JP2008242397A - Imaging lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging lens which is compact and whose chromatic aberration and coma aberration or the like are satisfactorily corrected. <P>SOLUTION: The imaging lens is constituted of a first aperture diaphragm SD1 forming a predetermined aperture, a second aperture diaphragm SD2 forming a predetermined aperture, a third aperture diaphragm SD3 forming a predetermined aperture, a first lens group I having positive refractive power and a second lens group II having positive refractive power arranged in order from an object side to an image surface side. Thus, the quantity of light incident from a subject is regulated by the second aperture diaphragm located in the middle, so as to decide the brightness of a lens system, and a lower side light beam in a peripheral area, for example, out of luminous flux incident from a subject is cut by the first aperture diaphragm located in the front and an upper side light beam in the peripheral area, for example, out of the luminous flux incident from the subject is cut by the third aperture diaphragm located in the rear, whereby the coma aberration is satisfactorily corrected while correcting aberrations such as the chromatic aberration. As a result, image quality around the image is improved, and the imaging lens suitable for a mobile camera or the like is obtained. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an imaging lens applied to a digital camera, a mobile camera, or the like that uses an imaging element such as a CCD or CMOS, and more particularly to an imaging lens having excellent achromatic performance.

In recent years, with the spread of information terminals such as personal computers and mobile phones, mobile cameras (digital cameras) have been connected to or mounted on these information terminals to capture and photograph the operator's face and surrounding scenery. Images are exchanged in real time via the Internet.
In order to popularize such a system, it is desirable that the necessary hardware is as cheap as possible, and the lens optical system of a mobile camera is generally formed of one aperture stop and resin in order from the object side. In addition, imaging lenses made up of a single aspheric lens are known (for example, Patent Document 1, Patent Document 2, Patent Document 3, etc.).

However, with one aperture stop and one aspherical lens, it is difficult to correct longitudinal chromatic aberration and lateral chromatic aberration, and these chromatic aberrations remain largely present.
By the way, lateral chromatic aberration is also called magnification chromatic aberration, and is a phenomenon in which the size of an image varies depending on the wavelength. The outline of a subject appears as a color blur, resulting in a decrease in image quality. In particular, when the subject is a human face or the like, an unnatural color is added to the contour, which is not preferable.

Incidentally, the longitudinal chromatic aberration and lateral chromatic aberration in the conventional imaging lens are as follows when the reference wavelength is 587.6 nm, the focal length is normalized to 1 mm, and the angle of view (2ω) is 30 °. .
<Imaging Lens According to Patent Document 1>
Longitudinal chromatic aberration → -19.4 μm (wavelength 486.1 nm)
+8.23 μm (wavelength 656.3 nm)
Lateral chromatic aberration --2.92 μm (wavelength 486.1 nm)
+1.22 μm (wavelength 656.3 nm)
<Image pickup lens according to Patent Document 2>
Longitudinal chromatic aberration → -12.9 μm (wavelength 486.1 nm)
+5.71 μm (wavelength 656.3 nm)
Lateral chromatic aberration → −1.13 μm (wavelength 486.1 nm)
+0.495 μm (wavelength 656.3 nm)
<Image pickup lens according to Patent Document 3>
Longitudinal chromatic aberration → -9.51 μm (wavelength 486.1 nm)
+4.05 μm (wavelength 656.3 nm)
Lateral chromatic aberration → -1.57 μm (wavelength 486.1 nm)
+0.666 μm (wavelength 656.3 nm)

JP 2000-249911 A JP 2002-98885 A JP 2006-10990 A

  The present invention has been made in view of the above circumstances, and the object of the present invention is not only spherical aberration, astigmatism, and distortion, but also a low cost with a simple lens configuration. Chromatic aberration (longitudinal chromatic aberration, lateral chromatic aberration), coma aberration, etc. can be corrected well, and high-quality images can be obtained even at an angle of view (2ω) of about 30 ° or more. Mobile cameras, digital cameras, etc. It is in providing the imaging lens suitable for.

The imaging lens of the present invention has a first aperture stop having a predetermined aperture, a second aperture stop having a predetermined aperture, and a third aperture having a predetermined aperture, which are arranged in order from the object side to the image plane side. It is characterized by comprising an aperture stop, a first lens group having a positive refractive power, and a second lens group having a positive refractive power.
According to this configuration, since three aperture stops are arranged in front of the first lens group and the second lens group, spherical aberration, astigmatism, distortion, Select a lens with specifications that can correct chromatic aberration (vertical chromatic aberration, lateral chromatic aberration) satisfactorily. For example, the lower ray of the peripheral area is cut out of the light flux incident from the subject at the first aperture stop located in the front, and the light of the peripheral area is taken up of the light flux incident from the subject in the third aperture stop located at the rear. By cutting the upper ray, the coma aberration can be corrected well. As a result, the image quality around the image can be improved, and an imaging lens suitable for a mobile camera or the like can be obtained.

In the above configuration, the first lens group is joined to the first lens and arranged in order from the object side, and has a negative refractive power with a convex surface facing the object side, and is positively refracted. It is possible to adopt a configuration including a biconvex second lens having power, and the second lens group including a biconvex third lens having positive refractive power.
According to this configuration, in particular, the first lens is formed of a glass material having a large dispersion (small Abbe number), the second lens is formed of a glass material having a small dispersion (large Abbe number), and both lenses are formed. By joining, coma and the like can be corrected well, and chromatic aberration (vertical chromatic aberration, lateral chromatic aberration) can be corrected well.

In the above configuration, the third lens has a configuration in which R7 = −R8 when the radius of curvature of the object side surface is R7 and the radius of curvature of the image side surface is R8. be able to.
According to this configuration, since the third lens has a symmetrical shape with no front and back, the manufacturing cost can be reduced, and since there is no front and back, erroneous assembly can be prevented.

In the above configuration, the second lens group can include a fourth lens that is cemented to the image plane side of the third lens and has a negative refractive power with the concave surface facing the object side.
According to this configuration, the first lens is formed of a glass material having a large dispersion (small Abbe number) and the second lens is formed of a glass material having a small dispersion (large Abbe number), and both the lenses are cemented together to form the third lens. By composing both the lenses by forming the fourth lens from a glass material having a small dispersion (large Abbe number) and a fourth lens by a glass material having a large dispersion (small Abbe number), the coma aberration can be corrected well. Chromatic aberration (longitudinal chromatic aberration, lateral chromatic aberration) can be corrected more satisfactorily.

In the above-described configuration, a configuration in which the first lens group and the second lens group are the same and reversed in the optical axis direction can be employed.
According to this configuration, it is possible to reduce costs by using the same lens while satisfactorily correcting coma aberration, chromatic aberration (vertical chromatic aberration, lateral chromatic aberration) and the like.

  According to the imaging lens having the above configuration, not only spherical aberration, astigmatism, distortion, but also chromatic aberration (vertical chromatic aberration, lateral chromatic aberration), while achieving cost reduction with a simple lens configuration, The coma can be corrected well, and an imaging lens suitable for a mobile camera, a digital camera, or the like can be obtained.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments of the invention will be described with reference to the accompanying drawings.
1 and 2 show an embodiment of an imaging lens according to the present invention. FIG. 1 is a lens configuration diagram and FIG. 2 is an optical path diagram.
As shown in FIGS. 1 and 2, the imaging lens is arranged in order from the object side to the image plane side on the optical axis L, and has a first aperture stop SD1 having a predetermined aperture, and a first aperture having a predetermined aperture. It includes a two-aperture stop SD2, a third aperture stop SD3 having a predetermined aperture, a first lens group (I) having a positive refractive power, and a second lens group (II) having a positive refractive power. Note that the imaging plane P of the imaging element is disposed behind the second lens group (II).
The first lens group (I) includes a meniscus first lens 1 and a first lens 1 which are arranged in order from the object side to the image plane side and have negative refractive power with a convex surface facing the object side. And a biconvex second lens 2 having a positive refractive power.
The second lens group (II) is joined to the biconvex third lens 3 and the third lens 3 having positive refractive power, which are arranged in order from the object side to the image plane side, and on the object side. It is formed by the fourth lens 4 having a negative refractive power with the concave surface directed.

The first aperture stop SD1 is formed to have a predetermined aperture, and is disposed closest to the object side in the optical axis direction L. As shown in FIG. It is formed to cut side rays.
The second aperture stop SD2 is formed to have a predetermined aperture, and is disposed behind the first aperture stop SD1 in the optical axis direction L. As shown in FIG. 2, the amount of light incident from the subject is restricted. Thus, the brightness of the lens system is determined.
The third aperture stop SD3 is formed to have a predetermined aperture, and is arranged behind the second aperture stop SD2 in the optical axis direction L. As shown in FIG. For example, it is formed so as to cut the peripheral upper light beam.

  Here, in the first aperture stop SD1, the second aperture stop SD2, the third aperture stop SD3, the first lens 1 to the fourth lens 4, and the image plane P, as shown in FIG. i = 1 to 9), the radius of curvature of each surface Si is Ri (i = 1 to 9), the refractive index for the first lens 1 to the fourth lens 4d line is Ni (i = 1 to 4), and the Abbe number is It represents by νi (i = 1 to 4). The distance (thickness, air interval) on the optical axis L from the first aperture stop SD1 to the image plane P is represented by Di (i = 1 to 9).

<First lens group I>
The first lens 1 is formed of a glass material, and as shown in FIG. 1, is a meniscus lens having negative refractive power in which a surface S4 on the object side is convex and a surface S5 on the image side is concave. is there. The object side surface S4 and the image surface side surface S5 are both spherical.
The second lens 2 is made of a glass material, and as shown in FIG. 1, a biconvex lens having positive refractive power in which the object-side surface S5 is a convex surface and the image-side surface S6 is a convex surface. And is joined to the first lens 1. The object-side surface S5 and the image-side surface S6 are both spherical.
According to this, the first lens 1 is formed of a glass material having a large dispersion (small Abbe number), the second lens 2 is formed of a glass material having a small dispersion (large Abbe number), By joining the second lens 2, chromatic aberration (vertical chromatic aberration, lateral chromatic aberration) can be favorably corrected.

<Second lens group II>
The third lens 3 is made of a glass material, and as shown in FIG. 1, a biconvex lens having a positive refractive power in which the object-side surface S7 is a convex surface and the image-side surface S8 is a convex surface. It is. Note that both the object-side surface S7 and the image-side surface S8 are spherical.
As shown in FIG. 1, the fourth lens 4 is a meniscus lens having a negative refractive power in which the object-side surface S8 is a concave surface and the image-side surface S9 is a convex surface. Yes, it is cemented to the third lens 3. The object-side surface S8 and the image-side surface S9 are both formed into spherical surfaces.
According to this, the third lens 3 is formed of a glass material having a small dispersion (large Abbe number), the fourth lens 4 is formed of a glass material having a large dispersion (small Abbe number), By joining the fourth lens 4, chromatic aberration (vertical chromatic aberration, lateral chromatic aberration) can be favorably corrected.

Here, the first lens 1 and the fourth lens 4 are made of the same glass material and in the same shape, and the second lens 2 and the third lens 3 are made of the same glass material and It is formed in the same shape.
That is, the first lens group (I) composed of the first lens 1 and the second lens 2 and the second lens group (II) composed of the third lens 3 and the fourth lens 4 are inverted in the optical axis direction L. It is an arranged form.
According to this, it is possible to reduce costs by using the same lens while satisfactorily correcting various aberrations such as coma and chromatic aberration (vertical chromatic aberration, lateral chromatic aberration).

  Example 1 based on specific numerical values of the imaging lens having the above-described configuration is shown below. The main specification specifications and various numerical data (setting values) in the first embodiment are as follows.

<Specification specifications>
Working wavelength 1 (main wavelength) = 587.6 nm
Working wavelength 2 = 486.1 nm
Use wavelength 3 = 656.3nm
Focal length = 13.9mm
F value (FNo.) = 4.6
Maximum image height = 4.0mm
Angle of view (2ω) = 34 °
Diameter of the first aperture stop SD1 = 4.4 mm
Diameter of the second aperture stop SD2 = 3.0 mm
Aperture size of the third aperture stop SD3 = 3.4 mm
External diameter of first lens 1 = 9.0 mm
External diameter of second lens 2 = 9.0 mm
External diameter of third lens 3 = 9.0 mm
The outer diameter of the fourth lens 4 = 9.0 mm

<Curvature radius>
R1 = ∞ (first aperture stop SD1), R2 = ∞ (second aperture stop SD2), R3 = ∞ (third aperture stop SD3), R4 = 39.56 mm, R5 = 12.01 mm, R6 = −15. 36 mm, R7 = 15.36 mm, R8 = -12.01 mm, R9 = −39.56 mm

<Surface spacing on the optical axis>
D1 = 3.50 mm, D2 = 3.00 mm, D3 = 2.20 mm, D4 = 1.30, D5 = 3.89, D6 = 0.10 mm, D7 = 3.89 mm, D8 = 1.30 mm, D9 = 10.26 mm

<Refractive index (Nd)>
N1 = 1.673, N2 = 1.517, N3 = 1.517, N4 = 1.673
<Abbe number (νd)>
ν1 = 32.2, ν2 = 64.2, ν3 = 64.2, ν4 = 32.2

In Example 1, the longitudinal chromatic aberration and the lateral chromatic aberration are as follows.
<Vertical chromatic aberration>
-0.422 μm (wavelength 486.1 nm)
+0.454 μm (wavelength 656.3 nm)
<Horizontal chromatic aberration>
-0.241 μm (wavelength 486.1 nm)
+0.202 μm (wavelength 656.3 nm)
In addition, spherical aberration, astigmatism, and distortion are the results shown in FIG. In FIG. 3, S represents the aberration on the sagittal plane, and M represents the aberration on the meridional plane.
Further, the coma aberration results as shown in FIG. As a comparative example, FIG. 5 shows coma aberration in a specification in which the first aperture stop SD1 and the third aperture stop SD3 are omitted.

  According to the imaging lens of Example 1, not only spherical aberration, astigmatism, and distortion, but also chromatic aberration (vertical chromatic aberration, lateral chromatic aberration) and coma are good when the field angle (2ω) is 30 ° or more. Thus, an imaging lens suitable for a mobile camera, a digital camera, or the like that can improve the image quality around the screen is obtained.

  6 and 7 show another embodiment of the imaging lens according to the present invention. Since the configuration is the same as that of the above-described embodiment, the same reference numerals are given and description thereof is omitted.

  Example 2 based on specific numerical values of the imaging lens shown in FIGS. 6 and 7 is shown below. The main specification specifications and various numerical data (setting values) in the second embodiment are as follows.

<Specification specifications>
Working wavelength 1 (main wavelength) = 587.6 nm
Working wavelength 2 = 486.1 nm
Use wavelength 3 = 656.3nm
Focal length = 6.36mm
F value (FNo.) = 4.2
Maximum image height = 2.25mm
Angle of view (2ω) = 42 °
Aperture size of the first aperture stop SD1 = 2.4 mm
Diameter of the second aperture stop SD2 = 1.5 mm
Aperture size of the third aperture stop SD3 = 1.8 mm
External diameter of first lens 1 = 6.25 mm
Outer diameter of second lens 2 = 6.25 mm
External diameter of third lens 3 = 6.25 mm
The outer diameter of the fourth lens 4 = 6.25 mm

<Curvature radius>
R1 = ∞ (first aperture stop SD1), R2 = ∞ (second aperture stop SD2), R3 = ∞ (third aperture stop SD3), R4 = 51.17 mm, R5 = 5.29 mm, R6 = −8. 63 mm, R7 = 8.63 mm, R8 = −5.29 mm, R9 = −51.17 mm

<Surface spacing on the optical axis>
D1 = 1.75 mm, D2 = 1.30 mm, D3 = 0.30 mm, D4 = 0.80, D5 = 3.00, D6 = 0.10 mm, D7 = 3.00 mm, D8 = 0.80 mm, D9 = 3.95mm

<Refractive index (Nd)>
N1 = 1.728, N2 = 1.670, N3 = 1.670, N4 = 1.728
<Abbe number (νd)>
ν1 = 28.3, ν2 = 47.2, ν3 = 47.2, ν4 = 28.3

In Example 2, the longitudinal chromatic aberration and the lateral chromatic aberration are as follows.
<Vertical chromatic aberration>
-0.371 μm (wavelength 486.1 nm)
+0.716 μm (wavelength 656.3 nm)
<Horizontal chromatic aberration>
-0.821 μm (wavelength 486.1 nm)
+0.428 μm (wavelength 656.3 nm)
Further, spherical aberration, astigmatism, and distortion are the results shown in FIG. In FIG. 8, S represents the aberration on the sagittal plane, and M represents the aberration on the meridional plane.
Further, the coma aberration results as shown in FIG. As a comparative example, FIG. 10 shows coma aberration in a specification in which the first aperture stop SD1 and the third aperture stop SD3 are omitted.

  According to the imaging lens of Example 2, not only spherical aberration, astigmatism and distortion, but also chromatic aberration (vertical chromatic aberration, lateral chromatic aberration) and coma are good when the angle of view (2ω) is 30 ° or more. Thus, an imaging lens suitable for a mobile camera, a digital camera, or the like that can improve the image quality around the screen is obtained.

11 and 12 show still another embodiment of the imaging lens according to the present invention. FIG. 11 is a lens configuration diagram, and FIG. 12 is an optical path diagram.
In this embodiment, since the second lens group (II) is composed of only the third lens 3 (that is, the fourth lens 4 is omitted), the configuration is the same as that of the above-described embodiment. A description thereof will be omitted.
Here, the third lens 3 is formed such that the curvature radius R7 of the object-side surface S7 and the curvature radius R8 of the image-side surface S8 are R7 = −R8.
According to this, since the 3rd lens 3 makes symmetrical shape without front and back, manufacturing cost can be reduced, and since there is no front and back, incorrect assembly can be prevented.

  Example 3 based on specific numerical values of the imaging lens shown in FIGS. 11 and 12 is shown below. The main specification specifications and various numerical data (setting values) in Example 3 are as follows.

<Specification specifications>
Working wavelength 1 (main wavelength) = 587.6 nm
Working wavelength 2 = 486.1 nm
Use wavelength 3 = 656.3nm
Focal length = 14.0mm
F value (FNo.) = 4.6
Maximum image height = 4.0mm
Angle of view (2ω) = 33 °
Diameter of the first aperture stop SD1 = 4.8 mm
Diameter of the second aperture stop SD2 = 3.0 mm
Aperture size of the third aperture stop SD3 = 3.6 mm
External diameter of first lens 1 = 9.00 mm
External diameter of second lens 2 = 9.00 mm
External diameter of third lens 3 = 9.00 mm
The outer diameter of the fourth lens 4 = 9.00 mm

<Curvature radius>
R1 = ∞ (first aperture stop SD1), R2 = ∞ (second aperture stop SD2), R3 = ∞ (third aperture stop SD3), R4 = 39.56 mm, R5 = 12.01 mm, R6 = −15. 36 mm, R7 = 37.45 mm, R8 = −37.45 mm

<Surface spacing on the optical axis>
D1 = 3.50 mm, D2 = 3.50 mm, D3 = 1.73 mm, D4 = 1.30, D5 = 3.89, D6 = 037 mm, D7 = 3.89 mm, D8 = 11.80 mm

<Refractive index (Nd)>
N1 = 1.847, N2 = 1.658, N3 = 1.497
<Abbe number (νd)>
ν1 = 23.8, ν2 = 50.9, ν3 = 81.6

In Example 3, the longitudinal chromatic aberration and the lateral chromatic aberration are as follows.
<Vertical chromatic aberration>
-0.511 μm (wavelength 486.1 nm)
+0.825 μm (wavelength 656.3 nm)
<Horizontal chromatic aberration>
-0.550μm (wavelength 486.1nm)
+0.315 μm (wavelength 656.3 nm)
In addition, spherical aberration, astigmatism, and distortion are the results shown in FIG. In FIG. 13, S represents the aberration on the sagittal plane, and M represents the aberration on the meridional plane.
Further, the coma aberration results as shown in FIG. FIG. 15 shows coma aberration in a specification in which the first aperture stop SD1 and the third aperture stop SD3 are omitted as a comparative example.

  According to the imaging lens of Example 3, not only spherical aberration, astigmatism, and distortion, but also chromatic aberration (vertical chromatic aberration, lateral chromatic aberration) and coma are good when the angle of view (2ω) is 30 ° or more. Thus, an imaging lens suitable for a mobile camera, a digital camera, or the like that can improve the image quality around the screen is obtained.

  As described above, the imaging lens of the present invention has not only spherical aberration, astigmatism and distortion aberration but also chromatic aberration (vertical chromatic aberration, lateral direction) while achieving cost reduction with a simple lens configuration. Chromatic aberration) and coma can be corrected satisfactorily, so that it can be applied to mobile cameras, digital cameras, and the like, and is useful not only for information terminals but also for imaging lenses for other digital cameras.

It is a lens block diagram which shows one Embodiment of the imaging lens which concerns on this invention. FIG. 2 is an optical path diagram of the imaging lens shown in FIG. 1. FIG. 3 is an aberration diagram showing spherical aberration, astigmatism, and distortion in the example of the imaging lens shown in FIG. 1. FIG. 2 is an aberration diagram illustrating coma aberration related to the embodiment of the imaging lens illustrated in FIG. 1. It is an aberration diagram which shows the coma aberration regarding the comparative example of the imaging lens which employ | adopted one aperture stop. It is a lens block diagram which shows other embodiment of the imaging lens which concerns on this invention. FIG. 7 is an optical path diagram of the imaging lens shown in FIG. 6. FIG. 7 is an aberration diagram showing spherical aberration, astigmatism, and distortion in the example of the imaging lens shown in FIG. 6. FIG. 7 is an aberration diagram illustrating coma aberration related to the example of the imaging lens illustrated in FIG. 6. It is an aberration diagram which shows the coma aberration regarding the comparative example of the imaging lens which employ | adopted one aperture stop. It is a lens block diagram which shows other embodiment of the imaging lens which concerns on this invention. FIG. 12 is an optical path diagram of the imaging lens illustrated in FIG. 11. FIG. 12 is an aberration diagram showing spherical aberration, astigmatism, and distortion in the example of the imaging lens shown in FIG. 11. FIG. 12 is an aberration diagram illustrating coma aberration related to the example of the imaging lens illustrated in FIG. 11. It is an aberration diagram which shows the coma aberration regarding the comparative example of the imaging lens which employ | adopted one aperture stop.

Explanation of symbols

L Optical axis P Image surface SD1 First aperture stop SD2 Second aperture stop SD3 Third aperture stop I First lens group 1 First lens 2 Second lens II Second lens group 3 Third lens 4 Fourth lens

Claims (5)

Arranged in order from the object side to the image plane side,
A first aperture stop having a predetermined aperture;
A second aperture stop having a predetermined aperture;
A third aperture stop having a predetermined aperture;
A first lens group having a positive refractive power;
A second lens group having a positive refractive power;
An imaging lens comprising: The first lens group is arranged in order from the object side, and has a meniscus-shaped first lens having a negative refractive power with a convex surface facing the object side, and is joined to the first lens and has a positive refractive power. Comprising a biconvex second lens having
The second lens group includes a biconvex third lens having positive refractive power.
The imaging lens according to claim 1. The third lens is formed so that R7 = −R8, where R7 is the radius of curvature of the object side surface and R8 is the radius of curvature of the image side surface.
The imaging lens according to claim 2. The second lens group further includes a fourth lens having a negative refractive power which is cemented to the image plane side of the third lens and has a concave surface facing the object side.
The imaging lens according to claim 2. The first lens group and the second lens group are the same and are inverted in the optical axis direction.
The imaging lens according to claim 1, wherein:

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