WO2014073685A1

WO2014073685A1 - Image capture lens, image capture device, and portable terminal

Info

Publication number: WO2014073685A1
Application number: PCT/JP2013/080460
Authority: WO
Inventors: 川崎貴志
Original assignee: コニカミノルタ株式会社
Priority date: 2012-11-12
Filing date: 2013-11-11
Publication date: 2014-05-15
Also published as: JPWO2014073685A1

Abstract

Provided is an image capture lens, whereby it is possible to implement a wide angle of view, and which has desirable high performance with a low height. An image capture lens (10) is formed, in order from the object side, from a first lens (L1), a second lens (L2) having a biconvex shape, and a third lens (L3), wherein the third lens (L3) satisfies a conditional formula -0.5 < f/f3 < -0.0 ... (1), wherein f is the focal distance of the overall assembly, and f3 is the focal distance of the third lens (L3). With the configuration wherein the second lens (L2) has the biconvex shape, it is possible for the principal point location of the overall assembly to be brought near the imaging side and make for a short focus, making it easy to achieve a wide angle of field. With the second lens (L2) being imbued with a comparatively strong positive power, it is possible to avoid an occurrence of high-order aberration from a too-strong single-face index of refraction. Exceeding the lower bound of the conditional formula (1) allows shortening the back focus, and reducing the overall length of the optical assembly. Being below the upper bound thereof allows making the Petzval sum smaller, and correcting an imaging surface curvature.

Description

Imaging lens, imaging device, and portable terminal

The present invention relates to an imaging lens for acquiring a subject image, and an imaging apparatus and a portable terminal including the imaging lens, and in particular, an imaging lens, an imaging apparatus, and a portable terminal that can realize a wide angle of an angle of view of 75 ° or more and are suitable for a low profile. About.

In recent years, small and thin imaging devices have been installed in portable terminals, which are small and thin electronic devices such as mobile phones and PDAs (Personal Digital Assistants), thereby enabling not only audio information but also images to remote locations. Information can also be transmitted between each other. As an image pickup device used in these image pickup devices, a solid-state image pickup device such as a CCD (Charge Coupled Device) type image sensor or a CMOS (Complementary Metal-Oxide Semiconductor) type image sensor is used. In recent years, the pixel pitch of solid-state image sensors has been reduced, and higher resolution and higher performance have been achieved with higher pixels. On the other hand, downsizing of the image sensor itself is achieved while maintaining high pixels. Furthermore, attempts have been made to curve the imaging surface of the solid-state imaging device. Thus, there is a need for a compact and high-performance imaging lens suitable for a solid-state imaging device that is high in size, small, and can be curved. Potential applications and demands for lenses are increasing. Here, a three-lens configuration is suitable as a wide-angle, small, and high-performance imaging lens, and there are those disclosed in Patent Documents 1 and 2 as such imaging lenses.

Patent Document 1 describes a photographing lens that is suitable for a compact camera or a lens-equipped film unit, has a wide photographing field angle of about 80 °, and has a brightness of F3.5 to F4. The photographing lens includes a weak positive first lens, an aperture stop, a positive second lens, and a negative third lens, or a weak negative first lens, an aperture stop, a positive second lens, and a negative lens. It consists of a third lens. By the way, an imaging lens used for a solid-state imaging device having a small pixel size is required to have a characteristic different from that of a lens for a film camera, which requires a high resolving power to cope with a highly thinned pixel. . However, 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. Therefore, as in Patent Document 1, sufficient performance can be obtained with a brightness of about F3.5. Can not. Moreover, since the negative power of the third lens is too strong, the photographic lens of Patent Document 1 has a long back focus and is disadvantageous for shortening the optical total length.

Next, Patent Document 2 describes an imaging lens including a positive first lens, an aperture stop, a positive second lens, and a negative third lens. This photographic lens is widened because the second lens has a strong positive power. However, since the second lens has a meniscus shape with the convex surface facing the image side, the principal point position is shifted to the image side, resulting in an increase in the total optical length.

JP 2006-47944 A US Patent No. 08055633

The present invention has been made in view of the above background art, and an object thereof is to provide a high-performance imaging lens that can realize a wide angle and is suitable for a low profile.
Another object of the present invention is to provide an imaging apparatus incorporating the imaging lens and a portable terminal including the imaging apparatus.

In order to achieve the above object, an imaging lens according to the present invention includes, in order from the object side, a first lens, an aperture stop, a biconvex second lens, and a third lens. The third lens has the following conditions: Satisfy the formula
-0.5 <f / f3 <-0.0 (1)
However,
f: Focal length of the entire system (mm)
f3: focal length of the third lens (mm)

In the imaging lens, the second lens has a biconvex shape. In this way, in the configuration in which the second lens has a biconvex shape, the principal point position of the entire system can be appropriately shifted toward the image side and the focal length can be shortened. In addition, when the second lens has a relatively strong positive power, the refractive power can be shared between the object side surface and the image side surface, thereby preventing the occurrence of higher-order aberrations due to excessively strong refractive power on one side. Can do. Further, by arranging an aperture stop between the first lens and the second lens, the axial ray height of the second lens is increased. On the other hand, the combined power P (the reciprocal of the focal length f) of the three balls is, in the case of a thin lens, the axial ray height of each lens is h1, h2, h3, and the power of each lens is P1, P2, P3. Then, it is expressed by the following formula.
P = P1 + (h2 / h1) × P2 + (h3 / h1) × P3
From the above equation, the higher the axial ray height, the greater the influence on the combined power. Therefore, by increasing the axial ray height of the second lens having a strong positive power, it becomes easy to increase the combined power (shorten the focal length) and widen the angle.
Conditional expression (1) is a conditional expression for making the ratio between the focal length of the entire system and the focal length of the third lens appropriate. By exceeding the lower limit of the conditional expression (1), the negative power of the third lens becomes weak, so that the back focus can be shortened and the optical total length can be shortened. Moreover, since the third lens has a negative power by falling below the upper limit of conditional expression (1), the Petzval sum can be reduced and the curvature of field can be corrected.
The value f / f3 is more preferably in the range of the following formula.
−0.4 <f / f3 <−0.1 (1) ′

According to a specific aspect or aspect of the present invention, in the imaging lens, the first lens has a meniscus shape with a convex surface facing the object side. In this case, since the incident angle of the light beam from the object to the lens can be reduced, the occurrence of spherical aberration and coma aberration can be suppressed.

According to another aspect of the present invention, the third lens has a meniscus shape with a convex surface facing the image side. In this case, the incident angle of the light beam on the third lens can be reduced, and rapid refraction of the light beam can be avoided even in the peripheral region, so that a decrease in aperture efficiency can be suppressed and a high peripheral light amount can be maintained.

According to still another aspect of the present invention, the following conditional expression is satisfied.
−0.4 ≦ f / f1 <0.4 (2)
However,
f1: Focal length of the first lens (mm)

The conditional expression (2) is a conditional expression for making the ratio between the focal length of the entire system and the focal length of the first lens appropriate. By exceeding the lower limit of conditional expression (2), the first lens does not have a strong negative power, so that the principal point position of the entire system is not too close to the image plane, and the optical total length can be shortened. Also, by falling below the upper limit of conditional expression (2), the first lens does not have a strong positive power, so that the principal point does not move too close to the object side, and a sufficiently wide angle can be achieved.
The value f / f1 is more preferably in the range of the following formula.
−0.3 ≦ f / f1 <0.3 (2) ′

According to still another aspect of the present invention, the following conditional expression is satisfied.
−0.7 <f2 / f3 <0.0 (3)
However,
f2: focal length of the second lens (mm)

Conditional expression (3) is a conditional expression for making the ratio of the focal length of the second lens and the focal length of the third lens appropriate. By exceeding the lower limit of the conditional expression (3), the second lens has a strong positive power with respect to the negative power of the third lens, so that a wide angle can be achieved. Moreover, since the third lens has a weak negative power with respect to the positive power of the second lens by falling below the upper limit of the conditional expression (3), the curvature of field generated by the second lens, etc. Aberration can be corrected.
The value f2 / f3 is more preferably in the range of the following formula.
−0.45 <f2 / f3 <0.0 (3) ′

According to still another aspect of the present invention, the following conditional expression is satisfied.
0.0 <(r3 + r4) / (r3-r4) <0.5 (4)
However,
r3: radius of curvature of object side surface of second lens (mm)
r4: radius of curvature (mm) of the image side surface of the second lens

Conditional expression (4) is a conditional expression for making the shape of the second lens appropriate. By exceeding the lower limit of the conditional expression (4), the second lens has a biconvex shape in which the radius of curvature of the object side surface is larger than that of the image side surface. As a result, the incident angle of the light incident on the second lens on the object side surface is small. Therefore, spherical aberration and coma generated in the second lens can be suppressed. Further, by falling below the upper limit of the conditional expression (4), the positive power of the second lens is shared without being biased to either the object side surface or the image side surface, so that appropriate aberration correction can be performed.
The value (r3 + r4) / (r3-r4) is more preferably in the range of the following equation.
0.0 <(r3 + r4) / (r3-r4) <0.4 (4) ′

According to still another aspect of the present invention, the following conditional expression is satisfied.
-5.0 <P23 / P <0.0 (5)
However,
P: Refractive power of the entire imaging lens system P23: Refractive power of a so-called air lens formed by the image side surface of the second lens and the object side surface of the third lens. The value of P23 is expressed by the following equation (6). Given.

However,
n2: Refractive index with respect to d-line of second lens n3: Refractive index with respect to d-line of third lens R4: Radius of curvature of image side surface of second lens R5: Radius of curvature of object side surface of third lens D5: With second lens Air distance on the axis with the third lens

Conditional expression (5) is a conditional expression for optimizing the ratio between the refractive power of the air lens between the second lens and the third lens and the refractive power of the entire system. Since the image side surface of the second lens has a convex shape, the air lens has a meniscus shape with the convex surface facing the image side. By exceeding the lower limit of conditional expression (5), the negative refracting power of the air lens between the second lens and the third lens becomes too strong, so that the light beam jumps strongly and the incident angle to the sensor increases. Can be prevented. Further, by falling below the upper limit of conditional expression (5), the refractive power of the air lens between the second lens and the third lens becomes negative to some extent, so that the Petzval sum can be reduced.
The value P23 / P is more preferably in the range of the following formula.
-4.0 <P23 / P <-1.0 (5) '

According to still another aspect of the present invention, the following conditional expression is satisfied.
15 <ν3 <50 (7)
However,
ν3: Abbe number of the third lens

Conditional expression (7) is a conditional expression for optimizing the Abbe number of the third lens. Exceeding the lower limit of conditional expression (7) can prevent excessive correction of chromatic aberration. Moreover, an inexpensive resin with good availability can be used for the third lens. In addition, the chromatic aberration generated in the second lens can be appropriately corrected by falling below the upper limit of conditional expression (7).
The value ν3 is more preferably in the range of the following formula.
20 <ν3 <40 (7) '

According to still another aspect of the present invention, the optical system further includes a lens having substantially no power. Also in this case, it is possible to provide a high-performance imaging lens that achieves a wide angle while suppressing an increase in the total optical length.

In order to achieve the above object, an imaging apparatus according to the present invention includes the imaging lens described above and a solid-state imaging device having a photoelectric conversion unit on which a subject image is formed by the imaging lens.

Since the above-described imaging lens is used in the imaging device, a thin or small imaging device including a high-performance imaging lens with a wide angle of view can be provided.

According to a specific aspect or aspect of the present invention, in the imaging apparatus, the solid-state imaging device has an imaging surface that is curved so that the peripheral portion is positioned on the object side with respect to the central portion. Since the imaging surface of the solid-state imaging device is curved, the sensor surface as the imaging surface can be matched with the lens image surface even if field curvature occurs on the lens side. Therefore, an in-focus image can be obtained from the center to the periphery. Further, since the peripheral portion is curved toward the object side, the sensor is curved so as to receive the light beam incident on the sensor, so that the light beam incident angle to the sensor can be suppressed small.

According to another aspect of the present invention, the imaging surface of the solid-state imaging device is curved in a cylindrical shape with a concave surface facing the object side. It is relatively easy to manufacture a solid-state imaging device having a cylindrical imaging surface. As the cylindrical shape, there are a case where the short side direction is curved and a case where the long side direction is curved on the imaging surface of the solid-state imaging device. On the other hand, field curvature remains, which is disadvantageous in terms of aberration correction. If the shape is curved in the short side direction, even if it is curved with the same curvature, the amount of displacement of the curved portion is smaller than in the shape curved in the long side direction, making it easier to fabricate the image sensor. Become. On the other hand, when the shape is curved in the long side direction, even when it is curved with the same radius of curvature, the amount of displacement can be increased compared to the case where the short side direction is curved, and the shape of the imaging surface is brought closer to the curvature of the lens surface. This is advantageous in terms of aberration correction.

According to still another aspect of the present invention, the imaging surface of the solid-state imaging device is curved into a spherical shape with a concave surface facing the object side. It is relatively easy to manufacture a solid-state image sensor having a spherical imaging surface.

In order to achieve the above object, a portable terminal according to the present invention includes the above-described imaging device, and enables high-accuracy and wide-angle shooting while maintaining a thin or small size.

It is a figure explaining a camera module (imaging device) provided with an imaging lens of one embodiment of the present invention. It is a figure explaining the modification of the camera module shown in FIG. It is a block diagram explaining a portable terminal provided with the camera module of FIG. 4A and 4B are perspective views of the front side and the back side of the mobile terminal, respectively. It is sectional drawing of the imaging lens etc. of Example 1. 6A to 6E are aberration diagrams of the imaging lens of Example 1. FIG. FIG. 6 is a cross-sectional view of an imaging lens and the like according to a modification of Example 1. 8A to 8E are aberration diagrams of the imaging lens according to one modification of Example 1. FIG. FIG. 6 is a cross-sectional view of an imaging lens and the like of Example 2. 10A to 10E are aberration diagrams of the imaging lens of Example 2. FIG. FIG. 6 is a cross-sectional view of an imaging lens and the like of Example 3. 12A to 12E are aberration diagrams of the imaging lens of Example 3. FIG. 6 is a cross-sectional view of an imaging lens and the like of Example 4. FIG. 14A to 14E are aberration diagrams of the imaging lens of Example 4. FIGS.

Hereinafter, an imaging lens and the like according to an embodiment of the present invention will be described with reference to FIG. The imaging lens 10 illustrated in FIG. 1 has the same configuration as the imaging lens 11 of Example 1 described later.

FIG. 1 is a cross-sectional view illustrating a camera module including an imaging lens according to an embodiment of the present invention. The camera module 50 includes an imaging lens 10 that forms a subject image, an imaging device 51 that detects a subject image formed by the imaging lens 10, and a wiring board 52 that holds the imaging device 51 from behind and has wiring and the like. And a lens barrel portion 54 having an opening OP for holding the imaging lens 10 and the like and allowing light rays from the object side to enter. The imaging lens 10 has a function of forming a subject image on the image plane or the imaging plane (projected plane) I of the imaging element 51. The camera module 50 is used by being incorporated in an imaging device to be described later.

The imaging lens 10 includes a first lens L1, an aperture stop S, a second lens L2, and a third lens L3 in order from the object side. The first lens L1 has a meniscus shape with a convex surface facing the object side, the second lens L2 has a biconvex shape, and the third lens L3 has a meniscus shape with a convex surface facing the image side. ing.

The image sensor 51 is a sensor chip made of a solid-state image sensor. The photoelectric conversion unit 51a of the image sensor 51 is composed of a CCD (charge coupled device) or a CMOS (complementary metal oxide semiconductor), photoelectrically converts incident light for each RGB, and outputs an analog signal thereof. The photoelectric exchange surface of the photoelectric conversion unit 51a as the light receiving unit is an image surface or an imaging surface (projected surface) I.

The wiring board 52 has a role of aligning and fixing the image sensor 51 to other members (for example, the lens barrel portion 54). The wiring board 52 can receive a voltage and a signal for driving the image pickup device 51 and the driving mechanism 55a from an external circuit, and can output a detection signal to the external circuit.

As shown in FIG. 2, the imaging surface I of the photoelectric conversion unit 51a provided in the imaging device 51 can be curved so that the peripheral part A1 is located on the object side with respect to the central part A0. At this time, the imaging surface I of the imaging element 51 can be curved in a cylindrical shape with a concave surface facing the object side, or can be curved in a spherical shape with the concave surface facing the object side. For this reason, the imaging element 51 and the wiring board 52 can be provided with a support for keeping the photoelectric conversion unit 51a in a desired curved state. By appropriately curving the imaging surface I, the imaging surface I can be adjusted to the lens image surface even if the imaging lens 10 has a curvature of field, so that the focus from the central part A0 to the peripheral part A1 is in focus. An image can be obtained. In addition, since the peripheral portion A1 is bent toward the object side, the photoelectric conversion unit 51a is bent so as to receive the incident light, so that the light incident angle on the photoelectric conversion unit 51a can be suppressed to be small.

The parallel plate F is disposed and fixed on the imaging lens 10 side of the imaging element 51 by a holder member (not shown) so as to cover the imaging element 51 and the like.

The lens barrel portion 54 houses and holds the imaging lens 10. The lens barrel portion 54 enables the focusing operation of the imaging lens 10 by moving any one or more of the lenses L1 to L3 constituting the imaging lens 10 along the optical axis AX. For example, it has a drive mechanism 55a. The drive mechanism 55a reciprocates the specific lens or all the lenses along the optical axis AX. The drive mechanism 55a includes, for example, a voice coil motor and a guide. The drive mechanism 55a can be configured by a stepping motor or the like instead of the voice coil motor or the like. The above drive mechanism 55a is not essential and can be omitted. That is, in applications where it is not necessary to ensure a wide focus range of the imaging lens 10, the imaging lens 10 and its peripheral mechanisms can be simplified by omitting the drive mechanism 55a.

Next, an example of a mobile phone or other mobile communication terminal 300 equipped with the camera module 50 illustrated in FIG. 1 will be described with reference to FIGS. 3, 4A and 4B.

The mobile communication terminal 300 is a smartphone-type mobile communication terminal, and includes an imaging device 100 having a camera module 50, a control unit (CPU) 310 that comprehensively controls each unit and executes a program corresponding to each process, Between a display operation unit 320 that is a touch panel that displays data related to communication, captured video, and the like and accepts user operations, an operation unit 330 including a power switch, and the like, and an external server or the like via an antenna 341 A wireless communication unit 340 for realizing various types of information communication, a storage unit (ROM) 360 storing necessary data such as a system program, various processing programs, and a terminal ID of the mobile communication terminal 300, and a control unit 310 Various processing programs executed by the computer, data, processing data, or the imaging apparatus 100 That includes a temporary storage unit used the imaging data and the like as a work area for temporarily storing the (RAM) 370.

The imaging apparatus 100 includes a control unit 103, an optical system driving unit 105, an imaging element driving unit 107, an image memory 108, and the like in addition to the camera module 50 described above.

The control unit 103 controls each unit of the imaging apparatus 100. The control unit 103 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and the like, and various types of programs are read out from the ROM and expanded in the RAM in cooperation with the CPU. Execute the process. The control unit 310 is communicably connected to the control unit 103 of the imaging apparatus 100, and can exchange control signals and image data.

The optical system driving unit 105 controls the state of the imaging lens 10 by operating the driving mechanism 55a of the imaging lens 10 when performing focusing, exposure, and the like under the control of the control unit 103. The optical system driving unit 105 operates the driving mechanism 55a to appropriately move the specific lens or all the lenses in the imaging lens 10 along the optical axis AX, thereby causing the imaging lens 10 to perform a focusing operation.

The image sensor driving unit 107 controls the operation of the image sensor 51 when performing exposure or the like under the control of the control unit 103. Specifically, the image sensor drive unit 107 controls the image sensor 51 by scanning and driving based on the timing signal. Further, the image sensor driving unit 107 converts the detection signal output from the image sensor 51 or an analog signal as a photoelectric conversion signal into digital image data. Further, the image sensor driving unit 107 can perform various image processing such as distortion correction, color correction, and compression on the image signal detected by the image sensor 51.

The image memory 108 receives the digitized image signal from the image sensor driving unit 107 and stores it as readable and writable image data.

Here, the photographing operation of the mobile communication terminal 300 including the imaging device 100 will be described. When the camera mode in which the mobile communication terminal 300 is operated as a camera is set, subject monitoring (through image display) and image shooting execution are performed. In monitoring, an image of a subject obtained through the imaging lens 10 is formed on the imaging surface I (see FIG. 1 and the like) of the imaging element 51. The image sensor 51 is scanned and driven by the image sensor driving unit 107, and outputs an analog signal for one screen as a photoelectric conversion output corresponding to a light image formed at regular intervals.

This analog signal is converted into digital data after gain adjustment is appropriately performed for each primary color component of RGB in a circuit attached to the image sensor 51. The digital data is subjected to color process processing including pixel interpolation processing and Y correction processing, and a digital luminance signal Y and color difference signals Cb, Cr (image data) are generated and stored in the image memory 108. The stored digital data is periodically read out from the image memory 108 to generate a video signal thereof, and is output to the display operation unit 320 via the control unit 103 and the control unit 310.

The display operation unit 320 functions as a finder in monitoring and displays captured images in real time. In this state, focusing, exposure, and the like of the imaging lens 10 are set by driving the optical system driving unit 105 based on an operation input performed by the user via the display operation unit 320 at any time.

In such a monitoring state, when the user appropriately operates the display operation unit 320, still image data is captured. One frame of image data stored in the image memory 108 is read in accordance with the operation content of the display operation unit 320, and compressed by the image sensor driving unit 107. The compressed image data is recorded in the temporary storage unit 370, for example, via the control unit 103 and the control unit 310.

The above-described imaging device 100 is an example of an imaging device suitable for the present invention, and the present invention is not limited to this.

That is, the image pickup apparatus equipped with the camera module 50 or the image pickup lens 10 is not limited to the one built in the smartphone type mobile communication terminal 300, but is built into a mobile phone, a PHS (Personal Handyphone System), or the like. Alternatively, it may be incorporated in a PDA (Personal Digital Assistant), tablet personal computer, mobile personal computer, digital still camera, video camera, or the like. The control circuit and the like of the imaging device are not limited to those illustrated in FIG.

Hereinafter, returning to FIG. 1, the imaging lens 10 according to an embodiment of the present invention will be described in detail. The imaging lens 10 shown in FIG. 1 forms a subject image on an imaging surface (projected surface) I of an image sensor 51, and has a meniscus shape with a convex surface facing the object side in order from the object side. One lens L1, an aperture stop S, a second lens L2 having a biconvex shape, and a third lens L3 having a meniscus shape having a convex surface facing the image side. In the imaging lens 10 of the present embodiment, since the second lens L2 has a biconvex shape, the principal point position of the entire imaging lens 10 system can be moved toward the image side to shorten the focal length, and a wide angle can be easily realized. it can. In addition, when the second lens L2 has a relatively strong positive power, the refractive power can be shared between the object side surface S21 and the image side surface S22. Can be prevented. Furthermore, by arranging the aperture stop S between the first lens L1 and the second lens L2, the axial ray height of the second lens L2 is increased. On the other hand, as already explained, the higher the axial ray height of the three balls, the greater the influence on the combined power. Therefore, it is easy to increase the combined power by increasing the axial ray height of the second lens L2 having a strong positive power, so that a wide angle can be achieved.

The third lens L3 of the imaging lens 10 satisfies the following conditional expression (1), where f is the focal length (mm) of the entire system and f3 is the focal length (mm) of the third lens L3.
-0.5 <f / f3 <-0.0 (1)
Conditional expression (1) is a conditional expression for making the ratio between the focal length of the entire imaging lens 10 system and the focal length of the third lens L3 appropriate. By exceeding the lower limit of the conditional expression (1), the negative power of the third lens L3 becomes weak, so that the back focus can be shortened and the optical total length can be shortened. In addition, since the third lens L3 has a negative power by falling below the upper limit of the conditional expression (1), the Petzval sum can be reduced and the field curvature can be effectively corrected. .

The value f / f3 of conditional expression (1) is more preferably within the range of the following expression.
−0.4 <f / f3 <−0.1 (1) ′

In the imaging lens 10 of the embodiment, in addition to the conditional expression (1), the conditional expression (2) already described.
−0.4 ≦ f / f1 <0.4 (2)
Satisfied. Here, f1 is the focal length (mm) of the first lens L1.
The value f / f1 of conditional expression (2) is more preferably within the range of the following expression.
−0.3 ≦ f / f1 <0.3 (2) ′

In the imaging lens 10 of the embodiment, in addition to the conditional expression (1) and the like, the conditional expression (3) already described.
−0.7 <f2 / f3 <0.0 (3)
Satisfied. Here, f2 is the focal length (mm) of the second lens L2.
The value f2 / f3 of conditional expression (3) is more preferably within the range of the following expression.
−0.45 <f2 / f3 <0.0 (3) ′

In the imaging lens 10 of the embodiment, in addition to the conditional expression (1), the conditional expression (4) already described.
0.0 <(r3 + r4) / (r3-r4) <0.5 (4)
Satisfied. Here, r3 is the radius of curvature (mm) of the object side surface S21 of the second lens L2, and r4 is the radius of curvature (mm) of the image side surface S22 of the second lens L2.
The value (r3 + r4) / (r3-r4) of conditional expression (4) is more preferably within the range of the following expression.
0.0 <(r3 + r4) / (r3-r4) <0.4 (4) ′

In the imaging lens 10 of the embodiment, in addition to the conditional expression (1) and the like, the conditional expression (5) already described.
-5.0 <P23 / P <0.0 (5)
Satisfied. Here, P is the refractive power of the entire imaging lens 10, and P23 is the refractive power of a so-called air lens formed by the image side surface S22 of the second lens L2 and the object side surface S31 of the third lens L3.
The value P23 / P of conditional expression (5) is more preferably within the range of the following expression.
-4.0 <P23 / P <-1.0 (5) '

In the imaging lens 10 of the embodiment, in addition to the conditional expression (1), the conditional expression (7) already described.
15 <ν3 <50 (7)
Satisfied. Here, ν3 is the Abbe number of the third lens L3.
Note that the value ν3 of the conditional expression (7) is more preferably within the range of the following expression.
20 <ν3 <40 (7) '

Although the imaging lens 10 of the embodiment is not particularly illustrated, it may further include a lens that does not substantially have power.

〔Example〕
Hereinafter, specific examples of the imaging lens according to the present invention will be described. In each embodiment, r represents the radius of curvature, d represents the axial top surface spacing, nd represents the refractive index of the lens material with respect to the d-line, vd represents the Abbe number of the lens material, “eff. “dia.” means an effective diameter. In addition, the surface where “*” is written after each surface number is a surface having an aspherical shape. The aspherical shape is expressed by the following “Equation 1” where the vertex of the surface is the origin, the X axis is taken in the direction of the optical axis AX, and the height in the direction perpendicular to the optical axis AX is h.

However,
Ai: i-order aspherical coefficient R: radius of curvature K: conical constant The basic wavelength used by the imaging lens of each example is 587.56 nm, and the unit of the surface shape such as the radius of curvature is mm. .

[Example 1]
The lens surface data of Example 1 is shown in Table 1 below.
[Table 1]
Surface number r d nd vd eff.dia.
OBJ INFINITY INFINITY
1 * 1.7002 0.2000 1.63469 23.89 1.860
2 * 1.4776 0.3440 1.620
STO INFINITY 0.1310 1.450
4 * 3.3386 0.8270 1.54470 55.99 1.920
5 * -1.6398 1.3790 2.160
6 * -0.6454 0.7010 1.63469 23.89 2.380
7 * -0.9466 0.9390 3.180
IMG INFINITY
Here, OBJ means an object, STO means an aperture stop, and IMG means an imaging surface or an image surface.

The aspheric coefficients of the lens surfaces of Example 1 are shown in Table 2 below.
[Table 2]
1st surface K = -1.02250e + 000, A4 = -1.42140e-001, A6 = -1.99640e-001,
A8 = 2.80520e-001, A10 = -1.01730e-001
2nd side K = -1.49510e + 000, A4 = -1.11850e-001, A6 = -1.71480e-001,
A8 = 3.44610e-001, A10 = -5.85300e-002
4th surface K = -2.91260e + 000, A4 = -2.26670e-002, A6 = -1.17560e-002,
A8 = -2.02790e-002, A10 = 3.99000e-003
5th surface K = -3.76820e-001, A4 = -2.44320e-002, A6 = -4.93170e-002,
A8 = 3.60710e-002, A10 = -2.97790e-002
6th surface K = -9.30740e-001, A4 = -1.20140e-001, A6 = -1.94220e-001,
A8 = 5.56610e-001, A10 = -3.64520e-001, A12 = 8.57090e-002
7th surface K = -7.74580e-001, A4 = 7.68740e-002, A6 = -1.22190e-001,
A8 = 1.32590e-001, A10 = -4.47100e-002, A12 = 5.36070e-003
In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻⁰⁰² ) is represented using e (for example, 2.5e−002).

The characteristics of the imaging lens 10 of Example 1 are listed below.
FL 3.429
Fno 2.40
w 79.68
Ymax 2.800
BF 0.939
TL 4.521
Here, FL means the focal length of the entire imaging lens 10, Fno means the F value, w means the diagonal angle of view, Ymax means the half value of the diagonal length of the imaging surface of the image sensor 51, BF means back focus, and TL means the entire length of the system. In addition, the above code | symbol shall have the same meaning also in the subsequent Examples.

The single lens data of Example 1 is shown in Table 3 below.
[Table 3]
Lens number Surface number Focal length Effective diameter 1 1-2 -27.3077 1.860
2 4-5 2.1445 2.160
3 6-7 -33.1813 3.180

FIG. 5 is a cross-sectional view of the imaging lens 11 (10) of the first embodiment. The imaging lens 11 has, in order from the object (OBJ) side, a meniscus first lens L1 having a negative refractive power around the optical axis AX and a convex surface facing the object side, and a positive refractive power around the optical axis AX. And a second lens L2 having a biconvex shape and a meniscus third lens L3 having a negative refractive power around the optical axis AX and having a convex surface facing the image side. All the lenses L1 to L3 are made of a plastic material. An aperture stop (STO) S is disposed between the first lens L1 and the second lens L2. A parallel plate (not shown) having an appropriate thickness can be disposed between the light exit surface of the third lens L3 and the imaging surface (IMG) I.

6A to 6C are graphs showing various aberrations (spherical aberration, astigmatism, distortion) of the imaging lens 11 of Example 1, and FIGS. 6D and 6E are meridional coma aberrations of the imaging lens 11 of Example 1. FIG. Is shown.

FIG. 7 is a cross-sectional view of an imaging lens 12 (10) and the like according to a modification of the first embodiment. The imaging lens 12 in FIG. 7 has the same shape as the imaging lens 11 in FIG. However, the imaging surface (image surface) I is a cylindrical surface curved only in the longitudinal direction in the long side direction of the drawing. A specific curvature radius in the vertical direction of the imaging surface I is −100 mm.

8A to 8C are graphs showing various aberrations (spherical aberration, astigmatism, distortion) of the imaging lens 12 or the like of the modification of the first embodiment, and FIGS. 8D and 8E show the merit of the imaging lens 12 or the like of the modification. It shows dional coma.
[Example 2]
The lens surface data of Example 2 is shown in Table 4 below.
[Table 4]
Surface number r d nd vd eff.dia.
OBJ INFINITY INFINITY
1 * 1.9113 0.2000 1.63469 23.89 1.738
2 * 1.6491 0.2625 1.497
STO INFINITY 0.1300 1.328
4 * 3.6953 0.7852 1.54470 55.99 1.922
5 * -1.7964 1.5346 2.167
6 * -0.8103 0.4621 1.63469 23.89 2.549
7 * -1.0025 0.9260 3.218
IMG -10.0000

The aspherical coefficient of the lens surface of Example 2 is shown in Table 5 below.
[Table 5]
1st surface K = -7.90549e-001, A4 = -1.26901e-001, A6 = -1.31302e-001,
A8 = 1.40140e-001, A10 = -3.63597e-002
2nd surface K = -1.58533e + 000, A4 = -8.12124e-002, A6 = -1.05308e-001,
A8 = 1.53864e-001, A10 = 2.38903e-002
4th surface K = -3.46988e + 000, A4 = -6.32826e-003, A6 = -2.03710e-002,
A8 = 1.56187e-002, A10 = -1.01193e-002
5th surface K = 4.28155e-002, A4 = -1.48934e-002, A6 = -2.82596e-002,
A8 = 1.33315e-002, A10 = -1.05396e-002
6th surface K = -9.17482e-001, A4 = -6.58332e-002, A6 = -2.48431e-001,
A8 = 4.57717e-001, A10 = -2.68600e-001, A12 = 5.75106e-002
7th surface K = -6.89111e-001, A4 = 5.95923e-002, A6 = -1.14008e-001,
A8 = 1.44539e-001, A10 = -5.37087e-002, A12 = 7.26531e-003

The characteristics of the imaging lens 10 of Example 2 are listed below.
FL 3.194
Fno 2.40
w 89.96
Ymax 2.779
BF 0.926
TL 4.300

The single lens data of Example 2 is shown in Table 6 below.
[Table 6]
Lens number Surface number Focal length Effective diameter 1 1-2 -26.9071 1.738
2 4-5 2.3370 2.167
3 6-7 -100.0000 3.218

FIG. 9 is a cross-sectional view of the imaging lens 13 (10) and the like of the second embodiment. The imaging lens 13 includes, in order from the object side, a first meniscus lens L1 having a negative refractive power around the optical axis AX and a convex surface facing the object side, and a positive refractive power around the optical axis AX. A second lens L2 having a convex shape and a third meniscus lens L3 having a negative refractive power around the optical axis AX and having a convex surface facing the image side are provided. In this case, the imaging surface (image surface) I is a spherical surface that is concave on the object side. The imaging surface I may be a concave aspheric surface on the object side or a concave free-form surface. When an aspherical surface or a free-form surface is adopted for the spherical surface, it is possible to obtain a shape that matches the curvature of field generated by the lens, so that an improvement in the overall optical performance can be expected. All the lenses L1 to L3 are made of a plastic material. An aperture stop S is disposed between the first lens L1 and the second lens L2. A parallel plate (not shown) with an appropriate thickness can be disposed between the light exit surface of the third lens L3 and the concave imaging surface (image surface) I.

FIGS. 10A to 10C are graphs showing various aberrations (spherical aberration, astigmatism, distortion) of the imaging lens 13 of Example 2, and FIGS. 10D and 10E are meridional coma aberrations of the imaging lens 13 of Example 2. FIGS. Is shown.

Example 3
The lens surface data of Example 3 is shown in Table 7 below.
[Table 7]
Surface number r d nd vd eff.dia.
OBJ INFINITY INFINITY
1 * 2.5331 0.3000 1.54470 55.99 1.840
2 * 3.6086 0.2100 1.480
STO INFINITY 0.1310 1.080
4 * 3.3485 1.0790 1.53487 55.99 2.180
5 * -1.7397 0.6830 2.460
6 * -1.0240 0.2250 1.58300 29.99 2.560
7 * -1.4555 1.1762 3.340
IMG -5.0000

The aspherical coefficients of the lens surfaces of Example 3 are shown in Table 8 below.
[Table 8]
1st surface K = -3.38360e-001, A4 = -4.69760e-002, A6 = 1.55730e-002,
A8 = 6.35670e-003, A10 = -3.17180e-003
2nd surface K = 1.40170e + 001, A4 = -5.15470e-002, A6 = 7.14120e-002,
A8 = -5.07590e-002, A10 = -1.03690e-002
4th surface K = -1.58790e + 000, A4 = 4.75900e-003, A6 = -1.74190e-002,
A8 = 2.14080e-002, A10 = -1.55860e-002
5th surface K = -3.42700e-001, A4 = -2.34240e-002, A6 = -6.00410e-002,
A8 = 1.68470e-002, A10 = -2.33520e-003
6th surface K = -4.13100e-001, A4 = 1.57700e-001, A6 = -2.80390e-001,
A8 = 1.83450e-001, A10 = -1.34250e-001, A12 = 6.50760e-002
7th surface K = -4.76810e-001, A4 = 1.90300e-001, A6 = -1.88170e-001,
A8 = 1.23430e-001, A10 = -3.44440e-002, A12 = 3.66140e-003

The characteristics of the imaging lens 10 of Example 3 are listed below.
FL 2.705
Fno 2.40
w 111.32
Ymax 2.669
BF 1.186
TL 3.804

The single lens data of Example 3 is shown in Table 9 below.
[Table 9]
Lens number Surface number Focal length Effective diameter 1 1-2 14.2062 1.840
2 4-5 2.3113 2.460
3 6-7 -7.3328 3.340

FIG. 11 is a cross-sectional view of the imaging lens 14 (10) of the third embodiment. The imaging lens 14 includes, in order from the object side, a first meniscus lens L1 having a positive refractive power around the optical axis AX and a convex surface facing the object side, and a positive refractive power around the optical axis AX. A second lens L2 having a convex shape and a third meniscus lens L3 having a negative refractive power around the optical axis AX and having a convex surface facing the image side are provided. In this case, the imaging surface (image surface) I is a spherical surface that is concave on the object side. The imaging surface I may be a concave aspheric surface on the object side or a concave free-form surface. All the lenses L1 to L3 are made of a plastic material. An aperture stop S is disposed between the first lens L1 and the second lens L2. A parallel plate (not shown) with an appropriate thickness can be disposed between the light exit surface of the third lens L3 and the concave imaging surface (image surface) I.

12A to 12C are graphs showing various aberrations (spherical aberration, astigmatism, distortion) of the imaging lens 14 of the third embodiment, and FIGS. 12D and 12E are meridional coma aberrations of the imaging lens 14 of the third embodiment. Is shown.

Example 4
The lens surface data of Example 4 is shown in Table 10 below.
[Table 10]
Surface number r d nd vd eff.dia.
OBJ INFINITY INFINITY
1 * 1.9656 0.2770 1.54470 55.99 1.840
2 * 2.2505 0.2340 1.500
STO INFINITY 0.1310 1.240
4 * 3.1014 0.7170 1.54470 55.99 2.120
5 * -2.1769 0.2430 2.260
6 * -1.3771 0.3000 1.63469 23.89 2.600
7 * -1.8682 2.1974 2.820
IMG -5.0000

The aspherical coefficients of the lens surfaces of Example 4 are shown in Table 11 below.
[Table 11]
1st surface K = -1.24200e + 001, A4 = 1.35100e-001, A6 = -2.49940e-001,
A8 = 1.61080e-001, A10 = -4.57770e-002
2nd surface K = -2.28870e + 000, A4 = -1.74250e-002, A6 = -7.80380e-002,
A8 = 7.59100e-002, A10 = 2.33330e-003
4th surface K = 2.35670e + 000, A4 = -2.24390e-002, A6 = -2.16410e-002,
A8 = 2.73110e-002, A10 = -2.91430e-003
5th surface K = -4.70940e-002, A4 = -5.02360e-002, A6 = 2.41060e-002,
A8 = -7.04800e-002, A10 = 7.31840e-002
6th surface K = -1.54410e + 000, A4 = 3.00300e-002, A6 = 1.76620e-001,
A8 = -2.73140e-001, A10 = 1.80190e-001, A12 = -3.95500e-002
7th surface K = -1.36340e + 000, A4 = 9.82060e-002, A6 = 1.12900e-001,
A8 = -1.12990e-001, A10 = 4.08630e-002, A12 = -5.24860e-003

The characteristics of the imaging lens 10 of Example 4 are listed below.
FL 3.067
Fno 2.40
w 99.08
Ymax 2.669
BF 2.197
TL 4.010

The single lens data of Example 4 is shown in Table 12 below.
[Table 12]
Lens number Surface number Focal length Effective diameter 1 1-2 21.2274 1.840
2 4-5 2.4664 2.260
3 6-7 -10.8202 2.820

FIG. 13 is a cross-sectional view of the imaging lens 15 (10) and the like of the fourth embodiment. The imaging lens 15 includes, in order from the object side, a first meniscus lens L1 having a positive refractive power around the optical axis AX and a convex surface facing the object side, and a positive refractive power around the optical axis AX. A second lens L2 having a convex shape and a third meniscus lens L3 having a negative refractive power around the optical axis AX and having a convex surface facing the image side are provided. In this case, the imaging surface (image surface) I is a spherical surface that is concave on the object side. The imaging surface I may be a concave aspheric surface on the object side or a concave free-form surface. All the lenses L1 to L3 are made of a plastic material. An aperture stop S is disposed between the first lens L1 and the second lens L2. A parallel plate (not shown) with an appropriate thickness can be disposed between the light exit surface of the third lens L3 and the concave imaging surface (image surface) I.

14A to 14C are graphs showing various aberrations (spherical aberration, astigmatism, distortion) of the imaging lens 15 of Example 4. FIGS. 14D and 14E are meridional coma aberrations of the imaging lens 15 of Example 4. FIGS. Is shown.

Table 13 below summarizes the values of Examples 1 to 4 corresponding to the conditional expressions (1) to (5) and (7) for reference.
[Table 13]

In the above, the present invention has been described according to the embodiments and examples, but the present invention is not limited to the above-described embodiments and the like.

Claims

In order from the object side, the first lens, an aperture stop, a biconvex second lens, and a third lens,
The third lens is an imaging lens that satisfies the following conditional expression.
-0.5 <f / f3 <-0.0 (1)
However,
f: Focal length of the entire system (mm)
f3: Focal length (mm) of the third lens
The imaging lens according to claim 1, wherein the first lens has a meniscus shape with a convex surface facing the object side.
The imaging lens according to claim 1, wherein the third lens has a meniscus shape with a convex surface facing the image side.
The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
−0.4 ≦ f / f1 <0.4 (2)
However,
f1: Focal length (mm) of the first lens
The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
−0.7 <f2 / f3 <0.0 (3)
However,
f2: Focal length (mm) of the second lens
The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
0.0 <(r3 + r4) / (r3-r4) <0.5 (4)
However,
r3: radius of curvature of object side surface of the second lens (mm)
r4: radius of curvature (mm) of the image side surface of the second lens
The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
-5.0 <P23 / P <0.0 (5)
However,
P: refractive power of the entire imaging lens system P23: refractive power of a so-called air lens formed by the image side surface of the second lens and the object side surface of the third lens, and the value of P23 is expressed by the following formula ( 6).

However,
n2: Refractive index with respect to d-line of the second lens n3: Refractive index with respect to d-line of the third lens R4: Radius of curvature of the image side surface of the second lens R5: Radius of curvature of the object side surface of the third lens D5: On-axis air gap between the second lens and the third lens
The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
15 <ν3 <50 (7)
However,
ν3: Abbe number of the third lens
The imaging lens according to claim 1, further comprising a lens having substantially no power.
An imaging apparatus comprising: the imaging lens according to claim 1; and a solid-state imaging device having a photoelectric conversion unit on which a subject image is formed by the imaging lens.
The imaging device according to claim 10, wherein the solid-state imaging device has an imaging surface that is curved so that a peripheral portion is positioned closer to an object side than a center portion.
The imaging device according to claim 11, wherein the imaging surface of the solid-state imaging device is curved in a cylindrical shape with a concave surface facing the object side.
The imaging device according to claim 11, wherein the imaging surface of the solid-state imaging device is curved into a spherical shape with a concave surface facing the object side.
A portable terminal comprising the imaging device according to claim 10.