JP2000275516A - Image pickup lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image pickup lens which has various aberrations excellently corrected, small variation of various aberration in power variation, a large power variation rate, and a sufficient marginal light quantity by employing 6-group constitution and meeting specific conditions. SOLUTION: This image pickup lens is a lens system of six-group and nine- lens provided with a 1st lens group G1 with positive refracting power, an aperture stop S, and a 2nd lens group G2 with positive refracting power in order from the object side. For power variation from low power to high power, the stop S moves together with the 1st lens groups G1 while the air interval between the 1st lens group G1 and 2nd lens group G2 is decreased and the whole lens system moves approaching the object side. This image pickup lens meets conditions of 1.0<f1/fL<1.5, 1.0<f1/f2<1.5, and 1.0<D1/Dh<3.0. Neither f1 nor FL, etc., is explained here.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup lens, in particular, to a facsimile, an image scanner, a film scanner, and other optical systems having a finite distance between an object plane and an image plane such as a copying machine. The present invention relates to a variable magnification imaging lens capable of reading a document.

[0002]

2. Description of the Related Art In an optical apparatus such as a facsimile or an image scanner, a reduced image of a document is transmitted to a CC via a reading lens.
It is formed on a solid-state imaging device such as D. This reading lens needs to have good imaging performance in which the curvature of field, astigmatism, and distortion are sufficiently corrected, and has a resolution equivalent to that of a light receiving element such as a CCD sensor used. Must have. Further, the reading lens needs to be bright in order to secure a sufficient peripheral light amount and shorten the reading time.

The size of a document or a film read by a reading optical device such as a scanner is not fixed, but has various sizes. For this reason, it is preferable that the reading lens has a variable photographing magnification. Here, there is a case where a reading lens such as a scanner does not always need to keep the object-image distance constant when changing the photographing magnification. For example, even if a document or a film is fixed, if the solid-state image sensor moves together with the reading lens optical system so as to maintain an image-forming relationship during zooming, the object-image distance does not need to be always constant.
In order to handle documents of various sizes, it is necessary that various aberrations, especially spherical aberration, accompanying the change of the photographing magnification be small.

Conventionally, a reading optical apparatus using a lens having a constant object-image distance, that is, a so-called zoom lens, or a reading optical system limited to a document of a specific size, that is, reading using a plurality of optical systems having a fixed reading magnification. Optical equipment is known. However, a reading optical device such as a scanner or the like requires a high resolution, so that a zoom lens has a large number of lenses, and as a result, the device itself has been increased in size. In addition, in a device using a plurality of optical systems, similarly, the size of the entire device and the cost are increased.
For this reason, in order to avoid an increase in the size of the device, it may be necessary to use only a limited magnification.

[0005] As for macro lenses for photographing, there are conventionally known many lenses that can be used from an object at infinity to photographing at the same magnification. However, since this macro lens is a lens designed for photographing, it has problems such as insufficient resolution required as an optical system of a reader and insufficient peripheral light. And, in view of the circumstances described above, conventionally, as an optical system for a reading device, JP-A-5-196868, JP-A-5-273465, JP-A-6-94993 or JP-A-6-94994. An optical system disclosed in a gazette has been proposed.

[0006]

However, Japanese Patent Application Laid-Open No. 5-1968 / 1993
The lens disclosed in Japanese Patent Publication No. 68 has a high magnification at a high magnification.
It is low, about 0.2 times, and the zoom ratio is also about 1.5, which is not enough. The lens disclosed in JP-A-5-273465 is
Although the variable magnification ratio is high and the lens is bright and small, the fluctuation of spherical aberration due to zooming is large, and the peripheral light quantity is insufficient for a reading lens. The lenses disclosed in JP-A-6-94993 and JP-A-6-94994 have a low photographing magnification and a zoom ratio of about 2.4, which is not sufficient.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and various aberrations such as spherical aberration, coma aberration, and curvature of field have been well corrected, and the variation from a low magnification side to a high magnification side has been improved. It is an object of the present invention to provide a bright imaging lens having a small variation of various aberrations at a magnification, a large zoom ratio of a photographing magnification, and a sufficient peripheral light amount.

[0008]

In order to solve the above-mentioned problems, the present invention provides, in order from the object side, a first lens having a positive refractive power.
A lens group and at least a second lens group having a positive refractive power, wherein at the time of zooming from a low magnification side to a high magnification side, an air gap between the first lens group and the second lens group is reduced, The first lens group and the second lens group move to the object side.

In such a configuration, the first lens group G1 has the first
While reducing the distance from the surface to the object, the first lens group G1
The distance between the first lens group and the second lens group G2 is also reduced to perform zooming from the low-magnification side to the high-magnification side. It can be carried out. If the interval correction is not used, fluctuations in coma due to zooming cannot be suppressed, and astigmatism bending and field curvature fluctuations also increase.

When the on-axis air space (vertex space) between the first lens group G1 having a positive refractive power and the second lens group G2 having a positive refractive power decreases, the combined focal length of the entire image pickup lens optical system is reduced. Be shorter. As a result, it is possible to reduce an increase in the effective F-number on the high magnification side.
In general, the secondary spectrum in axial chromatic aberration increases in proportion to the square of the lateral magnification, and increases as the combined focal length of the lens system increases. For this reason, the first lens group G1 and the second lens group G2 are moved toward the object side so as to reduce the distance between them, and the composite focal length of the lens system is shortened to reduce the increase in the secondary spectrum. Further, the first lens group G
By reducing the distance between the first lens group G2 and the second lens group G2, it is possible to secure a sufficient peripheral light amount in non-vignetting.

Further, the imaging lens of the present invention has a suitable shape because the distance between the first lens group G1 and the second lens group G2 becomes narrower during zooming from a low magnification side to a high magnification side. . This shape corrects the curvature of astigmatism (astigmatic difference) and the variation in curvature of field due to zooming unique to a lens unit having two positive refractive powers.

In the present invention, it is desirable that the following conditional expression (1) is satisfied. (1) 1.0 <f1 / fL <1.5 Here, f1 represents the focal length of the first lens group G1, and fL represents the focal length of the entire imaging lens system at the minimum magnification. Conditional expression (1) defines an appropriate distribution of refractive power to the first lens group G1.

When the value exceeds the upper limit of conditional expression (1), it is advantageous for brightening the lens system. However, the refractive power of the second lens group G2 becomes relatively strong, and the spherical power becomes higher as the magnification becomes higher. It becomes difficult to correct the curvature of aberration and astigmatism. On the other hand, if the lower limit value of conditional expression (1) is not reached, it is disadvantageous because the lens system is made bright, and the refractive power of the first lens group G1 becomes too strong. In this case, the fluctuation of the spherical aberration increases. As a result, the first lens group G1 needs to have a complicated configuration in order to correct the fluctuation of the spherical aberration.
This leads to increased costs.

It is desirable that the present invention satisfies the following conditional expression (2). (2) 1.0 <f1 / f2 <1.5 where f1 is the combined focal length of the first lens group G1, f2
Represents the combined focal length of the second lens group G2. Conditional expression (2) defines an optimum distribution of refractive power between the first lens group G1 and the second lens group G2.

When the value exceeds the upper limit of conditional expression (2), the higher the magnification becomes, the more the emitted light from the first lens group G1 is diverged rather than converged. Becomes stronger. As a result, it becomes difficult to correct fluctuations in spherical aberration due to zooming. In addition, in order to secure a sufficient peripheral light amount, it is necessary to increase the effective diameter of the first lens group G1. Conversely, when the value goes below the lower limit of conditional expression (2), it is disadvantageous to brighten the lens system, and the refractive power of the first lens group G1 becomes stronger than that of the second lens group G2. Are increased, and the correction is insufficient with only the second lens group G2. In particular, it becomes difficult to correct spherical aberration and fluctuation of astigmatism due to zooming from the low magnification side to the high magnification side.

In the present invention, it is desirable that the following conditional expression (3) is satisfied. (3) 1.0 <Dl / Dh <3.0 where Dl is the axial air gap between the first lens group G1 and the second lens group G2 at the lowest magnification, and Dh is the first air gap at the highest magnification.
It shows the axial air gap between the lens group G1 and the second lens group G2. Conditional expression (3) defines the ratio of the on-axis air gap (apex gap) between the first lens group G1 and the second lens group G2 at the time of the lowest magnification and the highest magnification. This is a conditional expression for correcting aberrations in a well-balanced manner in all zooming regions to the side.

If the upper limit of conditional expression (3) is exceeded, the apex distance between the lowest magnification and the highest magnification changes greatly, so that spherical aberration and astigmatism greatly fluctuate, making it difficult to correct the aberration. . Further, it becomes difficult to secure the flatness of the image plane. Conversely, if the lower limit of conditional expression (3) is not reached, the air gap between the first lens group G1 and the second lens group G2 increases with zooming from the low magnification side to the high magnification side from the same magnification, or This means that the interval has not been corrected. In this case, when the light beam that has passed through the first lens group G1 on the high magnification side enters the second lens group G2, it is farther from the optical axis than when the conditional expression (3) is satisfied. Position (high ray height)
Therefore, it is difficult to correct the fluctuation of spherical aberration due to zooming to a high magnification side, the astigmatism in a high order becomes large, and it becomes difficult to obtain a flat image surface. Further, when the value goes below the lower limit of conditional expression (3), the effective F-number of the optical system becomes dark as described above, and the focal length on the high magnification side becomes longer, so that it becomes difficult to correct the secondary spectrum. More preferably, the lower limit of conditional expression (3) is 1.2
It is desirable that it be larger than. The lower limit of conditional expression (3) is
If the value is larger than 1.2, the change in the distance between the first lens group G1 and the second lens group G2 due to zooming becomes an appropriate amount, and the effect of correcting the aberration by correcting the distance increases.

In a preferred embodiment of the present invention, the second lens group G2 includes a meniscus lens component L21 having a concave surface facing the object side and a meniscus lens component L
21 and an air lens component Lm composed of a lens component L22 provided on the image side of the meniscus lens component.

In the present invention, it is desirable to satisfy the following conditional expression (4). (4) 1 <R1 / R2 Here, R1 is the object-side radius of curvature of the air lens component Lm,
R2 represents the image-side radius of curvature of the air lens component Lm.

Conditional expression (4) defines an appropriate ratio between the object-side radius of curvature of the air lens component Lm and the image-side radius of curvature, and indicates that the air lens Lm has a negative refractive power. Variations in spherical aberration, astigmatism, and coma due to zooming are reduced by an air lens Lm including a meniscus lens L21 having a concave surface facing the object side immediately after the image side of the aperture stop S and a lens L22 immediately behind the image side. Can be held down.

If the lower limit of conditional expression (4) is not reached, spherical aberration and astigmatism due to zooming will increase on the negative side, and it will be impossible to ensure the flatness of the image plane in all zooming regions.

In a preferred embodiment of the present invention, the first lens group G1 includes, in order from the object side, a first lens component L1 (= L11) having a positive refractive power with a convex surface facing the object side;
A second lens group G including a second lens component L2 having a negative refractive power, which is formed by laminating a lens component L12 having a positive refractive power and a lens component L13 having a negative refractive power.
Reference numeral 2 denotes, in order from the object side, a third lens component L3 (= L21) having a positive refractive power and a lens component L3 having a negative refractive power.
A fourth lens component L4 having a negative refractive power, which is formed by laminating a lens 22 with a lens component L23 having a positive refractive power.
A fifth lens component L5 having a positive refractive power and a sixth lens component L6 having a positive refractive power, which are formed by bonding a lens component L24 having a positive refractive power and a lens component L25 having a negative refractive power. It is desirable to have.

A Gaussian optical system is suitable for the construction of a small, high-performance, bright lens system. However, if you change the magnification with a general Gaussian type optical system,
Since the refractive power of the concave surface before and after the stop is strong, light rays are excessively refracted by the concave surface portion, causing fluctuation of coma due to zooming. Further, there is a large fluctuation due to zooming of spherical aberration and astigmatism (astigmatic difference). In the present invention, in order to correct these aberrations, the third lens component L3 (= 3) having a concave surface facing the object side immediately after the image plane side of the aperture stop S.
L21) is arranged, and an air lens Lm is provided between the lens component L22. This third lens component L3 (= L2
1) enables correction of fluctuation of coma aberration and spherical aberration due to zooming.

Further, by disposing a fifth lens unit L5 having a positive refracting power and a sixth lens unit L6 having a positive refracting power, the astigmatic difference peculiar to the Gaussian type is reduced. It is possible to suppress the tilt of the image plane due to zooming (fluctuation in field curvature), correct various aberrations including chromatic aberration with a good balance, and obtain a sufficient peripheral light amount.

Further, in order to correct coma, the first
The second lens component L2 of the lens group G1 is divided into a lens component L12 having a positive refractive power with the convex surface facing the object side and a lens component L13 having a negative refractive power, and an air gap is provided between L12 and L13. Is preferred.

It should be noted that the imaging lens according to the present invention can be used as a lens system having an enlargement magnification by exchanging the configuration of the object side and the image side and making the configurations opposite to each other.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, numerical embodiments of the present invention will be described with reference to the accompanying drawings.

(First Embodiment) FIG. 1 is a diagram showing a configuration of an imaging lens according to a first embodiment. From the object side,
Positive meniscus lens L1 (= L1) with the convex surface facing the object side
1), a cemented lens L2 of a biconvex lens L12 and a biconcave lens L13, an aperture S, a positive meniscus lens L3 (= L21) having a concave surface facing the object side, a negative meniscus lens L22 having a concave surface facing the object side, and an object side A cemented lens L4 with a positive meniscus lens L23 having a concave surface, a cemented lens L5 with a biconvex lens L24 and a biconcave lens L25,
This is a lens system including a biconvex lens L6 (= L26) and a six-group, nine-lens structure.

At the time of zooming from a low magnification to a high magnification, the aperture S moves together with the first lens group G1 while reducing the air gap between the first lens group G1 and the second lens group G2. Moves closer to the object side.

Table 1 shows the specification values of the imaging lens according to the present embodiment. In the lens data, the surface number is the number of the lens surface counted from the object side, r is the radius of curvature of each surface, d is the distance between each lens surface, νd is the Abbe number, and Nd is the d line (587.56 nm).
, Respectively. Β is a magnification, D0
Represents the distance from the object point to the first surface of the lens system, Bf represents the back focus, and Fno represents the F number. Note that the same reference numerals as in this embodiment are used in all the embodiments below.

[0031]

[Table 1]

FIG. 2 is a diagram showing various aberrations on the low magnification side of the imaging lens according to the present embodiment, and FIG. 3 is a diagram showing various aberrations on the high magnification side. In the aberration diagram, d is the d line, g
Represents the g-line (435.83 nm), the dotted line in the astigmatism diagram represents the aberration in the meridional image plane, and the solid line represents the aberration in the sagittal image plane. Note that the same reference numerals as in the present embodiment are used in the aberration diagrams of all the embodiments below. As is clear from the aberration diagrams, various aberrations including chromatic aberration are corrected in a well-balanced manner.

(Second Embodiment) FIG. 4 is a diagram showing a configuration of an imaging lens according to a second embodiment. From the object side,
Positive meniscus lens L1 (= L1) with the convex surface facing the object side
1), positive meniscus lens L12 with the convex surface facing the object side
A lens L2, a stop S, a positive meniscus lens L3 (= L21) with a concave surface facing the object side, and a biconcave lens L22 with a negative meniscus lens L13 having a convex surface facing the object side.
Lens L4 of lens and biconvex lens L23, lens L5 of lens of biconvex lens L24 and biconcave lens L25,
This is an imaging lens having a bi-convex lens L6 (= L26) and a six-group, nine-lens configuration.

At the time of focusing from low magnification to high magnification, the aperture S moves together with the second lens group G2 while reducing the air gap between the first lens group G1 and the second lens group G2, and the entire lens system becomes Move closer to the object side.

Table 2 shows the specification values of the imaging lens according to the present embodiment.

[0036]

[Table 2]

FIG. 5 is a diagram showing various aberrations on the low magnification side of the imaging lens according to this embodiment, and FIG. 6 is a diagram showing various aberrations on the high magnification side. As is clear from the aberration diagrams,
It can be seen that various aberrations including chromatic aberration are corrected in a well-balanced manner.

(Third Embodiment) FIG. 7 is a diagram showing a configuration of an imaging lens according to a third embodiment. From the object side,
Positive meniscus lens L1 (= L1) with the convex surface facing the object side
1), positive meniscus lens L12 with the convex surface facing the object side
A lens L2, a stop S, a positive meniscus lens L3 (= L21) with a concave surface facing the object side, and a biconcave lens L22 with a negative meniscus lens L13 having a convex surface facing the object side.
Lens L4 of lens and biconvex lens L23, lens L5 of lens of biconvex lens L24 and biconcave lens L25,
This is an imaging lens having a bi-convex lens L6 (= L26) and a six-group, nine-lens configuration.

At the time of zooming from a low magnification to a high magnification, the aperture S moves together with the second lens group G2 while reducing the air gap between the first lens group G1 and the second lens group G2, and the entire lens system becomes Move closer to the object side.

Table 3 shows the specification values of the imaging lens according to the present embodiment.

[0041]

[Table 3] β = -0.315 to -1.00 Fno (effective) = 4.80 to 6.52 Face number rd νd Nd 1) 27.9491 6.0 82.52 1.49782 2) 137.9680 0.2 3) 29.8771 8.0 82.52 1.49782 4) 181.4296 5.0 51.35 1.52682 5) 18.1540 d5 6) Aperture 5.5 7) -30.3642 10.0 64.10 1.51680 8) -29.8628 3.0 9) -15.7945 5.0 51.66 1.52944 10) 77.3784 10.0 82.52 1.49782 11) -25.3088 0.3 12) 45.9314 12.0 51.09 1.73350 13) -43.3444 2.5 48.04 1.71700 14) 40.3032 3.0 15) 72.5033 7.0 70.41 1.48749 16) -66.4211 Bf (variable interval table) β -0.315 -0.500 -0.750 -1.000 D0 291.936 192.524 136.601 109.202 d5 4.590 3.947 2.863 1.813 Bf 61.309 77.103 98.120 118.653 (Values for conditional expressions) f1 = 94.095 f2 = 81.000 fL = 84.226 (1) f1 / fL = 1.117 (2) f1 / f2 = 1.162 (3) Dl / Dh = 1.380 (4) R1 / R2 = 1.891

FIG. 8 is a diagram showing various aberrations on the low magnification side of the imaging lens according to the present embodiment, and FIG. 9 is a diagram showing various aberrations on the high magnification side. As is clear from the aberration diagrams,
It can be seen that various aberrations including chromatic aberration are corrected in a well-balanced manner.

(Fourth Embodiment) FIG. 10 is a diagram showing a lens configuration of an imaging lens according to a fourth embodiment. A positive meniscus lens L1 having a convex surface facing the object side in order from the object side
(= L11), a positive meniscus lens L12 having a convex surface facing the object side and a negative meniscus lens L having a convex surface facing the object side
13, a stop S, a positive meniscus lens L3 (= L21) having a concave surface facing the object side, a cemented lens L4 of a biconcave lens L22 and a biconvex lens L23,
Sixth group 9 including a cemented lens L5 of a biconvex lens L24 and a biconcave lens L25, and a biconvex lens L6 (= L26)
This is an imaging lens having a single lens configuration.

At the time of zooming from a low magnification to a high magnification, the aperture S moves together with the first lens group G1 while reducing the air gap between the first lens group G1 and the second lens group G2, and the entire lens system becomes Move closer to the object side.

Table 4 shows the specification values of the imaging lens according to the present embodiment.

[0046]

[Table 4] β = -0.315 to -1.00 Fno (effective) = 5.21 to 7.00 Face number rd νd Nd 1) 28.9037 6.0 82.52 1.49782 2) 148.1540 0.3 3) 25.1246 7.0 82.52 1.49782 4) 6872.0126 5.0 51.66 1.52944 5) 16.9821 5.0 6) Aperture d6 7) -51.2825 5.7 58.50 1.65160 8) -49.6010 3.0 9) -13.8946 3.0 51.66 1.52944 10) 127.4464 10.0 69.98 1.51860 11) -22.8954 0.3 12) 126.5845 8.0 52.30 1.74810 13) -40.8223 2.0 41.42 1.57501 14) 68.7389 2.2 15) 134.2061 8.0 64.10 1.51680 16) -53.8557 Bf (variable interval table) β -0.315 -0.500 -0.750 -1.000 D0 273.899 179.532 126.065 99.604 d6 7.425 7.287 6.983 5.983 Bf 58.497 73.394 93.459 113.287 (Values for conditional expressions) f1 = 86.162 f2 = 75.000 fL = 80.254 (1) f1 / fL = 1.0074 (2) f1 / f2 = 1.149 (3) D1 / Dh = 1.131 (4) R1 / R2 = 3.570

FIG. 11 is a diagram showing various aberrations on the low magnification side of the imaging lens according to this embodiment, and FIG. 12 is a diagram showing various aberrations on the high magnification side. As is clear from the aberration diagrams, various aberrations including chromatic aberration are corrected in a well-balanced manner.

(Fifth Embodiment) FIG. 13 is a diagram showing a lens configuration of an imaging lens according to a fifth embodiment. A positive meniscus lens L1 having a convex surface facing the object side in order from the object side
(= L11), a positive meniscus lens L12 having a convex surface facing the object side and a negative meniscus lens L having a convex surface facing the object side
13, a stop S, a positive meniscus lens L3 (= L21) having a concave surface facing the object side, a cemented lens L4 of a biconcave lens L22 and a biconvex lens L23,
This is an imaging lens having six groups and nine elements including a cemented lens L5 of a biconvex lens L24 and a biconcave lens L25, and a biconvex lens L6 (= L26).

At the time of zooming from a low magnification to a high magnification, the aperture S moves together with the first lens group G1 while reducing the air gap between the first lens group G1 and the second lens group G2. Move closer to the object side.

Table 5 shows the specification values of the imaging lens according to the present embodiment.

[0051]

[Table 5]

FIG. 14 is a diagram showing various aberrations of the imaging lens according to the present embodiment on the low magnification side, and FIG. 15 is a diagram showing various aberrations on the high magnification side. As is clear from the aberration diagrams, various aberrations including chromatic aberration are corrected in a well-balanced manner.

(Sixth Embodiment) FIG. 16 is a diagram showing a configuration of an imaging lens according to a sixth embodiment. In order from the object side, a positive meniscus lens L1 (=
L11), Positive meniscus lens L with the convex surface facing the object side
12 and a negative meniscus lens L13 having a convex surface facing the object side
Lens L2, stop S, positive meniscus lens L3 (= L21) having a concave surface facing the object side, biconcave lens L
22 and a biconvex lens L23, and a laminated lens L of a biconvex lens L24 and a biconcave lens L25
5 is an imaging lens having six groups and nine elements composed of a biconvex lens L6 (= L26).

At the time of zooming from low magnification to high magnification, the aperture S moves together with the second lens group G2 while reducing the air gap between the first lens group G1 and the second lens group G2. Move closer to the object side.

Table 6 shows the specification values of the imaging lens according to the present embodiment.

[0056]

[Table 6] β = -0.315 to -1.0 Fno (effective) = 4.94 to 7.13 Surface number rd νd Nd 1) 30.9328 7.0 82.52 1.49782 2) 325.5836 0.2 3) 27.7131 9.5 91.03 1.44679 4) 92.2894 4.5 51.66 1.52944 5) 17.9678 d5 6) Aperture 1.5 7) -20.5899 5.0 60.69 1.56384 8) -18.8491 5.2 9) -15.5477 5.2 51.66 1.52944 10) 35.7622 10.5 82.52 1.49782 11) -31.0837 0.3 12) 44.1421 12.6 51.09 1.73350 13) -32.3976 2.6 48.04 1.71700 14) 38.6739 2.4 15) 63.4931 7.0 64.10 1.51680 16) -62.1131 Bf (variable interval table) β -0.315 -0.500 -0.750 -1.000 D0 291.704 194.654 140.211 113.511 d5 5.439 4.559 3.398 2.265 Bf 56.520 72.052 92.574 112.591 (Values for conditional expressions) f1 = 88.000 f2 = 85.000 fL = 81.995 (1) f1 / fL = 1.073 (2) f1 / f2 = 1.035 (3) Dl / Dh = 1.843 (4) R1 / R2 = 1.212

FIG. 17 is a diagram showing various aberrations on the low magnification side of the imaging lens according to the present embodiment, and FIG. 18 is a diagram showing various aberrations on the high magnification side. As is clear from the aberration diagrams, various aberrations including chromatic aberration are corrected in a well-balanced manner.

(Seventh Embodiment) FIG. 19 is a view showing a lens configuration of an imaging lens according to a seventh embodiment. A positive meniscus lens L1 having a convex surface facing the object side in order from the object side
(= L11), a positive meniscus lens L12 having a convex surface facing the object side and a negative meniscus lens L having a convex surface facing the object side
13, a stop S, a positive meniscus lens L3 (= L21) having a concave surface facing the object side, a cemented lens L4 of a biconcave lens L22 and a biconvex lens L23,
This is an imaging lens having six groups and nine elements including a cemented lens L5 of a biconvex lens L24 and a biconcave lens L25, and a biconvex lens L6 (= L26).

At the time of zooming from a low magnification to a high magnification, the aperture S moves together with the second lens group G2 while reducing the air gap between the first lens group G1 and the second lens group G2, and the entire lens system becomes Move closer to the object side.

Table 7 shows the specification values of the imaging lens according to this example.

[0061]

[Table 7]

FIG. 20 is a diagram showing various aberrations on the low magnification side of the imaging lens according to the present embodiment, and FIG. 21 is a diagram showing various aberrations on the high magnification side. As is clear from the aberration diagrams, various aberrations including chromatic aberration are corrected in a well-balanced manner.

(Eighth Embodiment) FIG. 22 is a diagram showing a configuration of an imaging lens according to an eighth embodiment. In order from the object side, a biconvex lens L1 (= L11), a positive meniscus lens L12 with a convex surface facing the object side, a biconcave lens L13, an aperture S, and a positive meniscus lens L3 (=
L21), a cemented lens L4 of a biconcave lens L22 and a biconvex lens L23, a biconvex lens L24 and a biconcave lens L
25, a biconvex lens L6 (= L
26) is an imaging lens having seven groups and nine lenses.

In the present embodiment, the positive meniscus lens L1 constituting the second lens component L2 of the first lens G1
2 and the biconcave lens L13 are separated to better correct coma.

At the time of zooming from a low magnification to a high magnification, the aperture S moves together with the second lens group G2 while reducing the air gap between the first lens group G1 and the second lens group G2, and the entire lens system is changed. Move closer to the object side.

Table 8 shows the specification values of the imaging lens according to this example.

[0067]

[Table 8]

FIG. 23 is a diagram showing various aberrations on the low magnification side of the imaging lens according to this example, and FIG. 24 is a diagram showing various aberrations on the high magnification side. As is clear from the aberration diagrams, various aberrations including chromatic aberration are corrected in a well-balanced manner.

The lens components L1 to L6 in the above embodiments are not limited to a single lens or a laminated lens, but may be a lens group including a plurality of lenses.

[0070]

As described above, according to the present invention,
Various aberrations such as spherical aberration, coma, and curvature of field are well corrected, and there is little change in various aberrations from low magnification side to high magnification side including equal magnification. A bright imaging lens having a ratio as large as three times or more and having a sufficient peripheral light amount can be provided. Further, the imaging lens according to the present invention is suitable for a color copier, a color facsimile, a color image scanner, a color film scanner, and the like.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of an imaging lens according to a first example.

FIG. 2 is a diagram illustrating various aberrations on the low magnification side of the imaging lens according to the first example.

FIG. 3 is a diagram illustrating various aberrations on the high magnification side of the imaging lens according to the first example.

FIG. 4 is a diagram illustrating a configuration of an imaging lens according to a second example.

FIG. 5 is a diagram illustrating various aberrations on the low magnification side of the imaging lens according to the second example.

FIG. 6 is a diagram illustrating various aberrations on the high magnification side of the imaging lens according to the second example.

FIG. 7 is a diagram illustrating a configuration of an imaging lens according to a third example.

FIG. 8 is a diagram illustrating various aberrations on the low magnification side of the imaging lens according to the third example.

FIG. 9 is a diagram illustrating various aberrations on the high magnification side of the imaging lens according to Example 3;

FIG. 10 is a diagram illustrating a configuration of an imaging lens according to a fourth example.

FIG. 11 is a diagram illustrating various aberrations on the low magnification side of the imaging lens according to Example 4;

FIG. 12 is a diagram illustrating various aberrations on the high magnification side of the imaging lens according to Example 4;

FIG. 13 is a diagram illustrating a configuration of an imaging lens according to a fifth example.

FIG. 14 is a diagram illustrating various aberrations of the imaging lens according to the fifth example on the low magnification side.

FIG. 15 is a diagram illustrating various aberrations on the high magnification side of the imaging lens according to the fifth example.

FIG. 16 is a diagram illustrating a configuration of an imaging lens according to a sixth example.

FIG. 17 is a diagram illustrating various aberrations on the low magnification side of the imaging lens according to Example 6;

FIG. 18 is a diagram illustrating various aberrations on the high magnification side of the imaging lens according to Example 6;

FIG. 19 is a diagram illustrating a configuration of an imaging lens according to a seventh example.

FIG. 20 is a diagram illustrating various aberrations on the low magnification side of the imaging lens according to Example 7;

FIG. 21 is a diagram illustrating various aberrations on the high magnification side of the imaging lens according to Example 7;

FIG. 22 is a diagram illustrating a configuration of an imaging lens according to Example 8;

FIG. 23 is a diagram illustrating various aberrations on the low magnification side of the imaging lens according to Example 8;

FIG. 24 is a diagram showing various aberrations on the high magnification side of the imaging lens according to Example 8;

[Explanation of symbols]

 G1 first lens group G2 second lens group S aperture stop L1 first lens component L2 second lens component L3 third lens component L4 fourth lens component L5 fifth lens component L6 sixth lens component

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H087 KA08 MA09 PA06 PA20 PB09 QA02 QA07 QA12 QA14 QA21 QA26 QA34 QA42 QA45 RA36 SA06 SA09

Claims (3)

[Claims] 1. A first lens having a positive refractive power in order from the object side.
At least a lens group, an aperture stop, and a second lens group having a positive refractive power are provided. When zooming from a low magnification side to a high magnification side, an air gap between the first lens group and the second lens group is reduced. Decrease the first
The lens group and the second lens group move toward the object side, the focal length of the first lens group is f1, the focal length of the second lens group is f2, and the focal length of the entire imaging lens system at the minimum magnification is fL, the axial air gap between the first lens group and the second lens group at the lowest magnification is Dl, and the axial air gap between the first lens group and the second lens group at the highest magnification is Dh, An imaging lens which satisfies each condition of 1.0 <f1 / fL <1.5 1.0 <f1 / f2 <1.5 1.0 <D1 / Dh <3.0. 2. The second lens group includes a meniscus lens component having a concave surface facing the object side closest to the object side, the meniscus lens component, and a lens component provided on the image side of the meniscus lens component. Where R1 is the object-side radius of curvature of the air lens component and R2 is the image-side radius of curvature of the air lens component, and the condition of 1 <R1 / R2 is satisfied. The imaging lens according to claim 1, wherein: 3. The first lens group includes, in order from the object side,
A first lens component having a positive refractive power with the convex surface facing the object side, and a second lens component having a negative refractive power, which is a laminated lens of a lens component having a positive refractive power and a lens component having a negative refractive power; The second lens group includes, in order from the object side, a negative refraction comprising a laminated lens of a third lens component having a positive refractive power, a lens component having a negative refractive power, and a lens component having a positive refractive power. A fourth lens component having a power, a fifth lens component having a positive refractive power, and a sixth lens having a positive refractive power, which is a laminated lens of a lens component having a positive refractive power and a lens component having a negative refractive power. The imaging lens according to claim 1, further comprising a component.