JP5498049B2 - Imaging lens and imaging apparatus using the same - Google Patents

Description

  The present invention relates to an imaging lens suitable for a small mobile product such as a mobile phone, a digital camera, and a small photographic device equipped with the imaging device, and an imaging device using the imaging lens.

  2. Description of the Related Art In recent years, for example, small mobile products such as mobile phones that have an imaging device (camera module) are widely used, and it has become common to easily take a picture using such a small mobile product. . As an image pickup lens for a small image pickup apparatus mounted on such a small mobile product, a four-lens structure is proposed that is composed of a lens system that is bright and has a short optical total length and that has various aberrations corrected satisfactorily. (For example, refer to Patent Document 1).

  The imaging lens described in Patent Document 1 includes a first lens that is a biconvex lens having a positive power, which is arranged in order from the object side to the image plane side, and a lens surface on the object side that has a negative power. A second lens made of a meniscus lens having a convex surface, a third lens made of a meniscus lens having a convex lens surface on the image surface side, has negative power near the optical axis, and increases toward the periphery. And a fourth lens configured to increase the power.

  On the other hand, in an imaging device mounted on a small mobile product such as a cellular phone, an imaging lens with small chromatic aberration is required in order to reduce the thickness and increase the resolution for a pixel pitch of 1.4 μm or less.

JP 2008-90150 A

  However, the imaging lens described in Patent Document 1 has a problem in that when the pixel pitch is reduced to 1.4 μm or less, various aberrations increase and the image quality of the captured image deteriorates.

  The present invention has been made to solve the above-described problems in the prior art, and can be reduced in size, thickness, and cost, and has a high-pixel imaging device (for example, a pixel pitch of 1.4 μm, An imaging lens capable of improving the image quality of a captured image by satisfactorily correcting various aberrations, particularly spherical aberration and axial chromatic aberration, even when a CMOS image sensor having 5 megapixels) is used. And it aims at providing the imaging device using the said imaging lens.

In order to achieve the above object, the configuration of the imaging lens according to the present invention includes a first lens composed of a biconvex lens having a positive power, arranged in order from the object side to the image plane side, and a negative power. A second lens composed of a meniscus lens having a concave lens surface on the image surface side, a third lens composed of a meniscus lens having a positive power and a convex lens surface on the image surface side, and negative power. has both lens surfaces are aspherical shape, and a fourth lens lens surface on the image side is concave in the vicinity of the optical axis,
The radius of curvature of the lens surface on the object side of the first lens is R11, the radius of curvature of the lens surface on the image plane side of the first lens is R12, and the refractive index of the second lens with respect to the d-line (587.5600 nm) is N2. The Abbe number of the second lens with respect to the d-line is ν2, the refractive index of the first lens with respect to the d-line is N1, the Abbe number of the first lens with respect to the d-line is ν1, and the refractive index of the third lens with respect to the d-line. Is N3, the Abbe number of the third lens with respect to the d-line is ν3, the refractive index of the fourth lens with respect to the d-line is N4, and the Abbe number of the fourth lens with respect to the d-line is ν4, the following conditional expression (1 ) To (9) are preferably satisfied.

1.26 <| R11 / R12 | <1.46 (1)
1.60 <N2 < 1.625 (2)
23 <ν2 <28 (3)
1.50 <N1 <1.55 (4)
55 <ν1 (5)
1.50 <N3 <1.55 (6)
55 <ν3 (7)
1.50 <N4 <1.55 (8)
55 <ν4 (9)
According to the configuration of the imaging lens of the present invention, a small and thin imaging lens can be realized with a small number of lenses. In addition, by using a pair of meniscus lenses whose concave lens surfaces are concave as the second and third lenses, the angle of light incident on the second and third lenses is reduced, and ray aberration is reduced. Can be small. In addition, since both lens surfaces of the fourth lens are aspherical, distortion and curvature of field can be favorably corrected. Further, by satisfying the conditional expression (1), it is possible to sufficiently reduce the spherical aberration and the longitudinal chromatic aberration, in particular, as compared with the conventional configuration. As a result, even when a high-pixel imaging device (for example, a CMOS image sensor with a pixel pitch of 1.4 μm and a number of pixels of 5 megapixels) is used, various aberrations are corrected and imaging is performed. The image quality can be improved. Further, by satisfying the conditional expressions (2) and (3), it is possible to use a low-cost plastic lens as the second lens while satisfactorily correcting the axial chromatic aberration. In addition, since the plastic lens can be used as the second lens in this way, it is easy to mold the lens including provision of an aspherical shape and a shape of the edge portion. And, by increasing the degree of freedom in designing the shape of the edge portion, a structure for preventing the image quality of the captured image from being deteriorated due to flare or ghost is designed for the second lens, or the edge portion is easy to assemble. It becomes possible to design the shape.
Further, according to this preferred example, since the low-cost plastic lens can be used as the first, third, and fourth lenses, it is possible to further reduce the cost of the imaging lens. In addition, since plastic lenses can be used as the first, third and fourth lenses in this way, as in the case of the second lens, molding of a lens including provision of an aspherical shape or a shape of the edge portion. Becomes easier. Then, by increasing the degree of freedom in designing the shape of the edge portion, a structure for preventing the image quality of the captured image from being deteriorated due to flare or ghost is designed for the first, third, and fourth lenses. It is possible to design the shape of the edge portion that is easy to assemble.

  As described above, according to the configuration of the imaging lens of the present invention, it is possible to reduce the size, the thickness, and the cost, and various aberrations, in particular, spherical aberration and axial chromatic aberration are corrected well, and the mobile phone Provided is a high-performance imaging lens capable of supporting a high-pixel imaging device (for example, a CMOS image sensor having a pixel pitch of 1.4 μm and a number of pixels of 5 megapixels) mounted on a small mobile product such as be able to.

  In addition, the configuration of the imaging apparatus according to the present invention includes an imaging element that converts an optical signal corresponding to a subject into an image signal and outputs the image signal, and an imaging lens that forms an image of the subject on an imaging surface of the imaging element. An image pickup apparatus provided with the image pickup lens of the present invention as the image pickup lens.

  According to the configuration of the image pickup apparatus of the present invention, the use of the image pickup lens of the present invention as an image pickup lens enables a compact and high-performance image pickup apparatus, and thus a compact and high-performance portable device on which the image pickup apparatus is mounted. Mobile products such as telephones can be provided.

  As described above, according to the present invention, it is possible to achieve a reduction in size, thickness, and cost, and a high-pixel imaging device (for example, a CMOS having a pixel pitch of 1.4 μm and a number of pixels of 5 megapixels). Even when an image sensor is used, an imaging lens capable of improving various image quality, particularly spherical aberration and axial chromatic aberration, and improving the image quality of the captured image, and the imaging lens are used. An imaging device can be provided.

1 is a layout diagram illustrating a configuration of an imaging lens according to a first embodiment of the present invention. Aberration diagrams of the imaging lens in Example 1 of the present invention ((a) is a spherical aberration diagram (axial chromatic aberration diagram), (b) is an astigmatism diagram, and (c) is a distortion aberration diagram). Arrangement | positioning figure which shows the structure of the imaging lens in the 2nd Embodiment of this invention Aberration diagrams of the imaging lens in Example 2 of the present invention ((a) is a spherical aberration diagram (axial chromatic aberration diagram), (b) is an astigmatism diagram, and (c) is a distortion aberration diagram). Arrangement | positioning figure which shows the structure of the imaging lens in the 3rd Embodiment of this invention. Aberration diagrams of the imaging lens in Example 3 of the present invention ((a) is a spherical aberration diagram (axial chromatic aberration diagram), (b) is an astigmatism diagram, and (c) is a distortion aberration diagram). Conditional expression (1) of the imaging lens of the present invention: 1.26 <| R11 / R12 | <1 . Graph showing the effect of 46

  Hereinafter, the present invention will be described more specifically using embodiments.

[First Embodiment]
FIG. 1 is a layout diagram showing a configuration of an imaging lens according to the first embodiment of the present invention.

  As shown in FIG. 1, the imaging lens 7 of the present embodiment includes an aperture stop 5 arranged in order from the object side (left side in FIG. 1) to the image plane side (right side in FIG. 1), and a positive A first lens 1 composed of a biconvex lens having power; a second lens 2 composed of a meniscus lens having negative power and having a concave lens surface on the image plane side; and having positive power on the image plane side A third lens 3 composed of a meniscus lens having a convex lens surface, a fourth lens having negative power, both lens surfaces being aspherical, and the lens surface on the image side being concave near the optical axis. And a lens 4. Here, the power is an amount defined by the reciprocal of the focal length. The imaging lens 7 is a single-focus lens for imaging that forms an optical image (forms an image of a subject) on the imaging surface S of an imaging device (for example, a CCD), and the imaging device corresponds to the subject. An optical signal is converted into an image signal and output. An imaging device is configured using the imaging element and the imaging lens 7.

  The aspherical shape of the lens surface is given by the following (Equation 1) (the same applies to the second and third embodiments described later).

However, in the above (Equation 1), Y is the height from the optical axis, X is the distance from the tangential plane of the aspherical vertex of the aspherical shape whose height from the optical axis is Y, and R ₀ is the aspherical vertex. A radius of curvature, κ is a conical constant, and A4, A6, A8, A10, and A12 represent fourth-order, sixth-order, eighth-order, tenth-order, and twelfth-order aspherical coefficients, respectively.

  The imaging lens 7 of the present embodiment is configured to satisfy the following conditional expressions (1) to (3).

1.26 <| R11 / R12 | <1.46 (1)
1.60 <N2 < 1.625 (2)
23 <ν2 <28 (3)
Here, R11 is the radius of curvature of the lens surface on the object side of the first lens 1, R12 is the radius of curvature of the lens surface on the image plane side of the first lens 1, and N2 is the d-line (587.5600 nm) of the second lens 2. The refractive index ν 2 is the Abbe number of the second lens 2 with respect to the d-line . A preferable range of ν 2 is 24 < ν 2 <28.

  The conditional expression (1) is a conditional expression regarding the shape of the first lens 1 mainly for correcting spherical aberration and axial chromatic aberration. When | R11 / R12 | is 1.0 or less, it becomes difficult to satisfactorily correct spherical aberration and axial chromatic aberration.

  According to the configuration of the imaging lens 7 of the present embodiment, a small and thin imaging lens can be realized with a small number of lenses. Further, by using a pair of meniscus lenses whose concave lens surfaces are concave as the second and third lenses 2 and 3, the angle of light incident on the second and third lenses 2 and 3 is reduced. Ray aberration can be reduced. In addition, since both lens surfaces of the fourth lens 4 are aspherical, distortion and curvature of field can be favorably corrected. In addition, satisfying the conditional expression (1) makes it possible to correct particularly spherical aberration and axial chromatic aberration well. As a result, even when a high-pixel imaging device (for example, a CMOS image sensor with a pixel pitch of 1.4 μm and a number of pixels of 5 megapixels) is used, various aberrations are corrected and imaging is performed. The image quality can be improved. Furthermore, by satisfying the conditional expressions (2) and (3), it is possible to use a low-cost plastic lens as the second lens 2 while satisfactorily correcting the axial chromatic aberration. In addition, since a plastic lens can be used as the second lens 2 in this way, it is easy to mold the lens including provision of an aspherical shape and a shape of the edge portion. Then, by increasing the degree of freedom in designing the shape of the edge portion, a structure for preventing the image quality of the captured image from being deteriorated due to flare or ghost is designed for the second lens 2, or the edge portion that is easy to assemble is designed. It becomes possible to design the shape.

  From the above, according to the configuration of the imaging lens 7 of the present embodiment, it is possible to achieve a reduction in size and thickness and cost, and various aberrations, particularly spherical aberration and axial chromatic aberration are corrected well. A high-performance imaging lens capable of supporting a high-pixel imaging device (for example, a CMOS image sensor having a pixel pitch of 1.4 μm and a number of pixels of 5 megapixels) mounted on a small mobile product such as a cellular phone. Can be provided.

  A transparent parallel plate 6 is disposed between the fourth lens 4 and the imaging surface S of the imaging device. Here, the parallel plate 6 is a plate equivalent to an optical low-pass filter, an IR cut filter, and a face plate (cover glass) of the image sensor.

  Respective surfaces (hereinafter also referred to as “optical surfaces”) from the object-side lens surface of the first lens 1 to the image-plane-side surface of the parallel plate 6 are referred to as “first surface” and “second surface” in order from the object side. ”,“ Third surface ”,“ fourth surface ”,...,“ Eighth surface ”,“ ninth surface ”,“ tenth surface ”(second and third implementations to be described later) The same applies to the form of

  Further, it is desirable that the imaging lens 7 of the present embodiment is configured to satisfy the following conditional expressions (4) to (9).

1.50 <N1 <1.55 (4)
55 <ν1 (5)
1.50 <N3 <1.55 (6)
55 <ν3 (7)
1.50 <N4 <1.55 (8)
55 <ν4 (9)
Here, N1 is the refractive index of the first lens 1 with respect to the d-line, ν1 is the Abbe number of the first lens 1 with respect to the d-line, N3 is the refractive index of the third lens 3 with respect to the d-line, and ν3 is d of the third lens 3. Abbe number with respect to the line, N4 is the refractive index of the fourth lens 4 with respect to the d line, and ν4 is the Abbe number with respect to the d line of the fourth lens 4.

  By satisfying the conditional expressions (4) to (9), a low-cost plastic lens can be used as the first, third, and fourth lenses 1, 3, and 4, so that the cost of the imaging lens can be further reduced. Can be achieved. In addition, since plastic lenses can be used as the first, third and fourth lenses 1, 3 and 4 in this way, as in the case of the second lens 2, the aspherical shape and the shape of the edge portion are given. It becomes easy to mold the lens including it. And the structure for preventing the fall of the image quality of the picked-up image by a flare or a ghost with respect to the 1st, 3rd and 4th lenses 1, 3, and 4 by the design freedom degree of the shape of an edge part becoming high. It is possible to design the shape of the edge portion that is easy to assemble.

Example 1
Hereinafter, the imaging lens according to the present embodiment will be described in more detail with specific examples.

  The following (Table 1) shows specific numerical examples of the imaging lens in the present embodiment.

  In the above (Table 1), r (mm) is the radius of curvature of the optical surface, d (mm) is the thickness or surface spacing on the axes of the first to fourth lenses 1 to 4 and the parallel plate 6, and N is the first The refractive indexes of the first to fourth lenses 1 to 4 and the parallel plate 6 with respect to the d-line, and ν represent the Abbe numbers of the first to fourth lenses 1 to 4 and the parallel plate 6 with respect to the d-line (Example 2 below). 3 is the same). Note that the imaging lens 7 shown in FIG. 1 is configured based on the data shown in Table 1 above.

  As can be seen from the above (Table 1), the total optical length, which is the distance along the optical axis from the apex of the object-side lens surface of the first lens 1 to the imaging surface S of the imaging device, is 4.5 mm. Thinning is achieved. Further, all of the first to fourth lenses 1 to 4 are plastic lenses (obviously from the values of the refractive index and the Abbe number in the above (Table 1)), and the cost is reduced.

Further, the following (Table 2A) and (Table 2B) show the aspherical coefficients (including the conical constant) of the imaging lens in the present example. In the following (Table 2A) and (Table 2B), “E + 00”, “E-02” and the like represent “10 ⁺⁰⁰ ” and “10 ⁻⁰² ”, respectively (Examples 2 and 3 below) The same applies to.

  As shown in the above (Table 2A) and (Table 2B), in the imaging lens 7 of the present embodiment, all the lens surfaces of the first to fourth lenses 1 to 4 are aspherical. However, it is not necessarily limited to such a configuration. It is sufficient that at least both lens surfaces of the fourth lens 4 are aspherical.

  The following (Table 3) shows the F number (F value) Fno, the focal length f (mm) of the entire optical system, the half angle of view ω (°), and the maximum image height Y ′ of the imaging lens 7 in the present embodiment. (Mm) and the values of conditional expressions (1) to (9) are shown.

  As shown in Table 3 above, an imaging lens having a bright F value (Fno) of 2.8 is realized.

  FIG. 2 shows aberration diagrams of the imaging lens in the present example. In FIG. 2, (a) is a diagram of spherical aberration, the solid line is the g line (435.8300 nm), the long broken line is the C line (656.2700 nm), and the two-dot chain line is the value for the d line (587.5600 nm). Show. (B) is a figure of astigmatism, the solid line shows sagittal field curvature, and the broken line shows meridional field curvature. (C) is a diagram of distortion. The axial chromatic aberration can be read from the spherical aberration diagram of FIG. 2A, and the difference between the spherical aberration value for the d-line (two-dot chain line) and the spherical aberration value for the g-line (solid line) is This is referred to as “axial chromatic aberration of g line with respect to d line”.

  As is apparent from the aberration diagram shown in FIG. 2, the imaging lens 7 of the present embodiment is well corrected for various aberrations, particularly spherical aberration and longitudinal chromatic aberration, and is mounted on a small mobile product such as a cellular phone. It can be seen that it can be applied to a pixel imaging device (for example, a CMOS image sensor having a pixel pitch of 1.4 μm and a number of pixels of 5 megapixels).

  Here, when the imaging lens 7 of the present embodiment is used, how much the degree of correction of aberration is improved as compared with the case where the imaging lens disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2008-90150) is used. Explain what they do.

  Read the maximum abscissa value of spherical aberration, astigmatism, and distortion aberration with reference to “0” in each aberration diagram for each of the plus and minus sides, and the absolute values on the plus and minus sides are large. Is regarded as an aberration value for evaluating the effect of aberration correction.

  As for spherical aberration and astigmatism, those normalized by respective maximum image heights used in the present embodiment and the embodiment of Patent Document 1 are compared. For distortion aberration, the values read directly from the aberration diagrams are compared regardless of the maximum image height.

  For axial chromatic aberration, the difference (absolute value) between the spherical aberration value for the d line and the spherical aberration value for the g line when the pupil coordinate (ordinate) of the spherical aberration diagram is “0” is read The examples normalized by the maximum image heights used in the example and the example of Patent Document 1 are compared (the same applies to Examples 2 and 3 below).

  The values obtained as described above are shown below (Table 4).

  As shown in Table 4 above, when the imaging lens 7 of this example is used, the spherical aberration and the axial chromatic aberration are reduced by half or 1/3 compared to the case where the imaging lens of Patent Document 1 is used. It can be seen that the number has decreased.

[Second Embodiment]
FIG. 3 is a layout diagram illustrating the configuration of the imaging lens according to the second embodiment of the present invention.

  As shown in FIG. 3, the imaging lens 14 of the present embodiment includes an aperture stop 12 arranged in order from the object side (left side in FIG. 3) to the image plane side (right side in FIG. 3), and a positive A first lens 8 composed of a biconvex lens having power; a second lens 9 composed of a meniscus lens having negative power and having a concave lens surface on the image plane side; and having positive power on the image plane side A third lens 10 made of a meniscus lens having a convex lens surface, a fourth lens having negative power, both lens surfaces being aspherical, and the lens surface on the image side being concave near the optical axis. And a lens 11.

  A transparent parallel plate 13 similar to the parallel plate 6 of the first embodiment is disposed between the fourth lens 11 and the image pickup surface S of the image pickup device.

  The imaging lens 14 of the present embodiment is also configured to satisfy the conditional expressions (1) to (3).

  In addition, it is desirable that the imaging lens 14 of the present embodiment is also configured to satisfy the conditional expressions (4) to (9).

  Also by the configuration of the imaging lens 14 of the present embodiment, the same operational effects as the operational effects of the configuration of the imaging lens 7 of the first embodiment can be obtained.

(Example 2)
Hereinafter, the imaging lens according to the present embodiment will be described in more detail with specific examples.

  The following (Table 5) shows specific numerical examples of the imaging lens in the present embodiment. The imaging lens 14 shown in FIG. 3 is configured based on the following data (Table 5).

  As can be seen from the above (Table 5), the total optical length, which is the distance along the optical axis from the apex of the object-side lens surface of the first lens 8 to the imaging surface S of the imaging device, is 4.7 mm. Thinning is achieved. Further, all of the first to fourth lenses 8 to 11 are plastic lenses (obviously apparent from the values of the refractive index and the Abbe number in Table 5 above), and cost reduction is also achieved.

  The following (Table 6A) and (Table 6B) show the aspherical coefficients (including conical constants) of the imaging lens in this example.

  In addition, as shown in the above (Table 6A) and (Table 6B), in the imaging lens 14 of the present embodiment, all the lens surfaces of the first to fourth lenses 8 to 11 are aspherical. However, it is not necessarily limited to such a configuration. It is sufficient that at least both lens surfaces of the fourth lens 11 are aspherical.

  The following (Table 7) shows the F number (F value) Fno, the focal length f (mm) of the entire optical system, the half angle of view ω (°), and the maximum image height Y ′ of the imaging lens 14 in the present embodiment. (Mm) and the values of conditional expressions (1) to (9) are shown.

  As shown in Table 7 above, a bright imaging lens having an F value (Fno) of 2.8 is realized.

  FIG. 4 is an aberration diagram of the imaging lens in the present example. In FIG. 4, (a) is a diagram of spherical aberration, where the solid line indicates the g line, the long broken line indicates the C line, and the two-dot chain line indicates the value for the d line. (B) is a figure of astigmatism, the solid line shows sagittal field curvature, and the broken line shows meridional field curvature. (C) is a diagram of distortion. The axial chromatic aberration can be read from the spherical aberration diagram of FIG. 4A, as in the case of Example 1.

  As is apparent from the aberration diagram shown in FIG. 4, the imaging lens 14 of the present example is well-corrected for various aberrations, particularly spherical aberration and longitudinal chromatic aberration, and is mounted on a small mobile product such as a cellular phone. It can be seen that it can be applied to a pixel imaging device (for example, a CMOS image sensor having a pixel pitch of 1.4 μm and a number of pixels of 5 megapixels).

  The following (Table 8) evaluated how much the degree of correction of aberration is improved when the imaging lens 14 of the present embodiment is used compared to the case where the imaging lens of Patent Document 1 is used. Results are shown.

  As shown above (Table 8), when the imaging lens 14 of this example is used, the spherical aberration is reduced to 1/3 compared to the case where the imaging lens of Patent Document 1 is used, and the axis It can be seen that the upper chromatic aberration is reduced to 2/3 to 2/9. It can also be seen that astigmatism is reduced to 3/5 compared to the case where the imaging lens of Patent Document 1 is used.

[Third Embodiment]
FIG. 5 is a layout diagram illustrating a configuration of an imaging lens according to the third embodiment of the present invention.

  As shown in FIG. 5, the imaging lens 21 of the present embodiment includes an aperture stop 19 arranged in order from the object side (left side in FIG. 5) to the image plane side (right side in FIG. 5), and a positive A first lens 15 composed of a biconvex lens having power; a second lens 16 composed of a meniscus lens having negative power and having a concave lens surface on the image plane side; and has positive power on the image plane side A third lens 17 made of a meniscus lens having a convex lens surface, a fourth lens having negative power, both lens surfaces being aspherical, and the lens surface on the image side being concave near the optical axis. And a lens 18.

  A transparent parallel plate 20 similar to the parallel plate 6 of the first embodiment is disposed between the fourth lens 18 and the imaging surface S of the imaging device.

  The imaging lens 21 of the present embodiment is also configured to satisfy the conditional expressions (1) to (3).

  Moreover, it is desirable that the imaging lens 21 of the present embodiment is also configured to satisfy the conditional expressions (4) to (9).

  Also by the configuration of the imaging lens 21 of the present embodiment, the same operational effects as the operational effects of the configuration of the imaging lens 7 of the first embodiment can be obtained.

(Example 3)
Hereinafter, the imaging lens according to the present embodiment will be described in more detail with specific examples.

  The following (Table 9) shows specific numerical examples of the imaging lens in the present embodiment. The imaging lens 21 shown in FIG. 5 is configured based on the following data (Table 9).

  As can be seen from the above (Table 9), the total optical length, which is the distance along the optical axis from the apex of the object-side lens surface of the first lens 15 to the imaging surface S of the imaging device, is 4.5 mm. Thinning is achieved. In addition, all of the first to fourth lenses 15 to 18 are plastic lenses (obtained from the values of the refractive index and Abbe number in Table 9 above), and cost reduction is also achieved.

  The following (Table 10A) and (Table 10B) show the aspherical coefficients (including conical constants) of the imaging lens in this example.

  As shown in the above (Table 10A) and (Table 10B), in the imaging lens 21 of the present embodiment, all the lens surfaces of the first to fourth lenses 15 to 18 are aspherical. However, it is not necessarily limited to such a configuration. It is sufficient that at least both lens surfaces of the fourth lens 18 are aspherical.

  The following (Table 11) shows the F number (F value) Fno, the focal length f (mm) of the entire optical system, the half field angle ω (°), and the maximum image height Y ′ of the imaging lens 24 in the present embodiment. (Mm) and the values of conditional expressions (1) to (9) are shown.

  As shown in Table 11 above, an imaging lens having a bright F value (Fno) of 2.8 is realized.

  FIG. 6 is an aberration diagram of the imaging lens in the present example. In FIG. 6, (a) is a diagram of spherical aberration, where the solid line indicates the value for the g line, the long broken line indicates the value for the C line, and the two-dot chain line indicates the value for the d line. (B) is a figure of astigmatism, the solid line shows sagittal field curvature, and the broken line shows meridional field curvature. (C) is a diagram of distortion. The axial chromatic aberration can be read from the spherical aberration diagram of FIG. 6A, as in the case of Example 1.

  As is apparent from the aberration diagram shown in FIG. 6, the imaging lens 21 of the present embodiment is well corrected for various aberrations, particularly spherical aberration and longitudinal chromatic aberration, and is mounted on a small mobile product such as a cellular phone. It can be seen that it can be applied to a pixel imaging device (for example, a CMOS image sensor having a pixel pitch of 1.4 μm and a number of pixels of 5 megapixels).

  The following (Table 12) evaluated how much the degree of correction of aberration is improved when the imaging lens 21 of the present embodiment is used compared to the case where the imaging lens of Patent Document 1 is used. Results are shown.

  As shown above (Table 12), when the imaging lens 21 of this example is used, the spherical aberration is reduced to 1/3 compared to the case where the imaging lens of Patent Document 1 is used, and the axis It can be seen that the upper chromatic aberration is reduced to 2/3 to 2/9.

[Condition (1): 1.26 <| R11 / R12 | < Effect by Satisfying 1.46 ]
The values of | R11 / R12 | in Examples 1 and 2 of Patent Document 1 are 0.37 and 0.05, respectively, and the values of | R11 / R12 | in Examples 1 to 3 of the present invention are 1 respectively. .46, 1.40, 1.26. The following (Table 13) shows a combination of the above (Table 4), (Table 8), and (Table 12) with these values included.

  FIG. 7 shows the result of the above graph processing (Table 13).

  As is clear from the graph shown in FIG. 7, it can be seen that satisfying 1.0 <| R11 / R12 | can particularly favorably correct spherical aberration and longitudinal chromatic aberration. In addition, the graph shown in FIG. 7 shows that a particularly preferable range of | R11 / R12 | is 1.25 <| R11 / R12 | <1.50.

  The imaging lens of the present invention can be reduced in size, thickness, and cost, and can be used as a high-pixel imaging device (for example, a CMOS image sensor having a pixel pitch of 1.4 μm and a number of pixels of 5 megapixels). Therefore, the present invention is particularly useful in the field of small mobile products such as a mobile phone having a built-in image sensor in which high pixel count is desired.

1, 8, 15 First lens 2, 9, 16 Second lens 3, 10, 17 Third lens 4, 11, 18 Fourth lens 5, 12, 19 Aperture stop 6, 13, 20 Parallel plates 7, 14, 21 Imaging lens S Imaging surface

Claims (2)

A first lens composed of a biconvex lens having a positive power and arranged in order from the object side to the image surface side, and a first lens composed of a meniscus lens having a negative power and a concave lens surface on the image surface side. A second lens, a third lens composed of a meniscus lens having a positive power and a convex lens surface on the image surface side, and a negative power, both lens surfaces being aspherical, the image surface side and a fourth lens lens surface is concave in the vicinity of the optical axis,
The radius of curvature of the lens surface on the object side of the first lens is R11, the radius of curvature of the lens surface on the image plane side of the first lens is R12, the refractive index of the first lens with respect to the d-line is N1, and the first lens The Abbe number of the second lens with respect to the d line is ν1, the refractive index of the second lens with respect to the d line (587.5600 nm) is N2, the Abbe number of the second lens with respect to the d line is ν2, and the refractive index of the third lens with respect to the d line. Is N3, the Abbe number of the third lens with respect to the d-line is ν3, the refractive index of the fourth lens with respect to the d-line is N4, and the Abbe number of the fourth lens with respect to the d-line is ν4, the following conditional expression (1 An imaging lens satisfying (9) to (9) .
1.26 <| R11 / R12 | <1.46 (1)
1.60 <N2 < 1.625 (2)
23 <ν2 <28 (3)
1.50 <N1 <1.55 (4)
55 <ν1 (5)
1.50 <N3 <1.55 (6)
55 <ν3 (7)
1.50 <N4 <1.55 (8)
55 <ν4 (9) An imaging apparatus comprising: an imaging device that converts an optical signal corresponding to a subject into an image signal and outputs the image signal; and an imaging lens that forms an image of the subject on an imaging surface of the imaging device,
An imaging apparatus using the imaging lens according to claim 1 as the imaging lens.

Images