JP4916372B2 - Imaging lens and imaging apparatus - Google Patents

Description

  The present invention relates to an imaging lens suitable for use in combination with an imaging element and an imaging apparatus having the imaging lens.

  2. Description of the Related Art Conventionally, various information devices including an imaging device configured using an imaging device such as a solid-state imaging device have been proposed. Such an information device is configured as, for example, a so-called digital camera or camera-equipped mobile phone device. An image pickup apparatus used in such information equipment includes an image pickup element and an image pickup lens that forms an image of an object (subject) on an image pickup surface of the image pickup element.

  In particular, in an imaging apparatus used in an information device configured to be small so as to be suitable for carrying, the imaging lens is required to be small and thin. In addition, for such an imaging lens, there is an increasing demand for a reduction in manufacturing cost.

  In such an imaging apparatus, as the number of pixels in the imaging element is increased and the density is increased, the imaging lens is also required to have high optical performance such as high resolution.

  Thus, in order to realize an imaging lens that can be reduced in size and thickness and can be manufactured at a low cost, a single lens configuration is employed rather than a two-or-more lens configuration. It is known to be promising. It is also known that high optical performance can be maintained by appropriately adopting a lens having an aspherical surface. For example, Patent Document 1 and Patent Document 2 describe an imaging lens including a lens having positive refractive power having an aperture stop and a biconvex shape in order from the object side to the image side.

JP 2003-344758 A JP 2004-93965 A

  However, in the imaging lenses described in Patent Document 1 and Patent Document 2, it is difficult to realize high optical specifications and optical performance that have been required in recent years.

  In other words, in the imaging lenses described in Patent Documents 1 and 2, various aberrations, particularly coma, curvature of field, and astigmatism remain, so that the image height is reduced to an actual size, for example, 0. .9 mm (0.9 mm corresponds to ½ of the diagonal of the “1/10 type” image sensor) and the necessary spatial frequency, for example, 111 lp / mm, when the lens shape is enlarged similarly. It was found that a contrast of (111 lp / mm is a half of the Nyquist frequency of the “1/10 type” 310,000-pixel imaging device) cannot be obtained sufficiently.

  Therefore, the present invention has been proposed in view of the above-described problems, and various aberrations are favorably corrected, downsizing and thinning are achieved, and the manufacturing cost is reduced, An object of the present invention is to provide an imaging lens capable of realizing high optical specifications and optical performance, and to provide an imaging device having such an imaging lens.

  In order to solve the above-described problems, an imaging lens according to the present invention has the following configuration.

[Configuration 1]
In order from the object side to the image side, an aperture stop and a lens having a positive refractive power having a biconvex shape are arranged, and at least one surface of the lens is aspherical. When the refractive index Nd of the line is 1.6 to 2.0, the focal length is f, the radius of curvature of the first surface of the lens is R1, and the radius of curvature of the second surface of the lens is R2, the following conditional expression (1) and (2) are satisfied.

0 . 98 ≦ R1 / f <2 (1)
−10 <R2 / f <−1.1 (2)
Note that the expressions of convexity and concaveness of the refractive power and the surface shape are based on paraxial curvature.

[Configuration 2]
In the imaging lens having Configuration 1, when the distance from the aperture stop to the image plane is fs, the center thickness of the lens is d, and the distance from the top surface of the second surface of the lens to the image plane is fb, the following conditional expression ( 3), (4) and (5) are satisfied.

1.2 <fs / f <2.5 (3)
0.4 <d / fs <0.6 (4)
0.4 <fb / fs <0.6 (5)
[Configuration 3]
An imaging lens having Configuration 1 or Configuration 2 and an imaging device having an imaging surface arranged on the image plane of the imaging lens are provided.

The imaging lens according to the present invention can be configured as a small imaging lens having the above-described [Configuration 1], which is bright, has a wide angle of view, and has various aberrations corrected satisfactorily. This imaging lens has an optical performance suitable for use in combination with a small imaging device with a high pixel density and high density. In addition, since this imaging lens uses a high refractive index glass material having a refractive index Nd of about 1.6 to 2.0 as a material forming the lens, without excessively increasing the curvature of each surface, Necessary refractive power can be obtained.
Further, increasing the refractive index Nd of the material forming the lens means that the effective distance (optical distance) between the first surface and the second surface of the lens, which is two optical surfaces having refractive power in this imaging lens. Since it can be enlarged, it is effective for improving the performance not only near the center of the image but also to the periphery.
Furthermore, if a high refractive index glass material having a high refractive index Nd is used as a material for forming the lens so that the curvature of each surface of the lens is not excessively increased, the processing of the molding die and this molding die were used. Molding can be facilitated.

  In addition, since the imaging lens according to the present invention has [Configuration 2], the distance from the aperture stop to the image plane (hereinafter, referred to as “imaging lens total length (fs)”) is small, and the second surface of the lens is arranged. It can be configured as a small imaging lens having a sufficiently large distance from the top to the image plane (hereinafter referred to as “back focus (fb)”).

  Furthermore, the image pickup apparatus according to the present invention has [Configuration 3], so that the image pickup lens has a small image pickup lens in which various aberrations are well corrected. By using the small solid-state imaging device thus obtained, it can be configured as a small-sized and high-performance imaging device.

  That is, the present invention corrects various aberrations, achieves downsizing and thinning, and realizes high optical specifications and optical performance while realizing low manufacturing cost. In addition, an imaging apparatus having such an imaging lens can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view illustrating a configuration of an imaging lens according to Embodiment 1 of the present invention.

  As shown in FIG. 1, an imaging lens according to the present invention includes an aperture stop S and a lens L having positive refractive power having a biconvex shape arranged in order from the object side to the image side. .

  For example, an image pickup surface of an image pickup element is disposed on the image plane of the image pickup lens. As described above, the imaging device is configured by the imaging lens and the imaging element in which the imaging surface is positioned on the image plane of the imaging lens.

  In this imaging apparatus, a filter 1 made of a plane-parallel plate is disposed between the lens L of the imaging lens and the image plane. The filter 1 is a wavelength selection filter for preventing an unnecessary wavelength band from entering the image sensor, a low-pass filter for preventing the occurrence of moire fringes, a cover glass of the image sensor, or the like. Or, they are arranged in combination. In addition, when arrange | positioning combining these various filters as the filter 1, you may arrange | position each filter through the air layer mutually, and may arrange | position each filter mutually joined.

  In order to secure a physical space for disposing the filter 1 and to reduce the influence of dust and defects adhering to the surface of the filter 1 and defects inside the filter 1 on the formed image. It is desirable to increase the back focus sufficiently. By sufficiently increasing the back focus, the allowable size of dust and defects on the surface of the filter 1 and inside can be increased, which is preferable from the viewpoint of ease of manufacturing.

  Since this imaging lens has a single lens configuration, the lens L is a convex lens having a positive refractive power. By making the lens L biconvex, the positive refractive power of the lens L can be shared by the object side surface and the image side surface, so that the refractive power of each surface does not become too large. . It is preferable from the point of error sensitivity to share positive refractive power in each surface. A biconvex lens is also preferable from the viewpoint of ease of manufacture.

  In this imaging lens, in order to satisfactorily correct various aberrations, it is preferable that the lens L has at least one surface, and preferably both surfaces are aspherical.

  Further, in this imaging lens, the imaging lens total length fs (distance from the aperture stop S to the image plane) is reduced, and the back focus fb (distance from the top surface of the second surface of the lens L to the image plane) is sufficiently increased. In order to satisfactorily correct various aberrations, when the focal length of the imaging lens is f, the radius of curvature of the first surface of the lens L is R1, and the radius of curvature of the second surface of the lens L is R2, It is desirable that the following conditional expressions (1) and (2) are satisfied.

0 . 98 ≦ R1 / f <2 (1)
−10 <R2 / f <−1.1 (2)
Furthermore, in this imaging lens, in order to achieve both the reduction of the imaging lens total length fs, the expansion of the back focus fb, and the correction of various aberrations within a preferable range, when the center thickness of the lens L is d, It is desirable that the conditional expressions (3), (4) and (5) are satisfied.

1.2 <fs / f <2.5 (3)
0.4 <d / fs <0.6 (4)
0.4 <fb / fs <0.6 (5)
In this imaging lens, an appropriate optical material such as optical glass or synthetic resin material (plastic) can be used as a material forming the lens L. For example, the optical constants of the materials of these lenses L are those in which the refractive index Nd at the d-line (wavelength 587.6 nm) is 1.4 to 2.1 and the Abbe number νd at the d-line is 20 to 85. preferable. Further, as materials of these lenses L, those having a refractive index Nd of 1.45 to 1.9 and an Abbe number νd of 20 to 70 are more preferable from the viewpoint of easy availability and manufacturing cost.

  Moreover, in this imaging lens, by using a high refractive index glass material having a refractive index Nd of about 1.6 to 2.0 as a material forming the lens L, without excessively increasing the curvature of each surface, Necessary refractive power can be obtained.

  In addition, increasing the refractive index Nd of the material forming the lens L is an effective distance (optical distance between the first surface and the second surface of the lens L, which is two optical surfaces having refractive power in the imaging lens). ) Can be increased, which is effective in improving the performance not only near the center of the image but also to the periphery.

  Further, by using a high refractive index glass material having a high refractive index Nd as a material forming the lens L, if the curvature of each surface of the lens L is not excessively increased, the processing of the molding die and the molding die can be performed. The used molding can be facilitated.

  The lens L can be molded by a precision mold press. If the lens L is molded by a precision mold press, when the lenses L are molded, the shift amount between the first surface and the second surface is 5 μm or less, and the inclination of the axis between the first surface and the second surface (molding tilt). Can be made within 1 minute, and an imaging lens having high imaging performance can be configured.

  Hereinafter, the present invention will be specifically described by giving examples according to the present invention. In addition, this invention is not limited to the structure of a following example.

The symbols used in the following description of each example are as follows.
R: radius of curvature of refracting surface [mm]
D: Distance between top surfaces of refractive surfaces [mm]
Nd: Refractive index of lens material at d-line νd: Abbe number of lens material at d-line f: Focal length of entire lens system [mm]
F: F number 2Y: Image size (Y: Maximum image height) [mm]

The shape of the aspherical surface is represented by the following aspherical expression in an orthogonal coordinate system in which the intersection of the surface and the optical axis is the origin and the optical axis direction is the Z axis.
Z = Ch ² / [1 + √ {1- (1 + K) C 2 h 2} ] ^{+ A4h 4 + A6h 6 + A8h} 8 + A10h 10 + A12h 12 + A14h 14

However, symbols in this aspherical expression are as follows.
h = √ (X ² + Y ² )
C: Paraxial curvature (C = 1 / R)
K: Conic constant A4 to A14: 4th to 14th aspheric coefficients

[Example 1]
The lens data in Example 1 of the present invention is shown in [Table 1] below.

  The imaging lens has a focal length of 1.36 mm, an F number of 2.80, and a maximum image height of 0.88 mm.

In the imaging lens according to the first embodiment, the following relationship is established.
R1 / f = 0.98
R2 / f = −3.85
fs / f = 1.62
d / fs = 0.51
fb / fs = 0.41

  That is, the above conditional expressions (1) to (5) are satisfied.

  FIG. 1 is a cross-sectional view illustrating a configuration of an imaging lens according to Embodiment 1 of the present invention.

  2A and 2B are aberration diagrams of the imaging lens according to Example 1 of the present invention. FIG. 2A shows astigmatism (“×” indicates sagittal, “+” indicates meridional), and FIG. 2B indicates spherical aberration (“ “+” Indicates d-line (587.6 nm), “Δ” indicates F-line (486.1 nm), “□” indicates C-line (656.3 nm)), (c) indicates distortion, (d) Indicates meridional coma aberration (“+” indicates d-line (587.6 nm), “Δ” indicates F-line (486.1 nm), and “□” indicates C-line (656.3 nm)).

  In the imaging lens according to the first embodiment, as shown in FIG. 2, various aberrations are favorably corrected, and it is suitable as an imaging lens constituting a small and thin imaging device in combination with a small imaging element having high resolution. is there.

It is sectional drawing which shows the structure of the imaging lens in Example 1 of this invention. FIG. 5 is an aberration diagram (astigmatism, spherical aberration, distortion, and meridional coma) of the imaging lens according to Example 1 of the present invention. FIG. 5 is an aberration diagram (astigmatism, spherical aberration, distortion, and meridional coma) of the imaging lens according to Example 1 of the present invention.

Explanation of symbols

1 Filter S Aperture stop L Lens

Claims (3)

In order from the object side to the image side, a lens having a positive refractive power having an aperture stop and a biconvex shape is arranged, and at least one surface of the lens is an aspheric surface,
The refractive index Nd at the d-line of the lens material is 1.6 to 2.0, the focal length is f, the radius of curvature of the first surface of the lens is R1, and the radius of curvature of the second surface of the lens is R2. Then, the following conditional expressions (1) and (2) are satisfied.
0 . 98 ≦ R1 / f <2 (1)
−10 <R2 / f <−1.1 (2) When the distance from the aperture stop to the image plane is fs, the center thickness of the lens is d, and the distance from the top of the second surface of the lens to the image plane is fb, the following conditional expressions (3), ( The imaging lens according to claim 1, wherein 4) and (5) are satisfied.
1.2 <fs / f <2.5 (3)
0.4 <d / fs <0.6 (4)
0.4 <fb / fs <0.6 (5) The imaging lens according to claim 1 or 2, and
An imaging device comprising: an imaging device having an imaging surface arranged on an image surface of the imaging lens.

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