JP2016126254A - Imaging lens, imaging apparatus, and projection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging lens which sufficiently secures resolution up to a peripheral part and has a super wide angle, regardless of low distortion.SOLUTION: The imaging lens includes, in order from an object side, a first group Gr1 having negative refractive power as a whole, an aperture diaphragm S, and a second lens group Gr2 having positive refractive power as a whole. An image formation area CA is shifted with respect to an optical axis AX. The first lens group Gr1 includes at least one asymmetrical lens NS having a non-axial symmetrical shape in a direction where the image formation area CA is shifted with respect to the optical axis AX.SELECTED DRAWING: Figure 1

Description

  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 and a projection apparatus that incorporate the imaging lens.

  In recent years, a projection apparatus that enlarges and projects an image onto a screen, which is a projection surface, 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. 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 only a simple movement of a person is detected, the number of pixels on the order of VGA (Video Graphics Array) is sufficient. 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.

  If the above-described imaging device is to be incorporated into the short-focus projector arranged at a position 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 an optical system in which distortion is suppressed to a very small value by using a relay 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. Further, the optical system of Patent Document 2 has a very small distortion, but the angle of view is not enough at around 90 °, and the use of a relay optical system makes the total optical length very large. Therefore, it is inevitable to increase the size of the imaging device.

JP 2013-109268 A US Pat. No. 7,768,715

  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 imaging lens having a super wide angle while sufficiently resolving power to the peripheral portion and low distortion.

  Another object of the present invention is to provide an imaging device and a projection device incorporating the imaging lens.

  In order to achieve the above object, an imaging lens according to the present invention includes, in order from the object side, a first lens group having a negative refractive power as a whole, an aperture stop, and a second lens group having a positive refractive power as a whole. And the imaging region is shifted with respect to the optical axis, and the first lens group has an asymmetric lens having a shape that is non-axisymmetric with respect to the direction in which the imaging region is shifted with respect to the optical axis. Including at least one sheet. 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.

  The imaging lens has a so-called retrofocus type lens configuration in which a negative lens group and a positive lens group are arranged in this order from the object side, so that the lens is small but has a sufficiently wide angle. In addition, since the imaging region of the imaging lens is shifted with respect to the optical axis and is asymmetrical with respect to the optical axis, the imaging lens is placed on the edge side of the subject, that is, on the periphery or on the outer side of the imaging lens. Even if it is arranged and the entire subject is photographed, the photographing range can be captured efficiently. In addition, since the first lens group includes the asymmetric lens, it is possible to obtain a high-resolution image up to the peripheral portion while suppressing distortion.

In a specific aspect of the present invention, the imaging lens satisfies the following conditional expression.
-4.0 <FG1 / f <-2.0 (1)
Here, FG1 is the focal length of the first lens group, and f is the focal length of the entire imaging lens system.
Conditional expression (1) is a conditional expression for achieving both widening of the imaging lens and shortening of the optical total length. By exceeding the lower limit value of conditional expression (1), the negative refractive power of the first lens group can be appropriately maintained, and a wider-angle lens system can be obtained. On the other hand, by falling below the upper limit value of conditional expression (1), the negative refractive power of the first lens group does not become excessively strong, and the optical total length of the imaging lens can be shortened.

In another aspect of the present invention, in the first lens group, the first lens arranged closest to the object side has a rotationally symmetric shape and satisfies the following conditional expression.
−55.0 <FL1 / f <−10.0 (2)
Here, FL1 is the focal length of the first lens, and f is the focal length of the entire imaging lens system.
Conditional expression (2) is a conditional expression for appropriately setting the focal length of the first lens. By exceeding the lower limit value of the conditional expression (2), the negative refractive power of the first lens group can be appropriately maintained, and a wider-angle lens system can be obtained. On the other hand, by falling below the upper limit value of the conditional expression (2), the negative refractive power of the first lens group does not become excessively strong, and distortion generated in the first lens group can be suppressed to a small level.

  In yet another aspect of the present invention, the first lens is a glass spherical lens having a meniscus rotationally symmetric shape with a convex surface facing the object side. In this case, even if the central portion of the first lens protrudes from the peripheral portion, it is possible to suppress damage to the lens surface due to being made of glass. In addition, the processing cost can be reduced by using a spherical shape that is rotationally symmetric.

  In still another aspect of the invention, the first lens group has at least two negative lenses. In this case, light rays in the periphery of the subject that are incident at a very wide angle can be dispersed and refracted by a plurality of negative lenses. Therefore, distortion, field curvature, coma, and the like are less likely to occur, resulting in a low-distortion and high-resolution imaging lens.

  In still another aspect of the present invention, the first lens group includes at least one lens having a D-cut shape in which a part of the outer shape is a straight line. In this case, in an unused area that is generated when the imaging area shifts and the light beam passes only on one side of the lens, unnecessary light is prevented from internally reflecting and reaching the imaging surface. The thickness in the radial direction can be reduced.

  In still another aspect of the present invention, the second lens group is composed of rotationally symmetric lenses and is symmetric about the optical axis. Since the second lens group has little effect of correcting various aberrations such as distortion, the second lens group may not include an asymmetric lens like the first lens group. In this way, by forming the second lens group with a rotationally symmetric lens, it is possible to facilitate processing and assembly of the lens.

  In still another aspect of the present invention, the second lens group includes a cemented lens in which one positive lens and one negative lens are bonded. In this case, even for an ultra-wide angle lens system in which correction of chromatic aberration is difficult, chromatic aberration can be corrected by inserting a cemented lens into the lens system. In the second lens group, the effective lens diameter tends to be relatively small, and the processing difficulty and cost of the cemented lens can be reduced.

  In yet another aspect of the present invention, the asymmetric lens has a free-form surface shape. In this case, the degree of freedom of the shape in the light passage region is improved, and the imaging lens with low distortion and high resolution is obtained.

  In yet another aspect of the present invention, the asymmetric lens has a rotationally symmetric shape and is arranged eccentric with respect to the optical axis. In this case, the degree of freedom of the shape in the light passage region is relatively improved, and the imaging lens has a low distortion and a high resolution. Further, since it is a rotationally symmetric optical surface, it is less difficult to process than a surface formed by a free-form surface, and it becomes easier to correct the surface shape. For this reason, a more accurate surface shape can be obtained.

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

  By incorporating the above-described imaging lens, the imaging apparatus can capture a wide range from a close distance, and can obtain an image with good aberration correction up to the periphery.

  A projection apparatus according to the present invention includes the imaging lens described above and an image display element disposed at an imaging position of the imaging lens, and enlarges and projects an image formed by the image display element using the imaging lens. .

  The projection device functions as a projection lens for magnifying and projecting an image formed by the image display element onto the subject surface by arranging the image display element at the imaging position of the imaging lens. It becomes. The imaging lens described above can be used as a projection lens without any problem, and the projection apparatus can project a high-resolution image from the very close range to a large screen with low distortion on the large screen. it can.

It is a conceptual diagram explaining an imaging device etc. provided with the imaging lens of 1st 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. (A) is a distortion grid diagram of the image acquired with the imaging device of Example 1, (B) is a distortion grid diagram of the image acquired with the imaging device of the comparative example. It is a conceptual diagram explaining the use condition of the imaging device of a comparative example. (A) And (B) is a MTF characteristic figure which shows the performance of the imaging device of Example 1. FIG. It is a figure explaining the MTF evaluation position on a to-be-photographed object surface. FIG. 6 is a cross-sectional view of an imaging lens and the like in the imaging apparatus of Example 2. FIG. 6 is a distortion grid diagram of an image acquired by the imaging apparatus according to the second embodiment. (A) And (B) is a MTF characteristic figure which shows the performance of the imaging device of Example 2. FIG. FIG. 7 is a cross-sectional view of an imaging lens and the like in the imaging apparatus of Example 3. FIG. 10 is a distortion grid diagram of an image acquired by the imaging apparatus of Example 3. (A) And (B) is a MTF characteristic figure which shows the performance of the imaging device of Example 3. FIG. It is a conceptual diagram explaining the projection apparatus of 2nd Embodiment.

[First Embodiment]
Hereinafter, with reference to FIG. 1 etc., the imaging lens and imaging device which are 1st Embodiment of this invention are demonstrated. The imaging lens 10 illustrated in FIG. 1 has the same configuration as the imaging lens 11 of Example 1 described later.

  As shown in FIG. 1, the imaging apparatus 100 includes an imaging lens 10 that forms a subject image (object image), an imaging element 51 that detects a subject 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 lens 10 forms a subject image on the imaging surface (imaging plane) I of the imaging element 51, and in order from the object side, the first lens group Gr1, the aperture stop S, and the second lens group. Gr2.

  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 image sensor 51 is arranged so as to be shifted with respect to the optical axis AX of the imaging lens 10 in order to greatly bias the imaging area IA with respect to the imaging lens 10. Here, the optical axis AX means not an optical axis (center axis) of each lens constituting the imaging lens 10 but an axis that passes through the center of the aperture stop S and is perpendicular to the section of the aperture stop S.

  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 can receive a voltage and a signal for driving the image pickup device 51 and the driving mechanism 55a from an external circuit, and can output a detection signal to the external circuit.

  On the imaging lens 10 side of the imaging element 51, a parallel plate F such as an infrared cut filter or a seal glass of the imaging element 51 is disposed and fixed by a holder member (not shown) so as to cover the imaging element 51 and the like.

  The lens barrel 54 houses and holds the imaging lens 10. In the lens barrel portion 54, any one or more of the first and second lenses Gr1 and Gr2 constituting the imaging lens 10 are moved along the optical axis AX so that the imaging lens 10 is focused. In order to enable the operation, for example, a drive mechanism 55a can be provided.

  Hereinafter, the imaging lens 10 will be described in detail. An imaging lens 10 shown in FIG. 1 includes, in order from the object side, a first lens group Gr1 having a negative refractive power as a whole, an aperture stop S, and a second lens group Gr2 having a positive refractive power as a whole. . The first lens group Gr1 is disposed at a position farther from the aperture stop S than the second lens group Gr2. As shown in FIG. 2, the imaging area CA of the imaging lens 10 is shifted with respect to the optical axis AX and is asymmetric with respect to the optical axis AX. Specifically, when the imaging device 100 is disposed so as to face the lower end of the subject BS and be close to the lower end of the subject BS as shown in FIG. 1, the imaging region CA is shifted downward with respect to the optical axis AX. Among the imaging lenses 10, the first lens group Gr1 on the object side includes at least one asymmetric lens NS having a non-axisymmetric shape with respect to the direction in which the imaging area CA is shifted with respect to the optical axis AX. . The asymmetric lens NS is axially symmetric with respect to a direction perpendicular to the direction in which the optical axis AX and the imaging area CA are shifted (direction perpendicular to the paper surface).

  The asymmetric lens NS has, for example, a free-form surface shape. In the example of FIG. 1, the second lens L2 of the first lens group Gr1 has a free-form surface shape. Alternatively, the asymmetric lens NS may have a rotationally symmetric shape, for example, and may be arranged eccentric to the optical axis AX. Here, the eccentricity is caused by shifting or tilting the central axis of the lens with respect to the optical axis AX. By including the asymmetric lens NS as described above, the imaging lens 10 improves the degree of freedom of shape in the light passage region, and becomes a lens with low distortion and high resolution. Note that, when the rotationally symmetric lens is decentered with respect to the optical axis AX as in the latter asymmetric lens NS, since it is a rotationally symmetric optical surface, it is less difficult to process than a surface formed with a free-form surface. This makes it easier to correct the surface shape. For this reason, a more accurate surface shape can be obtained.

  In addition, the first lens group Gr1 may include at least one lens having a D-cut shape in which a part of the outer shape is a straight line. As already described, the first lens group Gr1 tends to be located away from the aperture stop S. When the imaging area CA of the imaging lens 10 is shifted with respect to the optical axis AX, the light beam is Only one side of the one lens group Gr1 passes, and the one side where the light beam does not pass becomes an unused area. Therefore, if the first lens group Gr1 includes at least one lens having a D-cut shape in which a part of the outer shape is a straight line, unnecessary light is reflected from the inner surface and reaches the imaging surface. The thickness of the imaging lens 10 in the radial direction can be reduced.

The imaging lens 10 satisfies the following conditional expression.
-4.0 <FG1 / f <-2.0 (1)
Here, FG1 is the focal length of the first lens group Gr1, and f is the focal length of the entire imaging lens 10 system.
Conditional expression (1) is a conditional expression for achieving both widening of the imaging lens 10 and shortening of the optical total length. By exceeding the lower limit value of conditional expression (1), the negative refractive power of the first lens group Gr1 can be appropriately maintained, and a wider-angle lens system can be obtained. On the other hand, by falling below the upper limit value of conditional expression (1), the negative refractive power of the first lens group Gr1 does not become excessively strong, and the optical total length of the imaging lens 10 can be shortened.

  The first lens group Gr1 has at least two negative lenses. The first lens L1 has a meniscus rotationally symmetric shape with a convex surface facing the object side, and is a glass spherical lens.

In the first lens group Gr1, the first lens L1 arranged closest to the object side may have a rotationally symmetric shape. In this case, the imaging lens 10 satisfies the following conditional expression.
−55.0 <FL1 / f <−10.0 (2)
Here, FL1 is the focal length of the first lens L1, and f is the focal length of the entire imaging lens 10.
Conditional expression (2) is a conditional expression for appropriately setting the focal length of the first lens L1. By exceeding the lower limit value of the conditional expression (2), the negative refractive power of the first lens group Gr1 can be appropriately maintained, and a wider-angle lens system can be obtained. On the other hand, by falling below the upper limit value of conditional expression (2), the negative refractive power of the first lens group Gr1 does not become excessively strong, and distortion generated in the first lens group Gr1 can be suppressed to a small level. .

  The second lens group Gr2 is composed of rotationally symmetric lenses, and is symmetric about the optical axis AX. The second lens group Gr2 in which the light from the imaging area IA, which is the range for imaging the subject BS, tends to pass through the same part of the lens, corrects various aberrations such as distortion aberration mainly caused by the first lens group Gr1. Therefore, the second lens group Gr2 may not include the asymmetric lens NS like the first lens group Gr1. In this way, by forming the second lens group Gr2 with a rotationally symmetric lens, it is possible to facilitate processing and assembly of the lens.

  Further, the second lens group Gr2 includes a cemented lens CS in which one positive lens and one negative lens are bonded together. Correction of chromatic aberration tends to be difficult with an ultra-wide-angle lens system, and it is desirable to include a cemented lens CS for correcting chromatic aberration in the imaging lens system. At that time, by putting the cemented lens CS in the second lens group Gr2 capable of relatively reducing the lens effective diameter, it is possible to reduce the processing difficulty and cost of the cemented lens CS.

  In the above, it is assumed that the imaging lens 10 is arranged on the lower end side of the subject BS, as shown in FIG. 1, but it is not limited to the lower end side, and may be arranged on the upper end side and the left and right end sides. In this case, the imaging area CA may be shifted and arranged in accordance with the direction of each imaging area IA. Further, the angle around the optical axis AX of the asymmetric lens NS constituting the first lens group Gr1 may be rotated, for example, in units of 90 °.

  Hereinafter, the usage state of the imaging apparatus 100 will be described. As shown in FIG. 2, the light ray IR that is an image from the subject surface PS enters the imaging apparatus 100. The ray IR incident on the imaging device 100 sequentially has an area AR1 above the lenses L1 to L3 constituting the first lens group Gr1 of the imaging lens 10, that is, a biased area in the direction shifted with respect to the optical axis AX. Passes through and forms an image on the imaging surface I through the second lens group Gr2. In the imaging apparatus 100, the light beam IR does not pass through the area AR2 below the lenses L1 to L3 constituting the first lens group Gr1.

  The imaging lens 10 and the imaging apparatus 100 described above have a so-called retrofocus type lens configuration in which a negative lens group and a positive lens group are arranged in this order from the object side. Become. In the present embodiment, it is assumed that the angle of view required for the imaging lens 10 is about 25 cm from the subject BS to the imaging lens 10 (imaging distance) and the diagonal length of the imaging area IA is about 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. In addition, 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 area 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.

  Further, in the present embodiment, it is assumed that the entire subject is photographed from the end side of the subject BS, not the subject BS that is placed facing the subject BS and photographed from the front. Here, if the imaging area CA is arranged so as to be substantially symmetric with respect to the optical axis AX of the imaging lens 10, it will be reflected in a range that is not originally required. Therefore, the imaging range can be efficiently captured by shifting the imaging area CA to one side with respect to the optical axis AX of the imaging lens 10. When the imaging area CA is shifted with respect to the optical axis AX of the imaging lens 10, the light beam passes through only a part of the lens away from the aperture stop S (first lens group Gr1 in the present embodiment). It will not be. Therefore, it is not necessary to configure such a lens with a rotationally symmetric shape. In particular, at least one lens of the first lens group Gr1, which is a negative lens group, which is far from the aperture stop S and is highly effective in correcting distortion, is non-axisymmetric with respect to the direction in which the imaging area CA is shifted. With this configuration, it is possible to obtain a high-resolution image up to the peripheral portion while suppressing distortion. For the unnecessary portion (region AR2 below the lenses L1 to L3), the lens can be cut as described above. By mounting the imaging lens 10 as described above, it is possible to obtain the imaging device 100 that can shoot a wide range from a close distance and that has been favorably corrected for aberrations up to the peripheral portion.

〔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.
f: focal length of imaging lens Fno: F-number R: paraxial radius of curvature D: axial distance Nd: refractive index νd of lens material with respect to d-line: Abbe number of lens material Si: shift amount Ti: tilt amount The shift is a shift in the Y-axis direction when the left-right direction toward the subject is the X-axis (right direction is positive) and the up-down direction is Y-axis (upward direction is positive). Further, tilt is rotation around the X axis, and counterclockwise is positive.
In addition, the symbol Surf.N means a surface number, the symbol INF means infinity or ∞, the symbol P-Surf. Means the subject surface PS, and the symbol I-Surf. (Imaging plane) I, symbol STOP means a stop, and PR means a prism.

ただし、
Ａｉ：ｉ次の非球面係数
Ｒ ：曲率半径
Ｋ ：円錐定数
また、自由曲面形状は、上記非球面形状と同じく、面の頂点を原点とし、光軸方向にＺ軸をとり、光軸と垂直方向の高さをｈとして以下の「数２」で表す。

ただし、
Ｃｊ：x^myⁿの係数
Ｒ ：曲率半径
Ｋ ：円錐定数 In each example, the surface indicated by “*” after each surface number is an aspheric surface, and the aspheric surface has an origin at the apex of the surface and a Z axis in the optical axis direction. The height in the direction perpendicular to the optical axis is h, and is expressed by the following “Equation 1”.

However,
Ai: i-th order aspheric coefficient R: radius of curvature K: conic constant The free-form surface shape is the same as the above-mentioned aspheric surface shape, with the vertex of the surface as the origin, the Z axis in the optical axis direction, and perpendicular to the optical axis. The height in the direction is represented by h in the following “Equation 2”.

However,
Cj: x ^m y coefficient ⁿ R: radius of curvature K: conical constant

[Example 1]
The optical specification values of the imaging lens of Example 1 are shown below.
Fno: 2.80
Subject size: 1771mm x 1328mm

The data of the lens surface of the imaging lens of Example 1 is shown in Table 1 below.
[Table 1]
Surf.NR [mm] D [mm] Nd νd
P-Surf. 250.000
1 * 45.167 2.360 1.5447 56.2
2 * 17.235 11.926
3 ** -222.750 1.882 1.5447 56.2
4 ** 11.575 8.480
5 48.320 2.986 1.7241 47.1
6 7.163 20.485
7 (STOP) INF 0.242
8 23.219 5.000 1.9229 18.8
9 -49.368 4.802
10 8.991 3.998 1.7729 49.6
11 -6.184 1.001 1.9229 18.8
12 8.560 0.172
13 * 6.313 3.950 1.5447 56.2
14 * -5.712 0.873
15 INF 0.500 1.5163 64.1
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]
First side
K = 0.0000E + 00, A3 = 5.4115E-07, A4 = -1.7872E-06, A5 = 1.8317E-09,
A6 = -1.7892E-10, A8 = -2.3406E-13, A10 = -2.5831E-16,
A12 = 5.6916E-19, A14 = 0.0000E + 00
Second side
K = 0.0000E + 00, A3 = 1.5830E-05, A4 = 1.1826E-05, A5 = 6.4851E-08,
A6 = 1.0141E-07, A8 = -1.9922E-11, A10 = -2.9713E-13,
A12 = -8.1482E-16, A14 = 0.0000E + 00
Side 13
K = 0.0000E + 00, A3 = 0.0000E + 00, A4 = -5.5791E-04, A5 = 0.0000E + 00,
A6 = -1.3675E-05, A8 = 1.0787E-06, A10 = -7.9853E-10,
A12 = 2.1679E-09, A14 = -3.0682E-11
14th page
K = 0.0000E + 00, A3 = 0.0000E + 00, A4 = 2.4356E-03, A5 = 0.0000E + 00,
A6 = -3.5043E-05, A8 = -4.1868E-07, A10 = 1.2063E-07,
A12 = 7.9500E-10, A14 = 8.5635E-11

The free-form surface coefficients of the imaging lens of Example 1 are shown in Table 3 below.
[Table 3]

  FIG. 3 is a cross-sectional view of the imaging lens 11 and the like of the first embodiment. The imaging lens 11 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. In Example 1, the second lens L2 of the first lens group Gr1 is an asymmetric lens NS. The second lens L2 has a free-form surface shape and a rotationally asymmetric shape. Specifically, the second lens L2 has an axisymmetric shape with respect to the horizontal direction as viewed from the subject BS, that is, the X-axis direction (left-right direction), but the vertical direction in which the imaging area CA is shifted, that is, Y It has a non-axisymmetric shape with respect to the axial direction (vertical direction). The second lens group Gr2 includes a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7. Between the seventh lens L7 and the image sensor 51, a parallel flat plate F assuming an optical low-pass filter, an IR cut filter, a seal glass of the image sensor 51, and the like is provided. Reference numeral I denotes an imaging surface of the imaging lens 11 and an imaging surface of the imaging element 51 (the same applies to the following examples). In the present embodiment, it is assumed that the imaging device 100 is disposed at the center of the lower end of the subject BS, and the imaging area CA is shifted downward.

  FIG. 4A is a distortion grid diagram of an image acquired by the imaging apparatus 100 according to the first embodiment. In this distortion grid, the imaging device 100 is arranged on the lower end side of the subject BS, and for example, the subject BS of about 80 inches is photographed from a distance of 25 cm. On the other hand, FIG. 4B is a distortion lattice diagram of an image acquired under the same conditions as in Example 1 with an imaging device incorporating an ultra-wide angle lens as an imaging lens of a comparative example. As shown in FIG. 5, the imaging lens of the comparative example is arranged with the optical axis BX of the imaging lens IL inclined upward in order to make the angle of view in the vertical direction smaller. As can be seen from FIG. 4A, in the distortion lattice diagram of Example 1, the degree of compression due to distortion at the peripheral portion is greatly improved. On the other hand, as shown in FIG. 4 (B), the distortion lattice diagram of the comparative example is combined with trapezoidal distortion caused by tilting the optical axis BX upward, and barrel distortion caused by the super-wide-angle lens. Part of the image is greatly compressed. In this case, if characters are written at the upper end, it is considered that fine characters cannot be distinguished by this image compression.

6A and 6B are MTF (Modulation Transfer Function) characteristic diagrams on the object plane PS. 6A is an MTF characteristic diagram at positions F1 to F3 in the imaging area IA shown in FIG. 7, and FIG. 6B is an MTF characteristic at positions F4 to F6 in the imaging area IA shown in FIG. It is a figure (the following examples are also the same). In FIGS. 6A and 6B, Fi-X (i = 1 to 6) indicates the X-direction resolving power at the position of Fi, and Fi-Y (i = 1 to 6) indicates the position of Fi. The Y direction resolving power 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. 6A and 6B, the imaging apparatus 100 according to the first embodiment obtains sufficient resolution up to the peripheral portion.

(Example 2)
The optical specification values of the imaging lens of Example 2 are shown below.
Fno: 2.80
Subject size: 1771mm x 1328mm

Table 4 below shows data such as the lens surface of the imaging lens of Example 2.
[Table 4]
Surf.NR [mm] D [mm] Nd νd Si [mm] Ti [deg]
P-Surf. 250.000
1 * 42.328 2.000 1.5447 56.2 5.34 0.11
2 * 15.786 10.678 5.34 0.11
3 ** -69.110 1.530 1.5447 56.2
4 ** 11.405 11.507
5 36.641 1.743 1.7568 50.2
6 6.521 18.525
7 (STOP) INF 0.150
8 13.399 1.915 1.9229 18.8
9 -4214.430 4.250
10 8.989 3.358 1.7730 49.6
11 -4.632 1.000 1.9229 18.8
12 8.894 0.150
13 * 5.794 3.280 1.5447 56.2
14 * -5.188 0.876
15 INF 0.500 1.5163 64.1
16 (I-Surf.) INF

The aspheric coefficients of the imaging lens of Example 2 are shown in Table 5 below.
[Table 5]
First side
K = 0.0000E + 00, A3 = 1.4965E-05, A4 = 3.4806E-06, A5 = 7.6703E-09,
A6 = 1.5734E-08, A8 = -2.4911E-11, A10 = 4.4122E-16,
A12 = 1.0473E-17, A14 = 0.0000E + 00
Second side
K = 0.0000E + 00, A3 = -6.4119E-04, A4 = 3.5174E-05, A5 = -1.2788E-07,
A6 = 2.3073E-08, A8 = -1.2724E-10, A10 = 8.0621E-13,
A12 = 3.0636E-14, A14 = 0.0000E + 00
Side 13
K = 0.0000E + 00, A3 = 0.0000E + 00, A4 = -1.1703E-03, A5 = 0.0000E + 00,
A6 = -2.6058E-05, A8 = 3.5204E-06, A10 = 5.2613E-09,
A12 = 1.8971E-09, A14 = -3.0207E-12
14th page
K = 0.0000E + 00, A3 = 0.0000E + 00, A4 = 2.8000E-03, A5 = 0.0000E + 00,
A6 = -6.7766E-05, A8 = -9.3277E-07, A10 = 4.6036E-07,
A12 = -7.5496E-10, A14 = -3.3612E-12

The free-form surface coefficients of the imaging lens of Example 2 are shown in Table 6 below.
[Table 6]

  FIG. 8 is a cross-sectional view of the imaging lens 12 and the like of the second embodiment. The imaging lens 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. In Example 2, in the first lens group Gr1, the first and second lenses L1 and L2 are asymmetric lenses NS. The first lens L1 has a rotationally symmetric shape, but is decentered in the Y-axis direction with respect to the optical axis AX. Therefore, the first lens L1 has an axisymmetric shape with respect to the horizontal direction, that is, the X-axis direction (left-right direction) when viewed from the subject BS, but the vertical direction in which the imaging area CA is shifted, that is, the Y-axis direction ( It has a non-axisymmetric shape with respect to the vertical direction. The second lens L2 has a free-form surface shape and a rotationally asymmetric shape. Specifically, the second lens L2 has an axisymmetric shape with respect to the horizontal direction (left-right direction) when viewed from the subject BS, but with respect to the vertical direction (up-down direction) in which the imaging area CA is shifted. And has a non-axisymmetric shape. The second lens group Gr2 includes a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7. A parallel plate F is provided between the seventh lens L7 and the image sensor 51.

  FIG. 9 is a distortion grid diagram of an image acquired by the imaging apparatus 100 according to the second embodiment. As can be seen from FIG. 9, the degree of compression due to distortion at the peripheral portion is greatly improved by using the imaging device 100 of the second embodiment.

  10A and 10B are MTF characteristics diagrams on the object plane PS. As can be seen from FIGS. 10A and 10B, 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
Subject size: 1771mm x 1328mm

Table 7 below shows data such as the lens surface of the imaging lens of Example 3.
[Table 7]
Surf.NR [mm] D [mm] Nd νd Si [mm] Ti [deg]
P-Surf. 250.000
1 * 14.968 1.000 1.7207 51.8 1.42 1.02
2 * 6.111 4.456 1.42 1.02
3 * -46.583 1.082 1.5311 55.7 0.07 3.81
4 * 4.527 2.528 0.07 3.81
5 6.356 1.011 1.4958 68.8
6 2.304 1.827
7 (PR) INF 5.000 1.8470 23.8
8 (PR) INF 1.082
9 (STOP) INF 0.150
10 13.399 1.000 1.9229 18.8
11 -4214.430 1.301
12 8.989 1.279 1.7730 49.6
13 -4.632 1.000 1.9229 18.8
14 8.894 0.150
15 * 5.794 1.475 1.5311 55.7
16 * -5.188 0.692
17 INF 0.500 1.5163 64.1
18 (I-Surf.) INF

The aspheric coefficients of the imaging lens of Example 3 are shown in Table 8 below.
[Table 8]
First side
K = 4.3250E-01, A3 = -3.2968E-05, A4 = -1.5673E-05, A5 = -8.9319E-07,
A6 = -1.0340E-07, A8 = -1.3169E-10, A10 = 3.2117E-12,
A12 = 3.2704E-14, A14 = 0.0000E + 00
Second side
K = 3.9469E-02, A3 = 1.1383E-04, A4 = 1.0325E-04, A5 = 2.2657E-06,
A6 = 1.2032E-07, A8 = -4.6227E-09, A10 = 3.0461E-13,
A12 = -7.2479E-12, A14 = 0.0000E + 00
Third side
K = 0.0000E + 00, A3 = 0.0000E + 00, A4 = 1.7285E-03, A5 = 0.0000E + 00,
A6 = -3.5101E-06, A8 = -1.7441E-07, A10 = 9.5480E-10,
A12 = 2.8819E-11, A14 = 0.0000E + 00
4th page
K = 0.0000E + 00, A3 = 0.0000E + 00, A4 = 6.3746E-04, A5 = 0.0000E + 00,
A6 = 5.7079E-05, A8 = 1.1191E-05, A10 = -1.0380E-06,
A12 = 4.3856E-08, A14 = 0.0000E + 00
15th page
K = 0.0000E + 00, A3 = 0.0000E + 00, A4 = -1.0663E-02, A5 = 0.0000E + 00,
A6 = -1.4031E-03, A8 = 7.6487E-04, A10 = -1.1550E-04,
A12 = 1.8075E-05, A14 = -1.5225E-07
16th page
K = 0.0000E + 00, A3 = 0.0000E + 00, A4 = 3.1285E-02, A5 = 0.0000E + 00,
A6 = -3.0311E-03, A8 = -4.2725E-04, A10 = 3.7381E-04,
A12 = -7.1934E-06, A14 = -1.6942E-07

  FIG. 11 is a cross-sectional view of the imaging lens 13 and the like according to the third embodiment. The imaging lens 13 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, a third lens L3, and a prism PR. In Example 3, in the first lens group Gr1, the first and second lenses L1 and L2 are asymmetric lenses NS. The first and second lenses L1 and L2 have a rotationally symmetric shape, but are decentered in the Y-axis direction with respect to the optical axis AX. Therefore, the first and second lenses L1 and L2 have an axisymmetric shape with respect to the horizontal direction, that is, the X-axis direction (left-right direction) when viewed from the subject BS, but the vertical direction in which the imaging area CA is shifted. That is, it has a non-axisymmetric shape with respect to the Y-axis direction (vertical direction). The prism PR is assumed to be a prism for bending the optical path by 90 °. The second lens group Gr2 includes a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7. A parallel plate F is provided between the seventh lens L7 and the image sensor 51.

  FIG. 12 is a distortion grid diagram of an image acquired by the imaging apparatus 100 according to the third embodiment. As can be seen from FIG. 12, the degree of compression due to distortion in the peripheral portion is greatly improved by using the imaging device 100 of the third embodiment.

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

Table 9 below summarizes the values of Examples 1 to 3 corresponding to the conditional expressions (1) and (2) for reference.
[Table 9]

[Second Embodiment]
Hereinafter, an imaging lens, a projection device, and the like according to the second embodiment will be described. In addition, the projection apparatus of 2nd Embodiment gives the function as a projection lens to the imaging lens of 1st Embodiment, and the matter which is not demonstrated especially is the same as that of 1st Embodiment.

  As shown in FIG. 14, in the present embodiment, the projection apparatus 200 is disposed on the lower end side of the projection surface SC. The projection apparatus 200 performs enlargement projection from a close position of the projection surface SC, and assumes, for example, a projector application having an interactive function. One interactive function is image recognition of handwritten characters. The projection apparatus 200 includes a projection optical system 60, an illumination optical system 70, an image display element 80, and the like. In FIG. 14, a control system for driving the projection optical system 60, the illumination optical system 70, the image display element 80, and the like is omitted.

  Although a detailed description is omitted, the projection optical system 60 enlarges an image obtained from the image display element 80 and projects it on a screen or other projection target SB. As the projection optical system 60, the imaging lens 10 shown in FIG. The projection optical system 60 can perform focusing and zooming by moving some lens groups in the optical axis AX direction.

  Although not shown, the illumination optical system 70 includes a light source, a uniformizing optical system, and the like. As a light source of the illumination optical system 70, an LED, a mercury lamp, a laser, or the like can be used.

  The image display element 80 is a transmissive display element that forms video light, and forms an image by modulating the illumination light from the illumination optical system 70 according to an image signal. The image display element 80 is disposed at a position corresponding to the imaging position of the imaging lens 10. In addition, the image area GA displayed on the image display element 80 is shifted with respect to the optical axis AX similarly to the imaging area CA on the image sensor 51 of the first embodiment, and the optical axis AX is the center. It is asymmetric. The image display element 80 includes an image display panel that is a plate-like electronic component. The image display element 80 is not limited to a transmissive display element, and may be a reflective display element. In this case, the projection apparatus 200 is changed to an optical system suitable for each.

  The projection apparatus in the present embodiment has no problem even when the imaging lens 10 is used as a projection lens, and projects a high-resolution image from the very close range to a large screen with a small distortion aberration on a large screen. Can do.

  In the present embodiment, the projection optical system 60 (imaging lens 10) may be configured to share the projection lens and the imaging lens.

  Although the imaging lens according to the embodiment has been described above, the imaging lens according to the present invention is 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 embodiment described above, the imaging area CA avoids the optical axis AX, but may extend over the optical axis AX.

  DESCRIPTION OF SYMBOLS 10,11,12,13 ... Imaging lens 51 ... Imaging device 60 ... Projection optical system 70 ... Illumination optical system 80 ... Image display element 100 ... Imaging device 200 ... Projection device CA ... Imaging region, CS ... cemented lens, F ... parallel plate, Gr1, Gr2 ... lens group, I ... imaging surface, L1-L7 ... lens, NS ... asymmetric lens

Claims (12)

From the object side,
A first lens group having negative refractive power as a whole;
An aperture stop,
A second lens group having positive refractive power as a whole;
With
The imaging area is shifted with respect to the optical axis,
The imaging lens according to claim 1, wherein the first lens group includes at least one asymmetric lens having an axisymmetric shape with respect to a direction in which the imaging region is shifted with respect to the optical axis. The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
-4.0 <FG1 / f <-2.0
However,
FG1: focal length of the first lens group f: focal length of the entire imaging lens system 3. The first lens group according to claim 1, wherein the first lens disposed closest to the object side in the first lens group has a rotationally symmetric shape and satisfies the following conditional expression. The imaging lens described.
−55.0 <FL1 / f <−10.0
However,
FL1: Focal length of the first lens f: Focal length of the entire imaging lens system   The imaging lens according to claim 1, wherein the first lens has a meniscus rotationally symmetric shape with a convex surface facing the object side, and is a glass spherical lens.   The imaging lens according to claim 1, wherein the first lens group includes at least two negative lenses.   The imaging lens according to claim 1, wherein the first lens group includes at least one lens having a D-cut shape in which a part of the outer shape is a straight line.   The imaging lens according to any one of claims 1 to 6, wherein the second lens group is composed of rotationally symmetric lenses and is symmetric about the optical axis.   The imaging lens according to claim 1, wherein the second lens group includes a cemented lens obtained by bonding one positive lens and one negative lens.   The imaging lens according to claim 1, wherein the asymmetric lens has a free-form surface shape.   The imaging lens according to claim 1, wherein the asymmetric lens has a rotationally symmetric shape and is decentered with respect to the optical axis. The imaging lens according to any one of claims 1 to 10,
An image sensor;
An imaging apparatus comprising: The imaging lens according to any one of claims 1 to 10,
An image display element disposed at an imaging position of the imaging lens;
With
A projection apparatus characterized by enlarging and projecting an image formed by the image display element using the imaging lens.

Images