JPH09258100A - Photographing lens system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a lens system, lens working of which is simple and inexpensive even when the image plane size is small, which is comparatively bright, and where aberration compensation is excellently performed, by constituting the system of four single lenses and making the radius of curvature of each lens large. SOLUTION: This photographing lens system is constituted of four single lenses such as a 1st lens 10 being biconvex, a 2nd lens 20 being biconcave whose strong concave surface is faced to an object side, a 3rd lens 30 being positive whose strong convex surface is faced to an image side, and a 4th lens 40 whose strong convex surface is faced to the object side in order from the object side. It is desirable that the shaping factor of the 4th lens 40 satisfies 0.4<(r8 +r7 )/(r8 -r7 )<1.0. Provided that r7 is the radius of curvature of the surface of the 4th lens on the object side, and r8 is the radius of curvature of the surface of the 4th lens on the image side. Thus, the photographing lens system whose half viewing angle is about 20 deg., which is bright with an aperture ratio such as about 1:20, where the aberration compensation is excellently performed, the lens work of which is made simple and inexpensive, and which is suitable for a camera utilizing a solid-state image pickup element is obtained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an ITV for photographing with a solid-state image sensor.
The present invention relates to a taking lens system suitable for cameras, video cameras, electronic still cameras and the like.

[0002]

2. Description of the Related Art In recent years, solid-state image pickup devices (CC
There is an increasing demand for so-called electronic still cameras and the like for recording photographed images in D). A taking lens system of a camera using such an electric image device is required to have the following characteristics as compared with a photographic lens using a film.

Since the electric image device generally has a smaller latitude than a film, the aperture efficiency is made to be almost 100% in order to obtain a sufficient amount of peripheral light. Even if the above conditions are satisfied, the amount of peripheral light and the color shift occur due to the structure of the electric image element, so that the chief ray is incident on the entire screen at an angle close to vertical. An optical low-pass filter for removing moire, an infrared cut filter for correcting the spectral sensitivity, or an arrangement space for optical members for protecting the image plane and dust protection is secured between the lens and the image plane. Need a long back focus.

For this purpose, Japanese Patent Laid-Open No. 49-5 has already been used.
3036, JP-A-57-164708,
A taking lens system such as Japanese Patent Publication No. 7-95141 has been proposed. However, the half angle of view is as narrow as 16.5 °,
Has a caliber ratio of about 1: 4.3 and is dark, and has a half angle of view of 19.
At 5 °, the aperture ratio is 1: 2.8, and in all, the minimum radius of curvature of the refracting surface is as small as about half the focal length or less, so it is difficult to process the lens as the screen size decreases. Therefore, there is a problem that the manufacturing cost becomes high.

[0005]

An object of the present invention is to use a solid-state image pickup device having a half angle of view of about 20 °, a bright aperture ratio of about 1: 2.0, good aberration correction, simple lens processing, and low cost. The objective is to obtain a taking lens system suitable for a camera. In particular, it is an object of the present invention to provide a taking lens system in which lens processing is easy even if the radius of curvature of each lens is relatively large and the screen size is small.

[0006]

SUMMARY OF THE INVENTION The image pickup lens system of the present invention has, in order from the object side, a biconvex first lens, a biconcave second lens with a strong concave surface facing the object side, and a strong convex surface facing the image side. It is characterized by being composed of four single lenses including a positive third lens and a fourth lens having a strong convex surface facing the object side.

In the taking lens system of the present invention, it is preferable that the shaping factor of the fourth lens satisfies the conditional expression (1). (1) 0.4 <(r ₈ + r ₇ ) / (r ₈ −r ₇ ) <1.0 where r _{7 is} the radius of curvature of the object side surface of the fourth lens, and r _{8 is} the image of the fourth lens. The radius of curvature of the side surface is.

Further, it is preferable that the sum of the powers of the surfaces of the second lens and the third lens facing each other satisfies the conditional expression (2). (2) −1.1 <φ _r4 + φ _r5 <−0.1 where φ _r4 : surface power of the image side surface of the second lens, φ _r5 : surface power of the object side surface of the third lens, is there.

It is preferable that the axial dimension from the image-side surface r _{2 of} the first lens to the image-side surface r _{7 of} the fourth lens lens satisfies the conditional expression (3). (3) 1.1 <Σd _i <1.7 (i = 2 to 7) where, d _{i is} the axial distance between the i-th surface and the (i + 1) -th surface counted from the object side.

It is preferable that the radii of curvature of both surfaces of the second lens satisfy the conditional expression (4). (4) 0.4 <| r ₃ / r ₄ | <1.2 where r _{3 is} the radius of curvature of the object side surface of the second lens, r _{4 is the} radius of curvature of the image side surface of the second lens, Is. The diaphragm is arranged between the first lens and the second lens.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The taking lens system of the present invention comprises, in order from the object side, a biconvex first lens, a biconcave second lens with a strong concave surface facing the object side, and a strong convex surface facing the image side. It consists of four single lenses, a positive third lens directed to it and a fourth lens directed to a strong convex surface toward the object side. Even if the radius of curvature of each lens is made relatively large and the screen size becomes small The lens processing is simple and inexpensive, has a large aperture ratio of about 1: 2.0, is good in aberration correction, and is suitable for a camera using a fixed image sensor.

Conditional expression (1) relates to the shaping factor of the fourth lens closest to the image side, and is a condition necessary for making the telecentric about 5 ° or less. If the lower limit of conditional expression (1) is exceeded, the telecentric angle (the incident angle of the off-axis chief ray incident on the image plane) becomes too negative (inclined inward). If the upper limit is exceeded, the telecentric angle becomes 5 ° or more and the object of the present invention cannot be achieved.

Conditional expression (2) represents the range of the sum of the powers of the surfaces of the air lens formed by the facing surfaces of the second lens and the third lens, suppresses the occurrence of coma flare, and balances the image surface. It is a condition for taking. If the negative power becomes stronger than the lower limit, the coma flare due to the lower ray will largely occur on the outer side, and the field curvature will be overcorrected. If the negative power is weakened beyond the upper limit, a large amount of coma flare due to the lower ray will occur inside, and the field curvature will be undercorrected.
The imaging performance cannot be maintained.

Conditional expression (3) is the first condition in which the open diaphragm is arranged.
It defines the total range of the distance between the lens and the second lens and the on-axis dimension from the second lens to the fourth lens, and the off-axis chief ray is about 5 ° or less with respect to the image forming surface (imaging surface). This is a necessary condition for making the light incident. Therefore, conditional expression (4)
If the axial dimension becomes shorter than the lower limit of the above, the angle of incidence of the off-axis chief ray incident on the image plane cannot be suppressed to about 5 ° or less, and at the same time, the edge thickness of the third lens and the fourth lens becomes thin. Therefore, it becomes difficult to process and assemble the lens, especially when the screen size is small. If the axial dimension exceeds the upper limit and becomes longer, the back focus becomes shorter, and it becomes difficult to arrange optical members such as a low-pass filter and an infrared cut filter.

Conditional expression (4) relates to the range of the ratio of the radii of curvature of the surfaces on both sides of the second lens which is the only negative lens in the entire lens system, and is a condition for favorably correcting spherical aberration and coma. Is. If the radius of curvature of the object-side refracting surface r ₃ of the second lens becomes smaller or the radius of curvature of the image-side refracting surface r ₄ becomes greater than the lower limit of the conditional expression, excessive spherical aberration can be corrected. It disappears and a large amount of inward coma occurs.
On the other hand, if r ₃ becomes large or r ₄ becomes small and exceeds the upper limit of the conditional expression, spherical aberration will be undercorrected, and outer coma will occur, making it impossible to obtain good imaging performance.

The present invention will be described below with reference to specific numerical examples. The following Examples 1 to 6 are all
In order from the object side, a biconvex first lens 10, a diaphragm S, a biconcave second lens 20, a positive third lens 30, and a biconvex fourth lens 40 are included. The third lens is a biconvex lens except for the second embodiment, which is a meniscus lens, and each has a strong convex surface on the image side. Behind the fourth lens, the low-pass filter and the cover glass CG of the image sensor are arranged in Examples 1 to 4, and only the cover glass CG of the image sensor is arranged in Examples 5 and 6. There is. The image side surface of the cover glass CG is an imaging surface.

[Embodiment 1] FIGS. 1 and 2 show a first embodiment of the taking lens system of the present invention. FIG. 1 is a lens configuration diagram thereof, and FIG. Table 1 shows specific numerical data of this lens system. In the various aberration diagrams, SA is spherical aberration, SC is sine condition, d-line, g-line, C-line, chromatic aberration indicated by spherical aberration at each wavelength,
S is sagittal and M is meridional.

In the tables and drawings, F _NO is an F number, F is a focal length, W is a half angle of view, and f _B is a back focus.
R is the radius of curvature, D is the lens thickness or lens spacing, N _d is the d-line refractive index, and ν is the d-line Abbe number. The back focus f _B is an air-equivalent distance from the last surface of the fourth lens (r ₈ surface) to the image side surface of the cover glass CG (imaging surface, r ₁₁ ) (f _B = d ₈ + (d ₉ / N ₉ ) + (d ₁₀ / N ₁₀ )).

[0019]

Table 1 F _NO = 1: 2.1 F = 5.24 W = 20.1 f _B = 3.44 surface No. RDN _d ν _d 1 10.330 1.83 1.84666 23.9 2 -10.330 0.12--Aperture ∞ 0.62--3 -3.894 0.91 1.92286 21.3 4 7.056 0.17--5 12.268 2.76 1.72916 54.7 6 -4.000 0.15--7 8.372 3.13 1.72916 54.7 8 -29.058 1.42--9 ∞ 0.99 1.45854 68.0 10 ∞ 2.00 1.49176 57.4 11 ∞---

[Embodiment 2] FIGS. 3 and 4 show a second embodiment of the taking lens system of the present invention. FIG. 3 is a lens configuration diagram, FIG. 4 is a diagram showing various aberrations, and Table 2 is a concrete example. It is numerical data.

[0021]

[Table 2] F _NO = 1: 2.0 F = 5.24 W = 19.6 f _B = 2.46 No. RDN _d ν _d 1 5.577 2.04 1.83400 37.2 2 -20.675 0.14--Aperture ∞ 0.89--3 -4.744 0.80 1.92286 21.3 4 6.230 0.59--5 -19.000 1.93 1.74100 52.7 6 -3.673 0.20--7 5.310 2.14 1.74100 52.7 8 -31.021 0.44--9 ∞ 0.99 1.45854 68.0 10 ∞ 2.00 1.49176 57.4 11 ∞----

[Embodiment 3] FIGS. 5 and 6 show a third embodiment of the taking lens system of the present invention. FIG. 5 is a lens configuration diagram, FIG. 6 is a diagram showing various aberrations, and Table 3 is a concrete example. It is numerical data.

[0023]

[Table 3] F _NO = 1: 2.0 F = 5.24 W = 20.3 f _B = 3.02 surface No. RDN _d ν _d 1 11.539 4.30 1.80518 25.4 2 -14.624 0.19--Aperture ∞ 0.64--3 -4.541 0.80 1.75084 27.7 4 4.685 0.11--5 6.341 2.53 1.56873 63.1 6 -3.483 0.15--7 5.403 2.40 1.56873 63.1 8 -14.813 1.00--9 ∞ 0.99 1.45854 68.0 10 ∞ 2.00 1.49176 57.4 11 ∞---

[Embodiment 4] FIGS. 7 and 8 show a fourth embodiment of the taking lens system of the present invention. FIG. 7 is a lens configuration diagram, FIG. It is numerical data.

[0025]

[Table 4] F _NO = 1: 2.0 F = 5.24 W = 20.1 f _B = 3.07 surface No. RDN _d ν _d 1 10.549 4.05 1.80518 25.4 2 -18.466 0.44--Aperture ∞ 0.69--3 -4.004 0.80 1.92286 20.9 4 6.993 0.12--5 10.673 2.44 1.80400 46.6 6 -3.945 0.15--7 5.672 2.32 1.69349 50.8 8 -319.677 1.05--9 ∞ 0.99 1.45854 68.0 10 ∞ 2.00 1.49176 57.4 11 ∞---

[Embodiment 5] FIGS. 9 and 10 show a fifth embodiment of the taking lens system of the present invention. FIG. 9 is a lens configuration diagram, FIG. 10 is a diagram showing various aberrations, and Table 5 is a concrete example. It is numerical data.

[0027]

[Table 5] F _NO = 1: 2.0 F = 5.24 W = 20.1 f _B = 1.35 No. RDN _d ν _d 1 8.869 4.18 1.80740 35.4 2 -15.222 0.18--Aperture ∞ 0.63--3 -4.228 0.80 1.78470 26.2 4 4.895 0.12--5 6.635 2.36 1.64000 60.1 6 -3.531 0.15--7 5.147 4.07 1.64000 60.1 8 -100.000 0.69--9 ∞ 1.00 1.51633 64.1 10 ∞---

[Sixth Embodiment] FIGS. 11 and 12 show a sixth embodiment of the taking lens system of the present invention. FIG. 11 is a lens configuration diagram, FIG. 12 is a diagram showing various aberrations, and Table 6 is a concrete example. It is numerical data.

[0029]

[Table 6] F _NO = 1: 2.0 F = 5.24 W = 20.1 f _B = 2.55 No. RDN _d ν _d 1 11.095 4.21 1.83400 37.2 2 -20.772 0.59--Aperture ∞ 0.53--3 -4.069 0.80 1.69895 30.1 4 4.452 0.07--5 5.537 2.44 1.61800 63.4 6 -3.671 0.15--7 5.496 2.64 1.61800 63.4 8 -19.386 1.89--9 ∞ 1.00 1.51633 64.1 10 ∞---

Table 7 shows values for the conditional expressions of Examples 1 to 6.

[Table 7]

As is apparent from Table 7, the numerical values of Examples 1 to 6 satisfy the conditional expressions (1) to (4). Further, as is clear from the aberration diagrams, each aberration is satisfactorily corrected.

[0032]

According to the present invention, when the half angle of view is about 20 °,
It is possible to obtain a photographic lens system suitable for a camera using a solid-state image sensor, which has a bright aperture ratio of about 1: 2.0, good aberration correction, easy lens processing, and low cost.

[Brief description of drawings]

FIG. 1 is a lens configuration diagram of a first embodiment of a taking lens system according to the present invention.

FIG. 2 is a diagram illustrating various aberrations of the lens system in FIG. 1;

FIG. 3 is a lens configuration diagram of a second embodiment of the taking lens system according to the present invention.

FIG. 4 is a diagram illustrating various aberrations of the lens system in FIG. 3;

FIG. 5 is a lens configuration diagram of a third embodiment of the taking lens system according to the present invention.

FIG. 6 is a diagram illustrating various aberrations of the lens system in FIG. 5;

FIG. 7 is a lens configuration diagram of a fourth embodiment of the taking lens system according to the present invention.

8 is a diagram illustrating various aberrations of the lens system in FIG. 7;

FIG. 9 is a lens configuration diagram of a fifth embodiment of the taking lens system according to the present invention.

FIG. 10 is a diagram of various types of aberration of the lens system in FIG.

FIG. 11 is a lens configuration diagram of a sixth embodiment of a taking lens system according to the present invention.

12 is a diagram illustrating various aberrations of the lens system in FIG. 11;

[Explanation of symbols]

 10 1st lens 20 2nd lens 30 3rd lens 40 4th lens S diaphragm LF low pass filter CG cover glass

Claims (6)

[Claims] 1. A biconvex first lens in order from the object side,
From four single lenses, a biconcave second lens with a strong concave surface facing the object side, a positive third lens with a strong convex surface facing the image side, and a fourth lens with a strong convex surface facing the object side A photography lens system that is characterized by 2. The photographing lens system according to claim 1, wherein the shaping factor of the fourth lens satisfies the following conditional expression (1). (1) 0.4 <(r ₈ + r ₇ ) / (r ₈ −r ₇ ) <1.0 where r _{7 is} the radius of curvature of the object side surface of the fourth lens, and r _{8 is} the image of the fourth lens. Radius of curvature of the side surface. 3. The photographing lens system according to claim 1, wherein the sum of the powers of the surfaces of the second lens and the third lens facing each other satisfies the following conditional expression (2). (2) -1.1 <φ _r4 + φ _r5 <-0.1 where φ _{r4 is} the surface power of the image side surface of the second lens, and φ _{r5 is} the surface power of the object side surface of the third lens. 4. The axial dimension from the image-side surface r _{2 of} the first lens to the image-side surface r _{7 of} the fourth lens according to claim 1, wherein: A photographic lens system that satisfies (3). (3) 1.1 <Σd _i <1.7 (i = 2 to 7) where, d _i : axial distance between the i-th surface and the (i + 1) -th surface counted from the object side. 5. The photographing lens system according to claim 1, wherein the ratio of the radii of curvature of both surfaces of the second lens satisfies the following conditional expression (4). (4) 0.4 <| r ₃ / r ₄ | <1.2 where r _{3 is} the radius of curvature of the object side surface of the second lens, and r _{4 is the} radius of curvature of the image side surface of the second lens. 6. The photographing lens system according to claim 1, wherein a diaphragm is arranged between the first lens and the second lens.