JPH1020188A - Shooting lens - Google Patents

Abstract

(57) [Summary] [Object] To obtain a compact, small-sized photographic lens having high resolution, small distortion, long back focus, good telecentricity, and a small number of components. A first lens group including, in order from the object side, a negative lens having a concave surface on the image side and a positive lens having a convex surface on the image side; an aperture stop; and a second lens having a positive refractive power. A photographic lens composed of two lens groups; and satisfying the following conditional expressions (1) to (3). _{(1) 0.5 <| f I} -1 / f I-2 | <1.3 (2) 0.8 <F II /F<1.6 (3) 0.15 <D / F <0. 75 where f _{I-1 is} the focal length of the negative lens in the first lens group, f _{I-2 is} the focal length of the positive lens in the first lens group, F _{II is} the focal length of the second lens group, and F is the entire lens. D: Air gap between the negative lens and the positive lens in the first lens group.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photographing lens mainly used for a small-sized imaging device such as an electronic still camera.

[0002]

2. Description of the Related Art In recent years, electronic still cameras that can be easily photographed and viewed as compared with conventional cameras using silver halide films have become widespread. Also, a small and high-resolution electronic still camera is desired as a simple still image input device for a personal computer or the like that has been widely used in general households.

An electronic still camera used for such a purpose is desired to have high performance, and very small size and low cost are very demanded. Further, in an electronic still camera using an image sensor, the size of one pixel is reduced as the size of the image sensor is reduced, and a very high-resolution imaging optical system is required. Also, in this type of image sensor, an RGB color separation filter is often arranged before a pixel,
Since the angle of the light beam entering the pixel differs between the center and the periphery of the screen, this causes color unevenness, and requires a so-called telecentric optical system in which the light beam enters the pixel perpendicularly.

As this kind of optical system, a video camera,
Although it is possible to use conventional optical systems used in surveillance cameras and the like, these conventional optical systems are often used for moving images, and in order to be used in electronic still cameras and the like, resolution is required. But there is room for improvement. For example, the lens described in Japanese Patent Application Laid-Open No. 1-265216 is sometimes used for a surveillance camera, and although it has a bright and wide angle of view, it has a very large distortion and is not preferable as an electronic still camera. Further, the lens described in Japanese Patent Application Laid-Open No. 3-63613 is almost the same in angle of view as the taking lens of the present invention, but has a relatively large curvature of field and cannot be said to have high resolution. Is also undesirable.

[0005]

An object of the present invention is to provide a high-resolution and small distortion,
It is an object of the present invention to provide a compact photographic lens having a long back focus, good telecentricity, and a small number of components.

[0006]

SUMMARY OF THE INVENTION A taking lens according to the present invention comprises, in order from the object side, a first lens group consisting of a negative lens having a concave surface on the image side and a positive lens having a convex surface on the image side; And a second lens group having a positive refractive power; and further satisfying the following conditional expressions (1) to (3). _{(1) 0.5 <| f I} -1 / f I-2 | <1.3 (2) 0.8 <F II /F<1.6 (3) 0.15 <D / F <0. 75 where f _{I-1 is} the focal length of the negative lens in the first lens group, f _{I-2 is} the focal length of the positive lens in the first lens group, F _{II is} the focal length of the second lens group, and F is the entire lens. The focal length of the system, D: the air gap between the negative lens and the positive lens in the first lens group.

Each of the negative lens and the positive lens in the first lens group preferably comprises a meniscus negative lens having a strong concave surface on the image side and a positive lens having a convex surface on the image side. Is preferably satisfied. _{(4) 0.3 <| r 2} / r 4 | <0.6 where, r _2: curvature of the image side surface of the negative lens in the first lens group, r _4: positive in the first lens group The radius of curvature of the image-side surface of the lens.

Regarding the second lens group, it is preferable that the lens closest to the object side of the second lens group be composed of a single meniscus lens having a convex surface on the image plane side, and satisfy the following conditional expression (5). (5) 0.4 <| d _II-1 / r _II-1 | <1.0 where d _{II-1 is} the lens thickness of the meniscus single lens in the second lens group, and r _{II-1 is the} second. The radius of curvature of the image-side surface of the meniscus single lens in the two lens groups. It is preferable that the second lens group includes at least one cemented lens in which a positive lens and a negative lens are cemented, and satisfies the following conditional expressions (6) and (7). _{(6) 0.1 <N n -N} P <0.35 (7) 0.7 <| R / F | <1.5 where, N _n: d of the negative lens of the cemented lens in the second lens group N _p : refractive index of the d-line of the positive lens of the cemented lens in the second lens group; R: radius of curvature of the cemented surface of the cemented lens in the second lens group.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A photographic lens according to the present invention has, in order from the object side, a first lens group consisting of two lenses, a negative lens and a positive lens, and a first lens group having a positive refractive power with an air gap. It has a lens configuration in which two lens groups are arranged, and has a lens configuration in which a diaphragm is arranged between the first lens group and the second lens group. Further, the second lens group has a lens configuration including a cemented lens of one set of a positive lens and a negative lens.

The conditional expression (1) relates to the power of the negative lens and the positive lens in the first lens group. The first lens group has a weak positive or negative power as a whole. However, by appropriately distributing the power of the negative lens and the power of the positive lens within the range of the conditional expression (1), the luminous flux incident on the second lens group is obtained. Is appropriately corrected to obtain good performance. If the power of the negative lens in the first lens unit is increased beyond the lower limit of the conditional expression (1), the back focus can be lengthened, but the distortion and coma become worse and the total length of the lens becomes shorter. It becomes difficult to shorten.
If the power exceeds the upper limit and the power of the positive lens in the first lens group becomes too strong, the Petzval sum increases, making it difficult to obtain good off-axis performance and making it difficult to increase the back focus. .

Conditional expression (2) relates to the power of the second lens group, and is used to favorably correct the light beam incident on the second lens group to form an image. Conditional expression (2)
When the power of the second lens group is increased beyond the lower limit of
It becomes difficult to lengthen the back focus, and the telecentricity of the light flux formed on the image plane deteriorates. If the power of the second lens unit is weakened beyond the upper limit, particularly the curvature of field and astigmatism are degraded, the off-axis performance is deteriorated, and it becomes difficult to shorten the entire length of the lens.

Condition (3) relates to the air gap between the negative lens and the positive lens in the first lens group. By arranging the first lens group and the second lens group with an appropriate air gap defined by the conditional expression (3), good aberration correction can be achieved. When the lower limit of conditional expression (3) is exceeded and the air gap is narrow, coma and astigmatism increase, and it becomes difficult to obtain a good image plane. Exceeding the upper limit is not preferable because, in particular, it becomes difficult to correct distortion, and the overall length of the lens becomes longer.

Conditional expression (4) is a condition relating to the shapes of the negative lens and the positive lens constituting the first lens unit. It is preferable to determine the shapes of the negative lens and the positive lens within the range of conditional expression (4). It is possible to correct various aberrations. If the lower limit of conditional expression (4) is exceeded, the power of the negative lens will be too strong, and the occurrence of coma will increase, and the lens cannot be made compact. If the upper limit is exceeded, the power of the positive lens becomes too strong and the Petzval sum becomes large, so that field curvature and astigmatism cannot be satisfactorily corrected.

Conditional expression (5) relates to the shape of the lens closest to the object in the second lens group. If the radius of curvature of the surface on the image side becomes smaller than the lower limit of conditional expression (5), the radius of curvature of the surface on the object side also becomes smaller, which is not preferable in terms of easiness of lens processing and cost. . If the radius of curvature of the image-side surface is increased beyond the upper limit, it becomes difficult to balance spherical aberration on-axis with curvature of field off-axis.

Conditional expressions (6) and (7) are conditions relating to the refractive index difference between the negative lens and the positive lens of the cemented lens in the second lens unit, and the radius of curvature of the cemented surface, and in particular, favorably correct chromatic aberration. Is the condition for

If the lower limit of conditional expression (6) is exceeded, it becomes difficult to reduce the radius of curvature of the joint surface, which is not preferable in terms of working. When the value exceeds the upper limit, the refractive index of the positive lens becomes low, and it becomes difficult to reduce the field curvature.

If the lower limit of conditional expression (7) is exceeded, the radius of curvature of the joint surface will be too small, causing an increase in processing cost. When the upper limit is exceeded, it becomes difficult to suppress the curvature of field and astigmatism to a small level while maintaining good longitudinal chromatic aberration and lateral chromatic aberration.

Hereinafter, the present invention will be described with reference to specific numerical examples. The following Examples 1 to 8 are all
In order from the object side, a first lens group 10 including a negative lens 1n having a concave surface on the image side, a positive lens 1p having a convex surface on the image side, an aperture stop S, a meniscus single lens 2m, a positive lens 2p, and a negative lens The basic configuration is a second lens group 20 having a cemented lens with 2n, and a parallel flat glass G serving as a cover glass of the image sensor. Parallel flat glass G
In this type of photographic lens system, a crystal filter, an infrared cut filter, and a cover glass are used, and the image-side surface thereof is an imaging surface.

In the first to third embodiments, the second lens group 20 includes only a single meniscus lens 2m and a cemented lens of a positive lens 2p and a negative lens 2n. In the fourth embodiment, the positive lens 2p and the negative lens 2n A positive meniscus lens 2e having a convex surface facing the object side is further disposed behind the cemented lens of Example 5. In Examples 5 to 8, between the meniscus single lens 2m and the cemented lens of the positive lens 2p and the negative lens 2n. , A positive lens 2f. Also, the second
Except for Example 4, the cemented lenses of the lens group 20 are in the order of positive and negative from the object side, and Example 4 is in the order of negative and positive.

[Embodiment 1] FIGS. 1 and 2 show a first embodiment of a photographic lens according to the present invention. FIG. 1 is a diagram showing the lens configuration, and FIG. 2 is a diagram showing various aberrations. Table 1 shows specific numerical data of this lens. D-line, g
Line and C line indicate chromatic aberration and lateral chromatic aberration represented by spherical aberration at each wavelength, S indicates sagittal, and M indicates meridional.

In the tables and drawings, F _NO represents the F number, F represents the focal length of the entire lens system, W represents the half angle of view of the lens, and f _B represents the back focus. R is the radius of curvature, D is the lens thickness or lens interval, N _d is the refractive index of the d-line, and ν _d is the Abbe number of the d-line. Back focus f _B are Examples 1 to 3
Then, the air-equivalent distance (f _B = d) from the last surface (r9 surface) of the second lens group to the image side surface (r11) of the parallel flat glass G
₉ + (d ₁₀ / N ₁₀ ), and in Examples 4 to 8, in the second lens group, the image side surface (r
13) is an air-equivalent distance (f _B = d ₁₁ + (d ₁₂ / N ₁₂ )).

[0022]

[Table 1] F _NO = 1: 2.8 F = 10.00 W = 29.1 ° f _B = 9.27 Surface No. RDN _d ν _d 1 17.167 2.90 1.72916 54.7 2 7.305 2.28--3 -232.016 3.27 1.77250 49.6 4 -15.703 5.30-- Aperture ∞ 1.78--5 -12.105 9.38 1.83400 37.2 6 -10.967 0.24--7 16.535 7.11 1.69680 55.5 8 -7.997 3.15 1.84666 23.8 9 -45.743 4.56--10 ∞ 7.14 1.51633 64.1 11 ∞---

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

[0024]

[Table 2] F _NO = 1: 2.8 F = 10.00 W = 29.1 ° f _B = 10.86 Surface No.RDN _d ν _d 1 31.601 3.41 1.72916 54.7 2 8.879 2.58--3 -43.110 3.32 1.77370 49.4 4 -14.734 8.76-- Aperture ∞ 3.01--5 -20.454 9.93 1.88 300 40.8 6 -13.520 0.24--7 16.176 7.12 1.65 160 58.5 8 -9.439 2.88 1.84666 23.8 9 -71.227 6.15--10 ∞ 7.14 1.51633 64.1 11 ∞---

[Embodiment 3] FIGS. 5 and 6 show a third embodiment of a photographic lens according to the present invention. FIG. 5 is a diagram showing a lens configuration, and FIG. 6 is a diagram showing various aberrations. Table 3 shows specific numerical data.

[0026]

[Table 3] F _NO = 1: 2.8 F = 10.00 W = 29.1 ° f _B = 9.10 Surface No.RDN _d ν _d 1 20.746 2.47 1.72916 54.7 2 7.653 4.38--3 -24.867 3.10 1.77370 49.4 4 -12.703 7.67-- Aperture ∞ 6.73--5 -51.044 8.03 1.88 300 40.8 6 -15.056 0.24--7 16.624 7.31 1.65 160 58.5 8 -9.925 3.09 1.84666 23.8 9 204.495 4.70--10 ∞ 6.67 1.51633 64.1 11 ∞---

[Embodiment 4] FIGS. 7 and 8 show a fourth embodiment of the taking lens according to the present invention. FIG. 7 is a diagram showing the lens configuration and FIG. 8 is a diagram showing various aberrations. Table 4 shows specific numerical data.

[0028]

[Table 4] F _NO = 1: 2.8 F = 10.00 W = 29.0 ° f _B = 9.70 Surface No. RDN _d ν _d 1 30.083 2.14 1.69680 55.5 2 10.369 2.62--3 302.970 3.63 1.80610 40.9 4 -20.880 7.73--Aperture ∞ 2.18--5 -5.335 3.84 1.88 300 40.8 6 -6.956 0.24--7 19.557 2.49 1.84666 23.8 8 7.918 6.14 1.61800 63.4 9 -37.041 0.24--10 13.548 3.72 1.77 250 49.6 11 31.806 4.99--12 ∞ 7.14 1.51633 64.1 13 ∞- --

[Embodiment 5] FIGS. 9 and 10 show a fifth embodiment of the taking lens system according to the present invention. FIG. 9 is a diagram showing the lens arrangement, and FIG. 10 is a diagram showing various aberrations. Table 5 shows specific numerical data.

[0030]

[Table 5] F _NO = 1: 2.4 F = 10.00 W = 23.7 ° f _B = 9.68 Surface No. RDN _d ν _d 1 32.826 1.90 1.69680 55.5 2 9.515 2.02--3 191.485 3.40 1.80400 46.6 4 -18.934 6.10--Aperture ∞ 2.44--5 -9.515 7.56 1.83481 42.7 6 -12.988 0.24--7 -48.870 3.57 1.69680 55.5 8 -15.105 0.24--9 16.375 6.99 1.65 160 58.5 10 -11.342 1.90 1.84666 23.8 11 -232.660 5.88--12 ∞ 5.76 1.51633 64.1 13 ∞---

[Embodiment 6] FIGS. 11 and 12 show a sixth embodiment of the taking lens according to the present invention. FIG. 11 is a diagram showing the lens configuration, and FIG. 12 is a diagram showing various aberrations. Table 6 shows specific numerical data.

[0032]

[Table 6] F _NO = 1: 2.0 F = 10.00 W = 29.0 ° f _B = 7.87 Surface No.RDN _d ν _d 1 48.837 2.38 1.58904 53.2 2 11.784 2.62--3 251.357 3.50 1.78800 47.4 4 -23.947 8.12--Aperture ∞ 2.91--5 -6.127 4.70 1.69350 53.2 6 -8.601 0.48--7 60.069 3.77 1.75500 52.3 8 -17.769 0.12--9 14.363 5.81 1.56873 63.1 10 -11.699 2.38 1.84666 23.8 11 100.822 3.17--12 ∞ 7.13 1.51633 64.1 13 ∞ ---

[Embodiment 7] FIGS. 13 and 14 show a seventh embodiment of the taking lens according to the present invention. FIG. 13 is a diagram showing the lens configuration, and FIG. 14 is a diagram showing various aberrations. Table 7 shows specific numerical data.

[0034]

[Table 7] F _NO = 1: 2.8 F = 10.00 W = 29.0 ° f _B = 7.87 Surface No.RDN _d ν _d 1 18.590 2.38 1.63854 55.4 2 9.840 2.73--3 216.795 3.22 1.77250 49.6 4 -25.894 6.99--Aperture ∞ 1.85--5 -5.586 4.01 1.83481 42.7 6 -8.468 0.48--7 -58.443 3.30 1.77 250 49.6 8 -11.937 0.27--9 11.981 5.44 1.58913 61.2 10 -10.737 2.38 1.84666 23.8 11 230.251 3.00--12 ∞ 7.38 1.51633 64.1 13 ∞---

[Embodiment 8] FIGS. 15 and 16 show an eighth embodiment of the photographic lens of the present invention. FIG. 15 is a diagram showing the lens configuration and FIG. 16 is a diagram showing various aberrations. Table 8 shows specific numerical data.

[0036]

[Table 8] F _NO = 1: 2.8 F = 10.00 W = 29.0 ° f _B = 7.86 Surface No.RDN _d ν _d 1 43.007 2.38 1.63930 44.9 2 11.234 5.95--3 85.918 4.52 1.77250 49.6 4 -23.202 7.95--Aperture ∞ 3.10--5 -5.783 3.81 1.83481 42.7 6 -7.784 0.48--7 56.234 3.30 1.77 250 49.6 8 -18.530 0.26--9 13.967 5.06 1.58913 61.2 10 -10.492 2.38 1.84666 23.8 11 33.863 3.31--12 ∞ 6.90 1.51633 64.1 13 ∞ ---

Next, Table 9 shows values for the respective conditional expressions in Examples 1 to 8.

Table 9 Example 1 Example 2 Example 3 Example 4 Conditional expression (1) 0.919 0.657 0.598 0.976 Conditional expression (2) 1.135 1.292 1.394 1.133 Conditional expression (3) 0.228 0.258 0.438 0.262 Conditional expression (4) 0.465 0.603 0.602 0.497 Conditional expression (5) 0.855 0.734 0.533 0.552 Conditional expression (6) 0.150 0.195 0.195 0.229 Conditional expression (7) 0.800 0.944 0.993 1.355 Example 5 Example 6 Example 7 Example 8 Conditional expression (1) 0.922 0.968 1.216 0.999 Conditional expression (2) 1.148 1.125 1.037 1.460 Conditional expression (3) 0.202 0.262 0.273 0.595 Conditional expression (4) 0.503 0.492 0.380 0.484 Conditional expression (5) 0.582 0.546 0.474 0.489 Conditional expression (6) 0.195 0.278 0.258 0.258 Conditional expression (7) 1.134 1.170 1.074 1.049

As is clear from Table 9, the numerical values of Examples 1 to 8 satisfy the conditional expressions (1) to (7). Further, as is clear from the aberration diagrams, each aberration is satisfactorily corrected.

[0039]

According to the present invention, it is possible to obtain a compact photographing lens having a sufficient back focus, high resolution, small size, and small number of components.

[Brief description of the drawings]

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

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

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

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

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

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

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

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

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

FIG. 10 is a diagram illustrating various aberrations of the lens in FIG. 9;

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

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

FIG. 13 is a lens configuration diagram of a seventh embodiment of the taking lens according to the present invention.

FIG. 14 is a diagram illustrating various aberrations of the lens in FIG. 13;

FIG. 15 is a lens configuration diagram of an eighth embodiment of the taking lens according to the present invention.

FIG. 16 is a diagram illustrating various aberrations of the lens in FIG. 15;

[Explanation of symbols]

 Reference Signs List 10 first lens group 20 second lens group S stop G parallel flat glass

Claims (4)

[Claims] 1. A first lens group including, in order from an object side, a negative lens having a concave surface on the image side and a positive lens having a convex surface on the image side; an aperture stop; And a second lens group having: a photographing lens that further satisfies the following conditional expressions (1) to (3). _{(1) 0.5 <| f I} -1 / f I-2 | <1.3 (2) 0.8 <F II /F<1.6 (3) 0.15 <D / F <0. 75 where f _{I-1 is} the focal length of the negative lens in the first lens group, f _{I-2 is} the focal length of the positive lens in the first lens group, F _{II is} the focal length of the second lens group, and F is the entire lens. D: Air gap between the negative lens and the positive lens in the first lens group. 2. The photographic lens according to claim 1, wherein the negative lens in the first lens group is a meniscus negative lens having a strong concave surface on the image side, and further satisfies the following conditional expression (4). _{(4) 0.3 <| r 2} / r 4 | <0.6 where, r _2: curvature of the image side surface of the negative lens in the first lens group, r _4: positive in the first lens group The radius of curvature of the image-side surface of the lens. 3. The photographic lens according to claim 1, wherein the lens closest to the object in the second lens group is a single meniscus lens having a convex surface on the image side, and further satisfies the following conditional expression (5). (5) 0.4 <| d _II-1 / r _II-1 | <1.0 where d _{II-1 is} the lens thickness of the meniscus single lens in the second lens group, and r _{II-1 is the} second. The radius of curvature of the image-side surface of the meniscus single lens in the two lens groups. 4. The lens system according to claim 1, wherein the second lens group includes at least one cemented lens in which a positive lens and a negative lens are cemented, and satisfies the following conditional expressions (6) and (7). A satisfying shooting lens. _{(6) 0.1 <N n -N} P <0.35 (7) 0.7 <| R / F | <1.5 where, N _n: d of the negative lens of the cemented lens in the second lens group N _P : refractive index of the d-line of the positive lens of the cemented lens in the second lens group; R: radius of curvature of the cemented surface of the cemented lens in the second lens group.