JP2007047334A - Imaging lens system, image reader, imaging device, and display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a front diaphragm compatible with a telecentric lens system on the reducing conjugation side. <P>SOLUTION: The imaging lens system composed of: (1) a diaphragm r1; (2) a first group having a negative lens L1 whose curvature on the diaphragm r1 side face is great and a positive lens L2 whose curvature on the diaphragm r1 side face is less than that of the negative lens L1; (3) a second group having a positive lens L3; and (4) a third group having a positive lens L4 and a negative lens L5 in that order such that the face on the most reducing conjugation side face is convex with respect to the diaphragm r1, in this order from the magnifying conjugation side. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an imaging lens system, an image reading device, an imaging device, and a display device.

Telecentric lens systems have the property that the magnification of image formation does not change even when defocusing is changed, and are used as lens systems for measuring instruments, projectors, and observation devices. Recently, it has been used in lens systems for digital imaging devices and digital projectors (see Patent Documents 1 and 2).
The front aperture lens system is used particularly when the aperture diameter is variable (see Patent Document 1). That is, when a complicated aperture mechanism is set inside the lens system, Since many mechanical parts are inserted before and after the stop, it is difficult to ensure the positional accuracy between the lenses. 2. When feeding out is necessary, it is possible to avoid the necessity of moving a large and heavy aperture mechanism together.
An image reading lens requires an aperture efficiency of almost 100% up to the final side and a small distortion, and a five-lens configuration has a half angle of view of 20 ° or less, Fno. Are mostly in the vicinity of 4 (see Patent Document 3).
Japanese Patent Laid-Open No. 11-337819 JP 2000-19394 A JP-A-8-201689

However, it is known that a lens system that is telecentric on the reduction conjugate side can be realized by placing a pupil near the rear focal point. However, the lens system of the front diaphragm has a complicated diaphragm mechanism. If set inside, many mechanical parts are inserted before and after the aperture, making it difficult to secure the positional accuracy between the lenses, and it is necessary to move a large and heavy aperture mechanism as a unit when it needs to be extended. There is.
An object of the present invention is a lens system of a front diaphragm, and while the reduction conjugate side is telecentric, Fno. Is less than 2 ~ 3, the half angle of view is about 20 °, the number of lenses is not so many (about 5), the structure is simple, the aperture efficiency to the periphery is almost 100%, and the total thickness ratio It is to provide a new type of lens system that can be made small and thin.

According to the first aspect of the present invention, in order from the magnification conjugate side, a stop, a negative lens having a strong curvature on the surface on the stop side, and a positive lens having a curvature on the surface on the stop side that is weaker than the negative lens are provided. A group, a second group having a positive power, and a third group which is a lens having a positive lens and a negative lens arranged in this order and having a surface on the most reduced conjugate side convex to the stop. It is characterized by being an imaging lens system.
According to a second aspect of the present invention, in the imaging lens system according to the first aspect, the first lens unit is a negative meniscus lens having a convex surface facing away from the stop, and the negative lens and the stop opposite the stop. It is a lens in which the positive lens which is a positive meniscus lens having a convex surface is cemented with the positive lens.
According to a third aspect of the present invention, in the imaging lens system according to the first or second aspect, when the focal length of the entire system is f and the focal length of the second group is f2,
0.8 ≦ f2 / f ≦ 2 (1)
It is characterized by being.
According to a fourth aspect of the present invention, in the imaging lens system according to any one of the first to third aspects, the radius of curvature of the surface closest to the stop of the k-th group (k = 1, 2, 3) is set. Rkf, where the radius of curvature of the surface of the kth group that is farthest from the aperture is Rkr,
3 ≦ (R1r + R1f) / (R1r−R1f) ≦ 10 (2)
−7 ≦ (R3r + R3f) / (R3r−R3f) ≦ −1 (3)
It is characterized by being.

According to a fifth aspect of the present invention, in the imaging lens system according to any one of the first to fourth aspects, at least one surface of each lens is an aspherical surface.
According to a sixth aspect of the present invention, in the imaging lens system according to any one of the first to fifth aspects, the surface of the third group that is farthest from the stop is an aspherical surface, and the deviation from the reference spherical surface The amount of concave power is the direction that increases.
The invention according to claim 7 is the imaging lens system according to any one of claims 1 to 6, wherein the Abbe number νkp of the d-line of the positive lens in the k-th group (k = 1, 2, 3). When the Abbe number νkn of the d-line of the negative lens is
15 ≦ ν1p−ν1n (4)
15 ≦ ν3p−ν3n (5)
It is.
According to an eighth aspect of the present invention, in the imaging lens system according to any one of the first to sixth aspects, the stop is disposed in the vicinity of a front focal point of the lens system including the groups.
An invention according to a ninth aspect includes the imaging lens system according to any one of the first to seventh aspects, and an image sensor disposed on a reduction conjugate side of the imaging lens system. An image reading apparatus that reads a document image arranged on an enlargement conjugate plane of an image lens system.
An invention according to a tenth aspect includes the imaging lens system according to any one of the first to seventh aspects, and an imaging element disposed on a reduction conjugate side of the imaging lens system. This is an imaging device that photographs a subject on the magnification conjugate plane side of an image lens system.
An eleventh aspect of the invention includes the imaging lens system according to any one of the first to seventh aspects, and a display object disposed on a reduction conjugate plane, and the magnification of the imaging lens system. In this display device, the conjugate side is a display surface.

According to the first aspect of the present invention, it is a front diaphragm lens system, and while the reduction conjugate side is telecentric, Fno. , A wide half angle of view, and the number of lenses is not so large, the aperture efficiency is almost 100% to the periphery, and the total thickness ratio is small and thin.
According to the second aspect of the present invention, the cemented surface between the positive meniscus lens and the negative meniscus lens can be made concentric to the stop, and the occurrence of aberration can be reduced.
According to the third aspect of the present invention, the focal length of the second lens group when the lower limit of the expression (1) is exceeded is small (power is large), the spherical aberration is negative and excessive, and it is difficult to increase the diameter. And other problems such as the fact that the positive power of the third lens group must be increased in order to compensate for the shortage of positive power when the upper limit of the expression (1) is exceeded.
According to the fourth aspect of the present invention, at the upper limit of the expression (2) and the lower limit of the expression (3), the declination (absolute value) of each surface of the upper light beam becomes large, and a large amount of aberration is reversed. The higher order aberration remains even if the balance can be obtained. At the lower limit of the expression (2) and the upper limit of the expression (3), the refraction of the upper ray becomes straight and easy correction is easy, but the Petzval sum increases and it is difficult to correct the astigmatic difference. At the upper limit of the expression (3), it is difficult to correct distortion that tends to occur in a barrel shape. Therefore, these problems can be avoided by satisfying (2) and (3).
According to the fifth aspect of the present invention, more precise balance and more precise correction can be realized.
According to the sixth aspect of the invention, it is possible to correct distortion and field curvature while minimizing the occurrence of coma.
According to the seventh aspect of the invention, it is possible to control with good balance by the chromatic aberration of the first group and the third group.
According to the invention described in claim 8, a lens system that is telecentric on the reduction conjugate side can be realized.
According to the ninth to eleventh aspects of the present invention, it is possible to provide a device such as an image reading apparatus using the imaging lens system according to the first to seventh aspects.

The best mode for carrying out the invention will be described below.
FIG. 1 is an explanatory diagram of the imaging lens system of the present embodiment. In the light beam focused at the peripheral image height, the lower light beam passes through a portion close to the center of the lens and reaches the image formation point, and the sum of the declination angles is small and the occurrence of aberration is small. On the other hand, the upper ray inevitably passes through the periphery of the lens, and the necessary deviation angle θu is large, so that coma and chromatic aberration are likely to occur. In addition, since the lens group having a positive power as a whole is arranged behind the stop r1 and untargeted with the stop r1, negative distortion occurs.
Because of the above-mentioned properties of the front aperture lens system, first of all, there is little occurrence with respect to coma aberration of the upper ray, it is a lens type with the idea of erasing immediately even if it occurs, and excellent aberration correction capability, Is required. Chromatic aberration of chromatic aberration tends to occur as the light beam increases in the peripheral image height, and a lens type having the same properties as described above is required. It is known that distortion aberration and chromatic aberration of magnification can be canceled out automatically by disposing lenses symmetrically with respect to the stop r1. Of course, a symmetrical lens configuration is not possible with the front diaphragm, and a new idea is required to correct both aberrations.
Therefore, on the surface where the deflection angle θp due to the refraction of the chief ray is clockwise, it is divided and refracted by a plurality of surfaces to suppress the occurrence of negative distortion aberration per surface as much as possible, and the reduction of coma aberration is relatively small. The lens was constructed so that a declination due to refraction in the counterclockwise direction occurred on the surface near the conjugate surface. With regard to chromatic aberration of magnification, it is a new lens that has never been seen before, with high specifications and performance, taking dispersion into consideration.

Hereinafter, the imaging lens system of the present embodiment will be specifically described.
The imaging lens system of the present embodiment includes, in order from the magnification conjugate side, a stop r1, a negative lens L1 having a strong curvature on the surface r2 on the stop r1 side, and a positive lens L2 having a low curvature on the surface r3 on the stop r1 side. The first group, the second group consisting of a positive power lens L3, a positive lens L4 and a negative lens L5 are joined in this order, and the surface r7 closest to the reduction conjugate side has a surface convex to the stop r1. It consists of 3 groups.
In the case of this specification, which is a front stop, all the principal rays are incident on the first surface radially from the center of the stop r1, so that if the surface r2 on the first group stop r1 side is concave, even if the angle of view changes, the incident condition The difference between the two is small and the occurrence of aberration is small. This is convenient because it is a concentric surface with respect to the stop r1, and the coma aberration of the upper light ray is small, which is disadvantageous for the lower light beam, but the lower light beam passes near the center of the lens, so that aberration is generated. The absolute amount is small and acceptable.
The first group is constructed in the order of the negative lens L1 and the positive lens L2, and the curvature of the adjacent surface r3 of both lenses L1 and L2 is relaxed to reduce the occurrence of aberrations. Both lenses L1 and L2 may be separated. In this case, the lens back can be enlarged, and the arrangement of filters, prisms and the like is facilitated. In the second group, a positive power lens L3 is arranged, which can be composed of one or more lenses, and does not necessarily include a concave lens. The third group is a lens structure in which a positive lens L4 and a negative lens L5 are cemented, and the final surface is a convex surface at the stop r1. The light beam condensed on the reduction conjugate surface has a narrow width in the vicinity of the reduction conjugate surface, and other aberration corrections are possible while reducing the occurrence of coma, and correction of chromatic aberration of magnification at the third group joint surface. It is effective to correct distortion at the final surface.

In this configuration, the first group and the third group are arranged symmetrically with respect to the second group, and the ray path of the upper ray approaches symmetry. With respect to the upper ray, the converging coma aberration generated in the second group cancels out between the first surface of the first group and the final surface of the third group.
In addition, since the first group is a lens in which the negative meniscus lens L1 having the convex surface r3 facing the opposite side to the stop r1 and the positive meniscus lens L2 having the convex surface r4 facing the opposite side to the diaphragm r1, the cemented surface r3 is also formed. The diaphragm r1 can be concentric, and aberrations are reduced. Thereby, the occurrence of curvature of field, lateral chromatic aberration, and coma aberration of the upper ray can be suppressed, which is particularly effective when a wide angle of view is used.
Further, when the focal length of the entire system; f, the focal length of the second group; f2,
0.8 ≦ f2 / f ≦ 2 (1)
Meet the requirements of
When the lower limit of the expression (1) is exceeded, the focal length of the second group is small (the power is large), the spherical aberration is negative and excessive, making it difficult to increase the diameter, and the converging coma aberration of the second group is difficult. This is because the curvatures of the first surface and the final surface become tight to correct the high-order coma flare.
If the upper limit of the expression (1) is exceeded, the positive power of the third group must be increased to compensate for the lack of positive power, the curvature of the final surface becomes loose, and it becomes difficult to correct distortion. This is because it is difficult to reduce the total thickness of the third lens group.
Further, the radius of curvature of the surface closest to the diaphragm r1 in the k-th group (k = 1, 2, 3) (paraxial radius of curvature in the case of an aspheric surface): Rkf, the curvature of the surface farthest from the diaphragm r1 in the k-th group. When the radius is Rkr, the following is satisfied.
3 ≦ (R1r + R1f) / (R1r−R1f) ≦ 10 (2)
−7 ≦ (R3r + R3f) / (R3r−R3f) ≦ −1 (3)

Here, in both formulas (2) and (3), the symmetry of the ray path of the upper ray is defined for the shaping factor of the entrance / exit surfaces of the lens group, and coma aberration correction is performed satisfactorily. At the upper limit of equation (2) and the lower limit of equation (3), the declination (absolute value) on each surface of the upper ray increases, and the large aberration is canceled out by the aberration of the opposite sign, thus obtaining a balance. Even if possible, higher order aberrations remain. At the lower limit of the expression (2) and the upper limit of the expression (3), the refraction of the upper ray becomes straight and easy correction is easy, but the Petzval sum increases and it is difficult to correct the astigmatic difference. At the upper limit of the expression (3), it is difficult to correct distortion that tends to occur in a barrel shape. Therefore, these problems can be avoided by satisfying (2) and (3).
It is also effective that at least one surface of each lens is an aspherical surface. The imaging lens system of the present embodiment is a front stop, and is a type that can balance the converging coma aberration and the diverging coma aberration with a focus on correction of coma aberration of the upper ray. By using an aspherical surface for the surface where the declination of the upper ray increases, more precise balance and more precise correction can be realized, which is useful for higher performance and higher functionality.
The surface of the third lens group that is farthest from the stop r1 is most focused, and the surface is aspherical, so that distortion and field curvature can be corrected while minimizing the occurrence of coma. The amount of deviation from the reference spherical surface is set in a direction in which the concave power increases, and a good performance can be obtained by giving a divergence effect to the upper ray while keeping the paraxial curvature gentle.
In the k-th group, when the Abbe number of the d-line of the positive lens is νkp and the Abbe number of the d-line of the negative lens is νkn, the following is satisfied.
15 ≦ ν1p−ν1n (4)
15 ≦ ν3p−ν3n (5)
This condition is a condition necessary for correcting axial chromatic aberration and particularly chromatic aberration of magnification at the same time. The chromatic aberration of the first group and the third group can be controlled in a well-balanced manner to improve performance. Equation (5) is also a condition for correcting the chromatic aberration of coma aberration of the upper ray.
The stop r1 is disposed in the vicinity of the front focal point of the lens system to realize a lens system that is telecentric on the reduction conjugate side. The front focal point can be disposed on the magnification conjugate side of the lens system, and is compatible with the front aperture r1.

Next, a plurality of examples of the system including the imaging lens system as described above will be described.
(1) Image reading apparatus First, an image reading apparatus using the above-described imaging lens system, in which an original image is arranged on the enlargement conjugate plane and an image sensor (not shown) is arranged on the reduction conjugate side, is provided. Can do. Since this image reading apparatus has a bright lens system, the load on the illumination system is small and power is saved, and since the aperture efficiency is abundant, a more uniform illuminance distribution can be obtained.
(2) Imaging Device Further, it is possible to provide an imaging device in which the imaging lens system described above is used and an imaging element (not shown) is arranged on the reduction conjugate plane. In this image pickup apparatus, the whole or a part of the lens system can be extended with the position of the diaphragm r1 as it is, and close-up photography is possible, and the extension mechanism can be simplified. It is possible to further reduce the size of the lens system at the time of storage by storing the lens system at the time of non-photographing or shortening the aperture r1 and the lens interval.
(3) Display Device Further, it is possible to provide a display device in which the above-described imaging lens system is used, a display object (not shown) is disposed on the reduction conjugate surface, and the enlargement conjugate side is the display surface. An area-type light modulation element can be used as the display object, and a screen can be arranged on the enlargement conjugate side. According to this display device, it is small and bright, and the decrease in the amount of peripheral light can be reduced.

<Example>
In the following, six examples of the above-described imaging lens system including three lens groups and including five lenses will be described.
Each of the following embodiments will be described with an arrangement for producing a reduced image. In Examples 1 to 4, the reduction ratio M = −0.01778, which is representative of the conditions used in the imaging device or the display device. Examples 5 and 6 have a reduction ratio M = −0.11 and are often used in image reading apparatuses. The focal length: f = 100 and the maximum image height: H ′ = 37.5 are common. In all of the six examples, the maximum half angle of view: ω is about 20.5 °, and the aperture efficiency is 100% up to the image height at the outermost periphery. In order from the magnification conjugate side, gk is the k-th lens group, ri is the radius of curvature of the i-th surface including the stop, di is the lens thickness or air gap between the i-th surface and the (i + 1) -th surface, and nj is the first The refractive index of the d-line of the j-th lens, νj is the Abbe number. The aspherical surface used is expressed by the following equation, where the optical axis direction coordinate is X, the radial direction coordinate is Y, the paraxial radius of curvature is R, the conic constant is K, the higher order coefficients are M4, M6, M8,. It expresses like this.
X = Y ² / [R + R · √ {1− (1 + K) Y ² / R ² }
+ M4 * Y ⁴ + M6 * Y ⁶ + M8 * Y ⁸ + M10 * Y ¹⁰
In each example, a configuration diagram and an aberration diagram are respectively shown. In the configuration diagram, the same reference numerals as those in the above embodiment are used. “I = 0” is the object plane, and s is the stop.
The wavelength of the aberration diagram is based on the d line; 587.56 nm, and the chromatic aberration is Red = R; 630 nm, Blue = B; 470 nm. In the aberration diagrams, in order, spherical aberration and chromatic aberration of spherical aberration, and in the chromatic aberration diagram of curvature of field and curvature of field, the solid line is the sagittal image plane and the broken line is the meridional image plane. The vertical axis of the field curvature and distortion diagrams is the image height. The coma aberration is displayed from the bottom in order of image height ratio: p = 0.4, 0.8, 1.0, and each meridional and sagittal are displayed. Each aberration curve is filled with d, R, and B as required.
In Examples 5 and 6 which are the specifications of the image reading apparatus, the distortion is corrected to within 0.2%.

ｒ５面は非球面で、ｒ５は近軸曲率半径、ｋ＝０．０、Ｍ４＝−４．２６７Ｅ−０７、Ｍ６＝−１．３５４Ｅ−１０、Ｍ８＝４．９７１Ｅ−１４、Ｍ１０＝−１．０６５Ｅ−２０、ｒ９面は非球面で、ｒ９は近軸曲率半径、ｋ＝０．０、Ｍ４＝６．０７１Ｅ−０７、Ｍ６＝９．９９５Ｅ−１１、Ｍ８＝４．５３７Ｅ−１４、Ｍ１０＝１．００１Ｅ−１７である。 [Example 1]
FIG. 2 is a configuration diagram of this example, and FIG. 5 is an aberration diagram. FNo. = 2.0, half angle of view: ω = 2.54, telecentric, the values of the above equations are (1) = 1.21, (2) = 5.04, (3) = − 4.83, (4) = 23.1, (5) = 26.7.

The r5 surface is an aspherical surface, r5 is a paraxial radius of curvature, k = 0.0, M4 = −4.267E−07, M6 = −1.354E−10, M8 = 4.971E−14, M10 = −1. 0.05E-20, r9 surface is aspherical, r9 is paraxial radius of curvature, k = 0.0, M4 = 6.071E-07, M6 = 9.995E-11, M8 = 4.537E-14, M10 = 1.001E-17.

ｒ５面は非球面で、ｒ５は近軸曲率半径、ｋ＝０．０、Ｍ４＝−５．３９５Ｅ−０８、Ｍ６＝−１．５３４Ｅ−１１、Ｍ８＝６．７８０Ｅ−１６、Ｍ１０＝−９．０１５Ｅ−２１、ｒ９面は非球面で、ｒ９は近軸曲率半径、ｋ＝０．０、Ｍ４＝６．３５９Ｅ−０７、Ｍ６＝８．５９０Ｅ−１１、Ｍ８＝５．８７３Ｅ−１４、Ｍ１０＝−５．３６７Ｅ−１８である。 [Example 2]
FIG. 2 is a block diagram of the present embodiment, and FIG. 6 is an aberration diagram thereof. FNo. = 2.0, half angle of view: ω = 2.45, non-telecentric, the values of the above equations are (1) = 1.18, (2) = 4.24, (3) = − 4.20. (4) = 20.0 and (5) = 26.6.

The r5 surface is an aspherical surface, r5 is a paraxial radius of curvature, k = 0.0, M4 = −5.395E−08, M6 = −1.534E−11, M8 = 6.780E−16, M10 = −9. .015E-21, r9 surface is aspherical, r9 is paraxial radius of curvature, k = 0.0, M4 = 6.359E-07, M6 = 8.590E-11, M8 = 5.873E-14, M10 = -5.367E-18.

ｒ９面は非球面で、ｒ９は近軸曲率半径、ｋ＝０．０、Ｍ４＝１．０３５Ｅ−０６、Ｍ６＝１．４９４Ｅ−１０、Ｍ８＝１．３０７Ｅ−１４、Ｍ１０＝２．０７７Ｅ−１７である。 [Example 3]
FIG. 3 is a block diagram of the present embodiment, and FIG. 7 is an aberration diagram thereof. FNo. = 2.8, half angle of view: ω = 2.54, telecentric, the values of the above equations are (1) = 1.85, (2) = 8.26, (3) = − 5.60, (4) = 31.6, (5) = 32.1.

The r9 surface is an aspherical surface, and r9 is a paraxial radius of curvature, k = 0.0, M4 = 1.35E-06, M6 = 1.494E-10, M8 = 1.307E-14, M10 = 2.777E−. 17.

ｒ６面は非球面で、ｒ６は近軸曲率半径、ｋ＝０．０、Ｍ４＝−５．５２３Ｅ−０８、Ｍ６＝−９．２２２Ｅ−１１、Ｍ８＝１．８１４Ｅ−１６、Ｍ１０＝−３．８３３Ｅ−２１、ｒ１０面は非球面で、ｒ１０は近軸曲率半径、ｋ＝０．０、Ｍ４＝５．６８３Ｅ−０７、Ｍ６＝１．４６５Ｅ−１０、Ｍ８＝１．２０７Ｅ−１４、Ｍ１０＝２．８１６Ｅ−１７である。 [Example 4]
FIG. 4 is a configuration diagram of this example, and FIG. 8 is an aberration diagram thereof. FNo. = 2.0, half angle of view: ω = 2.54, telecentric, the values of the above equations are (1) = 1.22, (2) = 5.79, (3) = − 5.56, (4) = 24.7, (5) = 27.6.

The r6 surface is an aspherical surface, r6 is a paraxial radius of curvature, k = 0.0, M4 = −5.523E-08, M6 = −9.222E-11, M8 = 1.814E-16, M10 = −3. .833E-21, r10 surface is aspherical, r10 is paraxial radius of curvature, k = 0.0, M4 = 5.683E-07, M6 = 1.465E-10, M8 = 1.207E-14, M10 = 2.816E-17.

ｒ４面は非球面で、ｒ４は近軸曲率半径、ｋ＝０．０、Ｍ４＝１．９８７Ｅ−０８、Ｍ６＝１．６１９Ｅ−１１、Ｍ８＝−６．５７７Ｅ−１６、Ｍ１０＝１．５６３Ｅ−１８、ｒ５面は非球面で、ｒ５は近軸曲率半径、ｋ＝０．０、Ｍ４＝−２．０７１Ｅ−０７、Ｍ６＝−２．３８９Ｅ−１１、Ｍ８＝２．４１８Ｅ−１５、Ｍ１０＝−９．５０１Ｅ−２０、ｒ９面は非球面で、ｒ９は近軸曲率半径、ｋ＝０．０、Ｍ４＝６．２８２Ｅ−０７、Ｍ６＝８．０８１Ｅ−１１、Ｍ８＝４．３３１Ｅ−１４、Ｍ１０＝４．９９０Ｅ−１８である。 [Example 5]
FIG. 2 is a configuration diagram of this example, and FIG. 9 is an aberration diagram thereof. FNo. = 2.8, half angle of view: ω = 2.06, telecentric, the values of the above equations are (1) = 1.07, (2) = 4.88, (3) = − 2.59, (4) = 20.5 and (5) = 22.1.

The r4 surface is an aspherical surface, r4 is a paraxial radius of curvature, k = 0.0, M4 = 1.987E-08, M6 = 1.619E-11, M8 = −6.577E-16, M10 = 1.563E. −18, r5 surface is aspherical, r5 is paraxial radius of curvature, k = 0.0, M4 = −2.071E-07, M6 = −2.389E-11, M8 = 2.418E-15, M10 = -9.501E-20, r9 surface is aspherical, r9 is paraxial radius of curvature, k = 0.0, M4 = 6.282E-07, M6 = 8.081E-11, M8 = 4.331E- 14, M10 = 4.990E-18.

ｒ５面は非球面で、ｒ５は近軸曲率半径、ｋ＝０．０、Ｍ４＝−１．１９４Ｅ−０７、Ｍ６＝−３．３０８Ｅ−１１、Ｍ８＝２．５４４Ｅ−１５、Ｍ１０＝−５．３３９Ｅ−２０、ｒ９面は非球面で、ｒ９は近軸曲率半径、ｋ＝０．０、Ｍ４＝７．９５１Ｅ−０７、Ｍ６＝３．１７６Ｅ−１１、Ｍ８＝１．６２５Ｅ−１３、Ｍ１０＝−７．４８１Ｅ−１７である。
以上のとおり、各実施例の収差図は良好な特性を示している。 [Example 6]
FIG. 2 is a configuration diagram of this example, and FIG. 10 is an aberration diagram thereof. FNo. = 2.4, half angle of view: ω = 20.0, non-telecentric, the values of the above equations are (1) = 0.98, (2) = 5.28, (3) = − 3.38. , (4) = 22.1, (5) = 19.2.

The r5 surface is an aspheric surface, r5 is a paraxial radius of curvature, k = 0.0, M4 = −1.194E-07, M6 = −3.308E-11, M8 = 2.544E-15, M10 = −5. .339E-20, r9 surface is aspherical, r9 is paraxial radius of curvature, k = 0.0, M4 = 7.951E-07, M6 = 3.176E-11, M8 = 1.625E-13, M10 = −7.481E-17.
As described above, the aberration diagrams of the examples show good characteristics.

It is a block diagram of the imaging lens system which is one Embodiment of this invention. 1 is a configuration diagram of Example 1. FIG. FIG. 6 is a configuration diagram of Example 3. FIG. 6 is a configuration diagram of Example 4. FIG. 6 is an aberration diagram of Example 1. FIG. 6 is an aberration diagram of Example 2. FIG. 6 is an aberration diagram of Example 3. FIG. 6 is an aberration diagram of Example 4. FIG. 6 is an aberration diagram of Example 5. FIG. 6 is an aberration diagram of Example 6.

Explanation of symbols

L1 Negative lens L2 Positive lens L3 Positive lens L4 Positive lens L5 Negative lens r1 Aperture

Claims (11)

From the magnification conjugate side,
Aperture,
A first group consisting of a negative lens having a strong curvature on the diaphragm side surface and a positive lens having a curvature on the diaphragm side surface weaker than that of the negative lens;
A second group having positive power;
A third group which is a lens having a surface in which a positive lens and a negative lens are cemented in this order and a surface closest to the reduction conjugate is convex to the stop;
An imaging lens system comprising:   The first group is a lens in which the negative lens which is a negative meniscus lens having a convex surface facing the diaphragm opposite to the diaphragm and the positive lens which is a positive meniscus lens having a convex surface facing the diaphragm opposite to the diaphragm. The imaging lens system according to claim 1. When the focal length of the entire system is f and the focal length of the second group is f2,
0.8 ≦ f2 / f ≦ 2
The imaging lens system according to claim 1 or 2, wherein When the radius of curvature of the surface closest to the stop of the k-th group (k = 1, 2, 3) is Rkf, and the radius of curvature of the surface farthest from the stop of the k-th group is Rkr,
3 ≦ (R1r + R1f) / (R1r−R1f) ≦ 10
−7 ≦ (R3r + R3f) / (R3r−R3f) ≦ −1
The imaging lens system according to any one of claims 1 to 3, wherein   5. The imaging lens system according to claim 1, wherein at least one surface of each lens is an aspherical surface.   The surface farthest from the stop of the third group is an aspherical surface, and the amount of deviation from the reference spherical surface is a direction in which the concave power increases. Imaging lens system. When the Abbe number νkp of the d-line of the positive lens and the Abbe number νkn of the d-line of the negative lens in the k-th group (k = 1, 2, 3),
15 ≦ ν1p−ν1n
15 ≦ ν3p−ν3n
The imaging lens system according to any one of claims 1 to 6, wherein   The imaging lens system according to claim 1, wherein the stop is disposed in the vicinity of a front focal point of the lens system including the respective groups. An imaging lens system according to any one of claims 1 to 7,
An image sensor disposed on the reduction conjugate side of the imaging lens system;
With
An image reading apparatus for reading a document image arranged on an enlargement conjugate plane of the imaging lens system. An imaging lens system according to any one of claims 1 to 7,
An image sensor disposed on the reduction conjugate side of the imaging lens system;
With
An imaging apparatus for photographing a subject on the magnification conjugate plane side of the imaging lens system. An imaging lens system according to any one of claims 1 to 7,
A display object arranged on the reduced conjugate plane;
With
A display device, wherein a magnification conjugate side of the imaging lens system is a display surface.

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