WO2011132378A1 - Imaging lens, imaging device and mobile terminal - Google Patents

Abstract

Disclosed is an imaging lens assembly comprising four individual lenses. The imaging lens assembly is small, has a wide viewing angle, and enables excellent correction of various aberrations. The imaging lens assembly includes, in order from the object side, an aperture stop, a first lens, a second lens, a third lens, and a fourth lens. The first lens has positive refractive power and a convex face directed toward the image side. The second lens has negative refractive power and a concave face directed toward the image side. The third lens has positive refractive power and a convex face directed toward the image side. The fourth lens has at least one non-spherical face, has negative refractive power, and has a biconcave shape. In addition, in the imaging lens assembly, if the paraxial curvature radius of the object-side face of the first lens is r1 and the focal distance of the entire imaging lens assembly is f, the imaging lens assembly is formed so as to satisfy the conditions of 1.15<|r1/f|<4.50.

Description

Imaging lens, imaging device, and portable terminal

The present invention relates to an imaging lens, an imaging device, and a portable terminal equipped with the imaging lens.

In recent years, mobile phones and personal digital assistants equipped with imaging devices are becoming popular. A solid-state imaging device is used for the imaging device. As a solid-state image sensor, a CCD (Charge Coupled Device) type image sensor, a CMOS (Complementary Metal Oxide Semiconductor) type image sensor, and the like are known. It is desirable that the imaging lens used in such an imaging apparatus is small, has high performance, and has a wide shooting angle of view. A four-lens configuration has been proposed as such an imaging lens. A four-lens imaging lens can achieve higher performance than two or three-lens imaging lenses.

Patent Document 1 discloses a four-lens imaging lens aimed at improving performance. This imaging lens is a so-called reverse Ernostar type, and has first to fourth lenses in order from the object side. Each of the first, third, and fourth lenses has a positive refractive power. The second lens has a negative refractive power.

Further, the four-lens imaging lens disclosed in Patent Document 2 is downsized by shortening its overall length (distance on the optical axis from the most object-side lens surface to the image-side focal point of the entire imaging lens system). Is intended. This imaging lens is a so-called telephoto type, and has first to fourth lenses in order from the object side. Each of the first and third lenses has a positive refractive power. Each of the second and fourth lenses has a negative refractive power.

Japanese Patent Laid-Open No. 2004-341013 JP 2007-193195 A

However, the imaging lens described in Patent Document 1 has the following problems. First, this imaging lens has a narrow field angle. Further, this imaging lens is a reverse Ernostar type, and the fourth lens is a positive lens. Therefore, as compared with the case where the fourth lens is a negative lens as in the telephoto type, the principal point position of the optical system is on the image side, and as a result, the back focus becomes long. Therefore, this imaging lens is disadvantageous for miniaturization. Furthermore, since only one of the four lenses has a negative refractive power, it is difficult to correct the Petzval sum, and good performance cannot be ensured at the periphery of the image.

Also, the imaging lens described in Patent Document 2 has a problem that the size reduction and aberration correction are insufficient. Further, when the shooting angle of view is widened, there is a problem that it is difficult to increase the number of pixels of the image sensor with respect to performance degradation.

The present invention has been made in view of such problems, the purpose of which can ensure a wide angle of view, can be downsized, and can correct various aberrations satisfactorily. An object is to provide a four-lens imaging lens, an imaging device, and a portable terminal.

It should be noted that the scales of “wide angle of view” and “small size” are levels that satisfy the following formulas (6) and (7).

L / 2Y <1.00 (6)
f / 2Y <0.70 (7)

However, in equations (6) and (7), L, 2Y, and f are defined as follows: L is on the optical axis from the most object side lens surface to the image side focal point in the entire imaging lens system. Distance: 2Y is the diagonal length of the imaging surface of the solid-state imaging device (diagonal length of the rectangular effective pixel region of the solid-state imaging device); f is the focal length of the entire imaging lens system. The image side focal point refers to an image point when parallel light rays parallel to the optical axis are incident on the imaging lens.

In addition, when a parallel plate is placed between the lens surface closest to the image side in the entire imaging lens system and the focal position of the image side, the distance between the parallel plate portions is converted into a distance in air. Suppose that the value of L is calculated. Examples of the parallel plate include an optical low-pass filter, an infrared light cut filter, and a seal glass for a solid-state imaging device package.

The first aspect of the imaging lens according to the present invention includes an aperture stop, a first lens, a second lens, a third lens, and a fourth lens in order from the object side. The first lens has a positive refractive power and has a convex surface facing the image side. The second lens has a negative refractive power and has a concave surface facing the image side. The third lens has a positive refractive power and has a convex surface facing the image side. The fourth lens has at least one aspherical surface and is formed in a biconcave shape having negative refractive power. When the paraxial radius of curvature of the object side surface of the first lens is r1, and the focal length of the entire imaging lens system is f, the imaging lens is configured to satisfy the following conditional expression (1).

1.15 <| r1 / f | <4.50 (1)

An object of the present invention is to obtain an imaging lens that is small in size, can correct aberrations well, and has a wide shooting angle of view. The basic configuration for that purpose is an aperture stop, a first lens, a second lens, a third lens, and a fourth lens provided in this order from the object side as described above. That is, the lens configuration according to the present invention includes a positive lens group and a negative fourth lens as a whole, which are composed of a first lens, a second lens, and a third lens in order from the object side. Telephoto type. Such a lens configuration is advantageous for shortening the overall length of the imaging lens, that is, for miniaturization.

Also, by using two of the four lens elements as negative lenses, the number of diverging surfaces increases. As a result, the Petzval sum can be easily corrected, and an imaging lens having a good imaging performance up to the periphery of the screen while having a wide angle of view can be obtained. Further, by making at least one surface of the fourth lens disposed closest to the image side an aspherical surface, various aberrations in the peripheral portion of the screen can be favorably corrected.

Furthermore, by arranging the aperture stop on the most object side, the position of the exit pupil can be moved away from the imaging surface. This makes it possible to reduce the incident angle of the principal ray (angle formed between the principal ray and the optical axis) of the light beam that forms an image on the periphery of the imaging surface of the solid-state imaging device, and to secure so-called telecentric characteristics. It becomes possible. In addition, when a mechanical shutter is used, a configuration in which the shutter is disposed closest to the object side can be applied, so that an imaging lens with a short overall length can be obtained.

Further, by forming the fourth lens in a biconcave shape, the principal point position of the fourth lens is not excessively arranged on the image side. Thereby, the height of the light beam on the axis passing through the fourth lens can be appropriately maintained. This configuration is advantageous for correcting chromatic aberration on the axis. Further, by using the biconcave fourth lens, the peripheral portion of the fourth lens does not protrude greatly in the image plane direction. Accordingly, various optical elements disposed between the fourth lens and the solid-state image sensor (optical low-pass filter, infrared light cut filter, parallel flat plate such as seal glass of the solid-state image sensor package, solid-state image sensor substrate, etc. ), The back focus can be shortened and the overall length of the imaging lens can be shortened.

Conditional expression (1) defines conditions for appropriately setting the radius of curvature of the object side surface of the first lens. By satisfying conditional expression (1), the refractive power of the object side surface of the first lens can be suppressed to an appropriate range, and higher-order spherical aberration and coma aberration can be suppressed. In addition, by satisfying conditional expression (1), the principal point position of the first lens can be set appropriately, and an imaging lens in which a reduction in size and a wide field of view angle can be balanced can be obtained. .

It should be noted that a more preferable imaging lens can be obtained by narrowing the range indicated by the conditional expression (1). For example, a range defined by the following conditional expression (1) ′ can be applied.

1.30 <| r1 / f | <4.30 (1) '

The second aspect of the imaging lens according to the present invention satisfies the following conditional expression (2) in the first aspect. However, ν3 is the Abbe number of the third lens, and ν4 is the Abbe number of the fourth lens.

Ν3-ν4> 15 (2)

Conditional expression (2) defines conditions for appropriately setting the Abbe number of the fourth lens and correcting the aberrations appropriately. By satisfying conditional expression (2), chromatic aberration caused by the third lens having a positive refractive power can be appropriately corrected by the fourth lens having a negative refractive power.

Further, it is possible to obtain a more preferable imaging lens by tightening the restriction shown in the conditional expression (2). As an example, the following conditional expression (2) ′ can be applied.

Ν3-ν4> 25 (2) '

The third aspect of the imaging lens according to the present invention satisfies the following conditional expression (3) in the first aspect (also applicable to the second aspect). Here, f4 is the focal length of the fourth lens.

-0.9 <f4 / f <-0.3 (3)

Conditional expression (3) defines conditions for appropriately setting the focal length of the fourth lens. By setting the value of f4 / f below the upper limit of conditional expression (3), the negative refractive power of the fourth lens can be avoided from becoming larger than necessary. As a result, the light flux that forms an image on the periphery of the imaging surface of the solid-state imaging device is not excessively jumped up, so that the telecentric characteristics of the image-side light flux can be easily ensured. On the other hand, by setting the value of f4 / f to exceed the lower limit, the negative refractive power of the fourth lens can be appropriately maintained, the total lens length can be shortened, and field curvature, distortion, etc. It is possible to satisfactorily correct off-axis aberrations.

It is also possible to obtain a more preferable imaging lens by tightening the restriction shown in the conditional expression (3). As an example, the following conditional expression (3) ′ can be applied.

-0.71 <f4 / f <-0.52 (3) '

The fourth aspect of the imaging lens according to the present invention satisfies the following conditional expression (4) in the first aspect (which can also be applied to the second or third aspect).

1.7 <Pair12 / P <2.8 (4)

However, Pair 12 is the power of a so-called air lens formed by the first lens image side surface and the second lens object side surface, and is represented by the following [Equation 1]. P is the power of the entire imaging lens system.

Here, n1 is the refractive index of the first lens with respect to the d-line, n2 is the refractive index of the second lens with respect to the d-line, r2 is the paraxial radius of curvature of the image side surface of the first lens, and r3 is the first The paraxial radius of curvature of the object side surface of the two lenses, and d2 is the air space on the axis between the first lens and the second lens.

Conditional expression (4) prescribes conditions for making the power of the air lens between the first lens and the second lens appropriate, and making aberration correction appropriate. By setting the value of Pair12 / P to be lower than the upper limit of conditional expression (4), it is possible to avoid the power of the air lens between the first lens and the second lens from becoming too strong, so the Petzval sum is appropriate. Therefore, it becomes easy to correct curvature of field. On the other hand, since the refractive power of the air lens can be secured by setting the value of Pair12 / P to exceed the lower limit, the principal point position of the combined lens of the first lens, the second lens, and the third lens is the object. Move to the side. Thereby, the space | interval of this synthetic lens and a 4th lens can be enlarged, As a result, it leads to shortening of a lens full length.

Further, it is possible to obtain a more preferable imaging lens by tightening the restriction shown in the conditional expression (4). As an example, the following conditional expression (4) ′ can be applied.

1.90 <Pair12 / P <2.59 (4) '

The fifth aspect of the imaging lens according to the present invention satisfies the following conditional expression (4) in the first aspect (also applicable to the second to fourth aspects).

-3.5 <Pair23 / P <-2.5 (5)

However, Pair 23 is the 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 is represented by the following [Equation 2]. P is the power of the entire imaging lens system.

Here, n2 is the refractive index of the second lens for the d-line, n3 is the refractive index of the third lens for the d-line, r4 is the paraxial radius of curvature of the image side surface of the second lens, and r5 is the first 3 is a paraxial radius of curvature of the object side surface of the three lenses, and d4 is an air space on the axes of the second lens and the third lens.

Conditional expression (5) defines conditions for making the power of the air lens between the second lens and the third lens appropriate and correcting the aberration appropriately. The air lens between the second lens and the third lens is a biconvex lens. Therefore, when the power is increased, the curvature radii of the image side surface of the second lens and the object side surface of the third lens are reduced, and as a result, the peripheral portions of the second lens and the third lens are brought close to each other. For this problem, by setting the value of Pair 23 to exceed the lower limit of conditional expression (5), it is possible to avoid that the power of the air lens between the second lens and the third lens becomes too strong. The peripheral portion of the third lens and the peripheral portion of the third lens can be configured not to approach too much. Accordingly, it is possible to secure a space for arranging a light shielding member for preventing unnecessary light such as a ghost. On the other hand, by setting the Pair 23 to be lower than the upper limit of the conditional expression (5), the air lens between the first lens and the second lens has a negative Petzval value for canceling the large Petzval value, and the image Correction of surface curvature becomes easy.

It is also possible to obtain a more preferable imaging lens by tightening the restriction shown in the conditional expression (5). As an example, the following conditional expression (5) 'can be applied.

-3.20 <Pair23 / P <-2.65 (5) '

According to a sixth aspect of the imaging lens of the present invention, in the first aspect (which can also be applied to the second to fifth aspects), the image side surface of the fourth lens has an aspherical shape and is variable. The fourth lens is configured to have a curved point, and further, the negative refractive power of the fourth lens is decreased from the center of the lens toward the periphery.

Thus, the telecentric characteristics of the image-side light flux can be ensured by making the image side surface of the fourth lens an aspherical shape having a negative refractive power that decreases from the optical axis toward the periphery. It becomes easy. Further, according to such a configuration, it is not necessary to excessively weaken the negative refracting power at the lens peripheral portion on the image side surface of the second lens, so that off-axis aberration can be corrected well.

The “inflection point” here refers to a point on the aspheric surface where the tangent plane at the apex of the aspheric surface is perpendicular to the optical axis in the curve indicating the cross-sectional shape of the lens within the effective radius. It is.

In a seventh aspect of the imaging lens according to the present invention, the first lens is formed of a glass material in the first aspect (also applicable to the second to sixth aspects).

By forming the first lens having a relatively strong refractive power with a glass material, it is possible to reduce the displacement due to the temperature change of the image point of the entire imaging lens system. Furthermore, if plastic lenses are used as the second lens, the third lens, and the fourth lens, the overall cost of the imaging lens can be reduced. In addition, since the first lens is formed of a glass material, the plastic lens can be configured so as not to be exposed to the outside, so that problems such as scratches on the first lens can be avoided.

An eighth aspect of the imaging lens according to the present invention is the first lens, the second lens, the third lens, and the fourth lens in the first aspect (also applicable to the second to sixth aspects). Each lens is formed of a plastic material.

In recent years, a solid-state imaging device having a smaller imaging surface has been developed by reducing the pixel pitch even when the number of pixels is the same. An imaging lens used with such a solid-state imaging device needs to make the focal length of the entire system relatively short. Therefore, the curvature radius and outer diameter of each lens are considerably reduced. On the other hand, since a glass lens is manufactured by polishing, it takes time to manufacture compared to a plastic lens manufactured by injection molding. Therefore, by making all the lenses plastic lenses, even a lens with a small radius of curvature or outer diameter can be mass-produced at low cost. Further, since the plastic lens can be molded at a low pressing temperature, it is possible to suppress the wear of the molding die. Thereby, it is possible to reduce the cost by reducing the number of replacements and maintenance of the molding die.

An imaging apparatus according to the present invention includes the imaging lens of the first aspect (may be the second to eighth aspects) and a solid-state imaging element that photoelectrically converts a subject image formed by the imaging lens. .

According to the imaging apparatus having such a configuration, a wide angle of view can be secured, miniaturization can be achieved, and a high-quality image in which various aberrations are well corrected can be obtained.

The portable terminal according to the present invention has the above imaging device.

According to such a portable terminal, it is possible to reduce the size of the imaging device and to capture a wide-angle and high-quality image.

According to the present invention, a wide angle of view can be secured, downsizing can be achieved, and a high-quality image with various aberrations corrected well can be obtained.

It is a perspective view of the imaging device concerning an embodiment. It is the figure which showed typically the cross section along the optical axis of the imaging lens of the imaging device which concerns on embodiment. 1 is an external view of a mobile phone that is an example of a mobile terminal that includes an imaging device according to an embodiment. 1 is an external view of a mobile phone that is an example of a mobile terminal that includes an imaging device according to an embodiment. It is a figure which shows an example of the control block of a mobile telephone. 2 is a cross-sectional view of an imaging lens of Example 1. FIG. FIG. 3 is an aberration diagram of the imaging lens of Example 1. FIG. 3 is an aberration diagram of the imaging lens of Example 1. FIG. 3 is an aberration diagram of the imaging lens of Example 1. FIG. 3 is an aberration diagram of the imaging lens of Example 1. FIG. 3 is an aberration diagram of the imaging lens of Example 1. 6 is a cross-sectional view of an imaging lens of Example 2. FIG. 6 is an aberration diagram of the imaging lens of Example 2. FIG. 6 is an aberration diagram of the imaging lens of Example 2. FIG. 6 is an aberration diagram of the imaging lens of Example 2. FIG. 6 is an aberration diagram of the imaging lens of Example 2. FIG. 6 is an aberration diagram of the imaging lens of Example 2. FIG. 6 is a cross-sectional view of an imaging lens of Example 3. FIG. 6 is an aberration diagram of the imaging lens of Example 3. FIG. 6 is an aberration diagram of the imaging lens of Example 3. FIG. 6 is an aberration diagram of the imaging lens of Example 3. FIG. 6 is an aberration diagram of the imaging lens of Example 3. FIG. 6 is an aberration diagram of the imaging lens of Example 3. FIG. 6 is a cross-sectional view of an imaging lens of Example 4. FIG. FIG. 6 is an aberration diagram of the imaging lens of Example 4. FIG. 6 is an aberration diagram of the imaging lens of Example 4. FIG. 6 is an aberration diagram of the imaging lens of Example 4. FIG. 6 is an aberration diagram of the imaging lens of Example 4. FIG. 6 is an aberration diagram of the imaging lens of Example 4. 6 is a cross-sectional view of an imaging lens of Example 5. FIG. FIG. 10 is an aberration diagram of the imaging lens of Example 5. FIG. 10 is an aberration diagram of the imaging lens of Example 5. FIG. 10 is an aberration diagram of the imaging lens of Example 5. FIG. 10 is an aberration diagram of the imaging lens of Example 5. FIG. 10 is an aberration diagram of the imaging lens of Example 5. 6 is a cross-sectional view of an imaging lens of Example 6. FIG. 10 is an aberration diagram of the imaging lens of Example 6. FIG. 10 is an aberration diagram of the imaging lens of Example 6. FIG. 10 is an aberration diagram of the imaging lens of Example 6. FIG. 10 is an aberration diagram of the imaging lens of Example 6. FIG. 10 is an aberration diagram of the imaging lens of Example 6. FIG.

Hereinafter, the present invention will be described in detail with reference to embodiments, but the present invention is not limited thereto.

FIG. 1 is a perspective view of an imaging apparatus 50 according to the present embodiment. FIG. 2 is a diagram schematically showing a cross section of the imaging device 50 along the optical axis of the imaging lens.

As shown in FIG. 1, the imaging device 50 includes an imaging lens 10, a casing 53, and a substrate 52. These are integrally formed. The imaging lens 10 forms a subject image on the photoelectric conversion unit of the imaging element. The housing 53 acts as a light shielding member. The substrate 52 includes a support substrate 52a and a flexible printed circuit board 52b. The support substrate 52 a holds the image sensor 51. The flexible printed circuit board 52b has an external connection terminal (also referred to as an external connection terminal) 54 that transmits and receives electrical signals.

The image sensor 51 shown in FIG. 2 is, for example, a CMOS type image sensor. A plurality of pixels (photoelectric conversion elements) are two-dimensionally arranged at the center of the light receiving side surface of the image sensor 51. These pixels constitute a photoelectric conversion unit 51a as a light receiving unit. A signal processing circuit 51b is provided around the photoelectric conversion unit 51a. Although not shown, the signal processing circuit 51b includes a drive circuit unit, an A / D conversion unit, a signal processing unit, and the like. The driving circuit unit sequentially drives a plurality of pixels to acquire signal charges. The A / D conversion unit converts the signal charge from the drive circuit unit into a digital signal. The signal processing unit generates and outputs an image signal based on the digital signal from the A / D conversion unit.

A large number of pads are provided in the vicinity of the outer edge of the light receiving surface of the image sensor 51 (not shown). Each pad is connected to the support substrate 52a via a bonding wire W. The image sensor 51 converts the signal charge from the photoelectric conversion unit 51a into an image signal such as a digital YUV signal and outputs the image signal to a predetermined circuit on the support substrate 52a through the bonding wire W. “Y” is a luminance signal, “U” is a color difference signal (RY) between red and the luminance signal, and “V” is a color difference signal (BY) between blue and the luminance signal. .

Note that the image sensor 51 is not limited to a CMOS type image sensor, and may be another form such as a CCD type image sensor.

The substrate 52 includes the support substrate 52a and the flexible printed circuit board 52b as described above. The support substrate 52a supports the imaging element 51 and the housing 53 by one surface thereof. The support substrate 52a is made of a hard material. The flexible printed circuit board 52b is connected to the other surface of the support substrate 52a (the surface opposite to the image sensor 51). A large number of signal transmission pads are provided on both surfaces of the support substrate 52a. Pads provided on the surface of the support substrate 52 a on the image sensor 51 side are connected to the image sensor 51 via bonding wires W. The pad provided on the other surface is connected to the flexible printed circuit board 52b.

As shown in FIG. 1, one end of the flexible printed board 52b is connected to the support board 52a. An external connection terminal 54 is provided at the other end. Thereby, the support substrate 52a and an external circuit (for example, a control circuit included in a host device on which the imaging device is mounted: not shown) are connected. This path is used for receiving a voltage and a clock signal for driving the image sensor 51 from an external circuit and outputting a digital YUV signal to the external circuit. Furthermore, the flexible printed circuit board 52b has flexibility, and its intermediate part can be deformed. Thereby, a degree of freedom is given to the orientation and arrangement of the external connection terminals 54 with respect to the support substrate 52a.

As shown in FIG. 2, the housing 53 is fixedly disposed on the surface of the support substrate 52a on the image sensor 51 side. The housing 53 surrounds the image sensor 51 together with the support substrate 52a. The housing 53 is open at the end on the image sensor 51 side and the opposite end. The former end portion has a relatively large opening so as to surround the image sensor 51 and is fixed to the support substrate 52a. The latter end has a relatively small opening.

Inside the casing 53, a lens frame 55 made of a light shielding member is provided. The lens frame 55 holds the imaging lens 10 and the infrared light cut filter F. The infrared cut filter F is provided between the fourth lens L4 and the image sensor 51.

The imaging lens 10 includes an aperture stop S, a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4 in order from the object side. The first lens L1 has a positive refractive power and has a convex surface facing the image side. The second lens L2 has a negative refractive power and has a concave surface facing the image side. The third lens L3 has a positive refractive power and has a convex surface facing the image side. The fourth lens L4 has at least one aspheric surface and is formed in a biconcave shape having negative refractive power.

The aperture stop S and the lenses L1 to L4 are each held by a lens frame 55. The housing 53 includes the lens frame 55 and the imaging lens 10. The lens frame 55 is fitted to the housing 53 with its outer wall in contact with the inner wall of the housing 53. The end of the lens frame 55 on the first lens L1 side has a smaller diameter than other parts. The end of the lens frame 55 is fitted into a small opening (opening on the first lens L1 side) of the housing 53. Thereby, the lens frame 55 is positioned in the housing 53.

Further, although not shown, a fixed diaphragm for cutting unnecessary light can be arranged between the lenses L1 to L4 or between the lens L4 and the infrared light cut filter F. For example, the occurrence of ghosts and flares can be suppressed by arranging a rectangular fixed stop outside the path of the light beam.

3A and 3B are external views of the mobile phone 100 including the imaging device 50. FIG. The mobile phone 100 is an example of a mobile terminal.

The casing of the mobile phone 100 includes an upper casing 71 and a lower casing 72. The upper casing 71 and the lower casing 72 are connected via a hinge 73 so as to be foldable. The upper casing 71 is provided with display screens D1 and D2. The lower casing 72 is provided with an input unit 60 including a plurality of operation buttons. The imaging device 50 is built in a position below the display screen D2 of the upper casing 71. The imaging device captures light through a hole on the outer surface of the upper housing 71.

Note that the built-in position of the imaging device 50 is not limited to the above example. For example, it is also possible to arrange the imaging device above or on the side of the display screen D2 of the upper casing 71. Further, the mobile phone is not limited to a folding type.

FIG. 4 shows an example of the configuration of the control system of the mobile phone 100. The cellular phone 100 includes a wireless control unit 80, a storage unit 91, a temporary storage unit 92, a nonvolatile storage unit 93, and a control unit 101 in addition to the imaging device 50, the input unit 60, and the display units D1 and D2. Is done.

The imaging device 50 is connected to the control unit 101 via the flexible printed circuit board 52b, and outputs an image signal such as a luminance signal or a color difference signal to the control unit 101.

Control unit (CPU) 101 controls each unit of mobile phone 100 and executes a program corresponding to each process. The input unit 60 is used to input a number or the like. Display screens D1 and D2 display various data and captured images. The wireless communication unit 80 performs information communication with an external server. The storage unit (ROM) 91 stores necessary data such as a system program and various processing programs of the mobile phone 100 and a terminal ID. The temporary storage unit (RAM) 92 temporarily stores various processing programs and data executed by the control unit 101, various processing data, image data obtained by the imaging device 50, and the like. The temporary storage unit 92 is used as a work area when the control unit 101 executes various processes.

The control unit 101 stores the image signal input from the imaging device 50 in the nonvolatile storage unit (flash memory) 93 or displays it on the display screens D1 and D2. The control unit 101 also generates image information from the image signal from the imaging device 50 and transmits the image information to the external device via the wireless communication unit 80. Although not illustrated, the mobile phone 100 is provided with a microphone for inputting sound, a speaker for outputting sound, and the like.

Examples based on the above-described embodiments will be described below. However, the present invention is not limited to the following examples. The meanings of the symbols in the examples are as follows.
f: Focal length of the entire imaging lens system fB: Back focus F: F number 2Y: Diagonal length ENTP of the imaging surface of the solid-state imaging device: Entrance pupil position (distance from the first surface to the entrance pupil position)
EXTP: exit pupil position (distance from imaging plane to exit pupil position)
H1: Front principal point position (distance from the first surface to the front principal point position)
H2: Rear principal point position (distance from the final surface to the rear principal point position)
R: radius of curvature D: distance between lens surfaces on axis Nd: refractive index νd of lens material with respect to d-line: Abbe number of lens material

In the following examples, it is assumed that the lens surface with (*) after the surface number has an aspherical shape. This aspherical shape is expressed by the following [Equation 3], where the vertex of the lens surface is the origin, the optical axis direction is the X axis, and the height in the direction perpendicular to the optical axis is h. However, Ai is an i-th order aspheric coefficient, R is a radius of curvature, and K is a conic constant.

Regarding the “paraxial radius of curvature”, in actual lens measurement, the measured value of the shape in the vicinity of the center of the lens (specifically, the central region within 10% with respect to the outer diameter of the lens) is a minimum of two. An approximate radius of curvature obtained by fitting by multiplication can be regarded as a paraxial radius of curvature.

For example, when a secondary aspherical coefficient is used, a curvature radius obtained by considering the secondary aspherical coefficient in the reference curvature radius in the definition formula of the aspherical surface can be regarded as a paraxial curvature radius. (For example, as a reference, see pages 41 to 42 of “Lens Design Method” by Yoshiya Matsui (Kyoritsu Publishing Co., Ltd.)).

In the following (including lens data), a power of 10 is represented by using “E” (for example, 2.5 × 10 ⁻⁰² is represented as 2.5E-02). The unit of length in the examples is all “mm”.

The specifications of the imaging lens of Example 1 are shown below.
f = 4.2mm
fB = 0.3mm
F = 2.6
2Y = 6.496mm
ENTP = 0mm
EXTP = -4.02mm
H1 = 0.12mm
H2 = -3.9mm

The surface data of the imaging lens of Example 1 is shown below.
Surface number R (mm) D (mm) Nd νd Effective radius (mm)
1 (aperture) ∞ 0.05 0.81
2 * 7.171 1.20 1.53050 55.7 0.83
3 * -2.024 0.05 1.19
4 * 3.239 0.38 1.63200 23.4 1.37
5 * 1.559 0.98 1.43
6 * -2.462 0.99 1.53050 55.7 1.65
7 * -1.006 0.07 1.78
8 * -1000.000 1.17 1.58300 30.0 2.46
9 * 1.555 1.00 3.03
10 ∞ 0.10 1.51630 64.1 4.00
11 ∞ 4.00

The aspheric coefficient is shown below.
2nd surface K = -0.20718E + 01, A4 = -0.36313E-01, A6 = 0.11830E-01, A8 = -0.57783E-01, A10 = 0.61682E-01, A12 = -0.27237E-01
3rd surface K = 0.75244E + 00, A4 = 0.25038E-01, A6 = -0.41633E-02, A8 = 0.92866E-02, A10 = -0.79378E-02, A12 = 0.25524E-02
4th surface K = 0.28807E + 01, A4 = -0.96495E-01, A6 = 0.50122E-01, A8 = -0.25288E-01, A10 = 0.81904E-02, A12 = -0.14328E-02
5th surface K = -0.48544E + 01, A4 = 0.13793E-01, A6 = 0.16668E-02, A8 = -0.26951E-02, A10 = 0.18898E-02, A12 = -0.41199E-03
6th surface K = 0.88920E + 00, A4 = -0.95128E-04, A6 = 0.25248E-01, A8 = 0.52029E-02, A10 = -0.40951E-02, A12 = 0.83178E-03
7th surface K = -0.24966E + 01, A4 = -0.60130E-01, A6 = 0.18886E-01, A8 = -0.80677E-03, A10 = 0.21810E-03, A12 = 0.28575E-04
8th surface K = -0.50000E + 02, A4 = 0.53684E-02, A6 = -0.37709E-02, A8 = 0.48955E-03, A10 = 0.30177E-04, A12 = -0.16556E-04, A14 = 0.15236E-05
9th surface K = -0.78588E + 01, A4 = -0.21038E-01, A6 = 0.50329E-02, A8 = -0.11546E-02, A10 = 0.16622E-03, A12 = -0.13477E-04, A14 = 0.45286E-06

Single lens data of the imaging lens of Example 1 is shown below.
Lens Start surface Focal length (mm)
1 2 3.116
2 4-5.214
3 6 2.592
4 8 -2.662

In this embodiment, all the lenses are made of a plastic material.

FIG. 5 is a cross-sectional view of the imaging lens of Example 1. In the figure, S is an aperture stop, L1 is a first lens, L2 is a second lens, L3 is a third lens, L4 is a fourth lens, and I is an imaging surface. F is a parallel plate. Examples of the parallel plate F include an optical low-pass filter, an infrared light cut filter, and a seal glass for a solid-state image sensor. 6A to 6E are aberration diagrams of the imaging lens of Example 1 (spherical aberration, astigmatism, distortion, and meridional coma). In the spherical aberration diagram and the meridional coma aberration diagram shown below, the solid line represents the d line and the dotted line represents the g line. In the astigmatism diagrams, the solid line represents the sagittal image plane, and the dotted line represents the meridional image plane.

The overall specification of the imaging lens of Example 2 is shown below.
f = 4.2mm
fB = 0.3mm
F = 2.6
2Y = 6.496mm
ENTP = 0mm
EXTP = -4.11mm
H1 = 0.2mm
H2 = -3.9mm

The surface data of the imaging lens of Example 2 is shown below.
Surface number R (mm) D (mm) Nd νd Effective radius (mm)
1 (aperture) ∞ 0.05 0.81
2 * 5.653 1.00 1.53050 55.7 0.83
3 * -1.799 0.05 1.10
4 * 3.363 0.30 1.58300 30.0 1.21
5 * 1.267 0.90 1.37
6 * -3.493 1.29 1.53050 55.7 1.70
7 * -1.121 0.17 1.84
8 * -1000.000 1.15 1.58300 30.0 2.26
9 * 1.669 1.00 2.99
10 ∞ 0.10 1.51630 64.1 4.00
11 ∞ 4.00

The aspheric coefficient is shown below.
2nd surface K = -0.62493E + 01, A4 = -0.35853E-01, A6 = -0.11849E-01, A8 = -0.41891E-01,
A10 = 0.40321E-01, A12 = -0.28805E-01
3rd surface K = 0.44527E + 00, A4 = 0.43981E-01, A6 = -0.53848E-01, A8 = 0.24921E-01, A10 = -0.85540E-03, A12 = -0.49360E-02
4th surface K = -0.35353E + 02, A4 = -0.89985E-01, A6 = 0.35632E-01, A8 = -0.30909E-01, A10 = 0.22723E-01, A12 = -0.58970E-02
5th surface K = -0.54674E + 01, A4 = 0.87793E-02, A6 = -0.31144E-02, A8 = -0.16276E-02, A10 = 0.23602E-02, A12 = -0.68089E-03
6th surface K = 0.23984E + 01, A4 = 0.78116E-02, A6 = 0.10817E-01, A8 = 0.72807E-02, A10 = -0.36869E-02,
A12 = 0.54930E-03
7th surface K = -0.24482E + 01, A4 = -0.44188E-01, A6 = 0.66718E-02, A8 = 0.15832E-04, A10 = -0.76102E-05, A12 = 0.69488E-04
8th surface K = -0.50000E + 02, A4 = -0.46302E-02, A6 = -0.29461E-02, A8 = 0.62753E-03, A10 = 0.30291E-04, A12 = -0.28604E-04, A14 = 0.25037E-05
9th surface K = -0.66416E + 01, A4 = -0.20855E-01, A6 = 0.47167E-02, A8 = -0.11401E-02, A10 = 0.16788E-03, A12 = -0.13317E-04, A14 = 0.42303E-06

Single lens data of the imaging lens of Example 2 is shown below.
Lens Start surface Focal length (mm)
1 2 2.698
2 4 -3.678
3 6 2.617
4 8 -2.857

In this embodiment, all the lenses are made of a plastic material.

FIG. 7 is a cross-sectional view of the imaging lens of Example 2. In the figure, S is an aperture stop, L1 is a first lens, L2 is a second lens, L3 is a third lens, L4 is a fourth lens, and I is an imaging surface. F is a parallel plate similar to that of the first embodiment. 8A to 8E are aberration diagrams (spherical aberration, astigmatism, distortion, and meridional coma aberration) of the imaging lens of Example 2. FIG.

The overall specification of the imaging lens of Example 3 is shown below.
f = 4.2mm
fB = 0.3mm
F = 2.6
2Y = 6.496mm
ENTP = 0mm
EXTP = -4.02mm
H1 = 0.12mm
H2 = -3.9mm

The surface data of the imaging lens of Example 3 is shown below.
Surface number R (mm) D (mm) Nd νd Effective radius (mm)
1 (Aperture) ∞ 0.09 0.81
2 * 13.227 1.01 1.53050 55.7 0.84
3 * -1.811 0.05 1.14
4 * 2.260 0.30 1.63200 23.4 1.39
5 * 1.294 1.08 1.42
6 * -3.092 1.22 1.53050 55.7 1.66
7 * -1.051 0.05 1.87
8 * -1000.000 1.11 1.58300 30.0 2.13
9 * 1.438 1.00 2.95
10 ∞ 0.10 1.51630 64.1 4.00
11 ∞ 4.00

The aspheric coefficient is shown below.
2nd surface K = -0.34920E + 02, A4 = -0.45305E-01, A6 = -0.21418E-01, A8 = 0.39342E-02,
A10 = -0.16615E-01, A12 = 0.76559E-02
3rd surface K = 0.80969E + 00, A4 = 0.55827E-01, A6 = -0.56650E-01, A8 = 0.66295E-01, A10 = -0.40213E-01, A12 = 0.11999E-01
4th surface K = 0.33168E + 00, A4 = -0.11659E + 00, A6 = 0.57394E-01, A8 = -0.27653E-01, A10 = 0.11435E-01, A12 = -0.23040E-02
5th surface K = -0.42445E + 01, A4 = 0.20336E-01, A6 = -0.60324E-02, A8 = -0.14342E-02, A10 = 0.43358E-02, A12 = -0.12687E-02
6th surface K = 0.16781E + 01, A4 = 0.24643E-01, A6 = 0.70454E-02, A8 = 0.41919E-02, A10 = -0.33111E-02,
A12 = 0.63005E-03
7th surface K = -0.27399E + 01, A4 = -0.32625E-01, A6 = 0.77128E-02, A8 = 0.12717E-03, A10 = -0.16333E-03, A12 = -0.39698E-04
8th surface K = -0.50000E + 02, A4 = -0.87338E-03, A6 = -0.44454E-02, A8 = 0.44176E-03, A10 = 0.30435E-04, A12 = -0.12110E-04, A14 = -0.83835E-06
9th surface K = -0.76212E + 01, A4 = -0.20866E-01, A6 = 0.47799E-02, A8 = -0.11568E-02, A10 = 0.16737E-03, A12 = -0.13228E-04, A14 = 0.41684E-06

Single lens data of the imaging lens of Example 3 is shown below.
Lens Start surface Focal length (mm)
1 2 3.073
2 4-5.442
3 6 2.487
4 8 -2.463

In this embodiment, all the lenses are made of a plastic material.

FIG. 9 is a cross-sectional view of the imaging lens of Example 3. In the figure, S is an aperture stop, L1 is a first lens, L2 is a second lens, L3 is a third lens, L4 is a fourth lens, and I is an imaging surface. F is a parallel plate similar to that of the first embodiment. 10A to 10E are aberration diagrams of the imaging lens of Example 3 (spherical aberration, astigmatism, distortion, and meridional coma).

The overall specification of the imaging lens of Example 4 is shown below.
f = 4.2mm
fB = 0.33mm
F = 2.6
2Y = 6.496mm
ENTP = 0mm
EXTP = -4mm
H1 = 0.13mm
H2 = -3.87mm

The surface data of the imaging lens of Example 4 is shown below.
Surface number R (mm) D (mm) Nd νd Effective radius (mm)
1 (aperture) ∞ 0.05 0.81
2 * 8.333 1.28 1.54470 56.2 0.83
3 * -2.453 0.05 1.23
4 * 2.260 0.30 1.63200 23.4 1.46
5 * 1.426 0.98 1.50
6 * -3.893 1.26 1.54470 56.2 1.72
7 * -1.049 0.13 1.90
8 * -29.412 0.96 1.58300 30.0 2.14
9 * 1.375 1.00 2.94
10 ∞ 0.10 1.51630 64.1 3.50
11 ∞ 3.50

The aspheric coefficient is shown below.
2nd surface K = -0.29992E + 02, A4 = -0.16143E-01, A6 = -0.12498E-02, A8 = -0.18738E-01,
A10 = 0.20220E-01, A12 = -0.76632E-02
3rd surface K = 0.19094E + 01, A4 = 0.25177E-01, A6 = -0.25742E-02, A8 = 0.13407E-01, A10 = -0.96859E-02, A12 = 0.35976E-02
4th surface K = -0.12998E + 01, A4 = -0.84792E-01, A6 = 0.40730E-01, A8 = -0.16424E-01, A10 = 0.64168E-02, A12 = -0.11677E-02
5th surface K = -0.32444E + 01, A4 = -0.11193E-01, A6 = 0.11540E-01, A8 = -0.74331E-02, A10 = 0.40941E-02, A12 = -0.80650E-03
6th surface K = 0.29189E + 01, A4 = 0.16282E-01, A6 = 0.15777E-01, A8 = -0.28719E-02, A10 = -0.62557E-03, A12 = 0.20506E-03
7th surface K = -0.29291E + 01, A4 = -0.35491E-01, A6 = 0.13159E-01, A8 = -0.20597E-02, A10 = 0.31598E-03, A12 = -0.70180E-04
8th surface K = -0.41523E + 01, A4 = 0.51698E-02, A6 = -0.53902E-02, A8 = 0.49285E-03, A10 = -0.94161E-05, A12 = 0.30870E-05, A14 = -0.26956E-05
9th surface K = -0.75648E + 01, A4 = -0.19026E-01, A6 = 0.45805E-02, A8 = -0.11484E-02, A10 = 0.16725E-03, A12 = -0.13511E-04, A14 = 0.44252E-06

Single lens data of the imaging lens of Example 4 is shown below.
Lens Start surface Focal length (mm)
1 2 3.631
2 4-7.098
3 6 2.281
4 8-2.228

In this embodiment, all the lenses are made of a plastic material.

FIG. 11 is a cross-sectional view of the imaging lens of Example 4. In the figure, S is an aperture stop, L1 is a first lens, L2 is a second lens, L3 is a third lens, L4 is a fourth lens, and I is an imaging surface. F is a parallel plate similar to that of the first embodiment. 12A to 12E are aberration diagrams of the imaging lens of Example 4 (spherical aberration, astigmatism, distortion, and meridional coma).

The overall specification of the imaging lens of Example 5 is shown below.
f = 4.09mm
fB = 0.11mm
F = 2.6
2Y = 6.496mm
ENTP = 0mm
EXTP = -3.83mm
H1 = -0.16mm
H2 = -3.98mm

The surface data of the imaging lens of Example 5 is shown below.
Surface number R (mm) D (mm) Nd νd Effective radius (mm)
1 (Aperture) ∞ 0.07 0.79
2 * 11.111 1.23 1.72000 42.0 0.82
3 * -2.019 0.05 1.18
4 * 4.609 0.30 1.63200 23.4 1.29
5 * 1.553 0.89 1.37
6 * -2.823 1.15 1.53050 55.7 1.60
7 * -1.160 0.05 1.81
8 * -43.478 1.48 1.63200 23.4 2.07
9 * 1.901 1.00 2.99
10 ∞ 0.10 1.51630 64.1 3.50
11 ∞ 3.50

The aspheric coefficient is shown below.
2nd surface K = 0.23426E + 02, A4 = -0.37421E-01, A6 = -0.98015E-02, A8 = -0.99217E-02,
A10 = -0.55990E-02, A12 = 0.76228E-02
3rd surface K = 0.11432E + 01, A4 = 0.51536E-01, A6 = -0.55296E-01, A8 = 0.66572E-01, A10 = -0.39037E-01, A12 = 0.11168E-01
4th surface K = 0.25163E + 01, A4 = -0.10682E + 00, A6 = 0.52890E-01, A8 = -0.25369E-01, A10 = 0.12897E-01, A12 = -0.29611E-02
5th surface K = -0.61229E + 01, A4 = 0.18257E-01, A6 = -0.31884E-02, A8 = -0.24454E-02, A10 = 0.37818E-02, A12 = -0.10239E-02
6th surface K = 0.13787E + 01, A4 = 0.34598E-01, A6 = 0.12361E-01, A8 = 0.16317E-02, A10 = -0.32970E-02,
A12 = 0.79198E-03
7th surface K = -0.25718E + 01, A4 = -0.22929E-01, A6 = 0.45581E-02, A8 = 0.24246E-03, A10 = 0.27506E-04, A12 = -0.96709E-04
8th surface K = -0.50000E + 02, A4 = 0.72218E-02, A6 = -0.73412E-02, A8 = 0.14028E-02, A10 = -0.20820E-03, A12 = 0.25222E-04, A14 = -0.36231E-05
9th surface K = -0.10056E + 02, A4 = -0.16771E-01, A6 = 0.46587E-02, A8 = -0.11970E-02, A10 = 0.17374E-03, A12 = -0.13445E-04, A14 = 0.41868E-06

Single lens data of the imaging lens of Example 5 is shown below.
Lens Start surface Focal length (mm)
1 2 2.470
2 4 -3.854
3 6 2.994
4 8 -2.884

In the present embodiment, the first lens is made of a glass material. On the other hand, the second lens, the third lens, and the fourth lens are each formed of a plastic material.

FIG. 13 is a cross-sectional view of the imaging lens of Example 5. In the figure, S is an aperture stop, L1 is a first lens, L2 is a second lens, L3 is a third lens, L4 is a fourth lens, and I is an imaging surface. F is a parallel plate similar to that of the first embodiment. 14A to 14E are aberration diagrams of the imaging lens of Example 5 (spherical aberration, astigmatism, distortion, and meridional coma).

The overall specification of the imaging lens of Example 6 is shown below.
f = 3.98 mm
fB = 0.24mm
F = 2.6
2Y = 6.496mm
ENTP = 0mm
EXTP = -4.01mm
H1 = 0.26mm
H2 = -3.74mm

The surface data of the imaging lens of Example 6 is shown below.
Surface number R (mm) D (mm) Nd νd Effective radius (mm)
1 (aperture) ∞ 0.16 0.77
2 * -16.927 0.77 1.53050 55.7 0.80
3 * -1.508 0.05 1.06
4 * 2.091 0.30 1.63200 23.4 1.42
5 * 1.260 0.97 1.46
6 * -2.973 1.27 1.53050 55.7 1.74
7 * -1.099 0.11 1.88
8 * -58.824 1.26 1.63200 23.4 2.03
9 * 1.768 1.00 2.88
10 ∞ 0.10 1.51630 64.1 3.50
11 ∞ 3.50

The aspheric coefficient is shown below.
2nd surface K = 0.43855E + 02, A4 = -0.79606E-01, A6 = -0.54718E-01, A8 = 0.13505E-01, A10 = -0.40568E-01, A12 = 0.76382E-02
3rd surface K = 0.44667E + 00, A4 = 0.51317E-01, A6 = -0.73562E-01, A8 = 0.91114E-01, A10 = -0.65940E-01, A12 = 0.22020E-01
4th surface K = 0.55366E + 00, A4 = -0.12254E + 00, A6 = 0.48256E-01, A8 = -0.26197E-01, A10 = 0.12329E-01, A12 = -0.28055E-02
5th surface K = -0.38338E + 01, A4 = 0.15782E-01, A6 = -0.72480E-02, A8 = -0.19233E-02, A10 = 0.41450E-02, A12 = -0.10761E-02
6th surface K = 0.13155E + 01, A4 = 0.50068E-01, A6 = 0.50746E-02, A8 = 0.22222E-02, A10 = -0.16482E-02,
A12 = 0.28303E-03
7th surface K = -0.27748E + 01, A4 = -0.18058E-01, A6 = -0.13661E-02, A8 = 0.10369E-02, A10 = 0.47278E-03, A12 = -0.12591E-03
8th surface K = -0.30497E + 02, A4 = 0.27523E-01, A6 = -0.28955E-01, A8 = 0.10602E-01, A10 = -0.26272E-02, A12 = 0.40806E-03, A14 = -0.32768E-04
9th surface K = -0.99698E + 01, A4 = -0.11538E-01, A6 = 0.15814E-02, A8 = -0.69757E-03, A10 = 0.15444E-03, A12 = -0.15968E-04, A14 = 0.61423E-06

Single lens data of the imaging lens of Example 6 is shown below.
Lens Start surface Focal length (mm)
1 2 3.067
2 4-5.825
3 6 2.661
4 8 -2.694

In this embodiment, all the lenses are made of a plastic material.

FIG. 15 is a cross-sectional view of the imaging lens of Example 6. In the figure, S is an aperture stop, L1 is a first lens, L2 is a second lens, L3 is a third lens, L4 is a fourth lens, and I is an imaging surface. F is a parallel plate similar to that of the first embodiment. 16A to 16E are aberration diagrams of the imaging lens of Example 6 (spherical aberration, astigmatism, distortion, and meridional coma).

The values corresponding to the conditional expressions in the above embodiments are shown below.
Conditional Example Example 1 Example 2 Example 3 Example 4 Example 5 Example 6
(1) | r1 / f | 1.71 1.35 3.15 1.99 2.72 4.25
(2) ν3-ν4 25.7 25.7 25.7 26.2 32.3 32.3
(3) f4 / f -0.63 -0.68 -0.59 -0.53 -0.70 -0.68
(4) Pair12 / P 1.91 1.96 2.39 2.09 2.01 2.58
(5) Pair23 / P -2.97 -2.84 -3.15 -2.70 -2.71 -3.05
(6) L / 2Y 0.96 0.96 0.95 0.98 0.97 0.93
(7) f / 2Y 0.65 0.65 0.65 0.65 0.63 0.61

Since the plastic material has a large refractive index change due to temperature change, if all of the first lens to the fourth lens are made of plastic lenses, the image point position of the entire imaging lens system when the ambient temperature changes. Will fluctuate. In the imaging unit having such a specification that the image point variation cannot be ignored, for example, a positive first lens having a relatively large refractive index is used as a lens formed of a glass material (for example, a glass mold lens) as in the fifth embodiment. The second lens, the third lens, and the fourth lens are plastic lenses. Furthermore, the refractive power is distributed among the second lens, the third lens, and the fourth lens so as to cancel out this image point variation to some extent. With this configuration, the temperature characteristic problem can be reduced. In the case of using a glass mold lens, it is desirable to use a glass material having a glass transition point (Tg) of, for example, 400 ° C. or less in order to prevent the mold from being consumed as much as possible.

By the way, in recent years, it has been found that the temperature change of the plastic material can be reduced by mixing inorganic particles in the plastic material. In other words, generally, mixing fine particles with a transparent plastic material causes light scattering and lowers the transmittance, making it difficult to use as an optical material, but the size of the fine particles is smaller than the wavelength of the transmitted light beam. By doing so, scattering can be substantially prevented from occurring. The refractive index of the plastic material decreases with increasing temperature, but the refractive index of the inorganic particles increases with increasing temperature. Therefore, it is possible to configure such that the refractive index of these mixtures hardly changes by using these temperature dependences so that the changes in the refractive index 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 acrylic, a change in refractive index due to a temperature change can be reduced. In the above-described embodiment, the positive lens (L1) having a relatively large refractive power, or all the lenses (L1 to L4) are formed of a plastic material in which such inorganic particles are dispersed, thereby causing a change in temperature. It becomes possible to suppress the fluctuation of the image point position of the entire imaging lens system.

In the present embodiment, a design is not applied in which the principal ray incident angle of the light beam incident on the imaging surface of the solid-state imaging device is sufficiently small in the peripheral portion of the imaging surface. However, in recent years, it has become possible to reduce shading by reviewing the arrangement of the color filters of the solid-state imaging device and the on-chip microlens array. Specifically, the pitch of the arrangement of the color filters and the on-chip microlens array is set slightly smaller than the pixel pitch on the imaging surface of the imaging device. With this configuration, the color filter and the on-chip microlens array shift toward the imaging lens optical axis side with respect to the pixel as it goes to the periphery of the imaging surface, so that the obliquely incident light flux is efficiently guided to the pixel. Can do. Therefore, shading generated in the solid-state image sensor can be suppressed to a small level. The present embodiment can be said to be a design example that is aimed at widening the angle of view and reducing the size by reducing the above requirement.

S aperture stop L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens 50 imaging device 51 imaging element 52a support substrate 52b flexible printed circuit board 53 housing 55 lens frame 100 mobile phone

Claims (10)

An imaging lens for forming a subject image on a photoelectric conversion unit of a solid-state imaging device,
An aperture stop, a first lens, a second lens, a third lens, and a fourth lens arranged in order from the object side to the image side;
The first lens has a positive refractive power and has a convex surface facing the image side;
The second lens has a negative refractive power and has a concave surface facing the image side;
The third lens has a positive refractive power and has a convex surface facing the image side;
The fourth lens has at least one aspherical surface and is formed in a biconcave shape having negative refractive power,
When the paraxial radius of curvature of the object side surface of the first lens is r1, and the focal length of the entire system of the imaging lens is f,
1.15 <| r1 / f | <4.50
Satisfies the conditional expression
An imaging lens characterized by the above. When the Abbe number of the third lens is ν3 and the Abbe number of the fourth lens is ν4,
ν3-ν4> 15
Satisfies the conditional expression
The imaging lens according to claim 1. When the focal length of the fourth lens is f4,
-0.9 <f4 / f <-0.3
Satisfies the conditional expression
The imaging lens according to claim 1. When the power of the entire system of the imaging lens is P, and the power of the air lens formed by the image side surface of the first lens and the object side surface of the second lens is Pair 12,
1.7 <Pair12 / P <2.8
Satisfies the conditional expression
The imaging lens according to claim 1, wherein:
However, the Pair 12 has a refractive index with respect to the d-line of the first lens as n1, a refractive index with respect to the d-line of the second lens as n2, and a paraxial radius of curvature of the image side surface of the first lens as r2. When the paraxial radius of curvature of the object side surface of the second lens is r3, and the air space on the axis of the first lens and the second lens is d2,

It is represented by When the power of the entire system of the imaging lens is P, and the power of the air lens formed by the image side surface of the second lens and the object side surface of the third lens is Pair23,
-3.5 <Pair23 / P <-2.5
Satisfies the conditional expression
The imaging lens according to claim 1, wherein:
However, the Pair 23 has a refractive index with respect to the d-line of the second lens as n2, a refractive index with respect to the d-line of the third lens as n3, and a paraxial radius of curvature of the image side surface of the second lens as r4, When the paraxial radius of curvature of the object side surface of the third lens is r5, and the air space on the axis of the second lens and the third lens is d4,

It is represented by
The image side surface of the fourth lens is aspheric and has an inflection point,
The fourth lens has a negative refractive power that becomes weaker from the center toward the periphery.
The imaging lens according to claim 1. The first lens is made of a glass material;
The imaging lens according to claim 1. The first lens, the second lens, the third lens, and the fourth lens are each formed of a plastic material.
The imaging lens according to claim 1. The imaging lens according to any one of claims 1 to 8,
A solid-state imaging device that photoelectrically converts a subject image formed by the imaging lens;
An imaging device comprising: A portable terminal comprising the imaging device according to claim 9.

Images