JP2013109268A - Wide-angle optical system and imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wide angle optical system that has a satisfactory imaging performance and is reduced in size.SOLUTION: The wide angle optical system comprises, in order from the object side: a first lens 110 of negative a meniscus shape convex toward the object side; a second lens 120 of a negative meniscus shape, whose object side surface is an anamorphic surface having a horizontal curvature and a vertical curvature in a plane substantially orthogonal to an optical axis; a third positive lens 130 convex toward the object side; an aperture stop 140; and a fourth positive lens 150 convex toward the image side. If the focal distance of the entire lens system in the horizontal direction is Fh and the focal distance of the entire lens system in the vertical direction is Fv, a condition expressed by 1.10<Fv/Fh<1.30 is satisfied. A second anamorphic surface other than the object side surface of the second lens is provided in a surface having a power that is opposite in sign to the power of the object side surface of the second lens.

Description

  The present invention relates to a wide-angle imaging optical system and an imaging apparatus using the same.

  Imaging optical systems used for surveillance cameras, in-vehicle cameras, and the like are required to have good imaging performance over the entire screen while ensuring a wide angle of view. In particular, when an ultra-wide-angle optical system having an angle of view exceeding 180 degrees is used, distortion distortion tends to increase, and therefore, low distortion design is required. As a single-focus wide-angle optical system that can meet these demands, there is Patent Document 1 below.

Patent Document 1 proposes an anamorphic optical system that is an ultra-wide-angle imaging optical system that has an ultra-wide angle of view in the horizontal direction and suppresses the angle of view in the vertical direction and has relatively little image distortion.
However, surveillance cameras and in-vehicle cameras are often required to be small because the mounting space is often limited. However, the anamorphic optical system according to Patent Document 1 includes 10 lenses. Therefore, it has been difficult to realize a small imaging device.

JP 2007-163549 A

  The present invention provides a wide-angle optical system that has good imaging performance and is downsized.

In order to achieve the above object, the imaging optical system of the present invention has a negative meniscus first lens that is convex toward the object side in order from the object side, and different curvatures in the horizontal and vertical directions in a plane orthogonal to the optical axis. A negative meniscus second lens having an anamorphic surface on the object side, a positive third lens convex on the object side, an aperture stop, and a positive fourth lens convex on the image side. When the focal length in the horizontal direction of the entire system is Fh and the focal length in the vertical direction of the entire lens system is Fv, the following conditional expression (1) is satisfied:
1.10 <Fv / Fh <1.30 (1)
In addition, a second anamorphic surface different from the object side surface of the second lens is provided on a surface having a sign different from the power of the object side surface of the second lens.

  Preferably, the following conditional expression (2) is satisfied.

0.4 <r1v / r1h <0.8 (2)
Here, r1h is the radius of curvature in the horizontal direction, and r1v is the radius of curvature in the vertical direction.

  Preferably, the second lens and the fourth lens are made of a resin material.

  Preferably, the second anamorphic surface is formed on the fourth lens.

  In order to achieve the above object, an image pickup apparatus according to the present invention includes any one of the above-described image pickup optical systems and an image pickup element that converts an optical image formed by the image pickup optical system into an electric signal. .

  According to the present invention, it is possible to realize a wide-angle optical system and an imaging apparatus that are compact and lightweight and have good imaging performance.

It is a lens section of the wide angle optical system which is the present invention. 2 is a cross-sectional view in the horizontal direction of the wide-angle optical system of Embodiment 1. FIG. 2 is a cross-sectional view in the vertical direction of the wide-angle optical system of Embodiment 1. FIG. 6 is a cross-sectional view in the horizontal direction of the wide-angle optical system of Embodiment 2. FIG. 6 is a cross-sectional view in the vertical direction of the wide-angle optical system of Embodiment 2. FIG. 6 is a horizontal sectional view of a wide-angle optical system according to Embodiment 3. FIG. 6 is a cross-sectional view in the vertical direction of the wide-angle optical system of Embodiment 3. FIG. 6 is a cross-sectional view in the horizontal direction of the wide-angle optical system of Embodiment 4. FIG. 10 is a cross-sectional view in the vertical direction of the wide-angle optical system of Embodiment 4. FIG. FIG. 10 is a cross-sectional view in the horizontal direction of the wide-angle optical system of Embodiment 5. FIG. 10 is a cross-sectional view in the vertical direction of the wide-angle optical system of Embodiment 5. 1 is a diagram illustrating a basic configuration of an imaging apparatus according to an embodiment of the present invention.

  Hereinafter, embodiments of a wide-angle optical system of the present invention and an imaging apparatus using the same will be described with reference to the drawings. The wide-angle optical systems of Embodiments 1 to 5 are collectively referred to as the wide-angle optical system of this embodiment.

  FIG. 1 is a cross section of a wide-angle optical system according to the present invention. A single-focus single-angle wide-angle optical system 100 in which a first lens 110, a second lens 120, a third lens 130, an aperture stop 140, and a fourth lens 150 are disposed in order from the object side. Further, reference numeral 160 denotes a glass block provided in a design corresponding to a crystal low-pass filter, an infrared ray removal filter, a protective glass for protecting an image pickup device, a CCD (Charge Coupled Device), a CMOS (Complementary Mental-Oxide Semiconductor Device), and the like. It has an imaging surface 170 on which the light receiving surface of the image sensor is arranged. The incident light from the object side is the object side R1 surface 1, the image surface side R2 surface 2 of the first lens 110, the object side R3 surface 3 of the second lens 120, the image surface side R4 surface 4, and the object of the third lens 130. The imaging element is provided through the side R5 surface 5, the image surface side R6 surface 6, the surface 7 of the aperture stop 140, the object side R7 surface 8, the image surface side R8 surface 9, and the glass block 160 of the fourth lens 150. The light is focused on the imaging surface 170. Further, the distance between the R1 surface 1 and the R2 surface 2 which is the thickness of the lens is D1, the distance between the R2 surface 2 of the first lens and the R3 surface 3 of the second lens is D2, and the R3 surface is the thickness of the second lens. 3 is the distance between the R4 surface 4 and D4, the distance between the R4 surface 4 of the second lens and the R5 surface 5 of the third lens is D4, and the distance between the R5 surface 5 and the R6 surface 6 is the thickness of the third lens. D5, the distance between the R6 surface 6 of the third lens and the surface 7 of the diaphragm portion is D6, the distance between the surface 7 of the diaphragm portion and the R7 surface 8 of the fourth lens is D7, and the R7 surface 8 is the thickness of the fourth lens. And the distance between the R8 surface 9 and the R9 surface 10 of the fourth lens and the imaging surface is the back focus BF.

  FIG. 2 is a cross-sectional view of the wide-angle optical system of Embodiment 1 in the horizontal direction.

FIG. 3 is a cross-sectional view of the wide-angle optical system of Embodiment 1 in the vertical direction.
The first embodiment has a horizontal focal length of 0.719 mm for the entire system, and the first embodiment has a wide-angle optical system with a vertical focal length of 0.814 mm for the entire system, an F number of 2.4, a total lens length of 11.8 mm, and a back focus of 1.77 mm. It is a system.

  FIG. 4 is a horizontal sectional view of the wide-angle optical system according to the second embodiment.

FIG. 5 is a sectional view in the vertical direction of the wide-angle optical system according to the second embodiment.
The second embodiment has a horizontal focal length of 0.683 mm for the entire system, and the second embodiment has a wide-angle optical system with a vertical focal length of 0.776 mm for the entire system, an F number of 2.37, a total length of 11.4 mm, and a back focus of 1.77 mm. It is a system.

  FIG. 6 is a horizontal sectional view of the wide-angle optical system according to the third embodiment.

FIG. 7 is a cross-sectional view of the wide-angle optical system of Embodiment 3 in the vertical direction.
The third embodiment has a horizontal focal length of 0.676 mm for the entire system, and the third embodiment has a wide-angle optical system with a vertical focal length of 0.748 mm for the entire system, an F number of 2.43, a total lens length of 11.1 mm, and a back focus of 1.77 mm. It is a system.

  FIG. 8 is a horizontal sectional view of the wide-angle optical system according to the fourth embodiment.

FIG. 9 is a cross-sectional view of the wide-angle optical system of Embodiment 4 in the vertical direction.
The fourth embodiment has a horizontal focal length of 0.652 mm for the entire system, and the fourth embodiment has a wide-angle optical system with a vertical focal length of 0.789 mm for the entire system, an F number of 2.3, a total lens length of 11.2 mm, and a back focus of 1.77 mm. It is a system.

  FIG. 10 is a horizontal sectional view of the wide-angle optical system according to the fifth embodiment.

FIG. 11 is a cross-sectional view of the wide-angle optical system of Embodiment 5 in the vertical direction.
The fifth embodiment is a horizontal focal length of 0.667 mm for the entire system, the fourth embodiment is a wide-angle optical system having a vertical focal length of 0.83 mm for the entire system, an F number of 2.24, a total lens length of 11.2 mm, and a back focus of 1.77 mm. It is a system.
In the cross-sectional views of the embodiments, the left side is the object side (subject side), and the right side is the image side (imaging plane side). Reference numerals 100A to 100E denote wide-angle optical systems. The four lenses in order from the object side are a first lens 110 having a negative refractive power, a second lens 120 having a negative refractive power, and a third lens having a positive refractive power. The lens 130 includes an aperture stop 140 and a fourth lens 150 having a positive refractive power.

  Hereinafter, the configuration and operation of the wide-angle optical system of the present embodiment will be described.

In a wide-angle optical system, it is necessary to shorten the focal length in order to obtain a wide angle of view, but the back focus must be longer than the focal length due to mechanical limitations. Therefore, a lens group having a negative refractive power is arranged in the front, once incident light is diverged, and then condensed by a lens group having a positive refractive power at the rear, so that the principal point of the lens system is located at the rear of the lens. It is possible to ensure a long back focus compared to the focal length.
In the wide-angle optical systems 100A to 100E of the present embodiment, the first lens and the second lens having negative refractive power diverge light, and the third lens and the fourth sandwich the aperture stop having positive refractive power as a whole. Condensed with a lens. By disposing two negative lenses on the object side, various aberrations can be corrected satisfactorily while obtaining a sufficient negative refractive power for placing the principal point behind. The reason for using two negative lens groups is that a single lens is divided because it is difficult to manufacture in order to suppress the occurrence of field curvature aberration and astigmatism. In particular, the above-mentioned aberration that cannot be corrected by the first lens is corrected by making the second lens aspherical. Of the positive lens group on the image side, the chromatic aberration of magnification can be corrected by disposing the third lens before the aperture stop and the fourth lens after the aperture stop. By disposing the fourth lens having a strong refractive power after the aperture stop, it is possible to reduce the angle of incidence on the image plane 170 and correct both distortion and astigmatism.

  In the wide-angle optical system of the present embodiment, the first lens 110 is a meniscus lens having a convex surface facing the object side, the second lens 120 has a concave surface facing the image side, the third lens 130 has a convex surface facing the object side, The fourth lens 150 has a convex surface facing the image side. Since the first lens has a meniscus shape with the convex surface facing the object side, the incident angle of off-axis rays with respect to the surface 1 of the first lens can be kept small, and the occurrence of aberration can be suppressed. Further, the second lens has a shape with a concave surface facing the image side, and the third lens has a shape with a convex surface facing the object side, whereby various aberrations can be corrected satisfactorily. The fourth lens has a convex surface on the image side and an aspheric surface on the image side, so that the incident angle on the image surface can be reduced. By forming the second lens 120 and the fourth lens 150 from a resin material, weight reduction and cost reduction can be realized, and by forming the third lens 130 from a glass material, a material having a wide dispersion value can be selected. As a result, it is possible to satisfactorily correct chromatic aberration of magnification.

  In an ultra-wide-angle optical system, a four-lens configuration is appropriate for sufficient aberration correction while ensuring a field angle. If priority is given to optical performance, it is desirable that all four sheets be made of a glass material. However, considering the cost, there is a merit for those who frequently use resin materials. Practically, when used in an in-vehicle camera or a surveillance camera, the usage environment is often outdoors and severe environmental resistance is required. Therefore, it is preferable that the first lens is glass as viewed from the object side. Since it is necessary to pay attention to ultraviolet rays as well as exposure to wind and rain, it is difficult to make the first lens resin. If all the remaining second, third, and fourth lenses are made of resin, the sum of the power of the resin lenses becomes a strong positive. The resin lens has a refractive index variation about 10 times larger than that of glass, depending on the temperature. Therefore, if the second, third, and fourth lenses are made of resin, the refractive index changes due to temperature fluctuation, and the back focus of the lens shifts. In the super-wide-angle optical system having four power positive, positive, negative, and negative power balances as in the present application, if the three are made of resin, the power balance becomes poor. Therefore, by using the third or fourth lens as glass, it is possible to cancel out the temperature fluctuation in a direction that is mitigated. The third lens is a lens that corrects chromatic aberration in magnification, and preferably has high refraction and high dispersion. Therefore, it is preferable to use glass for the first and third lenses and resin for the second and fourth lenses.

  Each of the second lens and the fourth lens has at least one aspherical shape. By having an aspherical shape, aberration correction becomes easy, and it is possible to obtain a good resolution performance while being small. Resin materials are suitable for forming lenses with aspherical shapes, but resin materials generally have a larger surface shape change due to temperature changes and a higher refractive index than glass, and performance changes when environmental temperature changes. growing. Therefore, the negative second lens and the positive fourth lens are made resinous to balance, and the focus shift due to the environmental change is canceled and relaxed.

  The same applies to the anamorphic surface. The anamorphic surface can change the focal length in the horizontal direction and the vertical direction on the imaging surface. Therefore, since the anamorphic surface is rotationally asymmetric, the manufacturing difficulty is high, and the cost is higher than that of a conventional lens. Therefore, in order to realize an anamorphic optical system at a low cost, it is more suitable to provide an anamorphic surface on a resin lens having a high degree of freedom in molding.

  Although it is possible to satisfy the function by forming only one anamorphic surface, it is more preferable to disperse the anamorphic surface on a plurality of surfaces because the manufacturing difficulty can be kept low. The greater the difference in the focal length between the horizontal direction and the vertical direction of the anamorphic surface, the more effective the anamorphic optical system can be expected, but the greater the degree of rotational asymmetry, the greater the manufacturing difficulty. Therefore, if the anamorphic surfaces are dispersed in a plurality, the difference in focal length between the horizontal direction and the vertical direction of each anamorphic surface can be reduced, and the shape is close to the rotation target, so that the manufacturing difficulty level is reduced. be able to.

  In that case, the ratio of the horizontal angle of view and the vertical angle of view remains constant even if the temperature environment changes by adding a second anamorphic surface to a surface having a sign different from the curvature of the object surface of the second lens. Can be kept. That is, by providing one surface for each of the positive surface and the negative surface, it is possible to cancel the fluctuations in the horizontal focal length and the vertical focal length due to temperature changes. For this reason, it is desirable to form the first and second anamorphic surfaces by using resin materials for the second and fourth lenses, respectively.

As described above, in the wide-angle optical system of the present embodiment, the entire system is made compact while maintaining good optical performance by arranging an appropriate refractive power arrangement and an aspherical surface and an anamorphic surface for each lens. Is realized. Furthermore, conditions for obtaining good optical performance and reducing the size of the entire lens system will be described below.
The following shows the ratio of the focal lengths in the horizontal direction and the vertical direction in the imaging plane, which is preferable for reducing distortion. Here, Fh is the focal length of the entire lens system on the d-line in the horizontal direction, and Fv is the focal length of the entire lens system on the d-line in the vertical direction.

1.10 <Fv / Fh <1.30 (1)
For example, even if the horizontal direction of the image plane is an ultra-wide angle of 180 degrees or more, the vertical direction reduces the distortion when viewed by humans by narrowing the angle of view compared to the horizontal direction. doing. When the value of the relational expression (1) is 1.1 or less, it becomes almost equal to a rotationally symmetric lens, so the effect of making an anamorphic optical system is low. Distortion is also corrected only slightly. In other words, since the projection characteristics do not change, the change in appearance is poor. Since it is difficult and costly to mold a rotationally asymmetric lens, it is preferable not to use an anamorphic optical system when the value of the relational expression (1) is 1.1 or less. Conversely, when the above value is 1.3 or more, it is advantageous from the viewpoint of distortion correction, but the load on the anamorphic surface becomes large and it is difficult to withstand environmental changes. In other words, the shape of the surface is greatly different between the YZ section and the XZ section of the second lens. Here, Z is an axis in the optical axis direction, and X and Y are axes perpendicular to the Z axis and perpendicular to each other.

  Images obtained with an anamorphic optical system generally have distortion of the lens flare in the horizontal direction, ovalization of the blur when the aperture is fully open, change in the shape of the blur due to focus, and unevenness of the horizontal / vertical ratio of the lens distortion. Such an effect occurs.

  The following shows the ratio of the curvature radii in the horizontal direction and the vertical direction in the imaging plane, which is preferable for obtaining an image with good image quality while suppressing the above influence. Here, r1h is a curvature radius in the horizontal direction on the object side of the second lens, and r1v is a curvature radius in the vertical direction on the object side of the second lens.

0.4 <r1v / r1h <0.8 (2)
The object side surface of the second lens can change the focal length in the horizontal direction and the vertical direction by the anamorphic surface while maintaining a state in which the aberration is small. The closer the value of the relational expression (2) is to 1, the closer the lens is to the rotation target with respect to the optical axis, the difference between the horizontal and vertical focal lengths, and the above-described influence. When the value of the relational expression (2) is small, the horizontal and vertical focal lengths can be greatly changed, but the closer to 0, the larger the above-mentioned influence is received. In addition, the more the lens is rotationally asymmetric, the more difficult it is to maintain uniformity when molding resin is filled, resulting in uneven thickness in the lens, causing in-lens birefringence, and the internal refractive index becomes non-uniform. Therefore, the optical performance is deteriorated.

  If the upper limit of the relational expression (2) is exceeded, the effect as an anamorphic optical system is small, and it becomes a level that can be sufficiently realized by image processing without changing the horizontal and vertical focal length by the lens. Exceeding this increases the load on the anamorphic surface, which increases the tolerance of the lens and increases the manufacturing difficulty.

  Specific numerical data of each of the first to fifth embodiments will be shown below. In each numerical example, as shown in FIG. 1, the surface number i is assigned in order from the object side, Ri is the paraxial radius of curvature of the i-th surface, Di is the distance between the i-th surface and the i + 1-th surface, ni, νi Indicates the refractive index and Abbe number for the d-line, respectively.

  In addition, the aspherical shape of the lens described in each numerical example has a positive displacement in the direction from the object side to the image side, and the displacement in the optical axis direction at the position of the height H from the optical axis When X is based on the vertex

It is represented by However, r is a paraxial curvature radius, A, B, C, and D are aspherical coefficients, and K is a conic constant.

  Further, the anamorphic surface shape of the lens described in each of the numerical examples has a positive direction in the direction from the object side to the image side, and the displacement in the optical axis direction at the position of the height H from the optical axis. When X is based on the surface vertex

It is represented by However, let X be the variation in the optical axis direction with respect to the surface vertex. The variation in the X-axis direction is x, the variation in the Y-axis direction is y, the paraxial curvature in the X-axis direction is CUX, and the paraxial curvature in the Y-axis direction is CUY. Each coefficient is as follows.
Rotationally symmetric fourth order coefficient: AR
Sixth order coefficient of rotational symmetry: BR
Rotationally symmetric 8th order coefficient: CR
10th order coefficient of rotational symmetry: DR
Rotationally asymmetric fourth order coefficient: AP
Rotationally asymmetric sixth order coefficient: BP
Rotationally asymmetric 8th order coefficient: CP
Rotationally asymmetric 10th order coefficient: DP

2 and 3 show sectional views in the horizontal direction and the vertical direction in the first embodiment.
As shown in FIG. 2, the first lens has a meniscus shape with a convex surface facing the object side, the second lens has a meniscus shape with a concave surface on the image surface, the third lens has a meniscus shape with a convex surface facing the object side, and an aperture stop The fourth lens has a biconvex shape. Each of the second lens and the fourth lens is made of resin and has an anamorphic surface on one surface and an aspheric surface on one surface.
<Numerical Example 1>
Tables 1 to 5 show numerical values of Example 1.

  Table 1 shows the horizontal focal length fh (mm), vertical focal length fv (mm), F-number, horizontal angle of view Θ1 (°), vertical angle of view Θ2 (°), and lens in Example 1 Numerical values of the total length (mm) and the back focus BF (mm) are shown.

  Table 2 shows each lens corresponding to each surface number i of the wide-angle optical system in Example 1, the paraxial radius of curvature R (mm) of the diaphragm 140, the distance D (mm), the refractive index n with respect to the d-line, and with respect to the d-line. The Abbe number ν is shown.

  Table 3 shows aspherical coefficients of predetermined surfaces of the second lens 120 and the fourth lens 150 including the aspherical surface in Example 1.

  Table 4 shows anamorphic coefficients of predetermined surfaces of the second lens 120 and the fourth lens 150 including the anamorphic surface in the first embodiment.

  Table 5 shows each numerical value of the conditional expression. In Example 1, the values of the conditional expressions are satisfied, and a wide-angle optical system in which various aberrations are favorably corrected can be obtained while reducing the size and thickness of the optical system.

  According to Example 1, the lens has an anamorphic coefficient so that the curvature radius in the horizontal direction and the curvature radius in the vertical direction of the second lens are close to the upper limit value of the expression (2). Therefore, the radius of curvature in the horizontal direction and the vertical direction are not greatly different, and the focal length in the horizontal direction and the vertical direction are not greatly different. Therefore, the effect as an anamorphic optical system is small, but the lens is close to a rotationally symmetric lens. The manufacturing difficulty level is low, and the performance as designed can be obtained at low cost.

4 and 5 show sectional views in the horizontal direction and the vertical direction in the second embodiment.
As shown in FIG. 4, the first lens has a meniscus shape with a convex surface facing the object side, the second lens has a meniscus shape with a concave surface on the image surface, the third lens has a meniscus shape with a convex surface facing the object side, and an aperture stop The fourth lens has a biconvex shape. Each of the second lens and the fourth lens is made of resin and has an anamorphic surface on both surfaces and an aspheric surface on one surface.
<Numerical Example 2>
Tables 6 to 10 show the numerical values of Example 2.

  Table 6 shows the horizontal focal length fh (mm), vertical focal length fv (mm), F-number, horizontal field angle Θ1 (°), vertical field angle Θ2 (°), and total lens length in Example 2 (Mm) and numerical values of back focus BF (mm) are shown.

  Table 7 shows each lens corresponding to each surface number i of the wide-angle optical system in Example 2, the paraxial radius of curvature R (mm) of the diaphragm 140, the distance D (mm), the refractive index n with respect to the d-line, and with respect to the d-line. The Abbe number ν is shown.

  Table 8 shows aspherical coefficients of predetermined surfaces of the second lens 120 and the fourth lens 150 including the aspherical surface in Example 2.

  Table 9 shows anamorphic coefficients of predetermined surfaces of the second lens 120 and the fourth lens 150 including the anamorphic surface in Example 2.

  Table 10 shows each numerical value of the conditional expression. In Example 2, the values of the conditional expressions are satisfied, and a wide-angle optical system in which various aberrations are favorably corrected can be obtained while reducing the size and thickness of the optical system.

  According to the second embodiment, the effect as the anamorphic optical system is enhanced by reducing the values of the curvature radii in the horizontal direction and the vertical direction with respect to the first embodiment so as to reduce the value of the expression (2). ing. Therefore, although the manufacturing difficulty of the lens is high, the effect as an anamorphic optical system can be expected greatly, and the ratio of the focal lengths in the horizontal direction and the vertical direction can be sufficiently changed.

6 and 7 show sectional views in the horizontal direction and the vertical direction in the third embodiment.
As shown in FIG. 6, the first lens has a meniscus shape with a convex surface facing the object side, the second lens has a meniscus shape with a concave surface on the image surface, the third lens has a meniscus shape with a convex surface facing the object side, and an aperture stop The fourth lens has a biconvex shape. Each of the second lens and the fourth lens is made of resin and has an anamorphic surface on both surfaces and an aspheric surface on both surfaces.
<Numerical Example 3>
Tables 11 to 15 show the numerical values of Example 3.

  Table 11 shows the horizontal focal length fh (mm), the vertical focal length fv (mm), the F number, the horizontal field angle Θ1 (°), the vertical field angle Θ2 (°), and the total lens length of the entire system in Example 3. (Mm) and numerical values of back focus BF (mm) are shown.

  Table 12 shows each lens corresponding to each surface number i of the wide-angle optical system in Example 3, the paraxial radius of curvature R (mm) of the diaphragm 140, the distance D (mm), the refractive index n with respect to the d line, and with respect to the d line. The Abbe number ν is shown.

  Table 13 shows aspherical coefficients of predetermined surfaces of the second lens 120 and the fourth lens 150 including the aspherical surface in Example 3.

  Table 14 shows anamorphic coefficients of predetermined surfaces of the second lens 120 and the fourth lens 150 including the anamorphic surface in Example 3.

  Table 15 shows each numerical value of the conditional expression. Example 3 satisfies the values of the conditional expressions, and a wide-angle optical system in which various aberrations are favorably corrected can be obtained while reducing the size and thickness of the optical system.

  According to Example 3, an anamorphic surface is formed only on the second lens. Compared with Example 1, the value of equation (2) is small and the effect as an anamorphic surface is large. However, there are also restrictions on design and manufacturing in order to form an anamorphic surface with only a single lens. Therefore, the focal length ratio between the horizontal direction and the vertical direction of the entire optical system is smaller than that of the first embodiment. Since the anamorphic surface is concentrated only on the second lens, the load on the second lens increases and the manufacturing difficulty increases. However, only one lens needs to be adjusted in the horizontal and vertical directions. The difficulty level can be kept low.

8 and 9 show sectional views in the horizontal direction and the vertical direction in the fourth embodiment.
As shown in FIG. 8, the first lens has a meniscus shape with a convex surface facing the object side, the second lens has a meniscus shape with a concave surface on the image surface, the third lens has a meniscus shape with a convex surface facing the object side, and an aperture stop The fourth lens has a biconvex shape. The second lens and the fourth lens are each made of resin and have anamorphic surfaces on both sides.
<Numerical Example 4>
Tables 16 to 20 show the numerical values of Example 4.

  Table 16 shows the horizontal focal length fh (mm), vertical focal length fv (mm), F-number, horizontal field angle Θ1 (°), vertical field angle Θ2 (°), and total lens length in Example 4 (Mm) and numerical values of back focus BF (mm) are shown.

  Table 17 shows the respective lenses corresponding to the surface numbers i of the wide-angle optical system in Example 4, the paraxial radius of curvature R (mm) of the diaphragm 140, the distance D (mm), the refractive index n with respect to the d line, and the refractive index with respect to the d line. The Abbe number ν is shown.

  Table 18 shows aspherical coefficients of predetermined surfaces of the second lens 120 and the fourth lens 150 including the aspherical surface in Example 4. However, in Example 4, anamorphic surfaces are formed on both surfaces of the second lens 120 and the fourth lens 150, and there is no formation of an aspherical surface expressed by Equation 1.

  Table 19 shows anamorphic coefficients of predetermined surfaces of the second lens 120 and the fourth lens 150 including the anamorphic surface in Example 4.

  Table 20 shows each numerical value of the conditional expression. In Example 4, the values of the conditional expressions are satisfied, and a wide-angle optical system in which various aberrations are favorably corrected can be obtained while reducing the size and thickness of the optical system.

  According to the fourth embodiment, the anamorphic surface is increased with respect to the first embodiment. Specifically, an anamorphic surface is formed on the entire surface of two resin lenses. Since the effects of the anamorphic optical system are dispersed in the second lens and the fourth lens which are resin lenses, the difficulty of manufacturing individual lenses can be reduced.

10 and 11 show sectional views in the horizontal direction and the vertical direction in the fifth embodiment.
As shown in FIG. 10, the first lens has a meniscus shape with a convex surface facing the object side, the second lens has a meniscus shape with a concave surface on the image surface, the third lens has a meniscus shape with a convex surface facing the object side, and an aperture stop The fourth lens has a biconvex shape. The second lens and the fourth lens are each made of resin and have anamorphic surfaces on both sides.
<Numerical example 5>
Tables 21 to 25 show the numerical values of Example 5.

  Table 21 shows the horizontal focal length fh (mm), vertical focal length fv (mm), F-number, horizontal field angle Θ1 (°), vertical field angle Θ2 (°), and total lens length in Example 5 (Mm) and numerical values of back focus BF (mm) are shown.

  Table 22 shows each lens corresponding to each surface number i of the wide-angle optical system in Example 5, the paraxial radius of curvature R (mm) of the diaphragm 140, the distance D (mm), the refractive index n with respect to the d-line, and with respect to the d-line. The Abbe number ν is shown.

  Table 23 shows aspherical coefficients of predetermined surfaces of the second lens 120 and the fourth lens 150 including the aspherical surface in Example 5. However, in Example 5, anamorphic surfaces are formed on both surfaces of the second lens 120 and the fourth lens 150, and there is no formation of an aspherical surface expressed by Equation 1.

  Table 24 shows anamorphic coefficients of predetermined surfaces of the second lens 120 and the fourth lens 150 including the anamorphic surface in Example 4.

  Table 25 shows each numerical value of the conditional expression. In Example 5, the values of the conditional expressions are satisfied, and a wide-angle optical system in which various aberrations are well corrected can be obtained while reducing the size and thickness of the optical system.

  According to Example 5, with respect to Example 4, the difference in curvature between the horizontal direction and the vertical direction is increased to the production limit level for all anamorphic surfaces. This is an example in which the lens structure that can be used in the present invention is most effective as an anamorphic optical system.

  The wide-angle optical system and the imaging module of the present embodiment have been described above, but the present invention is not limited to these examples, and various modifications can be made without departing from the scope of the invention. For example, in the said Example, although it was set as the structure which provides an infrared removal filter in the glass block 170, it is not restricted to such a structure, You may give an infrared cut coat to the surface of the glass block 170. FIG. Further, infrared coating may be applied to other lens surfaces and filters such as a low-pass filter.

  According to the wide-angle optical system of the present embodiment, it is suitable for an imaging system using an imaging device, particularly a surveillance camera, a vehicle-mounted camera, and the like, and is a small-sized, thin, high-optical performance wide-angle optical system, and the wide-angle optical system. An imaging module having the above can be realized.

  FIG. 12 shows a cross-sectional view of an embodiment of an imaging apparatus using the imaging lens 100 according to the present invention. The imaging lens 100 and the imaging element 210 such as a CCD (Charge Coupled Device) or a CMOS (Complementary Mental-Oxide Semiconductor device) are defined and held by a housing 220. At this time, the imaging surface 160 of the imaging lens 100 is disposed so as to coincide with the light receiving surface of the imaging element 210.

  The subject image captured by the imaging lens 100 and formed on the light receiving surface of the imaging element 210 is converted into an electrical signal by the photoelectric conversion function of the imaging element 210 and output from the imaging apparatus 200 as an image signal.

  Since the imaging lens 100 as described above has a small number of components, is small and lightweight, and can be compact in mounting space, it is suitable for imaging apparatuses for various applications. In addition, although it is a wide-angle imaging lens, it can reduce the occurrence of distortion, and can form a subject image with high optical performance on the light-receiving surface on the image sensor 210, and can output an image signal with excellent visibility. Therefore, it is possible to realize an imaging device having a superiority in a camera for cameras, a vehicle-mounted camera, and the like.

DESCRIPTION OF SYMBOLS 100 ... Imaging optical system 110 ... 1st lens 120 ... 2nd lens 130 ... 3rd lens 140 ... Aperture stop 150 ... 4th lens 160 ... Glass block 170 ... Imaging surface 200 ... Imaging device 210 ... Imaging element 220 ... Housing

Claims (5)

A negative meniscus first lens having a negative meniscus convex on the object side in order from the object side and an anamorphic surface having different curvatures in the horizontal direction and the vertical direction on a plane orthogonal to the optical axis on the object side. 2 lenses, a positive third lens convex on the object side, an aperture stop, and a positive fourth lens convex on the image side. The focal length in the horizontal direction of the entire lens system is Fh, When the vertical focal length of the system is Fv, the following conditions are satisfied:
1.10 <Fv / Fh <1.30 (1)
An imaging optical system comprising a second anamorphic surface different from the object side surface of the second lens on a surface having a sign different from the power of the object side surface of the second lens. The imaging optical system according to claim 1, wherein the imaging optical system satisfies the following condition: 0.4 <r1v / r1h <0.8 (2)
Here, r1h is the radius of curvature in the horizontal direction, and r1v is the radius of curvature in the vertical direction.   The imaging optical system according to claim 1, wherein the second lens and the fourth lens are made of a resin material.   The imaging optical system according to claim 3, wherein the second anamorphic surface is formed on the fourth lens.   An imaging apparatus comprising: the imaging optical system according to any one of claims 1 to 4; and an imaging element that converts an optical image formed by the imaging optical system into an electrical signal.

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