop ST is disposed between the first lens L1 and the second lens L2. When viewing each lens with a paraxial surface shape, the first lens L1 is a positive meniscus lens convex toward the object side, the second lens L2 is a positive meniscus lens convex toward the image side, and the third lens L3 is The fourth lens L4 is a positive meniscus lens convex to the image side, and the fifth lens L5 is a negative meniscus lens concave to the image side.

  The imaging lens LN (FIG. 9) of Example 5 includes, in order from the object side, a positive first lens L1, a positive second lens L2, a negative third lens L3, a positive fourth lens L4, The negative fifth lens L5 is composed of an aspherical lens surface, and an aperture stop ST is disposed between the first lens L1 and the second lens L2. When viewing each lens with a paraxial surface shape, the first lens L1 is a positive meniscus lens convex toward the object side, the second lens L2 is a positive meniscus lens convex toward the image side, and the third lens L3 is The fourth lens L4 is a positive meniscus lens convex to the image side, and the fifth lens L5 is a negative meniscus lens concave to the image side.

  The imaging lens LN (FIG. 11) of Example 6 includes, in order from the object side, a positive first lens L1, a positive second lens L2, a negative third lens L3, and a positive fourth lens L4. The negative fifth lens L5 is composed of an aspherical lens surface, and an aperture stop ST is disposed between the first lens L1 and the second lens L2. When viewing each lens with a paraxial surface shape, the first lens L1 is a positive meniscus lens convex on the object side, the second lens L2 is a biconvex positive lens, and the third lens L3 is on the image side. The fourth lens L4 is a positive meniscus lens convex to the image side, and the fifth lens L5 is a negative meniscus lens concave to the image side.

  The imaging lens LN (FIG. 13) of Example 7 includes, in order from the object side, a positive first lens L1, a positive second lens L2, a negative third lens L3, and a positive fourth lens L4. The negative fifth lens L5 is composed of an aspherical lens surface, and an aperture stop ST is disposed between the first lens L1 and the second lens L2. When viewing each lens with a paraxial surface shape, the first lens L1 is a positive meniscus lens convex on the object side, the second lens L2 is a biconvex positive lens, and the third lens L3 is on the image side. The fourth lens L4 is a positive meniscus lens convex to the image side, and the fifth lens L5 is a negative meniscus lens concave to the image side.

DU Digital equipment LU Image pickup optical device LN Image pickup lens L1 to L5 First to fifth lenses ST Aperture stop (stop)
SR Image sensor SS Light receiving surface
IM image plane (optical image)
AX optical axis 1 signal processing unit 2 control unit 3 memory 4 operation unit 5 display unit

Claims (10)

An imaging lens for forming a subject image on an imaging surface of an imaging element, and in order from the object side, a positive first lens having a convex surface on the object side, an aperture stop, and a convex surface on the image side It consists of a positive second lens, a negative third lens, a positive fourth lens, and a negative fifth lens, and satisfies the following conditional expressions (1) and (4): Imaging lens;
0 <f1 / f2 <1.26 (1)
1.41 ≦ f1 / f <3.0 (4)
However,
f1: focal length of the first lens,
f2: focal length of the second lens,
f: focal length of the entire imaging lens system,
It is. The imaging lens according to claim 1, wherein the following conditional expression (2) is satisfied:
-4.0 <f3 / f <-1.1 (2)
However,
f3: focal length of the third lens,
f: focal length of the entire imaging lens system,
It is. The imaging lens according to claim 1 or 2, wherein the third lens is characterized in that it a concave surface facing the image side. The imaging lens according to any one of claims 1 to 3, characterized by satisfying the following conditional expression (3);
1.41 <f2 / f <10.0 (3)
However,
f2: focal length of the second lens,
f: focal length of the entire imaging lens system,
It is. The imaging lens according to any one of claims 1 to 4, characterized by satisfying the following conditional expression (5);
15 <νd3 <31 (5)
However,
νd3: Abbe number of the third lens with respect to the d-line,
It is. The image side surface of the fifth lens has an aspherical shape, has a negative refractive power at the center thereof, becomes weaker toward the periphery, has an inflection point, and has the following conditional expression (6 The imaging lens according to any one of claims 1 to 5 , wherein:
0.05 <T5 / f <0.2 (6)
However,
f: focal length of the entire imaging lens system,
T5: thickness of the fifth lens on the optical axis,
It is. Lens imaging lens according to any of claims 1-6, characterized in that all are made of plastic material. Includes an imaging lens according to any one of claims 1 to 7 and an imaging element for converting into an electrical signal an optical image formed on the imaging surface, a subject on an imaging surface of the imaging element An imaging optical apparatus, wherein the imaging lens is provided so that an optical image of the above is formed. 9. A digital apparatus, comprising the imaging optical device according to claim 8 to which at least one function of still image shooting and moving image shooting of a subject is added. The digital device according to claim 9 , wherein the digital device is a portable terminal.

Images