JP2010008660A - Imaging optical system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging optical system which excels imaging performance and is compact. <P>SOLUTION: The imaging optical system includes, in order from an object side, an aperture stop S, a first lens L1, a second lens L2, a third lens L3 and a fourth lens L4. The first lens is a biconvex lens, the second lens is a negative lens having a strong concave surface on an image side, the third lens is a positive lens having a strong convex surface on the image side, and the fourth lens is a negative lens having a storing concave surface on the object side. The imaging optical system satisfies following conditional expressions (A), (2), (4), (9) and (6): (A) -0.9<(r2+r3)/(r2-r3)<-0.08; (2) 0.01<1/ν2-1/ν1<0.03; (4)-2<f/r6<-0.05; (9) 0.1<d7/f<0.4; and (6)-2<f/r9<1; provided that f means a focal length of an entire system; ν1 and ν2 mean Abbe numbers of the first lens and the second lens respectively; r2 and r3 mean radii of curvature on the object side and the image side of the first lens respectively; r6 means the radius of curvature on the object side of the third lens; r9 means the radius of curvature on the image side of the fourth lens; and d7 means a distance on an optical axis between the third lens and the fourth lens. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an imaging optical system.

In recent years, with the thinning of cellular phones, portable terminals, notebook personal computers, and the like, there has been a demand for camera modules in which the length of the optical system in the optical axis direction is thinned to the limit. In order to meet this demand, many single-focus optical systems composed of about two to three aspheric lenses have been proposed.
In recent years, there has been a demand for a camera module that can be mounted on a mobile phone or a mobile terminal with high definition due to technological advancement of imaging (small but high pixel) and increasing market needs. As an optical system for improving the imaging performance and shortening the total length of the optical system, an optical system having four lenses has been proposed (Patent Document 1, Patent Document 2, and Patent Document 3).

Patent No. 4032667 Patent No.4032668 U.S. Pat. No. 7,079,330

  However, in Patent Documents 1 and 2, the curvature of field and the lateral chromatic aberration are not sufficiently corrected, and the imaging performance is not sufficient. In the optical system of Patent Document 3, a low-cost lens using a resin has been proposed. However, the astigmatic difference and the curvature of field are not sufficiently corrected, and the imaging performance is not sufficient. Furthermore, these tendencies become even more pronounced when trying to reduce these optical total lengths.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a compact imaging optical system having good imaging performance.

In order to achieve the above object, an imaging optical system according to the present invention includes, in order from the object side, an aperture stop, a first lens, a second lens, a third lens, and a fourth lens, and the first lens is a biconvex lens, The second lens is a negative lens having a strong concave surface on the image side, the third lens is a positive lens having a strong convex surface on the image side, and the fourth lens is a negative lens having a strong concave surface on the object side. It is characterized by satisfying (A), (2), (4), (9), (6).
-0.9 <(r2 + r3) / (r2-r3) <-0.08 (A)
0.01 <1 / ν2-1 / ν1 <0.03 (2)
-2 <f / r6 <-0.05 (4)
-2 <f / r9 <1 (6)
0.1 <d7 / f <0.4 (9)
Where f is the focal length of the entire system, r2 and r3 are the curvature radii of the object side and the image side of the first lens, ν1 and ν2 are the Abbe numbers of the first lens and the second lens, and r6 is the aforementioned Third
The radius of curvature on the object side of the lens, r9 is the radius of curvature on the image side of the fourth lens, and d7 is the air space on the optical axis of the third lens and the fourth lens.

In the imaging optical system of the present invention, the fourth lens has a negative convex surface at which the image side surface always has a convex shape on the image surface, and the object side surface satisfies the following conditional expression (7): It is a meniscus lens.
-4 <Y / Δda <-1 (7)
Where Y is the distance from the inflection point to the optical axis of the imaging optical system, Δda is the distance from the point P1 to P2, and P1 is the point where the side surface of the fourth lens object and the optical axis intersect, P2 is a point where an imaginary line passing through the inflection point and perpendicular to the optical axis intersects the optical axis.

The imaging optical system of the present invention is characterized in that the following conditional expression (1) is satisfied.
0.3 <f1 / f <1 (1)
Here, f1 is the focal length of the first lens.

The imaging optical system of the present invention is characterized in that the following conditional expression (3) is satisfied.
-1 <f / r4 <2 (3)
Here, r4 is the radius of curvature of the object side surface of the second lens.

The imaging optical system of the present invention is characterized in that the following conditional expression (5) is satisfied.
-0.4 <(r7-r8) / (r7 + r8) <0.4 (5)
Here, r7 and r8 are the radii of curvature of the image side of the third lens and the object side of the fourth lens, respectively.

The imaging optical system of the present invention is characterized in that the following conditional expression (8) is satisfied.
0.1 <d5 / f <0.3 (8)
Here, d5 is an air space on the optical axis of the second lens and the third lens.

  According to the present invention, it is possible to realize a small imaging optical system with good imaging performance.

Hereinafter, embodiments will be described. The imaging optical system of the present embodiment includes an aperture stop, a first lens, a second lens, a third lens, and a fourth lens in order from the object side. Here, the first lens is a biconvex lens. The second lens is a negative lens having a strong concave surface on the image side. The third lens is a positive lens having a strong convex surface on the image side. The fourth lens is a negative lens having a strong concave surface on the object side. In such a lens configuration, the following conditional expressions (A), (2), (4), (9), and (6) are satisfied.
-0.9 <(r2 + r3) / (r2-r3) <-0.08 (A)
0.01 <1 / ν2-1 / ν1 <0.03 (2)
-2 <f / r6 <-0.05 (4)
-2 <f / r9 <1 (6)
0.1 <d7 / f <0.4 (9)
Where f is the focal length of the entire system, r2 and r3 are the object-side and image-side radii of curvature of the first lens, r6 is the object-side radius of curvature of the third lens, and ν1 and ν2 are the first lens and the first lens, respectively. The Abbe number of the two lenses, r9 is the radius of curvature on the image side of the fourth lens, and d7 is the air space on the optical axis of the third lens and the fourth lens.

First, the lens configuration will be described. In this embodiment, the imaging optical system is arranged in order from the object side, aperture stop, first lens L1 (positive lens), second lens L2 (negative lens), third lens L3 (positive lens), and fourth lens L4 (negative). Lens). With this configuration, the on-axis light beam and the off-axis light beam are separated as the incident light beam moves from the first lens L1 to the fourth lens L4.

In the present embodiment, the first lens L1 mainly bears the power of the entire optical system. The first lens L1 particularly corrects axial aberrations. In addition, when the second lens L2 is a negative lens having a strong concave surface on the image side, particularly axial chromatic aberration can be corrected well. The third lens L3 is a positive lens having a strong convex surface on the image side. Accordingly, the shape of the second lens L2 and the shape of the third lens L3 are substantially targeted. In this way, coma is corrected well. Further, by arranging a strong concave surface on the image side in the fourth lens L4, distortion aberration and curvature of field are favorably corrected.

Next, conditional expressions will be described. Below the lower limit of conditional expression (A), the power of the image side surface (r3) of the first lens L1 becomes too weak. In this case, the first aberration is corrected while favorably correcting the axial aberration.
It becomes difficult to secure the power of the lens L1. If the upper limit of conditional expression (A) is exceeded, the power of the object side surface (r2) of the first lens L1 will become weak and it will be difficult to correct axial aberrations.

If the lower limit of conditional expression (2) is not reached, chromatic aberration cannot be corrected sufficiently. If the upper limit of conditional expression (2) is exceeded, it will be difficult to secure the power of the second lens L2 while satisfactorily correcting chromatic aberration. Therefore, it is not preferable in correcting other aberrations.

If the lower limit of conditional expression (4) is not reached, the power of the object side surface (r6) of the third lens L3 becomes too strong, and the influence on the on-axis aberration becomes large. Exceeding the upper limit of conditional expression (4) is not particularly preferable for correcting coma.

If the lower limit of conditional expression (6) is not reached, correction of astigmatism becomes difficult, which is not preferable. Exceeding the upper limit of the distortion conditional expression (6) is not preferable because it has an influence on aberration correction of curvature aberration and field curvature.

If the lower limit of conditional expression (9) is not reached, the difference in off-axis light beam separation between the second lens L2 and the third lens L3 becomes small. In this case, it is difficult to correct coma aberration, higher-order field curvature, and distortion, which is not preferable. If the upper limit of conditional expression (9) is exceeded, the power of the first lens L1 must be reduced in order to ensure the spread of the off-axis light beam incident on the third lens L3. in this case,
Since the total length becomes long, it is not preferable.

It is preferable that the following conditional expression (A) ′ is satisfied instead of conditional expression (A).
-0.7 <(r2 + r3) / (r2-r3) <-0.1 (A) '

Further, it is preferable that the following conditional expression (2) ′ is satisfied instead of conditional expression (2).
0.012 <1 / ν2-1 / ν1 <0.025… (2) '

Further, it is preferable that the following conditional expression (4) ′ is satisfied instead of conditional expression (4).
-2 <f / r6 <-0.1 (4) '

Further, it is preferable that the following conditional expression (9) ′ is satisfied instead of conditional expression (9).
0.2 <d7 / f <0.3 (9) '

Further, it is preferable that the following conditional expression (6) ′ is satisfied instead of conditional expression (6).
-2 <f / r9 <0.8 (6) '

Further, the imaging optical system of the present embodiment is a negative meniscus lens having an inflection point such that the image side surface of the fourth lens always has a convex shape on the image surface and the object side surface satisfies the following conditional expression. It is characterized by being.
-4 <Y / Δda <-1 (7)
Where Y is the distance from the inflection point to the optical axis of the imaging optical system, Δda is the distance from point P1 to P2, P1 is the point where the fourth lens object side surface and the optical axis intersect, and P2 passes A virtual line perpendicular to the optical axis is a point where the optical axis intersects (refer to FIG. 1 for inflection points, Y, Δda, P1, and P2)
.

It is preferable that the image side surface of the fourth lens L4 always has a convex shape on the image surface, and the object side surface is a negative meniscus lens having an inflection point that satisfies the conditional expression (7). By doing so, the fourth lens L4 has a shape close to concentric, and astigmatism and coma can be corrected well. In addition, since the object side surface has a positive power outside the axis, the curvature of field can be corrected well.

If the lower limit of conditional expression (7) is not reached, the incident angle to the lens becomes large, which is not preferable in terms of correcting astigmatism and coma aberration. Exceeding the upper limit of conditional expression (7) is not preferable because the astigmatic difference cannot be sufficiently corrected and manufacturing becomes difficult.

Further, it is preferable that the following conditional expression (7) ′ is satisfied instead of conditional expression (7).
-3 <Y / Δda <-1 (7) '

Further, the imaging optical system of the present embodiment is characterized in that the following conditional expression (1) is satisfied.
0.3 <f1 / f <1 (1)
Here, f1 is the focal length of the first lens.

Conditional expression (1) is closely related to conditional expression (A). If the lower limit of conditional expression (1) is not reached, the power of the first lens L1 becomes too strong. In this case, it is difficult to secure a space for correcting off-axis aberrations. In order to satisfactorily correct various off-axis aberrations, it is desirable that the lens working surfaces be arranged at an appropriate interval. However, if the lower limit of conditional expression (1) is not reached, it is difficult to secure the space. When the upper limit of conditional expression (1) is exceeded, the power of the second lens L2 becomes weak. In this case, since the telephoto effect is reduced, it is difficult to shorten the overall length while improving the imaging performance.

It is preferable that the following conditional expression (1) ′ is satisfied instead of conditional expression (1).
0.4 <f1 / f <0.8 (1) '

The imaging optical system of the present embodiment is characterized in that the following conditional expression (3) is satisfied.
-0.1 <f / r4 <2 (3)
Where r4 is the radius of curvature of the object side surface of the second lens.

If the lower limit of conditional expression (3) is not reached, correction of high-order spherical aberration is particularly difficult, which is not preferable. If the upper limit of conditional expression (3) is exceeded, it is difficult to secure the power of the second lens L2, which is not preferable, such as correction of longitudinal chromatic aberration.

It is preferable that the following conditional expression (3) ′ is satisfied instead of conditional expression (3).
-0.05 <f / r4 <1 (3) '

Further, the imaging optical system of the present embodiment is characterized in that the following conditional expression (5) is satisfied.
-0.4 <(r7-r8) / (r7 + r8) <0.4 (5)
Here, r7 and r8 are the radii of curvature of the image side of the third lens and the object side of the fourth lens, respectively.

In the lens configuration described above, an air lens exists between the third lens L3 and the fourth lens L4. If the lower limit of conditional expression (5) is not reached, the power of the air lens becomes strong, so that the overall power arrangement is not suitable for miniaturization. If the upper limit of conditional expression (5) is exceeded, the power of the air lens becomes weak, which is not preferable for correcting curvature of field and distortion.

Note that it is preferable to satisfy the following conditional expression (5) ′ instead of conditional expression (5).
-0.3 <(r7-r8) / (r7 + r8) <0.05 (5) '

The imaging optical system of the present embodiment is characterized by satisfying the following conditional expression (8).
0.1 <d5 / f <0.3 (8)
However, d5 is the air space on the optical axis of the second lens and the third lens.

If the lower limit of conditional expression (8) is surpassed, the difference in separation of off-axis light beams between the second lens L2 and the third lens L3 becomes small. In this case, it is difficult to correct coma aberration, higher-order field curvature, and distortion, which is not preferable. If the upper limit of conditional expression (8) is exceeded, the power of the first lens L1 must be reduced in order to ensure the spread of the off-axis light beam incident on the third lens L3. in this case,
Since the total length becomes long, it is not preferable.

It is preferable that the following conditional expression (8) ′ is satisfied instead of conditional expression (8).
-0.12 <d5 / f <0.28 (8) '

An imaging optical system according to Example 1 will be described. FIG. 1 is a cross-sectional view along the optical axis showing the optical configuration of the imaging optical system according to the first embodiment of the present invention when focusing on an object point at infinity. The numbers in r1, r2,... And the numbers in d1, d2,... Described in the lens cross-sectional views correspond to the numbers in the surface number column in the numerical data described later.

FIG. 2 shows spherical aberration (SA) at the time of focusing on an object point at infinity of the imaging optical system according to the first example.
It is a figure which shows astigmatism (AS), distortion aberration (DT), lateral chromatic aberration (CC), and longitudinal coma aberration (DZY) at 80% of image height. FIY represents the image height. In addition, the numerical value of the horizontal axis in spherical aberration, astigmatism and vertical coma aberration is ± 0.10, the numerical value of the horizontal axis in distortion aberration is ± 5.0, and the numerical value of the horizontal axis in lateral chromatic aberration is ± 0.01. The numerical value on the vertical axis in the longitudinal coma aberration is ± 1.00. The image height in the longitudinal coma aberration is 2.34. The symbols and numerical values in the aberration diagrams are the same in the examples described later.

  As shown in FIG. 1, the imaging optical system of Embodiment 1 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. is doing. In all the following examples, in the lens cross-sectional views, CG represents a cover glass, and P represents an image pickup surface of an electronic image pickup element.

  The first lens L1 is composed of a biconvex lens.

The second lens L2 is composed of a biconcave lens L2. Further, the lens surface on the image side is a strong concave surface.

The third lens L3 is a positive meniscus lens having a convex surface facing the image side. Also,
The lens surface on the image side is a strong convex surface.

The fourth lens L4 is a biconcave lens. Further, the object side surface is a strong concave surface.

  An aspheric surface is used for all lens surfaces.

An imaging optical system according to Example 2 will be described. FIG. 3 is a cross-sectional view along the optical axis showing the optical configuration of the imaging optical system according to the second embodiment of the present invention when focusing on an object point at infinity.

    4 shows spherical aberration (SA), astigmatism (AS), distortion (DT), chromatic aberration of magnification (CC), and 80% of image height when the imaging optical system according to the example 2 is focused on an object point at infinity. It is a figure which shows the longitudinal coma aberration (DZY) in FIG.

As shown in FIG. 3, the imaging optical system of Example 2 includes an aperture stop S and a first aperture in order from the object side.
The lens L1, the second lens L2, the third lens L3, and the fourth lens L4 are provided.

  The first lens L1 is composed of a biconvex lens.

The second lens L2 is composed of a biconcave lens L2. Further, the lens surface on the image side is a strong concave surface.

The third lens L3 is a positive meniscus lens having a convex surface facing the image side. Also,
The lens surface on the image side is a strong convex surface.

The fourth lens L4 is a biconcave lens. Further, the object side surface is a strong concave surface.

  An aspheric surface is used for all lens surfaces.

  An imaging optical system according to Example 3 will be described. FIG. 5 is a cross-sectional view along the optical axis showing the optical configuration of the imaging optical system according to the third embodiment of the present invention when focusing on an object point at infinity.

  FIG. 6 shows spherical aberration (SA), astigmatism (AS), distortion (DT), lateral chromatic aberration (CC), and 80% of the image height when the imaging optical system according to the example 3 is focused on an object point at infinity. It is a figure which shows the longitudinal coma aberration in (DZY).

  As shown in FIG. 5, the imaging optical system of Example 3 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. is doing.

  The first lens L1 is composed of a biconvex lens.

The second lens L2 is composed of a biconcave lens L2. Further, the lens surface on the image side is a strong concave surface.

The third lens L3 is a positive meniscus lens having a convex surface facing the image side. Also,
The lens surface on the image side is a strong convex surface.

  The fourth lens L4 is a negative meniscus lens having a concave surface directed toward the object side.

  An aspheric surface is used for all lens surfaces.

  FIG. 8 shows spherical aberration (SA), astigmatism (AS), distortion (DT), lateral chromatic aberration (CC), and 80% of the image height when the imaging optical system according to the example 4 is focused on an object point at infinity. It is a figure which shows the longitudinal coma aberration in (DZY).

  As shown in FIG. 7, the imaging optical system of Example 4 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. is doing.

  The first lens L1 is composed of a biconvex lens.

The second lens L2 is composed of a biconcave lens L2. Further, the lens surface on the image side is a strong concave surface.

The third lens L3 is a positive meniscus lens having a convex surface facing the image side. Also,
The lens surface on the image side is a strong convex surface.

  The fourth lens L4 is a negative meniscus lens having a concave surface directed toward the object side.

  An aspheric surface is used for all lens surfaces.

  FIG. 10 shows spherical aberration (SA), astigmatism (AS), distortion (DT), lateral chromatic aberration (CC), and 80% of the image height when the imaging optical system according to the example 5 is focused on an object point at infinity. It is a figure which shows the longitudinal coma aberration (DZY) in FIG.

  As shown in FIG. 9, the imaging optical system of Example 5 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. is doing.

  The first lens L1 is composed of a biconvex lens.

The second lens L2 is composed of a negative meniscus lens L2 having a concave surface facing the image side. Further, the lens surface on the image side is a strong concave surface.

The third lens L3 is a positive meniscus lens having a convex surface facing the image side. Also,
The lens surface on the image side is a strong convex surface.

  The fourth lens L4 is a negative meniscus lens having a concave surface facing the object side.

  An aspheric surface is used for all lens surfaces.

  Next, numerical data of optical members constituting the imaging optical system of each of the above embodiments will be listed. In the numerical data of each example, the r column represents the radius of curvature of each lens surface, the d column represents the thickness or air spacing of each lens, the nd column represents the refractive index of each lens at the d-line, and νd The column represents the Abbe number of each lens.

The aspherical shape is expressed by the following equation when the optical axis direction is z, the direction orthogonal to the optical axis is y, the conical coefficient is K, and the aspherical coefficients are A4, A6, A8, and A10. .
z = (y ² / r) / [1+ {1− (1 + K) (y / r) ² } ^1/2 ]
+ A4y ⁴ + A6y ⁶ + A8y ⁸ + A10y ¹⁰
Here, in the aspheric data, E represents a power of 10. In addition, when the aspheric coefficient is not described, the value of the aspheric coefficient is zero.

  The symbols of these specification values are common to the numerical data of the examples described later.

Numerical example 1
Unit mm

Surface data surface number r d nd νd Effective radius
1 (Aperture) ∞ 0.00 0.76
2 (Aspherical surface) 1.800 1.02 1.54300 55.98 0.81
3 (Aspherical surface) -3.017 0.05 0.82
4 (Aspherical surface) -5.871 0.33 1.58300 30.01 0.81
5 (Aspherical) 2.373 0.49 0.89
6 (Aspherical surface) -2.949 0.46 1.58300 30.01 1.00
7 (Aspherical surface) -1.655 1.18 1.22
8 (Aspherical surface) -2.862 0.50 1.54300 55.98 2.10
9 (Aspherical surface) 9.878 0.28 2.40
10 ∞ 0.30 1.51633 64.14
11 ∞ 0.30
Image plane ∞

Aspheric data 2nd surface
K = -0.928, A4 = 7.00000E-03, A6 = -3.50000E-03, A8 = -1.00000E-04, A10 = -3.00000E-03
Third side
K = -3.000, A4 = 4.00000E-02, A6 = 3.00000E-03, A8 = -5.00000E-04, A10 = -1.00000E-03
4th page
K = 1.475, A4 = 2.00000E-02, A6 = 4.81500E-02, A8 = 1.00000E-02, A10 = -4.05300E-04
5th page
K = 2.915, A4 = -3.21200E-02, A6 = -3.45200E-03, A8 = 1.87700E-02, A10 = 2.35000E-03
6th page
K = 5.000, A4 = 5.23300E-02, A6 = -1.00000E-02, A8 = 1.00000E-03, A10 = -9.89300E-03
7th page
K = -0.940, A4 = 4.39400E-02, A6 = 1.00000E-03, A8 = 5.00000E-04, A10 = 2.00000E-04
8th page
K = 0.393, A4 = 1.43100E-02, A6 = -3.04200E-03, A8 = 8.85000E-04, A10 = -9.02900E-07
9th page
K = -10.000, A4 = -3.37400E-02, A6 = 3.07400E-03, A8 = -4.93700E-04, A10 = 2.79500E-06

Various data Focal length 4.43
F number 2.9
Angle of view 65.6 °
Entrance pupil position 0
Exit pupil position -2.50
Front principal point position -2.28
Rear principal point position -4.14

Single lens data Lens Start surface Focal length
1 2 2.234
2 4 -2.834
3 6 5.672
4 8 -4.013

Numerical example 2
Unit mm

Surface data surface number r d nd νd Effective radius
1 (Aperture) ∞ 0.00 0.77
2 (Aspherical surface) 1.800 0.98 1.54300 55.98 0.81
3 (Aspherical surface) -3.000 0.05 0.80
4 (Aspherical surface) -5.184 0.33 1.58300 30.01 0.79
5 (Aspherical) 2.392 0.55 0.88
6 (Aspherical surface) -4.536 0.48 1.58300 30.01 1.08
7 (Aspherical surface) -1.952 1.20 1.29
8 (Aspherical surface) -2.767 0.46 1.54300 55.98 2.05
9 (Aspherical) 10.630 0.15 2.37
10 ∞ 0.30 1.51633 64.14
11 ∞ 0.40
Image plane ∞

Aspheric data 2nd surface
K = -0.901, A4 = 7.00000E-03, A6 = -3.50000E-03, A8 = -1.00000E-04, A10 = -3.00000E-03
Third side
K = -3.000, A4 = 4.00000E-02, A6 = -3.00000E-03, A8 = -5.00000E-04, A10 = -8.00000E-04
4th page
K = 1.193, A4 = 2.19800E-02, A6 = 3.78300E-02, A8 = 5.63800E-03, A10 = -5.00000E-04
5th page
K = 2.945, A4 = -3.46000E-02, A6 = 1.00000E-02, A8 = 1.00000E-02, A10 = 2.00000E-03
6th page
K = 5.000, A4 = 1.85700E-02, A6 = -7.00000E-03, A8 = -5.00000E-03, A10 = -4.14500E-03
7th page
K = -0.895, A4 = 3.47200E-02, A6 = 1.00000E-03, A8 = 5.00000E-04, A10 = 1.00000E-04
8th page
K = 0.353, A4 = 2.17300E-02, A6 = -1.13300E-03, A8 = 1.00000E-03, A10 = -1.13900E-05
9th page
K = 2.867, A4 = -3.41000E-02, A6 = 1.16100E-03, A8 = -8.10500E-06, A10 = -3.76300E-05

Various data Focal length 4.44
F number 2.9
Angle of view 65.7 °
Entrance pupil position 0
Exit pupil position -2.50
Front principal point position -2.35
Rear principal point position -4.03

Single lens data Lens Start surface Focal length
1 2 2.223
2 4 -2.741
3 6 5.456
4 8 -3.977

Numerical Example 3
Unit mm

Surface data surface number r d nd νd Effective radius
1 (Aperture) ∞ 0.00 0.79
2 (Aspherical surface) 1.760 0.89 1.54300 55.98 0.82
3 (Aspherical surface) -3.228 0.05 0.79
4 (Aspherical surface) -5.156 0.33 1.58300 30.01 0.77
5 (Aspherical) 2.663 0.59 0.84
6 (Aspherical surface) -3.094 0.44 1.58300 30.01 1.03
7 (Aspherical surface) -1.736 1.20 1.21
8 (Aspherical surface) -2.045 0.49 1.54300 55.98 1.92
9 (Aspherical surface) -60.000 0.24 2.29
10 ∞ 0.30 1.51633 64.14
11 ∞ 0.40
Image plane ∞

Aspheric data 2nd surface
K = -0.740, A4 = 1.00000E-03, A6 = -4.00000E-03, A8 = -3.00000E-03, A10 = -3.00000E-03
Third side
K = -0.189, A4 = 4.98000E-02, A6 = 5.87200E-03, A8 = -1.00700E-03, A10 = -1.00000E-03
4th page
K = 5.000, A4 = 5.73500E-02, A6 = 4.58400E-02, A8 = -1.00000E-02, A10 = 1.66000E-02
5th page
K = 5.000, A4 = -1.15300E-02, A6 = 5.00000E-03, A8 = 1.00000E-03, A10 = 1.00000E-03
6th page
K = 2.523, A4 = 2.82400E-02, A6 = 7.78900E-04, A8 = -1.00000E-02, A10 = 9.31300E-05
7th page
K = -0.996, A4 = 4.19200E-02, A6 = 8.00000E-03, A8 = 1.00000E-03, A10 = 1.00000E-04
8th page
K = -5.000, A4 = -8.70200E-03, A6 = -5.38600E-03, A8 = 1.58900E-03, A10 = -6.74800E-05
9th page
K = -15.000, A4 = -8.62900E-03, A6 = -4.74900E-03, A8 = 6.92400E-04, A10 = -6.66100E-05

Various data Focal length 4.64
F number 2.9
Angle of view 63.5 °
Entrance pupil position 0
Exit pupil position -2.63
Front principal point position -2.45
Rear principal point position -4.23

Single lens data Lens Start surface Focal length
1 2 2.229
2 4 -2.942
3 6 6.010
4 8 -3. 894

Numerical Example 4
Unit mm

Surface data surface number r d nd νd Effective radius
1 (Aperture) ∞ 0.00 0.79
2 (Aspherical) 1.600 1.88 1.54300 55.98 0.85
3 (Aspherical surface) -6.552 0.05 0.81
4 (Aspherical surface) -38.728 0.33 1.63493 23.90 0.80
5 (Aspherical) 2.515 0.72 0.84
6 (Aspherical surface) -2.628 0.56 1.58300 30.01 1.02
7 (Aspherical surface) -1.505 1.03 1.30
8 (Aspherical surface) -1.091 0.53 1.54300 55.98 2.01
9 (Aspherical surface) -2.684 0.20 2.34
10 ∞ 0.30 1.51633 64.14
11 ∞ 0.30
Image plane ∞

Aspheric data 2nd surface
K = -0.617, A4 = 9.00000E-03, A6 = -6.41512E-04, A8 = -5.00000E-04, A10 = -5.00000E-04
Third side
K = -3.147, A4 = 2.33204E-02, A6 = 1.00000E-02, A8 = 1.00000E-03, A10 = 9.94409E-04
4th page
K = 5.000, A4 = 3.76976E-02, A6 = 1.88823E-02, A8 = 1.60917E-02, A10 = 5.00000E-04
5th page
K = 4.798, A4 = 4.63203E-03, A6 = 1.01598E-04, A8 = 1.00000E-03, A10 = 5.00000E-04
6th page
K = 5.000, A4 = -2.50659E-02, A6 = 5.00000E-03, A8 = 3.72668E-05, A10 = -1.50000E-04
7th page
K = -2.315, A4 = -4.99932E-02, A6 = 5.00000E-03, A8 = 5.00000E-04, A10 = 1.00000E-04
8th page
K = -2.472, A4 = 4.50995E-02, A6 = -1.56525E-02, A8 = 2.31748E-03, A10 = -1.04691E-04
9th page
K = -8.082, A4 = 2.49381E-02, A6 = -1.16649E-02, A8 = 1.55737E-03, A10 = -1.27575E-04

Various data Focal length 4.60
F number 2.9
Angle of view 64.2 °
Entrance pupil position 0
Exit pupil position -3.00
Front principal point position -1.81
Rear principal point position -4.30

Single lens data Lens Start surface Focal length
1 2 2.451
2 4 -3.672
3 6 5.062
4 8 -3.819

Numerical Example 5
Unit mm

Surface data surface number r d nd νd Effective radius
1 (Aperture) ∞ 0.00 0.80
2 (Aspherical) 1.600 1.75 1.54454 55.91 0.81
3 (Aspherical surface) -7.500 0.05 0.74
4 (Aspherical surface) -9.823 0.33 1.63493 23.90 0.72
5 (Aspherical surface) 1.905 0.83 0.76
6 (Aspherical surface) -2.539 0.55 1.58393 30.21 1.01
7 (Aspherical surface) -1.498 1.02 1.28
8 (Aspherical surface) -1.251 0.57 1.54454 55.91 2.00
9 (Aspherical surface) -3.520 0.20 2.32
11 ∞ 0.30 1.51633 64.14
12 ∞ 0.30
Image plane ∞

Aspheric data 2nd surface
K = -0.704, A4 = 9.00000E-03, A6 = -1.00000E-03, A8 = -7.57500E-06, A10 = 2.00000E-04
Third side
K = 5.000, A4 = 4.50400E-02, A6 = 4.06900E-03, A8 = -1.00000E-03, A10 = -1.00000E-04
4th page
K = 5.000, A4 = 3.00000E-02, A6 = 4.00000E-02, A8 = 1.00000E-03, A10 = 5.00000E-04
5th page
K = 2.073, A4 = -3.07000E-02, A6 = 2.00000E-02, A8 = 3.18700E-04, A10 = -2.18200E-04
6th page
K = 4.580, A4 = -2.76000E-02, A6 = 4.79100E-03, A8 = 1.00000E-03, A10 = 2.00000E-04
7th page
K = -2.196, A4 = -5.00000E-02, A6 = 3.74400E-03, A8 = 5.00000E-04, A10 = 1.00000E-04
8th page
K = -2.417, A4 = 4.64600E-02, A6 = -1.73400E-02, A8 = 3.12300E-03, A10 = -2.01400E-04
9th page
K = -10.000, A4 = 1.37700E-02, A6 = -8.48400E-03, A8 = 9.57400E-04, A10 = -6.48800E-05

Various data Focal length 4.60
F number 2.9
Angle of view 62.8 °
Entrance pupil position 0
Exit pupil position -3.0095
Front principal point position -1.8594
Rear principal point position -3.9392

Single lens data Lens Start surface Focal length
1 2 2.47835
2 4 -3.72720
3 6 5.16771
4 8 -3.88669

Next, the values of the conditional expressions in each example are listed.
Conditional Example 1 Example 2 Example 3 Example 4 Example 5
(A) -0.25 -0.25 -0.29 -0.82 -0.65
(1) 0.50 0.50 0.48 0.53 0.53
(2) 0.02 0.02 0.02 0.02 0.02
(3) -0.76 -0.86 -0.90 -0.12 0.47
(4) -1.50 -0.98 -1.50 -1.75 -1.83
(5) -0.27 -0.17 -0.08 0.16 0.09
(6) 0.45 0.42 -0.08 -1.72 -1.32
(7) -3.59 -3.04 -2.90 -2.90 -2.85
(8) 0.11 0.12 0.13 0.16 0.18
(9) 0.27 0.27 0.26 0.22 0.22

  In each of the above embodiments, all lens elements are made of resin to achieve weight reduction and cost reduction. In addition, all lens surfaces are formed of aspherical surfaces to prevent image deterioration due to improved imaging performance and eccentricity. The shutter may be disposed in front of the aperture stop, or the shutter part may be fixed at the time of focusing.

  The present invention is useful for an imaging optical system of an electronic imaging apparatus such as a camera, a mobile phone, and a small information terminal.

It is sectional drawing which follows the optical axis which shows the optical structure of the imaging optical system concerning Example 1 of this invention. FIG. 6 is a diagram illustrating spherical aberration, astigmatism, distortion, lateral chromatic aberration, and longitudinal coma when the imaging optical system according to the example 1 is focused on an object point at infinity. It is sectional drawing which follows the optical axis which shows the optical structure of the imaging optical system concerning Example 2 of this invention. FIG. 6 is a diagram illustrating spherical aberration, astigmatism, distortion, lateral chromatic aberration, and longitudinal coma when the imaging optical system according to Example 2 is focused on an object point at infinity. It is sectional drawing which follows the optical axis which shows the optical structure of the imaging optical system concerning Example 3 of this invention. FIG. 10 is a diagram illustrating spherical aberration, astigmatism, distortion, lateral chromatic aberration, and longitudinal coma when the imaging optical system according to Example 3 is focused on an object point at infinity. It is sectional drawing which follows the optical axis which shows the optical structure of the imaging optical system concerning Example 4 of this invention. FIG. 10 is a diagram illustrating spherical aberration, astigmatism, distortion, lateral chromatic aberration, and longitudinal coma when the imaging optical system according to Example 4 is focused on an object point at infinity. It is sectional drawing which follows the optical axis which shows the optical structure of the imaging optical system concerning Example 5 of this invention. FIG. 10 is a diagram illustrating spherical aberration, astigmatism, distortion, lateral chromatic aberration, and longitudinal coma when the imaging optical system according to Example 5 is focused on an object point at infinity.

Explanation of symbols

CG ... cover glass P ... imaging surface of electronic imaging device L1 ... first lens L2 ... second lens L3 ... third lens L4 ... fourth lens S ... aperture stop

Claims (6)

From the object side,
An aperture stop,
A first lens;
A second lens;
A third lens;
A fourth lens,
The first lens is a biconvex lens;
The second lens is a negative lens having a strong concave surface on the image side,
The third lens is a positive lens having a strong convex surface on the image side,
The fourth lens is a negative lens;
An imaging optical system characterized by satisfying the following conditional expressions (A), (2), (4), (9), (6).
-0.9 <(r2 + r3) / (r2-r3) <-0.08 (A)
0.01 <1 / ν2-1 / ν1 <0.03 (2)
-2 <f / r6 <-0.05 (4)
-2 <f / r9 <1 (6)
0.1 <d7 / f <0.4 (9)
Where f is the focal length of the entire system,
r2 and r3 are the curvature radii of the object side and the image side of the first lens,
ν1 and ν2 are Abbe numbers of the first lens and the second lens,
r6 is the radius of curvature of the third lens on the object side,
r9 is the radius of curvature of the fourth lens on the image side,
d7 is an air space on the optical axis of the third lens and the fourth lens. The fourth lens is a negative meniscus lens having an inflection point such that the image side surface always has a convex shape on the image surface, and the object side surface satisfies the following conditional expression (7): The imaging optical system according to claim 1.
-4 <Y / Δda <-1 (7)
Where Y is the distance from the inflection point to the optical axis of the imaging optical system,
Δda is an interval from points P1 to P2, where P1 is a point where the fourth lens object side surface and the optical axis intersect, and P2 passes through an inflection point on the fourth lens object side surface and is perpendicular to the optical axis. A point where an imaginary line intersects the optical axis,
It is. The imaging optical system according to claim 1, wherein the following conditional expression (1) is satisfied.
0.3 <f1 / f <1 (1)
Here, f1 is the focal length of the first lens. The imaging optical system according to any one of claims 1 to 3, wherein the following conditional expression (3) is satisfied.
-1 <f / r4 <2 (3)
Here, r4 is the radius of curvature of the object side surface of the second lens. The imaging optical system according to any one of claims 1 to 4, wherein the following conditional expression (5) is satisfied.
-0.4 <(r7-r8) / (r7 + r8) <0.4 (5)
Here, r7 and r8 are the radii of curvature of the image side of the third lens and the object side of the fourth lens, respectively. The imaging optical system according to any one of claims 1 to 5, wherein the following conditional expression (8) is satisfied.
0.1 <d5 / f <0.3 (8)
Here, d5 is an air space on the optical axis of the second lens and the third lens.

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