JP2011257625A - Lens system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zoom lens system suitable for an imaging device intended for monitoring, etc.SOLUTION: A lens system 10 is provided that includes, in order from an object side 10a, a movable first lens group G1 with negative refractive power when zooming, a stationary stop S when zooming, a movable second lens group G2 with positive refractive power when zooming and a stationary third lens group G3 with positive refractive power when zooming. The first lens group G1 approaches toward a stop S when zooming from a wide-angle end to a telephoto end. The second lens group G2 is composed of a positive first lens L21 and a cemented lens L2B arranged in order from the object side 10a. The cemented lens L2B is composed of a negative second lens L22, a positive third lens L23 and a negative fourth lens L24 arranged in order from the object side 10a, and approaches toward the stop S when zooming from the wide-angle end to the telephoto end.

Description

  The present invention relates to a wide-angle lens system.

  Patent Document 1 describes a zoom lens that has a wide angle of view and high optical performance over the entire zoom range and the entire object distance range. This zoom lens has a first lens group having a negative refractive power and a second lens group having a positive refractive power in order from the object side to the image side. During zooming from the wide-angle end to the telephoto end, the first lens The first and second lens groups move so that the distance between the group and the second lens group in the optical axis direction becomes small.

JP2009-271165A

  Wide-angle lens systems, in particular, super-wide-angle lens systems with a total angle of view exceeding 140 degrees, are being considered for use for a wide variety of purposes such as surveillance as the performance of image sensors such as CCDs and CMOSs increases. Yes. A lens system mounted on an image pickup apparatus including such an image pickup device has a small F-number (FNo) that is high-resolution, can be zoomed, and can obtain a bright image from the wide-angle end to the telephoto end. Is desired.

  One aspect of the present invention includes, in order from the object side, a first lens group having a negative refractive power that moves during zooming, a diaphragm (aperture diaphragm) that does not move during zooming, This is a lens system including a second lens group having a positive refractive power that moves at the time of shifting and a third lens group having a positive refractive power that does not move at the time of zooming. The first lens group approaches the diaphragm when zooming from the wide-angle end to the telephoto end. The second lens group includes a first lens having a positive refractive power arranged in order from the object side and a cemented lens. The cemented lens is a second lens having a negative refractive power arranged in order from the object side. And a third lens having a positive refractive power and a fourth lens having a negative refractive power. Further, when zooming from the wide-angle end to the telephoto end, the lens approaches the aperture.

  In this lens system, the second lens group includes a variator (magnification group) and a function of correcting aberration. The second lens group is composed of a first lens having a positive refractive power mainly having a function as a variator, and a cemented lens having three bonded layers mainly having a function as aberration correction. By moving the second lens group with respect to the stop during zooming, it becomes possible to obtain a clearer image in various environments.

  In other words, by adopting a type that does not move the diaphragm during zooming, for example, a device (iris) having a plurality of diaphragm blades called a galvano type and a mechanism that can control the diaphragm value relatively large. Device) is easy to adopt. Therefore, this lens system can widen the adjustment range of the aperture value with respect to the change in brightness depending on the installation location and day and night, and is suitable for an imaging apparatus used in various environments. One example of such an imaging device is a highly sensitive surveillance camera.

  On the other hand, the aperture value may be changed manually or automatically. However, if the aperture value is reduced, the depth of focus becomes deep, and it becomes difficult to detect (adjust) the focus position (focus position). Further, in a system that employs a large number of lenses in order to increase the aberration correction capability, the influence on the image quality due to the shift of the focus position becomes large. In this lens system, the ability to correct aberrations by combining a large number of lenses is obtained by adopting a cemented lens having three bonded lenses in the second lens group. Therefore, a clearer image can be obtained in various environments with different brightness and the like.

  Further, in this lens system, since various aberrations can be corrected by the third lens group, both the first lens group and the second lens group are provided at and near the telephoto end where the amount of light tends to be insufficient. It can be close to the aperture. Therefore, it is possible to provide a lens system having a small F-number from the wide-angle end to the telephoto end, and an ultra-wide-angle lens system that has a high resolution and can obtain a brighter image.

  In this lens system, the air gap between the first lens group and the diaphragm monotonously decreases when zooming from the wide-angle end to the telephoto end, and the air gap between the second lens group and the diaphragm is from the wide-angle end. It is desirable to decrease monotonously when zooming to the telephoto end. As a result, a bright lens system with a smaller F-number can be obtained.

  A typical example of this lens system is a super-wide-angle lens system, typically a fish-eye or close-to-fish-eye lens system with a half angle of view at the wide-angle end of at least 70 degrees.

In this lens system, it is desirable that the combined focal length f3 of the third lens group and the combined focal length fw of the lens system at the wide angle end satisfy the following condition (A).
5 <f3 / fw <30 (A)
When the condition (A) is not reached, the ratio of the power of the third lens group becomes too large, and it becomes difficult to ensure the amount of light. On the other hand, when the condition (A) is exceeded, the power of the third lens group becomes insufficient, and aberration correction becomes difficult.

In this lens system, it is desirable that the first lens group includes a plurality of lenses having a negative refractive power in order to obtain a super wide angle and to suppress the occurrence of aberrations due to the super wide angle. Further, in the lens having the most negative refractive power on the object side most likely to bend the light beam, in order to suppress the occurrence of aberration, the focal length f11 and the combined focal length fw of the lens system at the wide angle end Preferably satisfies the following condition (B).
| F11 | / fw> 3.50 (B)

In this lens system, it is desirable that the focal length f21 of the first lens of the second lens group and the combined focal length f2B of the cemented lens satisfy the following conditions.
0 <f21 / | f2B | <1.50 (1.0)

  In the second lens group having a positive power as a whole, most of the power is handled by the positive first lens, so that the field curvature generated in the first lens group can be easily corrected. If the upper limit of the expression (1.0) is exceeded, the power of the positive first lens is insufficient, and correction of field curvature tends to be insufficient. Furthermore, by suppressing the power of the cemented lens, it is possible to satisfactorily correct various aberrations other than the curvature of field that occur in the first lens group and various aberrations such as chromatic aberration that are increased by the positive first lens. Therefore, it is possible to provide a bright lens system that is an ultra-wide-angle variable magnification type and that has various aberrations corrected satisfactorily.

  Since various aberrations can be satisfactorily corrected in this lens system, this lens system can be adapted to day and night. Therefore, it is possible to provide a fish-eye zoom lens system that can be applied to an imaging device for monitoring purposes. In the day / night lens system, it is desirable that the chromatic aberration is corrected well over a wide range from the visible wavelength range (400 to 700 nm) to the near infrared wavelength range (700 to 1000 nm).

In this lens system, an Abbe number ν22 of the negative second lens of the cemented lens of the second lens group, an Abbe number ν23 of the positive third lens, and an Abbe number ν24 of the negative fourth lens are further provided. It is desirable to satisfy the following conditions.
30.0 <ν23−ν22 <76.1 (2.1.0)
30.0 <ν23−ν24 <76.1 (2.2.0)
ν23> 70.0 (3.0)

  A third low-dispersion (high Abbe number) positive third lens disposed in the center of the cemented lens, a high-dispersion (low Abbe number) negative second lens disposed on the object side and the image side, and a negative second lens By combining the four lenses, it is possible to improve the on-axis / magnification chromatic aberration correction capability in the second lens group. Conditions (2.1.0) and (2.2.0) are conditions suitable for a day / night lens system, and together with condition (1.0), in the second lens group, The power distribution is slightly increased so that the on-axis / magnification chromatic aberration of the cemented lens is easily corrected. At the same time, the condition (3.0) is that the positive first lens of the first lens group and the second lens group is secured by securing the Abbe number of the positive third lens disposed in the center of the cemented lens. As a result, the ability to correct axial chromatic aberration and lateral chromatic aberration, which are increased, is improved.

In this lens system, the refractive index n22 of the negative second lens of the cemented lens of the second lens group, the refractive index n23 of the positive third lens, and the refractive index n24 of the negative fourth lens are further provided. It is desirable to satisfy the following conditions.
n22-n23> 0.13 (4.1.0)
n24-n23> 0.13 (4.2.0)
By reducing the refractive index of the positive third lens disposed in the center of the cemented lens and increasing the refractive indices of the negative second lens and the negative fourth lens disposed on the object side and the image side thereof The ability to correct various aberrations in the second lens group can be improved.

In this lens system, it is further desirable to satisfy the following conditions.
0.15 <f21 / | f2B | <0.30
45.0 <ν23−ν22 <76.1
35.0 <ν23−ν24 <76.1
ν23> 80.0

  It is a lens system that can be used both day and night, and can provide an economical and sufficient lens system. Since this lens system is bright and has high aberration correction capability, it is also suitable for applications such as obtaining high-resolution images or manually changing magnification. One application for manually changing the magnification is also referred to as varifocal, and is a lens system that does not have an autofocus mechanism or an electric focus mechanism and does not have an electric zoom mechanism. It is a monitoring application installed at a predetermined place. In particular, by limiting to the visible light wavelength range (400 to 700 nm), it is possible to provide a lens system that can correct the field curvature more satisfactorily and obtain a higher resolution image. This lens system can also be applied to a system having an autofocus mechanism and / or an automatic iris mechanism.

The lens system preferably further satisfies the following conditions.
0 <f21 / | f2B | <0.75 (1.1)
By increasing the power ratio of the first lens of the second lens group, it is possible to improve the field curvature correction capability, and to provide a lens system that can obtain a bright and high-resolution image.

In this lens system, the Abbe number ν22 of the negative second lens of the cemented lens of the second lens group, the Abbe number ν23 of the positive third lens, and the Abbe number ν24 of the negative fourth lens are as follows. It is desirable to satisfy the conditions.
20.0 <ν23−ν22 <76.1 (2.1.1)
20.0 <ν23−ν24 <76.1 (2.2.1)
ν23> 60.0 (3.1)
By targeting visible light, the correction ability for axial chromatic aberration and lateral chromatic aberration can be set slightly lower than day and night, and a low-cost lens system can be provided.

In this lens system, the refractive index n22 of the negative second lens of the cemented lens of the second lens group, the refractive index n23 of the positive third lens, and the refractive index n24 of the negative fourth lens are as follows. It is desirable to satisfy the following conditions.
n22-n23> 0.16 (4.1.1)
n24-n23> 0.16 (4.2.1)
The ability to correct aberrations such as astigmatism and coma can be further increased, and a higher resolution image can be obtained.

In this lens system, it is further desirable to satisfy the following conditions.
0 <f21 / | f2B | <0.15
45.0 <ν23−ν22 <76.1
30.0 <ν23−ν24 <76.1
ν23> 80.0
A lens system of a high resolution type in the visible light region, which is economical and has sufficient performance can be provided.

  Another aspect of the present invention is an imaging apparatus including the lens system described above and an imaging element that acquires an image (image) formed by the lens system. This lens system has a good imaging performance while having a wide angle of view. Therefore, it is possible to provide an imaging device that can handle day and night, an imaging device that can acquire a higher resolution image in the visible light region, and the like.

It is a figure which shows schematic structure of the lens system and imaging device which concern on 1st Embodiment, (a) shows arrangement | positioning at a wide-angle end, (b) shows arrangement | positioning of a telephoto end. FIG. 3 is a diagram illustrating lens data of the lens system according to the first embodiment. It is a figure which shows the numerical values of the lens system which concerns on 1st Embodiment, (a) is basic data, (b) is aspherical data, (c) is zoom data, (d) is the focal distance of each lens. Show. FIG. 3 is a diagram showing longitudinal aberration at the wide-angle end of the lens system according to the first embodiment. FIG. 4 is a diagram illustrating longitudinal aberration at the telephoto end of the lens system according to the first embodiment. It is a figure which shows schematic structure of the lens system and imaging device which concern on 2nd Embodiment, (a) shows arrangement | positioning at a wide-angle end, (b) shows arrangement | positioning of a telephoto end. The figure which shows the lens data of the lens system which concerns on 2nd Embodiment. It is a figure which shows the numerical values of the lens system which concerns on 2nd Embodiment, (a) is basic data, (b) is aspherical data, (c) is zoom data, (d) is the focal distance of each lens. Show. The figure which shows the longitudinal aberration of the wide-angle end of the lens system which concerns on 2nd Embodiment. The figure which shows the longitudinal aberration of the telephoto end of the lens system which concerns on 2nd Embodiment. It is a figure which shows schematic structure of the lens system and imaging device which concern on 3rd Embodiment, (a) shows arrangement | positioning at a wide-angle end, (b) shows arrangement | positioning of a telephoto end. The figure which shows the lens data of the lens system which concerns on 3rd Embodiment. It is a figure which shows the numerical values of the lens system which concerns on 3rd Embodiment, (a) is basic data, (b) is aspherical data, (c) is zoom data, (d) is the focal distance of each lens. Show. The figure which shows the longitudinal aberration of the wide-angle end of the lens system which concerns on 3rd Embodiment. The figure which shows the longitudinal aberration of the telephoto end of the lens system which concerns on 3rd Embodiment. It is a figure which shows schematic structure of the lens system and imaging device which concern on 4th Embodiment, (a) shows arrangement | positioning at a wide-angle end, (b) shows arrangement | positioning of a telephoto end. The figure which shows the lens data of the lens system which concerns on 4th Embodiment. It is a figure which shows the numerical values of the lens system which concerns on 4th Embodiment, (a) is basic data, (b) is aspherical data, (c) is zoom data, (d) is the focal distance of each lens. Show. The figure which shows the longitudinal aberration of the wide-angle end of the lens system which concerns on 4th Embodiment. The figure which shows the longitudinal aberration of the telephoto end of the lens system which concerns on 4th Embodiment. It is a figure which shows schematic structure of the lens system and imaging device which concern on 5th Embodiment, (a) shows arrangement | positioning at a wide-angle end, (b) shows arrangement | positioning of a telephoto end. The figure which shows the lens data of the lens system which concerns on 5th Embodiment. It is a figure which shows the numerical values of the lens system which concerns on 5th Embodiment, (a) is basic data, (b) is aspherical data, (c) is zoom data, (d) is the focal distance of each lens. Show. The figure which shows the longitudinal aberration of the wide-angle end of the lens system which concerns on 5th Embodiment. The figure which shows the longitudinal aberration of the telephoto end of the lens system which concerns on 5th Embodiment. It is a figure which shows schematic structure of the lens system and imaging device which concern on 6th Embodiment, (a) shows arrangement | positioning at a wide-angle end, (b) shows arrangement | positioning of a telephoto end. The figure which shows the lens data of the lens system which concerns on 6th Embodiment. It is a figure which shows the numerical values of the lens system which concerns on 6th Embodiment, (a) is basic data, (b) is aspherical data, (c) is zoom data, (d) is the focal distance of each lens. Show. The figure which shows the longitudinal aberration of the wide-angle end of the lens system which concerns on 6th Embodiment. The figure which shows the longitudinal aberration of the telephoto end of the lens system which concerns on 6th Embodiment. It is a figure which shows schematic structure of the lens system and imaging device which concern on 7th Embodiment, (a) shows arrangement | positioning at a wide-angle end, (b) shows arrangement | positioning of a telephoto end. The figure which shows the lens data of the lens system which concerns on 7th Embodiment. It is a figure which shows the numerical values of the lens system which concerns on 7th Embodiment, (a) is basic data, (b) is aspherical data, (c) is zoom data, (d) is the focal distance of each lens. Show. The figure which shows the longitudinal aberration of the wide-angle end of the lens system which concerns on 7th Embodiment. The figure which shows the longitudinal aberration of the telephoto end of the lens system which concerns on 7th Embodiment. It is a figure which shows schematic structure of the lens system and imaging device which concern on 8th Embodiment, (a) shows arrangement | positioning at a wide-angle end, (b) shows arrangement | positioning of a telephoto end. The figure which shows the lens data of the lens system which concerns on 8th Embodiment. It is a figure which shows the numerical values of the lens system which concerns on 8th Embodiment, (a) is basic data, (b) is aspherical data, (c) is zoom data, (d) is the focal distance of each lens. Show. The figure which shows the longitudinal aberration of the wide-angle end of the lens system which concerns on 8th Embodiment. The figure which shows the longitudinal aberration of the telephoto end of the lens system which concerns on 8th Embodiment. It is a figure which shows schematic structure of the lens system and imaging device which concern on 9th Embodiment, (a) shows arrangement | positioning at a wide-angle end, (b) shows arrangement | positioning of a telephoto end. The figure which shows the lens data of the lens system which concerns on 9th Embodiment. It is a figure which shows the numerical values of the lens system which concerns on 9th Embodiment, (a) is basic data, (b) is aspherical data, (c) is zoom data, (d) is the focal distance of each lens. Show. The figure which shows the longitudinal aberration of the wide angle end of the lens system which concerns on 9th Embodiment. The figure which shows the longitudinal aberration of the telephoto end of the lens system which concerns on 9th Embodiment. It is a figure which shows schematic structure of the lens system and imaging device which concern on 10th Embodiment, (a) shows arrangement | positioning at a wide-angle end, (b) shows arrangement | positioning of a telephoto end. The figure which shows the lens data of the lens system which concerns on 10th Embodiment. It is a figure which shows the numerical values of the lens system which concerns on 10th Embodiment, (a) is basic data, (b) is aspherical data, (c) is zoom data, (d) is the focal distance of each lens. Show. The figure which shows the longitudinal aberration of the wide angle end of the lens system which concerns on 10th Embodiment. The figure which shows the longitudinal aberration of the telephoto end of the lens system which concerns on 10th Embodiment.

  FIG. 1 shows a schematic configuration of an imaging apparatus using a typical lens system according to an embodiment of the present invention. The imaging apparatus 1 includes a lens system 10 and an imaging element 11 that converts an image formed by the lens system 10 into digital data. A typical image pickup device 11 is a semiconductor image pickup device such as a CCD or a CMOS. The lens system 10 includes, in order from the object side 10a, a first lens group G1 having a negative refractive power, a stop (aperture stop) S, a second lens group G2 having a positive refractive power, And a third lens group G3 having a refractive power of 2.

  1A shows the arrangement of the lens system 10 at the wide-angle end (WIDE), and FIG. 1B shows the arrangement of the lens system 10 at the telephoto end (TELE). The lens system 10 is a varifocal lens, which fixes the third lens group G3 and the diaphragm S, and moves the first lens group G1 and the second lens group G2 along the optical axis, thereby wide-angle. You can zoom between the end and the telephoto end. Specifically, when zooming from the wide-angle end to the telephoto end, the first lens group G1 is brought closer to the stationary stop S to shorten the air interval. Further, when zooming from the wide-angle end to the telephoto end, the second lens group G2 is brought closer to the stationary diaphragm S to shorten the air interval.

  The movement of the first lens group G1 and the second lens group G2 can be typically a monotonous movement, but may be a movement including a return. In this lens system 10, the focus adjustment can be performed by the first lens group G1 and / or the second lens group G2 that move during zooming. In particular, in the lens system 10 that performs zooming manually, it is desirable to perform focus adjustment using the first lens group G1 or the second lens group G2. The third lens group G3 can be fixed during focus adjustment. Focus adjustment may be performed by moving the third lens group G3. In a system that performs zooming by moving the first lens group G1 and the second lens group G2 by a motor or the like, it is desirable to perform focusing by the third lens group G3.

  The lens system 10 includes ten lenses L11 to L14, L21 to L24, and L31 to L32 grouped into three lens groups G1, G2, and G3. The first lens group G1 closest to the object side 10a is a lens group having a negative refractive power as a whole, and is arranged in order from the object side 10a to a negative meniscus lens L11 convex to the object side 10a and to the object side 10a. The lens includes a convex negative meniscus lens L12, a biconcave negative lens L13, and a positive meniscus lens L14 convex on the object side 10a.

  This lens system 10 is a retro-focus type super-wide-angle lens system having three groups of negative-positive-positive and preceded by a negative lens group. This is a lens system having an angle of 140 degrees or more. The first lens group G1 includes a role of converting a light beam having a steep incident angle from the object side into parallel to the optical axis and introducing the light beam into the second lens group G2.

  The second lens group G2 is a lens group that has a positive refractive power as a whole, and is a biconvex positive lens (positive first lens) L21 and a cemented lens that is bonded to three in order from the object side 10a. (Balsam lens, 3 balsam) L2B. The cemented lens L2B includes a negative meniscus lens (negative second lens) L22 that is convex on the object side 10a, a biconvex positive lens (positive third lens) L23, and a negative meniscus lens that is convex on the image side 10b. (Negative fourth lens) L24.

  The second lens group G2 includes a variator (a variable power group), a function of correcting aberrations due to the wide angle of view generated by the first lens group G1, and correcting aberrations on the optical axis. . One or both surfaces of the preceding first lens L21 are aspherical surfaces, and the positive aspherical surface of the first lens L21 is responsible for most of the convergence (positive) power of the second lens group G2. . The cemented lens L2B is a type in which both sides of a positive single lens L23 are sandwiched between two negative lenses L22 and L24, and has a high aberration correction capability but a long combined focal length.

  The third lens group G3 is a lens group having a positive refractive power as a whole, and includes a biconcave negative lens L31 and a biconvex positive lens L32 in order from the object side 10a. The image pickup device 11 is disposed on the image side 10b of the third lens group G3 with a single glass cover glass CG interposed therebetween.

  The third lens group G3 includes a function of correcting an undercorrected aberration of the first lens group G1 and the second lens group G2, and corrects spherical aberration and axial chromatic aberration, thereby contributing to a high F value. . That is, in this lens system 10, a combination of the second lens group G2 including the positive lens L21 and the triplet type cemented lens L2B and the diaphragm S that restricts the light rays incident on the second lens group G2. As a result, the aberration correction capability of the second lens group G2 can be improved, and an image in which aberration is favorably corrected at an ultra-wide field angle can be obtained. Further, the third lens group G3 is arranged to separate (load) the aberration correction function, so that the diaphragm S is fixed (not moved), and the second lens group G2 is easily moved.

  This lens system 10 has a plurality of (typically two) diaphragm blades called a galvano type as a diaphragm (stop, iris) S, and a device having a mechanism capable of controlling a diaphragm value relatively large. (Iris device) S is adopted. Since the lens system 10 does not require a mechanism for moving the iris device S, the lens system 10 can be easily assembled as the lens system 10 even when the iris device S is large and relatively heavy. Therefore, the imaging apparatus 1 provided with this lens system 10 can widen the aperture adjustment range with respect to changes in brightness depending on the installation location and day and night, and is a highly sensitive surveillance camera (imaging apparatus) that is employed for monitoring purposes. ) Easy to use in various environments.

  The iris device S may be a device that manually changes the aperture value or a device that can automatically change the aperture value (auto iris). The iris device S is a system that employs a large number of lenses in order to increase the aberration correction capability because it becomes difficult to adjust the focus position (focus position) because the depth of focus becomes deep when the light beam is narrowed down. Also, the influence on the image quality due to the shift of the focus position becomes large. In this lens system 10, a cemented lens L2B bonded to three lenses is used for the second lens group G2, and aberration correction capability is obtained by combining a plurality of lenses, and the effect on the focal position is reduced. . Therefore, it is possible to provide the lens system 10 and the imaging device 1 that can obtain a clearer image in various environments with different brightness and the like.

  The effect of the bright F value is maximized in a dim environment such as early morning or evening. At the time of installation, it is unlikely to work in these dimly lit environments, and installation is performed in a somewhat bright environment.

  Since spherical aberration exists in the optical system, the focal position moves when the aperture is small and the aperture is small. If there is a focus shift, it may be out of focus if it is released after focusing in a narrowed state. The movement of the open position and the focal position of the small stop tends to increase because the spherical aberration tends to increase particularly in a bright lens having an F value of 1.2 at the wide angle end as in the optical system described below. In order to reduce the focal position movement due to narrowing down, it is important to reduce spherical aberration, chromatic spherical aberration, and axial chromatic aberration.

These aberrations on the optical axis are corrected mainly in the following points in the optical system described below.
Three-piece balsam L2B of the second lens group G2 ··· Spherical aberration, chromatic spherical aberration, axial chromatic aberration Two negative and positive components of the third lens group G3 ··· Axial chromatic aberration imparted to the third lens group G3 Corrected aspherical surfaces ・ ・ Spherical aberrations are corrected

  Moreover, there is also an advantage that variation in performance when assembling the lens system 10 can be suppressed by adopting the cemented lens L2B having three sheets bonded to the second lens group G2. The second lens group G2 has a function as a variator of the zoom lens, and generally tends to have high tolerance sensitivity. In this lens system 10, the second lens group G2 has a simple configuration with a positive lens L21 having an aspherical surface and a cemented lens (balsam lens) L2B bonded with three lenses, and suppresses tolerances during assembly. it can.

  In order to strongly correct mainly chromatic aberration of magnification for visible and high resolution applications and mainly for longitudinal chromatic aberration for day and night applications, it has anomalous dispersion as the positive lens L23 of the cemented lens L2B with three lenses. It is necessary to use glass material. However, in general, a glass material having anomalous dispersion has a negative temperature coefficient that is negatively large, and the focus position may shift with respect to temperature fluctuations. If this lens is attached to a camera that does not have an autofocus mechanism, the focus position varies depending on the temperature, which may impair high resolution. In the negative / positive / negative type balsam lens L2B, the negative lens L22 and / or L24 is made of a material having a positively large temperature coefficient, thereby canceling out the focus variation due to the negatively large temperature coefficient of the refractive index of the positive lens L23. There is also an advantage of being able to do it.

  Further, the first lens group G1 tends to move away from the stop S at the telephoto end, but by adding an aberration correction function by the third lens group G3, the first lens group G1 is stopped at the telephoto end. It is suppressed that the amount of light incident on the second lens group G2 close to S is insufficient. Typically, the first lens group G1 can approach the stop S almost monotonically from the wide-angle end to the telephoto end. Accordingly, it is possible to provide a lens system capable of zooming at an ultra-wide angle with a small F-number from the wide-angle end to the telephoto end and excellent aberration correction.

  Further, in the lens system 10, as described above, the third lens group G3 is configured by two negative and positive lenses L31 and L32, and at least one of both surfaces S18 and S19 of the positive lens L32 is non-visible. By using a spherical surface, the aberration correction capability in the third lens group G3 is enhanced. The third lens group G3 can also be regarded as an independent rear part of the second group of the second group of varifocals. The third lens group G3 mainly corrects axial aberrations and is effective in lowering the F value. That is, the spherical aberration due to the low F value can be corrected by the aspherical surface of the final lens L32. In addition, spherical aberration due to the low F value can be corrected by the difference in refractive index between the two positive and negative lenses of the third lens group G3. Further, when used in the visible to near-infrared region, axial chromatic aberration can be corrected by the Abbe number difference between the two positive and negative lenses of the third lens group G3.

  As a whole, the second lens group G2 corrects wide-angle aberrations (field curvature, coma aberration, lateral chromatic aberration) generated by the first lens group G1. The biconvex positive lens (positive first lens) L21 has an aspherical surface and can correct field curvature among aberrations generated by the first lens group G1, but coma aberration, spherical aberration, and on-axis. There is a possibility of increasing chromatic aberration. The cemented lens (balsam lens) L2B bonded with three lenses has various aberrations (coma aberration, astigmatism, lateral chromatic aberration) of the first lens group G1 and various aberrations (coma aberration, Astigmatism and axial chromatic aberration) are corrected.

The lens system 10 is preferably designed so that the combined focal length f3 of the third lens group G3 and the combined focal length fw of the lens system 10 at the wide angle end satisfy the following condition (A).
5 <f3 / fw <30 (A)
If the condition (A) is not reached, the power ratio of the third lens group G3 becomes too large, and it becomes difficult to secure the light quantity. On the other hand, if the condition (A) is exceeded, the power of the third lens group G3 is insufficient, and aberration correction becomes difficult.

  In the first lens group G1 having a negative power for realizing an ultra wide angle in the lens system 10, three negative power lenses L11, L12, and L13 are arranged in order from the object side 10a. A light beam having a large angle (light beam) is gradually refracted and converted to an angle nearly parallel to the optical axis. For this reason, although the half angle of view is as large as 70 degrees or more at the wide angle end, the occurrence of aberration due to the wide angle of view is suppressed. In particular, the negative power lens disposed closest to the object side 10a is a negative meniscus lens L11 that is convex on the object side 10a. By reducing the power of the lens, a light beam having a high ray height with respect to the optical axis is incident at a wide angle. Even in this case, it is possible to capture the incident light beam by refracting it substantially parallel to the optical axis while suppressing the astigmatism and coma aberration, which are likely to increase with the widening of the angle of view.

Therefore, it is desirable that the lens system 10 is designed so that the focal length f11 of the negative meniscus lens L11 and the combined focal length fw of the lens system at the wide angle end satisfy the following condition (B).
| F11 | / fw> 3.50 (B)
Further, the first lens group G1 has a positive power lens L14 disposed on the most image side 10b, and among various aberrations generated by the three negative power lenses L11 to L13, in particular, spherical aberration. In addition, on-axis / magnification chromatic aberration can be corrected. The convex negative meniscus lens L11 closest to the object side of the first lens group G1 closest to the object side 10a is intended to bend the steep incident light from the object side without difficulty and to guide it to the image side. A meniscus lens configuration is suitable. Negative meniscus lenses tend to have a longer negative focal length, and wide-angle lenses tend to have a shorter focal length. For this reason, unlike a general digital camera, the value of condition (B) becomes large.

  In the second lens group G2 having a zooming function with a positive power, the aspherical surface S10 on the object side 10a of the positive lens L21 has a positive power and the curvature of field generated in the first lens group G1. Can be corrected. However, the aspherical surface S10 has a small radius of curvature in order to give the lens L21 sufficient positive power, and may increase spherical aberration, coma, astigmatism, and axial chromatic aberration. . Therefore, it is preferable to suppress the occurrence of spherical aberration, coma aberration, and astigmatism by setting both surfaces of the lens L21 to aspheric surfaces S10 and S11.

  Further, the aspherical surface S11 on the image side 10b of the lens L21 and the surface S12 on the object side 10a of the cemented lens L2B have a positive power and are optimized so as to reduce the declination with respect to the incident light beam. It is desirable to make it. The light beam can be converged while suppressing an increase in aberration. Further, it is desirable that the object-side surface S12 of the cemented lens L2B has a large radius of curvature so that increase in spherical aberration and coma can be suppressed.

  In the cemented lens L2B, a cemented (bonded) surface S13 of the image side 10b surface of the lens L22 and the object side 10a surface of the lens L23, an image side 10b surface of the lens L23, and an object side 10a surface of the lens L24. The cemented surface S14 has strong negative power and various aberrations (mainly spherical aberration, astigmatism, coma aberration and axial chromatic aberration) generated by the aspheric surface S10 of the first lens group G1 and the lens L21. Easy to correct. Further, it is desirable that the surface S15 on the image side 10b of the cemented lens L2B has a strong positive power so that the light beams diverged from the two cemented surfaces S13 and S14 of the cemented lens L2B can be converged again. However, since the surface S15 has a strong positive power, there is a possibility of increasing spherical aberration, coma aberration, and on-axis / magnification chromatic aberration when the light beam is converged. Various aberrations that are insufficiently corrected in the second lens group G2 can be compensated for in the third lens group G3.

  The cemented lens L2B included in the second lens group G2 includes three negative and positive lenses. The surface S12 closest to the object side 10a is convex to the object side 10a, and the surface S15 closest to the image side 10b is the image side 10b. Convex, biconvex shape. From the viewpoint of aberration correction, the final surface of the cemented lens L2B included in the second lens group G2 that is a variator is desirably a convex diverging surface on the object side 10a. The most convex surface S12 of the object side 10a on the object side 10a has a strong refractive effect because the refractive index of the negative lens L22 is high. Further, the most convex surface S15 of the image side 10b on the image side 10b has a strong refractive effect because the refractive index of the negative lens L24 is high. Because of these effects, the refractive power necessary for the variator of the second lens group G2 can be increased, so that high resolution can be obtained even with a simple configuration. Therefore, in this lens system 10, the surface shape of the final surface S15 is intentionally made convex to the image side 10b, so that the final surface S15 is used as a refracting surface, and the F value is 1.2 with a simple configuration. Achieving a low F value.

  With this lens system 10, it is possible to provide a brighter lens system with a fisheye lens or a super-wide angle close to it, with good aberration correction. The lens system 10 can be used in various applications, but typical ones are for day / night monitoring purposes (day and night) and for obtaining high-resolution visible light images.

  In day / night applications (day and night), it is required that chromatic aberration is well corrected over a wide range from the visible light wavelength range (400 to 700 nm) to the near infrared wavelength range (700 to 1000 nm). For monitoring purposes, there is a demand for a lens system that does not have an autofocus mechanism or an electric focus mechanism and does not have an electric zoom mechanism. In such a lens system, the lens system is bright and has small axial chromatic aberration. Desired.

For day / night applications, chromatic aberration correction capability is particularly required, so it is desirable that the focal length f21 of the first lens and the combined focal length f2B of the cemented lens satisfy the following conditions.
0 <f21 / | f2B | <1.50 (1.0)
More preferably, the upper limit of the condition (1.0) satisfies the following condition.
f21 / | f2B | <0.90 (1.01)
Further, it is more desirable that the upper limit of the condition (1.0) satisfies the following condition.
f21 / | f2B | <0.30 (1.02)
Further, it is more desirable that the lower limit of the condition (1.0) satisfies the following condition.
0.15 <f21 / | f2B | (1.03)

Further, the Abbe number ν22 of the negative second lens L22 of the cemented lens L2B of the second lens group G2, the Abbe number ν23 of the positive third lens L23, and the Abbe number ν24 of the negative fourth lens L24 are as follows. It is desirable to satisfy the following conditions.
30.0 <ν23−ν22 <76.1 (2.1.0)
30.0 <ν23−ν24 <76.1 (2.2.0)
ν23> 70.0 (3.0)

The lower limit of the condition (2.1.0) is a requirement for ensuring the ability to correct axial chromatic aberration and lateral chromatic aberration in the day / night combination type, and it is desirable that the following condition is satisfied.
35.0 <ν23−ν22 (2.1.01)
More preferably, the lower limit of the condition (2.1.0) satisfies the following condition.
45.0 <ν23−ν22 (2.1.02)
More preferably, the lower limit of the condition (2.1.0) satisfies the following condition.
50.0 <ν23−ν22 (2.1.03)
More preferably, the lower limit of the condition (2.1.0) satisfies the following condition.
60.0 <ν23−ν22 (2.1.04)

The lower limit of the condition (2.2.0) is also a requirement for ensuring the ability to correct axial chromatic aberration and lateral chromatic aberration in the day / night combination type, and it is desirable that the following condition is satisfied.
35.0 <ν23−ν24 (2.2.01)
It is desirable that the lower limit of the condition (2.2.0) further satisfies the following conditions.
40.0 <ν23−ν24 (2.2.02)

Condition (3.0) is also a requirement for ensuring the ability to correct axial chromatic aberration and lateral chromatic aberration in the day / night combination type, and it is desirable that the following condition is satisfied.
ν23> 80.0 (3.01)
It is desirable that the condition (3.0) further satisfies the following conditions.
ν23> 90.0 (3.02)

Furthermore, in the day / night combination type, it is desirable that the refractive index n22 of the negative lens L22 of the cemented lens L2B, the refractive index n23 of the positive lens L23, and the refractive index n24 of the negative lens L24 satisfy the following conditions.
n22-n23> 0.13 (4.1.0)
n24-n23> 0.13 (4.2.0)

In the high resolution type lens system 10 in the visible light region, since distortion aberration correction capability is particularly required, the focal length f21 of the first lens L21 of the second lens group and the combined focal length f2B of the cemented lens L2B However, it is desirable that the power of the first lens L21 is large compared to the day / night combination type that satisfies the following conditions.
0 <f21 / | f2B | <0.75 (1.1)
More preferably, the upper limit of the condition (1.1) satisfies the following condition.
f21 / | f2B | <0.65 (1.11)
More preferably, the upper limit of the condition (1.1) satisfies the following condition.
f21 / | f2B | <0.40 (1.12)
More preferably, the upper limit of the condition (1.1) satisfies the following condition.
f21 / | f2B | <0.15 (1.13)
More preferably, the upper limit of the condition (1.1) satisfies the following condition.
f21 / | f2B | <0.05 (1.14)

Even in the high-resolution type in the visible light region, the ability to correct axial chromatic aberration and lateral chromatic aberration is required, and the Abbe number ν22 of the negative second lens L22 of the cemented lens L2B of the second lens group G2 is positive. It is desirable that the Abbe number ν23 of the third lens L23 and the Abbe number ν24 of the negative fourth lens L24 satisfy the following conditions.
20.0 <ν23−ν22 <76.1 (2.1.1)
20.0 <ν23−ν24 <76.1 (2.2.1)
ν23> 60.0 (3.1)

The lower limit of the condition (2.1.1) is a requirement for ensuring the ability to correct axial chromatic aberration and lateral chromatic aberration in the high resolution type, and it is desirable that the following condition is satisfied.
35.0 <ν23−ν22 (2.1.1.1)
More preferably, the lower limit of the condition (2.1.1) satisfies the following condition.
45.0 <ν23−ν22 (2.1.12)
More preferably, the lower limit of the condition (2.1.1) satisfies the following condition.
50.0 <ν23−ν22 (2.1.13)
More preferably, the lower limit of the condition (2.1.1) satisfies the following condition.
60.0 <ν23−ν22 (2.1.14)
The lower limit of the condition (2.2.1) is also a requirement for ensuring the ability to correct axial chromatic aberration and lateral chromatic aberration in the high resolution type, and it is desirable that the following condition is satisfied.
30.0 <ν23−ν24 (2.2.1.1)
It is desirable that the lower limit of the condition (2.2.1) further satisfies the following conditions.
34.0 <ν23−ν24 (2.2.12)
It is desirable that the lower limit of the condition (2.2.1) further satisfies the following conditions.
60.0 <ν23−ν24 (2.2.13)

Condition (3.1) is a requirement for ensuring the ability to correct longitudinal chromatic aberration and lateral chromatic aberration in the high resolution type, and it is desirable that the following condition is satisfied.
ν23> 80.0 (3.11)
It is desirable that the condition (3.1) further satisfies the following condition.
ν23> 90.0 (3.12)

Further, in order to obtain astigmatism and coma correction capability in the high resolution type, the refractive index n22 of the second lens L22 of the cemented lens L2B, the refractive index n23 of the positive third lens L23, and the negative fourth It is desirable that the refractive index n24 of the lens L24 satisfies the following conditions.
n22-n23> 0.16 (4.1.1)
n24-n23> 0.16 (4.2.1)

In the following, some embodiments of the day / night type and the high resolution type will be described.
(First embodiment)
FIG. 1 shows a schematic configuration of an example of an imaging apparatus using a day / night combined type lens system. 1A shows the arrangement of the lens system 10 at the wide-angle end (WIDE), and FIG. 1B shows the arrangement of the lens system 10 at the telephoto end (TELE). The lens system 10 is a varifocal lens that is manually zoomed, and performs focus adjustment by moving the first lens group G1 or the second lens group G2 during zooming.

  One of the uses of the image pickup apparatus 1 is an image pickup apparatus for crime prevention purposes, and after being fixed at an installation place, the first lens group G1 and the second lens group G2 are moved to be suitable for the installation place and the monitoring target. The magnification and focus adjustment are performed manually, for example. The lens system 10 has an ability to form an image in a wavelength range of visible light and near-infrared light (for example, a wavelength of 400 nm to 1000 nm), and can acquire an image to be monitored throughout the day and night. Therefore, in the apparatus 1 including the lens system 10, once magnification adjustment and focus adjustment are performed, an image to be monitored can be acquired day and night (day and night). Since this imaging device 1 can obtain a high-resolution image without delay with a simple configuration, it can be used for disaster prevention purposes such as monitoring of dams, rivers, roads, volcanoes, etc., in addition to crime prevention purposes. It can be used not only for acquiring images of monitoring points but also for various monitoring purposes such as in-vehicle sensors.

  FIG. 2 shows data for each lens. FIG. 3 shows various numerical values of the lens system. In the lens data, Ri is a radius of curvature (mm) of each lens (each lens surface) arranged in order from the object side 10a, di is a distance (mm) between each lens surface arranged in order from the object side 10a, Di Is an effective diameter (mm) of each lens surface arranged in order from the object side 10a, nd is a refractive index (d line) of each lens arranged in order from the object side 10a, and νd is arranged in order from the object side 10a. The Abbe number (d line) of a lens is shown. In FIG. 3B, “En” means “10 to the power of n”. For example, “E-02” means “10 to the power of −2”, and “E + 01” means “10 to the power of 1”. The same applies to the following embodiments.

  The lens system 10 includes ten lenses L11 to L14, L21 to L24, and L31 to L32 grouped into three lens groups G1, G2, and G3 from the object side 10a toward the image sensor 11 on the image side 10b. Has been. The individual configurations of these lenses L11 to L14, L21 to L24, and L31 to L32 are as described above.

In this lens system 10, the magnification is changed by the movement of the first lens group G1 and the second lens group G2, and the distances d8, d9, and d15 are changed. Further, both surfaces S10 and S11 of the positive lens L21 closest to the object side 10a of the second lens group G2 and both surfaces S18 and S19 of the positive lens L32 closest to the image side 10b of the third lens group G3 are aspheric. . In the aspherical surface, X is the coordinate in the optical axis direction, Y is the coordinate perpendicular to the optical axis, the light traveling direction is positive, R is the paraxial radius of curvature, and the coefficients K, A, and B in FIG. , C and D are represented by the following formula. The same applies to the following embodiments.
X = (1 / R) Y ² / [1+ {1− (1 + K) (1 / R) ² Y ² } ^1/2 ]
+ AY ⁴ + BY ⁶ + CY ⁸ + DY ¹⁰

The above-mentioned conditions (A) and (B) of the lens system 10 and the conditions (1.0), (2.1.0), (2.2.0), (3.0), (4) for both day and night .1.0) and (4.2.0) are as follows:
Condition (A) | f3 | /fw=16.74
Condition (B) | f11 | /fw=10.69
Condition (1.0) f21 / | f2B | = 0.28
Condition (2.1.0) ν23−ν22 = 50.23
Condition (2.2.0) ν23−ν24 = 38.83
Condition (3.0) ν23 = 81.54
Condition (4.1.0) n22-n23 = 0.41
Condition (4.2.0) n24-n23 = 0.34

  4 and 5 show longitudinal aberration diagrams at the wide-angle end and the telephoto end, respectively. Various aberrations are well corrected not only in the visible light wavelength region but also in the near infrared wavelength region, and clear images of visible light and near infrared light can be obtained at the wide-angle end and the telephoto end. In addition, spherical aberration and lateral chromatic aberration indicate a wavelength of 850 nm (short broken line) that is near infrared light, a wavelength of 650 nm (long broken line), a wavelength of 550 nm (solid line), and a wavelength of 450 nm (dashed line) that are visible light. Yes. In the astigmatism, tangential ray (T) and sagittal ray (S) aberrations are shown. The same applies to the following embodiments.

  This lens system 10 is a super-wide-angle lens having a full angle of view at the wide angle end of 160 degrees (half angle of view of 80 degrees) and a full angle of view of 59 degrees (half angle of view of 29.5 degrees) at the telephoto end. It is a varifocal lens with a magnification of 2.7 times that can vary between 2.2 and 6.0 mm. Further, the F value at the wide angle end is 1.2 and the F value at the telephoto end is 1.9, and a bright and clear image can be obtained from the wide angle end to the telephoto end.

  This lens system 10 has conditions (A), (B), (1.0), (2.1.0), (2.2.0), (3.0), (4.1.0). And (4.2.0) is satisfied. Further, in the condition (1.0), the conditions (1.02) and (1.03), and in the condition (2.1.0), the condition (2.1.03) and the condition (2.2.0) Satisfies the condition (2.2.01) and the condition (3.0) satisfies the condition (3.01). Therefore, the lens system according to the first embodiment is an example of a day / night type lens system in which performance and cost are balanced.

(Second embodiment)
FIG. 6 shows a schematic configuration of an imaging apparatus that uses a different lens system for both day and night. The imaging apparatus 1 also includes a negative and positive three-group lens system 10 and an imaging element 11 that converts an image formed by the lens system 10 into digital data. 6A shows the arrangement of the lens system 10 at the wide-angle end (WIDE), and FIG. 6B shows the arrangement of the lens system 10 at the telephoto end (TELE). FIG. 7 shows the data of each lens, and FIG. 8 shows the numerical values of the lens system.

  This lens system 10 is also a varifocal lens, and is composed of ten lenses L11 to L14, L21, which are grouped into three lens groups G1, G2, and G3 from the object side 10a toward the image sensor 11 on the image side 10b. It is comprised by L24 and L31-L32. The shape of each lens is such that the lens L14 of the first lens group G1 is a biconvex positive lens, and the lens L32 of the third lens group G3 is a positive meniscus lens convex to the image side 10b. Common to the lens system of the first embodiment. Therefore, detailed description is omitted.

In this lens system 10, the conditions (A) and (B) described above, and the conditions (1.0), (2.1.0), (2.2.0), (3.0) for day and night are also used. , (4.1.0) and (4.2.0) are expressed as follows.
Condition (A) | f3 | /fw=22.34
Condition (B) | f11 | /fw=11.32
Condition (1.0) f21 / | f2B | = 0.22
Condition (2.1.0) ν23−ν22 = 66.67
Condition (2.2.0) ν23−ν24 = 42.62
Condition (3.0) ν23 = 94.94
Condition (4.1.0) n22-n23 = 0.56
Condition (4.2.0) n24-n23 = 0.32

  As shown in longitudinal aberration diagrams at the wide-angle end and the telephoto end in FIGS. 9 and 10, various aberrations are well corrected not only in the visible light wavelength region but also in the near-infrared light wavelength region. At the edge, a clear image of visible light and near infrared light can be obtained.

  This lens system 10 is a super-wide-angle lens having a full angle of view at the wide angle end of 160 degrees (half angle of view of 80 degrees) and a full angle of view of 59 degrees (half angle of view of 29.5 degrees) at the telephoto end. This is a varifocal lens system with a magnification of 2.7 times that can be varied between 2.2 and 6.0 mm. Further, the F value at the wide angle end is 1.2 and the F value at the telephoto end is 2.0, and a bright and clear image can be obtained from the wide angle end to the telephoto end.

  This lens system 10 has conditions (A), (B), (1.0), (2.1.0), (2.2.0), (3.0), (4.1.0). And (4.2.0) is satisfied. Furthermore, in the condition (1.0), the conditions (1.02) and (1.03), and in the condition (2.1.0), the condition (2.1.04) and the condition (2.2.0) Satisfies the condition (2.2.02) and the condition (3.0) satisfies the condition (3.02). Therefore, the lens system of Example 2 is an example of a lens system having very good performance as a day / night combined type.

(Third embodiment)
FIG. 11 shows a schematic configuration of an imaging apparatus using lens systems of different day / night types. The imaging apparatus 1 also includes a negative and positive three-group lens system 10 and an imaging element 11 that converts an image formed by the lens system 10 into digital data. FIG. 11A shows the arrangement of the lens system 10 at the wide-angle end (WIDE), and FIG. 11B shows the arrangement of the lens system 10 at the telephoto end (TELE). FIG. 12 shows data of each lens, and FIG. 13 shows various numerical values of the lens system.

  This lens system 10 also includes ten lenses L11 to L14, L21 to L24, and L31 to L32 grouped into three lens groups G1, G2, and G3 from the object side 10a toward the image pickup device 11 on the image side 10b. It is configured. The shape of each lens is such that the lens L13 of the first lens group G1 is a negative meniscus lens convex on the image side 10b, the lens L14 is a positive meniscus lens convex on the image side 10b, and the third lens group Except that the lens L32 of G3 is a positive meniscus lens convex on the object side 10a, it is common with the lens system of the first embodiment. Therefore, detailed description is omitted.

In this lens system 10, the conditions (A) and (B) described above, and the conditions (1.0), (2.1.0), (2.2.0), (3.0) for day and night are also used. , (4.1.0) and (4.2.0) are expressed as follows.
Condition (A) | f3 | /fw=10.76
Condition (B) | f11 | /fw=111.20
Condition (1.0) f21 / | f2B |: 0.85
Condition (2.1.0) ν23−ν22 = 76.05
Condition (2.2.0) ν23−ν24 = 55.36
Condition (3.0) ν23 = 94.94
Condition (4.1.0) n22-n23 = 0.48
Condition (4.2.0) n24-n23 = 0.37

  As shown in the longitudinal aberration diagrams at the wide-angle end and the telephoto end in FIGS. 14 and 15, various aberrations are well corrected not only in the visible light wavelength region but also in the near-infrared light wavelength region. At the edge, a clear image of visible light and near infrared light can be obtained.

  This lens system 10 is a super-wide-angle lens having a full angle of view at the wide angle end of 160 degrees (half angle of view of 80 degrees) and a full angle of view of 59 degrees (half angle of view of 29.5 degrees) at the telephoto end. This is a varifocal lens system with a magnification of 2.7 times that can be varied between 2.2 and 6.0 mm. Further, the F value at the wide angle end is 1.2 and the F value at the telephoto end is 2.0, and a bright and clear image can be obtained from the wide angle end to the telephoto end.

  This lens system 10 has conditions (A), (B), (1.0), (2.1.0), (2.2.0), (3.0), (4.1.0). And (4.2.0) is satisfied. Furthermore, in the condition (1.0), the conditions (1.01) and (1.03), and in the condition (2.1.0), the condition (2.1.04) and the condition (2.2.0) Satisfies the condition (2.2.02) and the condition (3.0) satisfies the condition (3.02). Therefore, the lens system of Example 3 is an example of a lens system in which the power of the cemented lens L2B is comparatively large, and the chromatic aberration correction performance is particularly good as a day / night combined type.

(Fourth embodiment)
FIG. 16 shows a schematic configuration of an imaging apparatus using a different lens system for both day and night. The imaging apparatus 1 also includes a negative and positive three-group lens system 10 and an imaging element 11 that converts an image formed by the lens system 10 into digital data. FIG. 16A shows the arrangement of the lens system 10 at the wide-angle end (WIDE), and FIG. 16B shows the arrangement of the lens system 10 at the telephoto end (TELE). The lens system 10 is also a varifocal lens, and the third lens group G3 and the diaphragm S are fixed, and the first lens group G1 and the second lens group G2 are moved along the optical axis, thereby wide-angle. You can zoom between the end and the telephoto end. When zooming from the wide-angle end to the telephoto end, the first lens group G1 once moves toward the image side 10b as shown by a dotted line m, passes through the intermediate region (MIDDLE), and then again. Move toward the telephoto end of the object side 10a.

  FIG. 17 shows data for each lens. FIG. 18 shows various numerical values of the lens system. This lens system 10 also includes ten lenses L11 to L14, L21 to L24, and L31 to L32 grouped into three lens groups G1, G2, and G3 from the object side 10a toward the image pickup device 11 on the image side 10b. It is configured. The shape of each lens is the same as that of the lens system of the first embodiment. Therefore, detailed description is omitted.

In this lens system 10, the conditions (A) and (B) described above, and the conditions (1.0), (2.1.0), (2.2.0), (3.0) for day and night are also used. , (4.1.0) and (4.2.0) are expressed as follows.
Condition (A) | f3 | /fw=11.55
Condition (B) | f11 | /fw=11.97
Condition (1.0) f21 / | f2B | = 0.38
Condition (2.1.0) ν23−ν22 = 31.95
Condition (2.2.0) ν23−ν24 = 31.95
Condition (3.0) ν23 = 81.54
Condition (4.1.0) n22-n23 = 0.28
Condition (4.2.0) n24-n23 = 0.28

  19 and 20 show longitudinal aberration diagrams at the wide-angle end and the telephoto end, and various aberrations are well corrected not only in the visible light wavelength region but also in the near-infrared light wavelength region. At the edge, a clear image of visible light and near infrared light can be obtained.

  This lens system 10 is a super-wide-angle lens having a full angle of view at the wide angle end of 160 degrees (half angle of view of 80 degrees) and a full angle of view of 59 degrees (half angle of view of 29.5 degrees) at the telephoto end. This is a varifocal lens system with a magnification of 2.7 times that can be varied between 2.2 and 6.0 mm. Further, the F value at the wide angle end is 1.2 and the F value at the telephoto end is 2.6, and the F value at the telephoto end is slightly large, but a bright and clear image can be obtained from the wide angle end to the telephoto end.

  This lens system 10 has conditions (A), (B), (1.0), (2.1.0), (2.2.0), (3.0), (4.1.0). And (4.2.0) is satisfied. Furthermore, the conditions (1.0) satisfy the conditions (1.01) and (1.03), and the condition (3.0) satisfies the condition (3.01). Therefore, the lens system of Example 4 is an example of a lens system that prioritizes correction of aberrations such as curvature of field over chromatic aberration performance by the cemented lens L2B as a day / night combination type.

(Fifth embodiment)
FIG. 21 shows a schematic configuration of an example of an image pickup apparatus using a different lens system of the day / night combination type. The imaging apparatus 1 also includes a negative and positive three-group lens system 10 and an imaging element 11 that converts an image formed by the lens system 10 into digital data. FIG. 21A shows the arrangement of the lens system 10 at the wide angle end (WIDE), and FIG. 21B shows the arrangement of the lens system 10 at the telephoto end (TELE).

  FIG. 22 shows data for each lens. FIG. 23 shows various numerical values of the lens system. This lens system 10 also includes ten lenses L11 to L14, L21 to L24, and L31 to L32 grouped into three lens groups G1, G2, and G3 from the object side 10a toward the image pickup device 11 on the image side 10b. It is configured. As for the shape of each lens, the lens L14 of the first lens group G1 is a biconvex positive lens, the lens L31 of the third lens group G3 is a negative meniscus lens convex to the image side 10b, and the lens L32 is Except for the positive meniscus lens convex on the image side 10b, it is common with the lens system of the first embodiment. Therefore, detailed description is omitted.

In this lens system 10, the conditions (A) and (B) described above, and the conditions (1.0), (2.1.0), (2.2.0), (3.0) for day and night are also used. , (4.1.0) and (4.2.0) are expressed as follows.
Condition (A) | f3 | /fw=18.05
Condition (B) | f11 | /fw=10.11
Condition (1.0) f21 / | f2B |: 0.17
Condition (2.1.0) ν23−ν22 = 38.92
Condition (2.2.0) ν23−ν24 = 46.46
Condition (3.0) ν23 = 70.24
Condition (4.1.0) n22-n23 = 0.42
Condition (4.2.0) n24-n23 = 0.36

  24 and 25 show longitudinal aberration diagrams at the wide-angle end and the telephoto end, and various aberrations are well corrected not only in the visible light wavelength region but also in the near-infrared light wavelength region. At the edge, a clear image of visible light and near infrared light can be obtained.

  This lens system 10 is a super-wide-angle lens having a full angle of view at the wide angle end of 160 degrees (half angle of view of 80 degrees) and a full angle of view of 59 degrees (half angle of view of 29.5 degrees) at the telephoto end. This is a varifocal lens system with a magnification of 2.7 times that can be varied between 2.2 and 6.0 mm. Further, the F value at the wide angle end is 1.2, and the F value at the telephoto end is 2.1, so that a bright and clear image can be obtained from the wide angle end to the telephoto end.

  This lens system 10 has conditions (A), (B), (1.0), (2.1.0), (2.2.0), (3.0), (4.1.0). And (4.2.0) is satisfied. Furthermore, in the condition (1.0), the conditions (1.02) and (1.03), and in the condition (2.1.0), the condition (2.1.01) and the condition (2.2.0) Satisfies the condition (2.2.02). Therefore, the lens system of Example 5 is an example of a lens system in which the power of the cemented lens L2B is relatively small and field curvature is improved as a day / night combination type.

(Sixth embodiment)
FIG. 26 shows a schematic configuration of an example of an imaging apparatus using a lens system of a type in which the resolution of the visible light region is increased. The imaging apparatus 1 also includes a negative and positive three-group lens system 10 and an imaging element 11 that converts an image formed by the lens system 10 into digital data. 26A shows the arrangement of the lens system 10 at the wide-angle end (WIDE), and FIG. 26B shows the arrangement of the lens system 10 at the telephoto end (TELE).

  FIG. 27 shows data for each lens. FIG. 28 shows various numerical values of the lens system. This lens system 10 also includes ten lenses L11 to L14, L21 to L24, and L31 to L32 grouped into three lens groups G1, G2, and G3 from the object side 10a toward the image pickup device 11 on the image side 10b. It is configured. The basic shape of each lens is the same as that of the lens system of the first embodiment. Therefore, detailed description is omitted.

In this lens system 10, the conditions (A) and (B) described above, and the conditions (1.1), (2.1.1), (2.2.1), (3.1) of the higher resolution type are used. ), (4.1.1) and (4.2.1) are expressed as follows.
Condition (A) | f3 | /fw=18.45
Condition (B) | f11 | /fw=10.72.
Condition (1.1) f21 / | f2B | = 0.09
Condition (2.1.1) ν23−ν22 = 50.23
Condition (2.2.1) ν23−ν24 = 34.92
Condition (3.1) ν23 = 81.54
Condition (4.1.1) n22-n23 = 0.41
Condition (4.1.2) n24-n23 = 0.32

  29 and 30 show longitudinal aberration diagrams at the wide-angle end and the telephoto end. In the spherical aberration and the lateral chromatic aberration, visible light having a wavelength of 650 nm (long broken line), a wavelength of 550 nm (solid line), and a wavelength of 450 nm (dashed line) is shown. The same applies to the following. In this embodiment, spherical aberration and astigmatism are corrected more satisfactorily, and clear images can be obtained at the wide-angle end and the telephoto end.

  This lens system 10 is a super-wide-angle lens having a full angle of view at the wide angle end of 160 degrees (half angle of view of 80 degrees) and a full angle of view of 59 degrees (half angle of view of 29.5 degrees) at the telephoto end. It is a varifocal lens with a magnification of 2.7 times that can vary between 2.2 and 6.0 mm. Further, the F value at the wide angle end is 1.2 and the F value at the telephoto end is 2.2, and a bright and clear image can be obtained from the wide angle end to the telephoto end.

  This lens system 10 has conditions (A), (B), (1.1), (2.1.1), (2.2.1), (3.1), (4.1.1) And (4.1, 2) is satisfied. Further, the condition (1.1) is the condition (1.13), the condition (2.1.1) is the condition (2.1.13), and the condition (2.2.1) is the condition (2. 2.12) and condition (3.1) satisfy condition (3.11). Therefore, the lens system of Example 6 is a lens system in which the power of the first lens L21 of the second lens group G2 is relatively large, and the performance and cost are balanced as a high-resolution type ultra-wide-angle varifocal lens. It is an example.

(Seventh embodiment)
FIG. 31 shows a schematic configuration of an example of an imaging apparatus using different high resolution type lens systems. The imaging apparatus 1 also includes a negative and positive three-group lens system 10 and an imaging element 11 that converts an image formed by the lens system 10 into digital data. FIG. 31A shows the arrangement of the lens system 10 at the wide angle end (WIDE), and FIG. 31B shows the arrangement of the lens system 10 at the telephoto end (TELE).

  FIG. 32 shows data for each lens. FIG. 33 shows various numerical values of the lens system. This lens system 10 also includes ten lenses L11 to L14, L21 to L24, and L31 to L32 grouped into three lens groups G1, G2, and G3 from the object side 10a toward the image pickup device 11 on the image side 10b. It is configured. The shape of each lens is such that the lens L14 of the first lens group G1 is a biconvex positive lens, and the lens L31 of the third lens group G3 is a negative meniscus lens convex to the image side 10b. This is common with the lens system of the sixth embodiment. Therefore, detailed description is omitted.

In this lens system 10, the conditions (A) and (B) described above, and the conditions (1.1), (2.1.1), (2.2.1), (3.1) of the higher resolution type are used. ), (4.1.1) and (4.2.1) are expressed as follows.
Condition (A) | f3 | /fw=18.90
Condition (B) | f11 | /fw=11.48
Condition (1.1) f21 / | f2B | = 0.02
Condition (2.1.1) ν23−ν22 = 66.67
Condition (2.2.1) ν23−ν24 = 62.68
Condition (3.1) ν23 = 94.94
Condition (4.1.1) n22-n23 = 0.56
Condition (4.2.1) n24-n23 = 0.41

  As shown in the longitudinal aberration diagrams at the wide-angle end and the telephoto end in FIGS. 34 and 35, spherical aberration and astigmatism are particularly well corrected, and a clear image can be obtained at the wide-angle end and the telephoto end. .

  This lens system 10 is a super-wide-angle lens having a full angle of view at the wide angle end of 160 degrees (half angle of view of 80 degrees) and a full angle of view of 59 degrees (half angle of view of 29.5 degrees) at the telephoto end. It is a varifocal lens with a magnification of 2.7 times that can vary between 2.2 and 6.0 mm. Further, the F value at the wide angle end is 1.2 and the F value at the telephoto end is 2.2, and a bright and clear image can be obtained from the wide angle end to the telephoto end.

  This lens system 10 has conditions (A), (B), (1.1), (2.1.1), (2.2.1), (3.1), (4.1.1) And (4.2.1) is satisfied. Furthermore, the condition (1.1) is the condition (1.14), the condition (2.1.1) is the condition (2.1.14), and the condition (2.2.1) is the condition (2. 2.13) and condition (3.1) satisfy condition (3.12). Therefore, in the lens system of Example 7, the power of the first lens L21 of the second lens group G2 is large, and further, the ability of correcting the chromatic aberration of the cemented lens L2B is large, and a high-resolution type ultra-wide-angle varifocal lens. This is an example of a lens system with very good aberration correction capability.

(Eighth embodiment)
FIG. 36 shows a schematic configuration of an example of an imaging apparatus using a different lens system of a high resolution type. The imaging apparatus 1 also includes a negative and positive three-group lens system 10 and an imaging element 11 that converts an image formed by the lens system 10 into digital data. 36A shows the arrangement of the lens system 10 at the wide angle end (WIDE), and FIG. 36B shows the arrangement of the lens system 10 at the telephoto end (TELE).

  FIG. 37 shows data for each lens. FIG. 38 shows various numerical values of the lens system. This lens system 10 also includes ten lenses L11 to L14, L21 to L24, and L31 to L32 grouped into three lens groups G1, G2, and G3 from the object side 10a toward the image pickup device 11 on the image side 10b. It is configured. The shape of each lens is the same as that of the lens system of the sixth embodiment, except that the lens L31 of the third lens group G3 is a negative meniscus lens convex to the image side 10b. Therefore, detailed description is omitted.

In this lens system 10, the conditions (A) and (B) described above, and the conditions (1.1), (2.1.1), (2.2.1), (3.1) of the higher resolution type are used. ), (4.1.1) and (4.2.1) are expressed as follows.
Condition (A) | f3 | /fw=22.78
Condition (B) | f11 | /fw=9.62
Condition (1.0) f21 / | f2B | = 0.61
Condition (2.1.0) ν23−ν22 = 50.23
Condition (2.2.0) ν23−ν24 = 31.95
Condition (3.0) ν23 = 81.54
Condition (4.1.1) n22-n23 = 0.41
Condition (4.2.1) n24-n23 = 0.28
As shown in the longitudinal aberration diagrams at the wide-angle end and the telephoto end in FIGS. 39 and 40, clear images can be obtained at the wide-angle end and the telephoto end.

  This lens system 10 is a super-wide-angle lens having a full angle of view at the wide angle end of 160 degrees (half angle of view of 80 degrees) and a full angle of view of 59 degrees (half angle of view of 29.5 degrees) at the telephoto end. It is a varifocal lens with a magnification of 2.7 times that can vary between 2.2 and 6.0 mm. Further, the F value at the wide angle end is 1.2, and the F value at the telephoto end is 2.1, so that a bright and clear image can be obtained from the wide angle end to the telephoto end.

  This lens system 10 has conditions (A), (B), (1.1), (2.1.1), (2.2.1), (3.1), (4.1.1) And (4.2.1) is satisfied. Further, the condition (1.1) is the condition (1.11), the condition (2.1.1) is the condition (2.1.13), and the condition (3.1) is the condition (3.11). Meet. Therefore, the lens system of Example 8 is a lens system in which the power of the cemented lens L2B is large as a high resolution type with respect to the power of the first lens L21 of the second lens group G2, and priority is given to correction of chromatic aberration. It is an example.

(Ninth embodiment)
FIG. 41 shows a schematic configuration of an example of an imaging apparatus using a different lens system of a high resolution type. The imaging apparatus 1 also includes a negative and positive three-group lens system 10 and an imaging element 11 that converts an image formed by the lens system 10 into digital data. FIG. 41A shows the arrangement of the lens system 10 at the wide-angle end (WIDE), and FIG. 41B shows the arrangement of the lens system 10 at the telephoto end (TELE).

  FIG. 42 shows data for each lens. FIG. 43 shows various numerical values of the lens system. This lens system 10 also includes ten lenses L11 to L14, L21 to L24, and L31 to L32 grouped into three lens groups G1, G2, and G3 from the object side 10a toward the image pickup device 11 on the image side 10b. It is configured. The shape of each lens is the same as that of the lens system of the sixth embodiment. Therefore, detailed description is omitted.

In this lens system 10, the conditions (A) and (B) described above, and the conditions (1.1), (2.1.1), (2.2.1), (3.1) of the higher resolution type are used. ), (4.1.1) and (4.2.1) are expressed as follows.
Condition (A) | f3 | /fw=27.18
Condition (B) | f11 | /fw=10.70
Condition (1.1) f21 / | f2B | = 0.30
Condition (2.1.1) ν23−ν22 = 20.64
Condition (2.2.1) ν23−ν24 = 20.64
Condition (3.1) ν23 = 70.24
Condition (4.1.1) n22-n23 = 0.29
Condition (4.2.1) n24-n23 = 0.29
As shown in FIGS. 44 and 45, which show longitudinal aberration diagrams at the wide-angle end and the telephoto end, clear images can be obtained at the wide-angle end and the telephoto end.

  This lens system 10 is a super-wide-angle lens having a full angle of view at the wide angle end of 160 degrees (half angle of view of 80 degrees) and a full angle of view of 59 degrees (half angle of view of 29.5 degrees) at the telephoto end. It is a varifocal lens with a magnification of 2.7 times that can vary between 2.2 and 6.0 mm. Further, the F value at the wide angle end is 1.2 and the F value at the telephoto end is 2.0, and a bright and clear image can be obtained from the wide angle end to the telephoto end.

  This lens system 10 has conditions (A), (B), (1.1), (2.1.1), (2.2.1), (3.1), (4.1.1) And (4.2.1) is satisfied. Further, the condition (1.1) satisfies the condition (1.12). Therefore, the lens system of Example 9 is an example of a high-resolution type ultra-wide-angle varifocal lens with priority on cost, and can be provided at low cost.

(Tenth embodiment)
FIG. 46 shows a schematic configuration of an example of an imaging apparatus using a different lens system of a high resolution type. The imaging apparatus 1 also includes a negative and positive three-group lens system 10 and an imaging element 11 that converts an image formed by the lens system 10 into digital data. 46A shows the arrangement of the lens system 10 at the wide-angle end (WIDE), and FIG. 46B shows the arrangement of the lens system 10 at the telephoto end (TELE).

  FIG. 47 shows data for each lens. FIG. 48 shows various numerical values of the lens system. This lens system 10 also includes ten lenses L11 to L14, L21 to L24, and L31 to L32 grouped into three lens groups G1, G2, and G3 from the object side 10a toward the image pickup device 11 on the image side 10b. It is configured. The shape of each lens is the same as that of the lens system of the sixth embodiment. Therefore, detailed description is omitted.

In this lens system 10, the conditions (A) and (B) described above, and the conditions (1.1), (2.1.1), (2.2.1), (3.1) of the higher resolution type are used. ), (4.1.1) and (4.2.1) are expressed as follows.
Condition (A) | f3 | /fw=21.34
Condition (B) | f11 | /fw=12.81
Condition (1.1) f21 / | f2B | = 0.14
Condition (2.1.1) ν23−ν22 = 40.36
Condition (2.2.1) ν23−ν24 = 31.87
Condition (3.1) ν23 = 64.14
Condition (4.1.1) n22-n23 = 0.33
Condition (4.2.1) n24-n23 = 0.33
As shown in the longitudinal aberration diagrams at the wide-angle end and the telephoto end in FIGS. 49 and 50, clear images can be obtained at the wide-angle end and the telephoto end.

  This lens system 10 is a super-wide-angle lens having a full angle of view at the wide angle end of 160 degrees (half angle of view of 80 degrees) and a full angle of view of 59 degrees (half angle of view of 29.5 degrees) at the telephoto end. It is a varifocal lens with a magnification of 2.7 times that can vary between 2.2 and 6.0 mm. Further, the F value at the wide angle end is 1.2, and the F value at the telephoto end is 2.1, so that a bright and clear image can be obtained from the wide angle end to the telephoto end.

  This lens system 10 has conditions (A), (B), (1.1), (2.1.1), (2.2.1), (3.1), (4.1.1) And (4.2.1) is satisfied. Further, in condition (1.1), condition (1.13), in condition (2.1.1), condition (2.1.11), and in condition (2.2.1), condition (2. 2.2.11) is satisfied. Therefore, in the lens system of Example 10, the power of the first lens L21 of the second lens group G2 is relatively large, and the high-resolution type ultra-wide-angle varifocal in which the curvature of field is well corrected at low cost. It is an example of a lens.

  In addition, this invention is not limited to these Examples, It is prescribed | regulated by the claim. The lens system 10 of the present invention includes not only a varifocal lens but also a zoom lens system provided with an autofocus mechanism and an electric focus mechanism.

  DESCRIPTION OF SYMBOLS 1 Imaging device, 10 Lens system, 11 Image sensor

Claims (14)

In order from the object side, the first lens group having a negative refractive power that moves during zooming, a diaphragm that does not move during zooming, and a positive refractive power that moves during zooming A lens system composed of a second lens group and a third lens group having a positive refractive power that does not move during zooming;
The first lens group approaches the aperture when zooming from the wide-angle end to the telephoto end,
The second lens group includes a first lens having a positive refractive power arranged in order from the object side and a cemented lens, and the cemented lens has a first lens having a negative refractive power arranged in order from the object side. A lens system that includes two lenses, a third lens having a positive refractive power, and a fourth lens having a negative refractive power, and approaches the aperture when zooming from the wide-angle end to the telephoto end. In claim 1,
The air distance between the first lens group and the diaphragm monotonously decreases when zooming from the wide-angle end to the telephoto end, and the air distance between the second lens group and the diaphragm is telephoto from the wide-angle end. Lens system that decreases monotonously when zooming to the edge.   3. The lens system according to claim 1, wherein the half angle of view at the wide angle end is at least 70 degrees. In any of claims 1 to 3,
A lens system in which the combined focal length f3 of the third lens group and the combined focal length fw of the lens system at the wide angle end satisfy the following conditions.
5 <f3 / fw <30 In any of claims 1 to 4,
The first lens group includes a plurality of lenses having negative refractive power, and the focal length f11 of the lens having the negative refractive power closest to the object side and the combined focal length fw of the lens system at the wide angle end are as follows: Meet the lens system.
| F11 | / fw> 3.50 In any of claims 1 to 5,
The lens system, wherein the focal length f21 of the first lens of the second lens group and the combined focal length f2B of the cemented lens satisfy the following conditions.
0 <f21 / | f2B | <1.50 In claim 6,
The Abbe number ν22 of the negative second lens, the Abbe number ν23 of the positive third lens, and the Abbe number ν24 of the negative fourth lens satisfy the following conditions: Lens system.
30.0 <ν23−ν22 <76.1
30.0 <ν23−ν24 <76.1
ν23> 70.0 In claim 6 or 7,
The refractive index n22 of the negative second lens of the cemented lens of the second lens group, the refractive index n23 of the positive third lens, and the refractive index n24 of the negative fourth lens satisfy the following conditions: Lens system.
n22-n23> 0.13
n24-n23> 0.13 In claim 8,
The lens system in which the focal length f21, the combined focal length f2B, the Abbe number ν22, the Abbe number ν23, and the Abbe number ν24 satisfy the following conditions.
0.15 <f21 / | f2B | <0.30
35.0 <ν23−ν22 <76.1
35.0 <ν23−ν24 <76.1
ν23> 80.0 In claim 6,
Furthermore, a lens system that satisfies the following conditions.
0 <f21 / | f2B | <0.75 In claim 10,
The Abbe number ν22 of the negative second lens, the Abbe number ν23 of the positive third lens, and the Abbe number ν24 of the negative fourth lens satisfy the following conditions: Lens system.
20.0 <ν23−ν22 <76.1
20.0 <ν23−ν24 <76.1
ν23> 60.0 In claim 10 or 11,
The refractive index n22 of the negative second lens of the cemented lens of the second lens group, the refractive index n23 of the positive third lens, and the refractive index n24 of the negative fourth lens satisfy the following conditions: Lens system.
n22-n23> 0.16
n24-n23> 0.16 In claim 12,
The lens system in which the focal length f21, the combined focal length f2B, the Abbe number ν22, the Abbe number ν23, and the Abbe number ν24 satisfy the following conditions.
0 <f21 / | f2B | <0.15
34.0 <ν23−ν22 <76.1
34.0 <ν23−ν24 <76.1
ν23> 80.0 A lens system according to any of claims 1 to 13,
An image pickup apparatus comprising: an image pickup device that acquires an image formed by the lens system.

Images