WO2016125848A1

WO2016125848A1 - Imaging lens and imaging device

Info

Publication number: WO2016125848A1
Application number: PCT/JP2016/053330
Authority: WO
Inventors: 佐野永悟
Original assignee: コニカミノルタ株式会社
Priority date: 2015-02-05
Filing date: 2016-02-04
Publication date: 2016-08-11

Abstract

An imaging lens 10 is provided with, in order from an object side, a first optical system 11 including only one reflecting optical element 11a having a positive power, and a second optical system 12 configured solely from dioptric lenses IL having a rotationally symmetrical shape and all having a shared optical axis AX, an intermediate image of the object being formed between the first optical system 11 and the second optical system 12, the lens furthest toward the object in the second optical system 12 having a negative power and a concave surface thereof toward the object, and conditional expressions (1) and (2) being satisfied. (1): -0.25 < FLd/FLob < -0.05. (2): 3.5 < YDobj/DM < 14.0. (In the conditional expressions, FLd is the focal distance of the second optical system 12, FLob is the focal distance of the lens furthest toward the object in the second optical system 12, YDobj is the length of the imaging lens 10 in the diagonal direction of the imaging range IA, and DM is the distance from a point on the optical axis AX of the reflecting optical element 11a to the object BS.

Description

Imaging lens and imaging apparatus

The present invention relates to an imaging lens that can be incorporated into a projection apparatus that performs projection from a position close to a projection surface, and an imaging apparatus incorporating the imaging lens.

In recent years, a projection apparatus for enlarging and projecting an image displayed on an image display element on a screen by a projection optical system is desired to have a wide-angle projection optical system that can be projected on a large screen even at a short projection distance while being small and light. ing. Under such circumstances, short-focus projectors that can be arranged at positions close to the screen, such as directly below or directly above the screen, have appeared.

In addition to simply projecting a PC screen onto a screen or the like, the projection device projects the PC screen onto a whiteboard or the like, writes handwritten characters on the screen, records the information as an image, Something with interactive functions, such as detecting the movement of the screen and advancing the page of the projection screen, has come out. In addition, a projection apparatus that realizes this requires various correction processes according to usage conditions such as trapezoidal distortion correction of a projected image and brightness correction according to the surrounding environment. Here, if simple trapezoidal distortion correction or brightness correction is performed, or if simple movements of a person are detected, the number of pixels in the imaging device is about VGA (Video Graphics Graphics Array). In order to superimpose characters on a projected image and capture them as image data, mega-class resolution is required. For this reason, it is desired that the imaging lens used for photographing the projected image has higher performance.

When an imaging apparatus such as that described above is incorporated into a short-focus projection apparatus that is disposed close to the screen as described above, the imaging lens needs to have a very wide angle. For this reason, it may be difficult to ensure a sufficient resolving power at the periphery of the projection surface. In addition, distortion at the periphery increases, and distortion correction is performed on the captured image, which may result in a decrease in resolution at the periphery. Therefore, there is a need for an optical system that suppresses as much as possible the barrel-shaped distortion that tends to occur in a wide-angle lens while having an ultra-wide angle.

Patent Document 1 proposes an optical system that uses a rotationally asymmetric anamorphic aspherical surface and suppresses barrel-shaped distortion as much as possible while having a wide angle. Further, Patent Document 2 proposes a low distortion optical system suitable for imaging from an oblique position by having a reflecting surface with power as well as a refractive optical system.

However, since the optical system of Patent Document 1 is supposed to be used in a vehicle, the horizontal angle of view is sufficiently wide, but the vertical angle of view is around 130 °, and a wide range is imaged from a very close range. Insufficient use. Moreover, the optical system of Patent Document 2 uses a lens having a rotationally asymmetric free-form surface as a refractive lens, and there is a problem that the difficulty of processing and assembly becomes high. Also, the image capturing range is only an image capturing range of about 14 inches with a shooting distance of about 20 cm, and it cannot be said that the angle of view is sufficiently wide.

JP 2013-109268 A JP 2012-133175 A

The present invention has been made in view of the above-described background art, and an object of the present invention is to provide an ultra-wide-angle imaging lens that has a sufficiently high resolving power to the peripheral portion and is low in distortion.

It is another object of the present invention to provide a small imaging device incorporating the imaging lens.

In order to achieve the above object, an imaging lens according to the present invention is an imaging lens for an imaging apparatus that images an object from an oblique direction using an imaging element, and is a reflective optical device having positive power in order from the object side. A first optical system including only one element, and a second optical system including only a refractive lens having a rotationally symmetric shape, and all the lenses have a common optical axis. An intermediate image of the object is formed between the two optical systems, and the lens closest to the object side of the second optical system has a negative power with the concave surface facing the object side, and satisfies the following conditional expression.
-0.25 <FLd / FLob <-0.05 (1)
3.5 <YDobj / DM <14.0 (2)
However, the value FLd is the focal length of the second optical system, the value FLob is the focal length of the lens closest to the object of the second optical system, and the value YDobj is the length in the diagonal direction of the imaging range of the imaging lens. The value DM is the distance from the point on the optical axis of the reflective optical element to the object. Here, the optical axis means an axis that passes through the center of the aperture stop and is perpendicular to the cross section of the aperture stop. Further, having a common optical axis means a state in which all the lenses are not decentered (a state in which neither a shift nor a tilt is performed).
In this specification, “the reflective optical element has positive power” means that the light beam incident on the reflecting surface from the object converges after reflecting off the reflecting surface and forms an intermediate image of the object. Means. That is, it is not determined by the definition formula of the reflecting surface shape.

In the above imaging lens, a reflective optical element having a positive power is disposed on the object side of the refractive optical system, and an intermediate image of the object is formed on the object side of the refractive optical system, so that a very large object image is captured at once. The reduction magnification can be shared between the first optical system and the second optical system without reducing the image on the surface (imaging surface). Thereby, in the imaging lens, an optical system having a wide angle and little aberration deterioration can be obtained. In addition, distortion occurring in the first optical system can be corrected by the second optical system, and a low distortion image can be obtained. Furthermore, if a wide-angle optical system is configured only by a refractive optical system, chromatic aberration of magnification is greatly generated by a strong negative power lens disposed on the object side, but chromatic aberration does not occur in the reflective optical element. The chromatic aberration of magnification that occurs in can be reduced. At that time, by configuring the reflective optical system with a single reflective optical element having power, the optical system can be simplified and the assemblability can be improved. As a result, a high-performance optical system can be obtained. it can.
Also, by making the object side surface of the most object side lens of the refractive optical system concave, the angle of view of the entire system can be widened. At that time, the refractive optical system is composed only of refractive lenses having a rotationally symmetric shape, and all the lenses have a common optical axis without being decentered, thereby improving the assemblability and result. As a result, a high-performance optical system can be obtained.
Conditional expression (1) is a conditional expression for achieving both widening of the angle of view and downsizing of the imaging lens. By falling below the upper limit value of conditional expression (1), the negative power of the most object-side lens of the second optical system can be appropriately maintained, and a wide angle of the optical system can be achieved. On the other hand, by exceeding the lower limit value of conditional expression (1), the negative power of the lens closest to the object side of the second optical system does not become too strong, and the effective diameter of the first optical system can be reduced, and imaging is performed. It is possible to reduce the size of the lens in the radial direction.
Conditional expression (2) is a conditional expression for achieving both a short imaging distance and a wide angle of view. By exceeding the lower limit value of conditional expression (2), a large screen can be imaged from a short distance, and the imaging lens system can be arranged closer to the object, that is, the subject. Thereby, when combining with projection apparatuses, such as a projector, it can prevent that the imaging device incorporating an imaging lens obstructs a projection device or a presenter. On the other hand, when the distance between the subject (object) and the imaging lens is close, the angle at which the light beam at the end of the object enters the imaging lens system becomes very large by falling below the upper limit value of conditional expression (2). It is possible to suppress degradation in resolution and distortion when the object is defocused by a small amount.

An imaging apparatus according to the present invention includes the imaging lens described above and an imaging element.

The above-described imaging device can capture an image of a wide range from a close distance by incorporating an imaging lens as described above, and can obtain an image in which aberrations are corrected well to the peripheral portion.

It is a conceptual diagram explaining an imaging device provided with the imaging lens of this embodiment. It is a conceptual diagram explaining an example of the use condition of the imaging device shown in FIG. FIG. 2 is a cross-sectional view of an imaging lens and the like in the imaging apparatus of Example 1. 4A and 4B are MTF characteristic diagrams illustrating the performance of the imaging apparatus according to the first embodiment. It is a figure explaining the MTF evaluation position on an object surface. FIG. 6 is a cross-sectional view of an imaging lens and the like in the imaging apparatus of Example 2. 7A and 7B are MTF characteristic diagrams illustrating the performance of the imaging apparatus according to the second embodiment. FIG. 7 is a cross-sectional view of an imaging lens and the like in the imaging apparatus of Example 3. 9A and 9B are MTF characteristic diagrams illustrating the performance of the imaging apparatus according to the third embodiment. FIG. 6 is a cross-sectional view of an imaging lens and the like in the imaging apparatus of Example 4. 11A and 11B are MTF characteristic diagrams illustrating the performance of the imaging apparatus according to the fourth embodiment. FIG. 10 is a cross-sectional view of an imaging lens and the like in the imaging apparatus of Example 5. 13A and 13B are MTF characteristic diagrams illustrating the performance of the imaging apparatus according to the fifth embodiment.

Hereinafter, an imaging lens and an imaging apparatus according to an embodiment of the present invention will be described with reference to FIG. The imaging lens 10 illustrated in FIG. 1 has the same configuration as an imaging lens 10A of Example 1 described later.

As shown in FIG. 1, the imaging device 100 includes an imaging lens 10 that forms an object image (subject image), an imaging element 51 that detects an object image formed by the imaging lens 10, and the imaging element 51 from behind. A wiring board 52 that holds wiring and the like, and a lens barrel portion 54 that holds the imaging lens 10 and the like and has an opening OP that allows a light beam from the object side to enter. The imaging apparatus 100 can be mounted on a projection apparatus such as a projector, and in this case, the imaging apparatus 100 is integrally provided inside or outside the projection apparatus. Further, the imaging device 100 may be provided as a separate body from the projection device. In the example of FIG. 1, the imaging device 100 is provided below the object BS corresponding to the screen and captures an object image from an obliquely downward direction. For example, an image from a projection device (not shown) is projected onto the object BS.

The imaging lens 10 forms an object image on the imaging surface (imaging plane) I of the imaging element 51, and in order from the object side, the first optical system 11, the optical path bending mirror 13, and the second optical. A system 12.

The image sensor 51 is a sensor chip made of a solid-state image sensor. The photoelectric conversion unit of the image sensor 51 is composed of a CCD (charge coupled device) or CMOS (complementary metal oxide semiconductor), photoelectrically converts incident light for each RGB, and outputs an analog signal thereof.

The wiring board 52 has a role of aligning and fixing the image sensor 51 to other members (for example, the lens barrel portion 54). The wiring board 52 is supplied with a voltage and a signal for driving the image sensor 51 and a driving circuit (not shown) associated therewith from an external circuit, and outputs a detection signal to the external circuit. Is possible. The wiring board 52 can have various image processing functions such as gradation correction and distortion correction, and has an interface function that enables information to be exchanged with an external circuit (for example, a control unit of the projection apparatus). Can be made.

The infrared cut filter F or the like is disposed and fixed on the imaging lens 10 side of the imaging element 51 by a holder member (not shown) so as to cover the imaging element 51 and the like.

The lens barrel portion 54 houses and holds the imaging lens 10. In the lens barrel portion 54, the focusing operation of the imaging lens 10 is possible by moving any one or more of the lenses constituting the second optical system 11 of the imaging lens 10 along the optical axis AX. Therefore, for example, a drive mechanism can be provided.

Hereinafter, the imaging lens 10 will be described in detail. The imaging lens 10 illustrated in FIG. 1 includes a first optical system 11, an optical path bending mirror 13, and a second optical system 12 in order from the object side.

The first optical system 11 of the imaging lens 10 includes only one reflective optical element 11a having a positive power. The reflective optical element 11a has a reflective surface AR that reflects the light beam IR from the object surface (subject surface) PS and guides it to the second optical system 12 side. The reflective surface AR of the reflective optical element 11a has a free-form surface shape or an aspheric shape. Thereby, the aberration which generate | occur | produces in the reflective optical element 11a can be suppressed to the minimum, and the high performance imaging lens 10 can be obtained as a result.

The second optical system 12 is composed only of a refractive lens IL having a rotationally symmetric shape. All the lenses constituting the second optical system 12 have a common optical axis AX. As described above, the reflective optical element 11a having a positive power is arranged on the object side of the second optical system 12 that is a refractive optical system, so that the first optical system 11 and the second optical system 12 are interposed. Forms an intermediate image of the object that is the subject. Here, the optical axis AX does not directly mean the optical axis (center axis) of each lens constituting the imaging lens 10, but passes through the center of the aperture stop S described later, and the cross section of the aperture stop S. It means the axis perpendicular to. Further, having a common optical axis AX means a state in which all the lenses are not decentered (a state in which no shift or tilt is performed).

The second optical system 12 includes, in order from the object side, a first lens group Gr1, an aperture stop S, and a second lens group Gr2. Of the second optical system 12, the first lens group Gr1 is disposed at a position relatively farther from the aperture stop S than the most image-side lens (the sixth lens L6 in FIG. 1) of the second optical system 11. ing. In the example of FIG. 1, the first lens group Gr1 is composed of only two lenses, a first lens L1 having a negative power and a second lens L2 having a positive power in order from the object side. When the second optical system 12 is composed of the first lens group Gr1 and the second lens group Gr2 with the aperture stop S interposed therebetween, the light flux at each image height that is relatively far from the aperture stop S is on the lens surface. It is important in terms of aberration correction that the first lens group Gr1 passing through relatively different positions includes a negative lens and a positive lens. In addition, since the first lens group Gr1 has a minimum two-lens configuration, the number of lenses having a large effective diameter can be minimized, which is advantageous in reducing the size and weight of the apparatus. Note that the first lens group Gr1 may have three or more lenses.

In the example of FIG. 1, the second lens group Gr2 is composed of third to sixth lenses L3 to L6. The second lens group Gr2 includes one cemented lens CS in which a negative lens (fourth lens L4 in FIG. 1) and a positive lens (fifth lens L5 in FIG. 1) are bonded together. By including the cemented lens CS in the second optical system 12, chromatic aberration can be favorably corrected. Further, when the second optical system 12 is the first lens group Gr1 and the second lens group Gr2 with the aperture stop S interposed therebetween, the cemented lens CS is disposed in the second lens group Gr2 having a relatively small effective diameter. Thus, since the cemented lens CS can be reduced, the size of the entire imaging lens 10 system can be reduced.

The lens closest to the object side of the second optical system 12 (the first lens L1 in FIG. 1) has a negative power with the concave surface facing the object side, and satisfies the following conditional expression.
-0.25 <FLd / FLob <-0.05 (1)
3.5 <YDobj / DM <14.0 (2)
However, the value FLd is the focal length of the second optical system 12, the value FLob is the focal length of the lens (first lens L1) closest to the object side of the second optical system 12, and the value YDobj is taken by the imaging lens 10. The length of the range IA in the diagonal direction, and the value DM is the distance from the point on the optical axis AX of the reflective optical element 11a to the object (subject) BS. Here, the shooting range IA of the imaging lens 10 is a range shot on the object plane (subject plane) PS and is determined by the size of the imaging element 51.

Conditional expression (1) is a conditional expression for achieving both widening of the angle of view and downsizing of the imaging lens 10. By falling below the upper limit value of the conditional expression (1), the negative power of the most object side lens (first lens L1) of the second optical system 12 can be appropriately maintained, and the wide angle of the optical system is achieved. can do. On the other hand, by exceeding the lower limit value of the conditional expression (1), the negative power of the most object-side lens (first lens L1) of the second optical system 12 does not become too strong, and the effective diameter of the first optical system 11 is increased. The imaging lens 10 can be reduced in the radial direction.
Conditional expression (2) is a conditional expression for achieving both a short imaging distance and a wide angle of view. By exceeding the lower limit value of the conditional expression (2), a large screen can be imaged from a short distance, and the imaging lens 10 system can be arranged closer to the object BS. Thereby, when combining with projection apparatuses, such as a projector, it can prevent that the imaging device 100 incorporating the imaging lens 10 obstructs a projection device or a presenter. On the other hand, when the distance between the object BS and the imaging lens 10 is short, the angle at which the light beam at the end of the object BS enters the imaging lens 10 system becomes very large by falling below the upper limit value of conditional expression (2). It is possible to suppress resolution degradation and distortion fluctuation when the object BS is defocused by a small amount due to the above. Note that even if the imaging lens 10 is tilted with respect to the object plane PS, the tilt of the imaging lens 10 is allowed if the range of the conditional expression (2) is satisfied.

The imaging lens 10 satisfies the following conditional expression.
2.0 <MRED / FLd <4.0 (3)
However, the value MRED is the maximum height from the optical axis AX of the use area of the reflective optical element 11a, and the value FLd is the focal length of the second optical system 12.

Conditional expression (3) is a conditional expression for achieving both size reduction in the radial direction and aberration correction of the entire imaging lens 10 system. Since the size of the entire imaging lens 10 in the radial direction is determined by the size of the reflective optical element 11a arranged closest to the object side, it is desirable to keep the size of the reflective optical element 11a as small as possible. However, if the size of the reflecting optical element 11a is kept too small, the power of the negative lens (first lens L1) closest to the object side of the second optical system 12 cannot be increased, which is disadvantageous in terms of aberration correction. It becomes. Therefore, by falling below the upper limit of conditional expression (3), the size of the reflective optical element 11a does not become too large, and the size in the radial direction of the entire imaging lens 10 system can be reduced. On the other hand, exceeding the lower limit value of the conditional expression (3) makes it possible to appropriately apply negative power to the most object side lens (first lens L1) of the second optical system 12, and the imaging lens 10 This is advantageous for aberration correction of the entire system.

The imaging lens 10 satisfies the following conditional expression.
0.35 <BF / FLd <1.3 (4)
However, the value BF is the distance on the optical axis AX between the image side surface S62 of the most image side lens (sixth lens L6) of the second optical system 12 and the imaging surface I, and the value FLd is the value of the second optical system 12. The focal length.
Conditional expression (4) is a conditional expression for appropriately setting the back focus of the imaging lens 10. By exceeding the lower limit value of the conditional expression (4), the back focus does not become too short, and a space for inserting a member such as the infrared cut filter F can be secured. On the other hand, by falling below the upper limit value of conditional expression (4), the back focus is not excessively lengthened, and the optical total length of the imaging lens 10 can be shortened.

The optical path bending mirror 13 is provided between the first optical system 11 and the second optical system 12. The optical path bending mirror 13 is an optical element having no power. As an example, the imaging lens 10 may be arranged in the same housing as the projection optical system. In such a case, it is necessary to arrange the imaging lens 10 so as not to disturb the layout of the projection optical system. Therefore, by providing the optical path bending mirror 13 having no power between the first optical system 11 and the second optical system 12, the optical path can be bent, for example, by 90 °, and the layout of the imaging lens 10 is arranged. The degree of freedom increases.

As described above, the infrared cut filter F is provided between the most image-side lens (the sixth lens L6 in FIG. 1) of the second optical system 12 and the imaging surface I of the imaging element 51. Since the image pickup device 51 used for the image pickup lens 10 generally has light receiving sensitivity also in the infrared wavelength region, the infrared cut filter F is provided for the purpose of projecting colors closer to human eyes. The infrared cut filter F has an oblique incidence characteristic of the light beam. However, by arranging the infrared cut filter F between the image side lens (sixth lens L6) of the second optical system 12 and the imaging surface I, the incident angle of the light beam. Is inserted in as small a position as possible, and the characteristic change or characteristic deterioration of the infrared cut filter F can be minimized.

In the above, as shown in FIG. 1, it is assumed that the imaging lens 10 is arranged on the lower end side of the object BS that is a subject. However, the imaging lens 10 is not limited to the lower end side, and may be arranged on the upper end side and the left and right end sides. Good.

Hereinafter, the usage state of the imaging apparatus 100 will be described. As shown in FIG. 2, the light ray IR corresponding to the image from the object plane PS enters the imaging apparatus 100. The light ray IR incident on the imaging device 100 is reflected by the reflective optical element 11a of the first optical system 11, is bent downward by the optical path bending mirror 13, and is reflected by the lenses L1 to L2 of the second optical system 12. Pass through L6 sequentially. In the imaging lens 10, an intermediate image of the object is formed between the first optical system 11 and the second optical system 12. The light beam IR that has passed through the second optical system 12 finally forms a reduced image on the imaging surface (imaging surface) I of the imaging device 51.

In the imaging lens 10 and the imaging apparatus 100 described above, the reflection optical element 11a having positive power is disposed on the object side of the refractive optical system, and an intermediate image of the object is formed on the object side of the refractive optical system. The first optical system 11 and the second optical system 12 can share the reduction magnification without forming a large object image on the imaging surface (imaging surface) I at once. Thereby, in the imaging lens 10, an optical system with a wide angle and little aberration deterioration can be obtained. Further, the distortion generated in the first optical system 11 can be corrected by the second optical system 12, and a low distortion image can be obtained. Further, when a wide-angle optical system is configured only by a refractive optical system, a chromatic aberration of magnification is greatly generated by a strong negative power lens (in FIG. 1, the first lens L1) disposed on the object side. Since no chromatic aberration occurs in the element 11a, lateral chromatic aberration that occurs in the entire system can be kept small. At that time, the optical system can be simplified and the assemblability can be improved by configuring the reflective optical system with a single reflective optical element 11a having power. As a result, a high-performance optical system is obtained. Can do.
Further, by making the object side surface (the object side surface S11 of the first lens L1 in FIG. 1) of the most object side lens of the refractive optical system into a concave shape, the angle of view of the entire system can be widened. At that time, the refraction optical system is composed of only the refraction lens IL having a rotationally symmetric shape, and all the lenses have a common optical axis AX without being decentered, thereby improving the assemblability. As a result, a high-performance optical system can be obtained.

In the present embodiment, it is assumed that the angle of view required for the imaging lens 10 is approximately 25 cm from the object BS to the imaging lens 10 (imaging distance) and the diagonal length of the imaging range IA is approximately 80 inches. For example, when photographing characters written on a whiteboard, it is desirable to capture images from a close range of about 25 cm as described above in order to prevent a person writing characters near the whiteboard from being captured. Further, it is desirable to image a large screen as much as possible, and a diagonal length of about 80 inches is assumed as a sufficient imaging range IA as described above. Under this condition, a super wide-angle lens with an angle of view of about 160 ° is required for the imaging lens.

〔Example〕
Embodiments of an imaging lens and an imaging apparatus according to the present invention will be described below. Symbols used in each example are as follows.
Fno: F number R: paraxial radius of curvature D: axial distance Nd: refractive index of lens material with respect to d-line νd: Abbe number of lens material Here, the symbol Surf.N means a surface number, and the symbol P− Surf. Means object surface or object surface PS, symbol R-Surf. Means reflection surface AR of the reflective optical element 11a, and symbol I-Surf. Means imaging surface (imaging surface) I. The symbol STOP means the aperture stop S. In addition, the symbol INF means infinity or ∞.

In each embodiment, the surface described with “*” after each surface number is a surface having an aspherical shape. The aspherical shape is expressed by the following “Equation 1” where the vertex of the surface is the origin, the Z axis is taken in the optical axis direction, and the height in the direction perpendicular to the optical axis is h.

However,
Ai: i-order aspherical coefficient R: radius of curvature K: conic constant Further, a surface described with “**” after the surface number is a surface having a free-form surface shape. The free-form surface shape is the same as the aspherical shape described above, with the vertex of the surface as the origin, the Z axis in the optical axis direction, the X and Y axes in the direction perpendicular to the optical axis, and the height in the direction perpendicular to the optical axis. This is represented by the following “Equation 2” where h is h.

However,
Cj: coefficient of X ^m Y ⁿ R: radius of curvature K: conic constant

[Example 1]
The optical specification values of the imaging lens of Example 1 are shown below.
Fno: 2.80
Image size: 4.88mm x 2.75mm

The data of the lens surface of the imaging lens of Example 1 is shown in Table 1 below.
[Table 1]
Surf.N R [mm] D [mm] Nd νd
P-Surf. 250.000
1 ** (R-Surf.) -22.419 102.460
2 -33.771 2.000 1.7234 37.9
3 -148.713 3.473
4 * -14.121 4.126 1.5447 56.2
5 * -9.182 18.686
6 (STOP) INF 1.781
7 11.079 2.073 1.7725 49.5
8 18.550 1.032
9 -7.893 2.075 1.7432 49.3
10 -3.922 1.254 1.8052 25.4
11 -9.365 0.500
12 * 18.983 2.094 1.5447 56.2
13 * -8.767 4.470
14 INF 0.500 1.5163 64.1
15 INF 3.477
16 (I-Surf.) INF

The aspheric coefficients of the imaging lens of Example 1 are shown in Table 2 below. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻⁰² ) is expressed using E (for example, 2.5E-02).
[Table 2]
4th page
K = -3.7277E + 00, A4 = 7.9872E-06, A6 = 8.4994E-08, A8 = -4.4094E-11,
A10 = 0.0000E + 00, A12 = 0.0000E + 00
5th page
K = -1.5110E + 00, A4 = -5.7455E-06, A6 = -5.6194E-08, A8 = 4.6420E-10,
A10 = 0.0000E + 00, A12 = 0.0000E + 00
12th page
K = -1.2081E + 01, A4 = -1.2476E-04, A6 = -2.6912E-06, A8 = 5.2842E-07,
A10 = 3.0031E-08, A12 = 0.0000E + 00
Side 13
K = -1.4909E + 00, A4 = -1.0381E-05, A6 = 2.5870E-07, A8 = 1.3577E-07,
A10 = 4.4146E-08, A12 = 0.0000E + 00

Table 3 below shows the free-form surface coefficients of the reflective optical elements of the imaging lens of Example 1. In the table of free-form surface coefficients, “*” represents a product, and “**” represents a power (the same applies to the following examples).
[Table 3]

FIG. 3 is a cross-sectional view of the imaging lens 10A and the like of the first embodiment. The imaging lens 10 A includes a first optical system 11, an optical path bending mirror 13, and a second optical system 12. The first optical system 11 includes a reflective optical element 11a having a positive power. The reflective surface of the reflective optical element 11a has a free-form surface shape. The second optical system 12 includes a first lens group Gr1, an aperture stop S, and a second lens group Gr2. The first lens group Gr1 includes a first lens L1 and a second lens L2. The second lens group Gr2 includes a third lens L3, a fourth lens L4, a fifth lens L5, and a sixth lens L6. An infrared cut filter F is provided between the sixth lens L6 and the image sensor 51. Note that symbol I is an imaging surface of the imaging lens 10A and indicates an imaging surface of the imaging element 51 (the same applies to the following examples). The imaging lens 10A reflects the optical path from the first optical system 11 to the second optical system 12 by the optical path bending mirror 13 having no power provided between the first optical system 11 and the second optical system 12. 11a is bent 90 ° downward. The second lens L2 and the sixth lens L6 are aspherical plastic lenses, and the other lenses are glass spherical lenses.

4A and 4B are MTF (Modulation Transfer Function) characteristic diagrams on the object plane PS. 4A is an MTF characteristic diagram of positions F1 to F3 in the imaging range IA of the object plane PS shown in FIG. 5, and FIG. 4B is a diagram of positions F4 to F6 of the imaging range IA of the object plane PS shown in FIG. It is a MTF characteristic view (the following examples are also the same). 4A and 4B, Fi-X (i = 1 to 6) represents the MTF in the X direction at the position of Fi, and Fi-Y (i = 1 to 6) represents the Y direction in the position of Fi. MTF is shown. The wavelength weights for calculating the MTF are as follows (the same applies to the following embodiments).
[Wavelength weight]
Wavelength weight
650nm 107
610nm 503
555nm 1000
510nm 503
470nm 91
As can be seen from FIGS. 4A and 4B, the imaging apparatus 100 according to the first embodiment obtains sufficient resolving power up to the periphery.

(Example 2)
The optical specification values of the imaging lens of Example 2 are shown below.
Fno: 2.80
Image size: 4.88mm x 2.75mm

Table 4 below shows data such as the lens surface of the imaging lens of Example 2.
[Table 4]
Surf.N R [mm] D [mm] Nd νd
P-Surf. 250.000
1 ** (R-Surf.) -19.671 76.152
2 -9.836 2.107 1.7234 37.9
3 -12.847 2.785
4 * -11.278 4.949 1.5447 56.2
5 * -7.838 6.093
6 (STOP) INF 1.712
7 9.456 2.101 1.7725 49.5
8 15.545 1.141
9 -7.162 1.981 1.7432 49.3
10 -3.422 1.312 1.8052 25.4
11 -8.845 0.500
12 * 33.889 2.148 1.5447 56.2
13 * -7.246 4.165
14 INF 0.500 1.5163 64.1
15 INF 3.172
16 (I-Surf.) INF

The aspheric coefficients of the imaging lens of Example 2 are shown in Table 5 below.
[Table 5]
4th page
K = -3.5532E + 00, A4 = 2.7559E-05, A6 = 9.1036E-07, A8 = -6.6603E-09,
A10 = 0.0000E + 00, A12 = 0.0000E + 00
5th page
K = -1.6151E + 00, A4 = -1.1264E-06, A6 = -6.0060E-07, A8 = 9.9039E-09,
A10 = 0.0000E + 00, A12 = 0.0000E + 00
12th page
K = -1.2714E + 01, A4 = -1.2231E-04, A6 = -2.0765E-06, A8 = 6.9404E-07,
A10 = 1.7491E-08, A12 = 0.0000E + 00
Side 13
K = -1.5447E + 00, A4 = 5.4918E-06, A6 = -2.6210E-07, A8 = -1.3819E-08,
A10 = 4.0415E-08, A12 = 0.0000E + 00

Table 6 below shows the free-form surface coefficients of the reflective optical elements of the imaging lens of Example 2.
[Table 6]

FIG. 6 is a cross-sectional view of the imaging lens 10B and the like of the second embodiment. The imaging lens 10 B includes a first optical system 11, an optical path bending mirror 13, and a second optical system 12. The first optical system 11 includes a reflective optical element 11a having a positive power. The reflective surface of the reflective optical element 11a has a free-form surface shape. The second optical system 12 includes a first lens group Gr1, an aperture stop S, and a second lens group Gr2. The first lens group Gr1 includes a first lens L1 and a second lens L2. The second lens group Gr2 includes a third lens L3, a fourth lens L4, a fifth lens L5, and a sixth lens L6. An infrared cut filter F is provided between the sixth lens L6 and the image sensor 51. The imaging lens 10B reflects the optical path from the first optical system 11 to the second optical system 12 by the optical path bending mirror 13 provided between the first optical system 11 and the second optical system 12 and having no power. 11a is bent 90 ° downward. The second lens L2 and the sixth lens L6 are aspherical plastic lenses, and the other lenses are glass spherical lenses.

7A and 7B are MTF characteristic diagrams on the object plane PS. As can be seen from FIGS. 7A and 7B, the imaging apparatus 100 according to the second embodiment obtains sufficient resolving power up to the periphery.

(Example 3)
The optical specification values of the imaging lens of Example 3 are shown below.
Fno: 2.80
Image size: 4.88mm x 2.75mm

Table 7 below shows data such as the lens surface of the imaging lens of Example 3.
[Table 7]
Surf.N R [mm] D [mm] Nd νd
P-Surf. 250.000
1 ** (R-Surf.) -23.683 106.145
2 * -60.062 1.926 1.5447 56.2
3 * -364.196 8.674
4 -46.206 2.753 1.8052 25.4
5 -72.398 1.949
6 * -20.641 6.301 1.5447 56.2
7 * -13.550 35.389
8 (STOP) INF 1.799
9 12.733 1.243 1.7725 49.5
10 22.972 5.922
11 -10.215 1.833 1.7200 50.2
12 -4.716 1.745 1.8052 25.4
13 -11.401 0.500
14 * 16.085 3.815 1.5447 56.2
15 * -11.024 4.580
16 INF 0.500 1.5163 64.1
17 INF 3.586
18 (I-Surf.) INF

The aspheric coefficients of the imaging lens of Example 3 are shown in Table 8 below.
[Table 8]
Second side
K = 6.1759E + 00, A4 = 2.4936E-06, A6 = -2.6284E-08, A8 = 2.8050E-11,
A10 = -4.2007E-13, A12 = 0.0000E + 00
Third side
K = -1.9638E + 01, A4 = -6.5800E-06, A6 = -2.0421E-08, A8 = -1.0453E-10,
A10 = -1.0738E-12, A12 = 4.8446E-15
6th page
K = -4.3930E + 00, A4 = 3.0046E-06, A6 = 4.5768E-08, A8 = 2.9497E-10,
A10 = 0.0000E + 00, A12 = 0.0000E + 00
7th page
K = -1.5160E + 00, A4 = -1.7862E-06, A6 = -1.1551E-08, A8 = 4.3523E-10,
A10 = 0.0000E + 00, A12 = 0.0000E + 00
14th page
K = -7.2612E + 00, A4 = -5.0498E-05, A6 = -7.5786E-07, A8 = 2.6346E-08,
A10 = 2.4744E-09, A12 = 0.0000E + 00
15th page
K = -1.3144E + 00, A4 = -1.0328E-05, A6 = 5.2076E-07, A8 = 2.3510E-08,
A10 = 1.9041E-09, A12 = 0.0000E + 00

Table 9 below shows the free-form surface coefficients of the reflective optical elements of the imaging lens of Example 3.
[Table 9]

FIG. 8 is a cross-sectional view of the imaging lens 10C of the third embodiment. The imaging lens 10 C includes a first optical system 11, an optical path bending mirror 13, and a second optical system 12. The first optical system 11 includes a reflective optical element 11a having a positive power. The reflective surface of the reflective optical element 11a has a free-form surface shape. The second optical system 12 includes a first lens group Gr1, an aperture stop S, and a second lens group Gr2. The first lens group Gr1 includes a first lens L1, a second lens L2, and a third lens L3. The second lens group Gr2 includes a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7. An infrared cut filter F is provided between the seventh lens L7 and the image sensor 51. The imaging lens 10 C reflects the optical path from the first optical system 11 to the second optical system 12 by the optical path bending mirror 13 provided between the first optical system 11 and the second optical system 12. 11a is bent 90 ° downward. The first lens L1, the third lens L3, and the seventh lens L7 are aspherical plastic lenses, and the other lenses are glass spherical lenses.

9A and 9B are MTF characteristic diagrams on the object plane PS. As can be seen from FIGS. 9A and 9B, the imaging apparatus 100 according to the third embodiment obtains sufficient resolving power up to the periphery.

Example 4
The optical specification values of the imaging lens of Example 4 are shown below.
Fno: 2.80
Imaging surface size: 3.672mm x 2.754mm

Data on the lens surface and the like of the imaging lens of Example 4 are shown in Table 10 below.
[Table 10]
Surf.N R [mm] D [mm] Nd νd
P-Surf. 160.000
1 ** (R-Surf.) -13.854 61.626
2 * -5.825 4.639 1.5447 56.2
3 * -8.850 1.518
4 -25.638 4.000 1.8061 40.9
5 -18.873 30.421
6 (STOP) INF 1.710
7 30.867 2.603 1.7200 50.2
8 -28.982 0.500
9 11.768 3.454 1.6228 57.0
10 -10.730 4.195 1.7847 26.2
11 13.052 2.202
12 1339.192 4.758 1.8467 23.7
13 -12.411 2.460
14 INF 0.500 1.5163 64.1
15 INF 1.748
16 (I-Surf.) INF

Table 11 below shows the aspheric coefficients of the imaging lens of Example 4.
[Table 11]
First side
K = -2.9094E + 00, A4 = -1.5013E-05, A6 = 1.0394E-08, A8 = 1.0976E-11,
A10 = -4.7970E-14, A12 = 5.9277E-17, A14 = -2.5635E-20,
A16 = -1.2964E-24
Second side
K = -1.8001E + 00, A4 = -9.3515E-05, A6 = -9.7020E-07, A8 = 8.4313E-09,
A10 = 4.8540E-11, A12 = 1.8885E-13, A14 = -4.6551E-15
Third side
K = -2.1753E + 00, A4 = -2.7042E-05, A6 = -7.3063E-08, A8 = 3.5012E-10,
A10 = 2.6185E-11, A12 = -4.3055E-14, A14 = -3.4322E-16

FIG. 10 is a cross-sectional view of the imaging lens 10D and the like of the fourth embodiment. The imaging lens 10 D includes a first optical system 11, an optical path bending mirror 13, and a second optical system 12. The first optical system 11 includes a reflective optical element 11a having a positive power. The reflective surface of the reflective optical element 11a has an aspherical shape. The second optical system 12 includes a first lens group Gr1, an aperture stop S, and a second lens group Gr2. The first lens group Gr1 includes a first lens L1 and a second lens L2. The second lens group Gr2 includes a third lens L3, a fourth lens L4, a fifth lens L5, and a sixth lens L6. An infrared cut filter F is provided between the sixth lens L6 and the image sensor 51. The imaging lens 10D reflects the optical path from the first optical system 11 to the second optical system 12 by the optical path bending mirror 13 provided between the first optical system 11 and the second optical system 12 and having no power. 11a is bent 90 ° downward. The first lens L1 is an aspheric plastic lens, and the other lenses are glass spherical lenses.

11A and 11B are MTF characteristic diagrams on the object plane PS. As can be seen from FIGS. 11A and 11B, the imaging apparatus 100 according to the fourth embodiment obtains sufficient resolving power up to the periphery.

(Example 5)
The optical specification values of the imaging lens of Example 5 are shown below.
Fno: F2.80
Imaging plane: 3.672mm × 2.754mm

Data on the lens surface and the like of the imaging lens of Example 5 are shown in Table 12 below.
[Table 12]
Surf.N R [mm] D [mm] Nd νd
P-Surf. 160.000
1 ** (R-Surf.) -14.011 62.096
2 * -5.928 4.832 1.5447 56.2
3 * -9.139 2.331
4 -24.511 4.073 1.8061 40.9
5 -18.043 29.392
6 (STOP) INF 1.703
7 27.137 2.578 1.7200 50.2
8 -29.052 0.500
9 12.100 3.314 1.6228 57.0
10 -10.130 4.069 1.7847 26.2
11 12.162 2.839
12 78.681 4.370 1.8467 23.7
13 -12.148 2.213
14 INF 0.500 1.5163 64.1
15 INF 1.501
16 (I-Surf.) INF

Table 13 below shows the aspheric coefficients of the imaging lens of Example 5.
[Table 13]
First side
K = -3.0709E + 00, A4 = -1.7238E-05, A6 = 1.4966E-08, A8 = 7.0197E-12,
A10 = -4.5496E-14, A12 = 5.6297E-17, A14 = -2.5635E-20,
A16 = 1.2506E-24
Second side
K = -1.8646E + 00, A4 = -1.3229E-04, A6 = -5.7713E-07, A8 = 9.5703E-09,
A10 = 2.7146E-11, A12 = 1.8885E-13, A14 = -4.6551E-15
Third side
K = -2.3679E + 00, A4 = -4.3296E-05, A6 = 1.4361E-07, A8 = 4.3657E-10,
A10 = 2.2597E-11, A12 = -4.3055E-14, A14 = -3.4322E-16

FIG. 12 is a cross-sectional view of the imaging lens 10E and the like of the fifth embodiment. The imaging lens 10 E includes a first optical system 11, an optical path bending mirror 13, and a second optical system 12. The first optical system 11 includes a reflective optical element 11a having a positive power. The reflective surface of the reflective optical element 11a has an aspherical shape. The second optical system 12 includes a first lens group Gr1, an aperture stop S, and a second lens group Gr2. The first lens group Gr1 includes a first lens L1 and a second lens L2. The second lens group Gr2 includes a third lens L3, a fourth lens L4, a fifth lens L5, and a sixth lens L6. An infrared cut filter F is provided between the sixth lens L6 and the image sensor 51. The imaging lens 10E reflects the optical path from the first optical system 11 to the second optical system 12 by an optical path bending mirror 13 provided between the first optical system 11 and the second optical system 12 and having no power. 11a is bent 90 ° downward. The first lens L1 is an aspheric plastic lens, and the other lenses are glass spherical lenses.

13A and 13B are MTF characteristic diagrams on the object plane PS. As can be seen from FIGS. 13A and 13B, the imaging apparatus 100 according to the fifth embodiment obtains sufficient resolving power up to the periphery.

Table 14 below summarizes the values of Examples 1 to 5 corresponding to the conditional expressions (1) to (4) for reference.
[Table 14]

Although the imaging lens and the like according to the embodiments have been described above, the imaging lens and the like according to the present invention are not limited to the above. For example, the specific configuration of the imaging lens 10 and the like is not limited to the illustrated one, and can be changed as appropriate according to the application.

In the above embodiment, the infrared cut filter F is provided between the image-side lens of the second optical system 12 and the image sensor 51. However, in addition to the infrared cut filter F, the optical low-pass filter and the image sensor 51 are formed as parallel plates. A seal glass or the like may be provided.

Claims

An imaging lens for an imaging apparatus that images an object from an oblique direction using an imaging element,
From the object side,
A first optical system including only one reflective optical element having positive power;
A second optical system composed of only a refractive lens having a rotationally symmetric shape, and all lenses having a common optical axis;
With
Forming an intermediate image of the object between the first optical system and the second optical system;
The most object side lens of the second optical system has a negative power with a concave surface facing the object side,
An imaging lens that satisfies the following conditional expression.
-0.25 <FLd / FLob <-0.05
3.5 <YDobj / DM <14.0
However,
FLd: focal length of the second optical system FLob: focal length of the lens closest to the object side of the second optical system YDobj: diagonal length of the imaging range of the imaging lens DM: on the optical axis of the reflective optical element Distance from point to object
The second optical system includes, in order from the object side, a first lens group, an aperture stop, and a second lens group.
The first lens group is located farther from the aperture stop than the most image-side lens of the second optical system, and is composed of only two lenses, a negative lens and a positive lens, in order from the object side. The imaging lens according to claim 1.
The imaging lens according to claim 1, wherein the imaging lens satisfies the following conditional expression.
2.0 <MRED / FLd <4.0
However,
MRED: Maximum height FLd from the optical axis of the use area of the reflecting optical element FLd: Focal length of the second optical system
The second optical system includes, in order from the object side, a first lens group, an aperture stop, and a second lens group.
The imaging lens according to any one of claims 1 to 3, wherein the second lens group includes one cemented lens in which a negative lens and a positive lens are bonded together.
The imaging lens according to any one of claims 1 to 4, further comprising an infrared cut filter between a lens closest to the image side of the second optical system and an imaging surface of the imaging element.
The imaging lens according to any one of claims 1 to 5, which satisfies the following conditional expression.
0.35 <BF / FLd <1.3
However,
BF: distance FLd on the optical axis between the image side surface of the lens on the most image side of the second optical system and the imaging surface FLd: focal length of the second optical system
The imaging lens according to any one of claims 1 to 6, wherein the reflective optical element has a free-form surface shape.
The imaging lens according to any one of claims 1 to 7, further comprising an optical path bending mirror having no power between the first optical system and the second optical system.
An imaging lens according to any one of claims 1 to 8,
An image sensor;
An imaging apparatus comprising: