JP2018120125A - Image-forming optical system and imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact image-forming optical system which has a wide angle, and can maintain a high resolution irrespective of a change in ambient temperature, and an imaging apparatus.SOLUTION: In order to solve the above problem, an image-forming optical system according to the present invention is formed by arranging, from a subject side, a front group, a diaphragm and a rear group in this order. The front group includes: a first lens arranged closest to the subject side; and a second and a third lens arranged in this order closer to an image side than the first lens. The first lens is a negative lens, and the second lens is a positive lens whose surface on the subject side is a concave surface and whose surface on the image side is a convex surface, a surface on the subject side of the third lens is a concave surface, the image-side surface of the second lens and the subject-side surface of the third lens have an air interval on an optical axis, and the two lenses are arranged adjacently so that both lenses are brought into contact with each other outside a range of an effective diameter of each lens. Further, an imaging apparatus according to the present invention is equipped with the image-forming optical system.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an imaging optical system and an imaging apparatus, and more particularly to a wide-angle imaging optical system and an imaging apparatus suitable for an imaging apparatus using a solid-state imaging device such as a CCD or a CMOS.

  2. Description of the Related Art Conventionally, driving support systems that perform various driving support by mounting an imaging device on a vehicle and displaying an image acquired by the imaging device on an image display device are known. As such a driving support system, for example, a back view monitor that displays an image behind the vehicle on the image display device or an around display that displays an image as if the image surrounding the vehicle is looking down from above the vehicle is displayed on the image display device. View monitors are known. Drive recorders are also becoming popular.

  In recent years, various advanced driving support systems such as a collision damage reduction brake system using an image sensing technology, a lane keeping assist system, and an inter-vehicle distance automatic control system have been put into practical use for realizing automatic driving. . In these advanced driving support systems, obstacles around the vehicle, lane positions, inter-vehicle distances, and the like are detected based on image data acquired by the imaging device.

There are various requirements for the imaging optical system of such an imaging apparatus. For example, with the recent increase in the number of pixels in a solid-state imaging device, a bright optical system with high resolution is also required in an in-vehicle imaging device.
Further, in order to monitor the periphery of the vehicle with a smaller number of imaging devices, an optical system with a wide angle of view is required. When the angle of view is widened, the amount of peripheral light can be reduced. However, to realize automatic driving, it is necessary to perform image recognition with high accuracy even in the peripheral portion of the image. Therefore, there is a demand for an optical system that has a wide angle and does not cause a decrease in the amount of light at the periphery of the image.

  Further, the use atmosphere temperature of the in-vehicle image pickup apparatus changes greatly. In many cases, an imaging optical system of an in-vehicle imaging apparatus uses a fixed focus lens with a fixed focal position. In the case of a fixed focus lens, image quality deteriorates when a focus shift occurs due to a change in the operating ambient temperature. Therefore, there is a need for an imaging optical system that can maintain high resolution even in a high temperature environment or a low temperature environment.

  The imaging optical system of the in-vehicle imaging device is required to be small and light while satisfying these various requirements and to be low in cost. These problems also apply to the imaging optical system of a monitoring imaging device used outdoors.

  As an imaging optical system that can be used for such an in-vehicle imaging device, for example, optical systems disclosed in Patent Documents 1 to 3 are known. In the optical systems disclosed in Patent Literature 1 to Patent Literature 3, by adopting an orthographic projection method or generating distortion in the peripheral portion of the image more than that, it is wide-angle and suppresses a decrease in the amount of light around the image. A bright optical system. Note that the distortion generated in the peripheral portion of the image can be corrected by image processing.

Japanese Patent Laid-Open No. 2006-133599 JP 2007-155976 A JP 2004-354572 A

  However, although the optical system described in Patent Document 1 has a small F-number of 1.6 and realizes a bright optical system, the number of lenses is as large as seven, and the size and weight reduction and cost reduction are not sufficient. .

  Since the optical system described in Patent Document 2 has an F number of 2.8, further improvement is required in terms of brightness. Further, the number of lenses constituting the optical system is as many as nine, which is not sufficient in terms of reduction in size and weight and cost.

  The optical system described in Patent Document 3 has a small F number of 2.0 and realizes a bright optical system. In addition, the number of lenses is six, and a reduction in size and weight is also achieved. However, in this optical system, focus shift can occur with changes in the ambient temperature, so it is difficult to maintain imaging performance at room temperature at high or low temperatures. The same applies to the optical systems disclosed in Patent Document 1 and Patent Document 2 in that focus shift can occur.

  An object of the present invention is to provide a compact imaging optical system and an imaging apparatus that have a wide angle and can maintain high resolution regardless of changes in ambient temperature.

  In order to solve the above problems, the imaging optical system according to the present invention is an imaging optical system in which a front group, a stop, and a rear group are sequentially arranged from the subject side, and the front group includes: A first lens arranged closest to the subject side, and a second lens and a third lens arranged in order on the image side of the first lens, wherein the first lens is a negative lens, The lens is a positive lens having a concave surface on the subject side and a convex surface on the image side, and the third lens has a concave surface on the subject side and is located on the image side of the second lens. The surface and the object side surface of the third lens have an air gap on the optical axis, and are arranged adjacent to each other so that they are in contact with each other outside the effective diameter range of each lens. To do.

  In order to solve the above problems, an imaging apparatus according to the present invention includes an imaging optical system according to the present invention, and an optical image formed by the imaging optical system on the image side of the imaging optical system. And an image sensor for converting the signal into an electrical signal.

  According to the present invention, it is possible to provide a compact imaging optical system and imaging apparatus that are wide-angled and can maintain high resolution regardless of changes in ambient temperature.

It is sectional drawing which shows the lens structural example at the time of infinity focusing of the imaging optical system of Example 1 of this invention. FIG. 4 is a spherical aberration diagram, an astigmatism diagram, and a distortion diagram when the imaging optical system of Example 1 is focused at infinity. 3 is a lateral aberration diagram of the imaging optical system of Example 1 when focusing on infinity. FIG. It is sectional drawing which shows the lens structural example at the time of infinity focusing of the imaging optical system of Example 2 of this invention. FIG. 6 is a spherical aberration diagram, an astigmatism diagram, and a distortion diagram when the imaging optical system of Example 2 is focused at infinity. 6 is a lateral aberration diagram of the imaging optical system of Example 2 when focusing on infinity. FIG. It is sectional drawing which shows the lens structural example at the time of infinity focusing of the imaging optical system of Example 3 of this invention. FIG. 6 is a spherical aberration diagram, astigmatism diagram, and distortion diagram when the imaging optical system of Example 3 is focused at infinity. FIG. 6 is a lateral aberration diagram of the imaging optical system according to Example 3 when focusing on infinity. It is sectional drawing which shows the example of a lens structure at the time of infinity focusing of the imaging optical system of Example 4 of this invention. FIG. 10 is a spherical aberration diagram, an astigmatism diagram, and a distortion diagram when the imaging optical system of Example 4 is focused at infinity. FIG. 6 is a lateral aberration diagram of the imaging optical system according to Example 4 when focusing on infinity. It is sectional drawing which shows the lens structural example at the time of infinity focusing of the imaging optical system of Example 5 of this invention. FIG. 10 is a spherical aberration diagram, an astigmatism diagram, and a distortion diagram when the imaging optical system of Example 5 is focused at infinity. FIG. 10 is a transverse aberration diagram for the imaging optical system of Example 5 when focusing on infinity. It is sectional drawing which shows the lens structural example at the time of infinity focusing of the imaging optical system of Example 6 of this invention. FIG. 10 is a spherical aberration diagram, an astigmatism diagram, and a distortion diagram when the imaging optical system of Example 6 is focused at infinity. FIG. 10 is a transverse aberration diagram for the imaging optical system of Example 6 when focusing on infinity. It is sectional drawing which shows the lens structural example at the time of infinity focusing of the imaging optical system of Example 7 of this invention. FIG. 10 is a spherical aberration diagram, an astigmatism diagram, and a distortion diagram when the imaging optical system of Example 7 is focused at infinity. FIG. 10 is a transverse aberration diagram for the imaging optical system of Example 7 when focusing on infinity. It is sectional drawing which shows the lens structural example at the time of infinity focusing of the imaging optical system of Example 8 of this invention. FIG. 10 is a spherical aberration diagram, an astigmatism diagram, and a distortion diagram when the imaging optical system of Example 8 is focused at infinity. FIG. 10 is a transverse aberration diagram for the imaging optical system of Example 8 when focusing on infinity. It is sectional drawing which shows the lens structural example at the time of infinity focusing of the imaging optical system of Example 9 of this invention. FIG. 10 is a spherical aberration diagram, astigmatism diagram, and distortion diagram when the imaging optical system of Example 9 is focused at infinity. FIG. 10 is a transverse aberration diagram for the imaging optical system of Example 9 when focusing on infinity.

  Hereinafter, embodiments of an imaging optical system and an imaging apparatus according to the present invention will be described. However, the imaging optical system and the imaging apparatus described below are one aspect of the imaging optical system and the imaging apparatus according to the present invention, and the imaging optical system according to the present invention is limited to the following aspects. is not.

1. Imaging optical system 1-1. Configuration of Imaging Optical System First, an embodiment of the imaging optical system according to the present invention will be described. The imaging optical system according to the present invention is an imaging optical system in which a front group, a stop, and a rear group are sequentially arranged from the subject side, and the front group is arranged closest to the subject side. A first lens, and a second lens and a third lens arranged in this order on the image side of the first lens, wherein the first lens is a negative lens, and the second lens is a surface on the subject side Is a positive lens having a concave surface and a convex surface on the image side, and the third lens has a concave surface on the subject side, the image side surface of the second lens and the third lens The object side surface is characterized in that it has an air space on the optical axis and is adjacently arranged so that both lenses are in contact with each other outside the range of the effective diameter of each lens.

  According to the imaging optical system according to the present invention, it is easy to widen the angle of view by using the first lens as a negative lens. In addition, the image side surface of the second lens and the object side surface of the third lens have an air space on the optical axis, and are disposed adjacent to each other so that they are in contact with each other outside the effective diameter range of each lens. By doing so, it is not necessary to join the second lens and the third lens with an adhesive or the like, and the adhesive is peeled off due to a change in the ambient temperature, causing an axial misalignment between the second lens and the third lens. As a result, it is possible to suppress a decrease in imaging performance. Therefore, it becomes easy to maintain high resolution regardless of changes in the ambient temperature. Furthermore, by arranging the second lens and the third lens adjacent to each other outside the effective diameter range of each lens, the light of the second lens and the third lens is assembled when the imaging optical system is assembled. Axis alignment becomes easy, the shift and tilt of the third lens can be suppressed, and a decrease in resolution can be prevented. And since the space | interval ring between a 2nd lens and a 3rd lens becomes unnecessary, manufacturing cost can be lowered | hung. For example, in the case of the second lens, the term “outside the effective diameter of each lens” refers to the outside of the maximum diameter of the light beam that passes through the surface on the image plane side of the second lens in the imaging optical system. In the case of a lens, it means the outside of the maximum diameter of the light beam that passes through the surface of the third lens on the subject side in the imaging optical system, and refers to a portion called the peripheral portion of the lens.

  As described above, the imaging optical system according to the present invention employs the above-described configuration to provide a small imaging optical system that is wide-angle and can maintain high resolution regardless of changes in the ambient temperature. Is possible. First, the configuration of the optical system according to the present invention will be described, and matters relating to conditional expressions will be described later.

  The imaging optical system according to the present invention includes a plurality of lenses. The front group is composed of lenses arranged on the subject side of the stop. The rear group is composed of lenses arranged on the image plane side with respect to the stop. Hereinafter, preferable configuration examples of the front group and the rear group will be described.

(1) Front group As long as the front group includes the first lens, the second lens, and the third lens, the specific lens configuration is not particularly limited.

  By disposing the first lens, which is a negative lens, on the most object side of the front group, negative distortion tends to occur in the peripheral portion of the image plane, but it is possible to suppress a decrease in the peripheral light amount. Also, negative distortion at the periphery of the image plane can be corrected by image processing. The first lens is preferably a negative lens having a convex surface on the subject side and an aspherical surface that weakens the convex power as it moves away from the optical axis. Thereby, it is possible to achieve high resolution while suppressing the curvature of field while increasing the amount of peripheral light. Therefore, it becomes easier to realize a bright optical system for the entire image plane.

  The second lens is a positive lens disposed closer to the image plane than the first lens. The surface of the second lens on the subject side is a concave surface, the surface on the image surface side is a convex surface, and an air gap is provided on the optical axis between the third lens and the coma aberration and the curvature of field are excellent. This makes it easy to realize an imaging optical system with high resolution.

  The third lens may be a positive lens or a negative lens, but the third lens is a positive lens from the viewpoint of suppressing the coma and obtaining an imaging optical system with higher resolution. It is more preferable. At this time, the image plane side of the third lens, which is a positive lens, is preferably convex on the image plane side.

  Note that the second lens and the third lens only need to be disposed on the image side of the first lens, and another lens may be disposed between the first lens and the second lens.

  However, from the viewpoint of reducing the size and weight and reducing the cost of the imaging optical system according to the present invention, the number of lenses constituting the front group is preferably small, and more preferably four or less lenses. For example, the front group includes, in order from the subject side, the first lens that is a negative lens, the second lens that is a positive lens, and the third lens that are substantially composed of three lenses. The image forming optical system according to the present invention is most preferable for reducing the size and weight and reducing the cost.

(2) Rear group The specific configuration of the rear group is not particularly limited. However, from the viewpoint of further widening the angle of view of the imaging optical system, the rear group preferably has a positive refractive power as a whole. By arranging positive refractive power in the rear group, the first lens is a negative lens, so it becomes easy to make a so-called retrofocus lens, and the lens barrel design is made with a long back focus. In addition to being more effective for facilitating, it is also effective for correcting various aberrations.

  At this time, the lens arranged closest to the subject in the rear group is preferably a positive lens. From the viewpoint of suppressing spherical aberration, the subject side of the positive lens arranged closest to the stop in the rear group is the subject side. A convex shape is preferable.

  From the viewpoint of reducing the size and weight and reducing the cost of the imaging optical system according to the present invention, the number of lenses constituting the rear group is preferably small, and more preferably four or less. At this time, by providing at least one negative lens, aberration correction and the like can be favorably performed.

  For example, in the rear group, in order from the subject side, the fourth lens that is a positive lens, the fifth lens that is a negative lens, and the sixth lens that is a positive lens, which are arranged closest to the stop, are substantially composed of three lenses. It is most preferable to be configured in order to reduce the size and weight and reduce the cost of the imaging optical system according to the present invention while maintaining high resolution.

  When the number of lenses constituting the imaging optical system is more than 6 including the front group and the rear group, it is advantageous to obtain a high-resolution imaging optical system, but the size and weight are reduced and the cost is reduced. It becomes difficult to plan. If the number of lenses constituting the imaging optical system is less than 6, it becomes difficult to obtain an imaging optical system with high resolution.

The material of the lenses constituting the front group and the rear group is not particularly limited, but from the viewpoint of preventing the deterioration of the imaging performance by suppressing the focus shift accompanying the change in the operating atmosphere temperature. The lenses constituting the group and the rear group are preferably made of glass.
In the case of a cemented lens, the adhesive peels off when the ambient temperature changes due to the difference between the linear expansion coefficient of the adhesive between the lens component and the linear expansion coefficient of each lens component. It becomes easy. For this reason, the imaging performance is likely to deteriorate due to changes in the ambient temperature. From this viewpoint, it is preferable that each of the front group and the rear group does not include a cemented lens.

1-2. Conditional Expressions Next, conditions that the imaging optical system should satisfy or conditions that should preferably be satisfied will be described.

  The imaging optical system satisfies the following conditional expression (1).

(1) 1.05 <(| L2R2 | + d23) / | L3R1 | <2.49
However,
L2R2: radius of curvature of the image side surface of the second lens L3R1: radius of curvature of the subject side surface of the third lens d23: air distance on the optical axis of the second lens and the third lens

1-2-1. Conditional expression (1)
By satisfying conditional expression (1), axial chromatic aberration can be corrected well, and an imaging optical system with higher resolution can be obtained. Further, by satisfying conditional expression (1), the air space on the optical axis between the second lens and the third lens is within an appropriate range, and when the imaging optical system is assembled, the second lens When the third lens is brought into contact with the peripheral edge of the lens, the image-side surface of the second lens and the object-side surface of the third lens are in contact with each other within the effective diameter range, and the lens surface is damaged. This can be prevented.

  On the other hand, when the numerical value of the conditional expression (1) is equal to or lower than the lower limit value, the air space on the optical axis between the second lens and the third lens becomes too small, and the imaging optical system is assembled. In addition, the image side surface of the second lens and the object side surface of the third lens are in contact with each other within the effective diameter range, and the lens surface may be damaged, resulting in a decrease in resolution. On the other hand, if the numerical value of conditional expression (1) exceeds the upper limit, the air space on the optical axis between the second lens and the third lens becomes too large, resulting in chromatic aberration and lowering the resolution. Therefore, it is not preferable.

  In obtaining these effects, the lower limit of conditional expression (1) is preferably 1.07, more preferably 1.10, and even more preferably 1.14. In addition, the upper limit value of conditional expression (1) is preferably 2.10, more preferably 1.80, and even more preferably 1.40.

1-2-2. Conditional expression (2) and conditional expression (3)
In the imaging optical system according to the present invention, it is preferable that conditional expression (2) and conditional expression (3) are satisfied when the front group includes at least one positive lens in addition to the second lens. Conditional expression (2) and conditional expression (3) are the positive lens included in the front group, the Abbe number of the positive lens having the smallest Abbe number with respect to the d line, and the positive lens included in the front group, This is an expression that defines the Abbe number of the positive lens having the largest Abbe number with respect to the d line.

(2) ν2 <47
(3) ν3> 65

However,
ν2: Abbe number of the positive lens having the smallest Abbe number with respect to the d line among the positive lenses included in the front group ν3: Of the positive lens included in the front group, the positive lens having the largest Abbe number with respect to the d line Abbe number

  By configuring the front group to include a positive lens satisfying conditional expression (2) and a positive lens satisfying conditional expression (3), axial chromatic aberration can be corrected well, and resolution A high imaging optical system can be obtained. When conditional expression (2) or conditional expression (3) is not satisfied, it is difficult to correct axial chromatic aberration well.

  In obtaining the effect, the upper limit value of conditional expression (2) is more preferably 45, still more preferably 43, and still more preferably 41. Note that if the positive lens is made of a glass material having an Abbe number less than the above upper limit, the above-described effects can be obtained on condition that the front group includes a positive lens made of a glass material that satisfies the conditional expression (3). For this reason, the lower limit value of the conditional expression (2) does not need to be specified in particular, but for example, the lower limit value can be 10 and may be 16.

  Similarly, in obtaining the above effect, the lower limit value of conditional expression (3) is more preferably 67, still more preferably 69, and even more preferably 71. Similarly to the conditional expression (2), if the positive lens is made of a glass material having an Abbe number larger than the lower limit, the front group includes a positive lens made of a glass material that satisfies the conditional expression (2). The above-described effects can be obtained on the condition. For this reason, the upper limit value of the conditional expression (3) need not be specified, but for example, the upper limit value can be 100 or 96.

1-2-3. Conditional expression (4)
The imaging optical system according to the present invention preferably satisfies the conditional expression (4) when the front group includes at least one positive lens in addition to the second lens. Conditional expression (4) indicates that the refractive index of the positive lens having the largest refractive index with respect to the d-line among the positive lenses included in the front group and the refractive index with respect to the d-line among the positive lenses included in the front group. It is a formula that defines the refractive index of the smallest positive lens.

(4) 0.15 <N2-N3
However,
N2: Refractive index of a positive lens having the largest refractive index with respect to d-line among positive lenses included in the front group N3: Refractive index of a positive lens having the smallest refractive index with respect to d-line among positive lenses included in the front group

  When the front group includes two or more positive lenses, it is possible to satisfactorily correct spherical aberration and obtain a higher-resolution imaging optical system by satisfying the conditional expression (4). it can. When the numerical value of the conditional expression (4) is less than or equal to the lower limit value, among the positive lenses included in the front group, the refractive index of the positive lens having the largest refractive index with respect to the d line becomes too small, and The difference in radius of curvature between the surface and the image-side surface is increased. For this reason, the refraction angle of the light beam incident on the outer peripheral portion (but within the effective diameter range) of the positive lens is increased, and the spherical aberration is increased.

  In obtaining the effect, the lower limit value of conditional expression (4) is more preferably 0.20, still more preferably 0.22, and still more preferably 0.24. If the numerical value of the conditional expression (4) is larger than the lower limit value, the above effect can be obtained. Therefore, the upper limit value does not need to be specified in particular, but can be set to, for example, 0.68, 0.52, and 0.45.

  Here, among the positive lenses included in the front group in the conditional expression (2), the positive lens having the smallest Abbe number with respect to the d line corresponds to the d lens among the positive lenses included in the front group in the conditional expression (4). A positive lens having the largest refractive index is preferable. Further, among the positive lenses included in the front group in the conditional expression (3), the positive lens having the largest Abbe number with respect to the d line is the refraction with respect to the d line among the positive lenses included in the front group in the conditional expression (4). A positive lens having the smallest ratio is preferable.

1-2-4. Conditional expression (5)
In the imaging optical system according to the present invention, in order from the subject side, the front group includes a first lens that is a negative lens, a second lens that is a positive lens, and a third lens that is disposed closest to the diaphragm. In the case of including, it is preferable that the following conditional expression (5) is satisfied.

(5) 1.3 <| f12 / f | <9.5
However,
f: Focal length of the imaging optical system f12: Focal length of the second lens

  When the conditional expression (5) is satisfied, astigmatism and lateral chromatic aberration can be satisfactorily corrected, and an imaging optical system with higher resolution can be obtained. If the numerical value of the conditional expression (5) is less than or equal to the lower limit value, the refractive power of the second lens becomes too large, so that it becomes difficult to correct astigmatism and the resolution is lowered. On the other hand, if the numerical value of the conditional expression (5) is greater than or equal to the upper limit value, the refractive power of the second lens becomes too small, so that it becomes difficult to correct lateral chromatic aberration and the resolution is lowered.

  In obtaining the above effect, the lower limit of conditional expression (5) is more preferably 1.4, and even more preferably 1.5. Further, the upper limit value of conditional expression (5) is more preferably 6.2, still more preferably 5.5, and even more preferably 4.7.

1-2-6. Conditional expression (6)
The imaging optical system according to the present invention preferably satisfies the following conditional expression (6).

(6) 2.2 <| f13 / f | <8.9
However,
f: Focal length of the imaging optical system f13: Focal length of the third lens

  When the conditional expression (6) is satisfied, spherical aberration and coma can be corrected well, and an imaging optical system with higher resolution can be obtained. When the numerical value of conditional expression (6) is less than or equal to the lower limit value, the refractive power of the third lens becomes too large, so that it becomes difficult to correct spherical aberration and the resolution is lowered. On the other hand, if the numerical value of conditional expression (6) is equal to or greater than the upper limit value, the refractive power of the third lens becomes too small, so that correction of coma aberration becomes difficult and resolution is lowered.

  In obtaining the above effect, the lower limit value of conditional expression (6) is more preferably 3.1, and even more preferably 4.2. The upper limit value of conditional expression (6) is more preferably 7.8, and further preferably 7.5.

2. Next, an imaging apparatus according to the present invention will be described. The imaging device according to the present invention converts the optical image formed by the imaging optical system according to the present invention and the imaging optical system provided on the image plane side of the imaging optical system into an electrical signal. And an image pickup device.

  In the present invention, the imaging device or the like is not particularly limited, and a solid-state imaging device such as a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor can also be used. Although the image height and resolution of the solid-state imaging device are not particularly limited, for example, the following is preferable.

  In the imaging optical system according to the present invention, the image height of the image sensor is preferably 5.5 mm or less, more preferably 5.0 mm or less, and further preferably 4.5 mm or less. However, in the imaging optical system and the imaging apparatus according to the present invention, the image height of the imaging element is not particularly limited, and an image having an appropriate size should be used according to the maximum image height of the imaging optical system. The present invention can also be applied to a case where the image height of the image sensor is larger than 5.5 mm.

  In the imaging optical system according to the present invention, the pixel pitch of the image sensor is preferably 2.0 μm or more, and more preferably 2.2 μm or more. However, in the imaging optical system and the imaging apparatus according to the present invention, the pixel pitch of the imaging element is not particularly limited, and the present invention can be applied to a pixel pitch of the imaging element of less than 2.0 μm. it can.

  Since the imaging optical system according to the present invention described above can achieve high resolution, it is suitable for the solid-state imaging device as described above. In addition, since the imaging device according to the present invention has a wide angle of view, a high ambient light amount, and can maintain high resolution regardless of changes in ambient temperature, the imaging device for vehicles used in various driving support systems Alternatively, it is suitable for an installation type imaging apparatus that is installed and installed on a moving body such as a vehicle or a building indoors or outdoors, such as an imaging apparatus for monitoring.

  Next, an Example is shown and this invention is demonstrated concretely. However, the present invention is not limited to the following examples. The optical system of each of the following examples is an imaging optical system used for the imaging device (optical device), and can be preferably applied to an installation type imaging device such as an in-vehicle imaging device. . In each lens cross-sectional view, the left side in the drawing is the subject side, and the right side is the image plane side.

(1) Configuration of Optical System FIG. 1 shows the lens configuration of the imaging optical system of Example 1 according to the present invention when focusing on infinity.

  The imaging optical system according to the first exemplary embodiment includes a front group G1, an aperture (aperture stop) S, and a rear group G2, which are arranged in order, and a subject image on an image plane I of an image sensor such as a CCD sensor or a CMOS sensor. Is imaged. In FIG. 1, “IRCF” is an infrared cut filter. Since these points are the same in the lens cross-sectional views shown in the other embodiments, the description thereof will be omitted below.

  The imaging optical system is substantially composed of six lenses. Specifically, the front group includes a first lens that is a negative lens, a second lens that is a positive lens, and a third lens that is a positive lens in order from the subject side. The rear group includes, in order from the subject side, a fourth lens that is a positive lens, a fifth lens that is a negative lens, and a sixth lens that is a positive lens.

  The first lens is an aspherical surface that has a convex surface on the subject side and weakens the convex power when separated from the optical axis. The second lens has a concave surface on the subject side and a convex surface on the image side. These surface shapes are as shown in Tables 1 and 2 described later.

(2) Numerical Examples Next, numerical examples to which specific numerical values of the imaging optical system are applied will be described. Table 1 shows surface data of the imaging optical system. In Table 1, “NS” is the order of the lens surfaces counted from the subject side, that is, the surface number, “R” is the radius of curvature of the lens surface, “D” is the distance on the optical axis of the lens surface, and “Nd”. Represents the refractive index with respect to the d line (wavelength λ = 587.56 nm), and “Vd” represents the Abbe number with respect to the d line. An asterisk “*” added next to the surface number indicates that the lens surface is aspheric. Further, “INF” described in the “R” column means “∞ (infinity)”.

  Table 2 shows the aspheric data. The aspheric surface data indicates the conical coefficient and the aspheric coefficient of each order when the aspheric surface is defined by the following equation.

但し、Ｘは光軸面頂からの非球面形状サグ量（像面の方向を正とする）、Ｈは光軸からレンズ外径方向への距離、Ｒは近軸曲率半径、εは円錐係数（ＥＰ）、Ａ、Ｂ、Ｃ、Ｄ、Ｅ、Ｆはそれぞれ２次、４次、６次、８次、１０次、１２次の非球面係数である。また、表２において「E−ａ」は「×１０^−ａ」を示す。

Where X is the amount of aspherical sag from the top of the optical axis surface (the direction of the image plane is positive), H is the distance from the optical axis to the lens outer diameter direction, R is the paraxial radius of curvature, and ε is the cone coefficient (EP), A, B, C, D, E, and F are secondary, fourth, sixth, eighth, tenth, and twelfth aspheric coefficients, respectively. In Table 2, “E−a” indicates “× 10 ^−a ”.

  Table 3 shows specification data of the imaging optical system. In Table 3, “F” is the focal length of the imaging optical system, “Fno” is the F number of the imaging optical system, and “2w” is the angle of view of the imaging optical system.

  Table 28 shows numerical values of the conditional expressions (1) to (6) of the imaging optical system. Since the items related to these tables are the same in the tables shown in other examples, the description thereof will be omitted below.

  FIG. 2 is a longitudinal aberration diagram of the imaging optical system when focusing on infinity. Spherical aberration (mm), astigmatism (mm), and distortion aberration (%) in order from the left side in the drawing.

  In the spherical aberration diagram, the vertical axis represents the F number (indicated by FNO in the figure), the solid line is the d line (wavelength 587.56 nm), the long broken line is the C line (wavelength 656.27 nm), and the short broken line is the F line (wavelength 486.13). nm).

  In the astigmatism diagram, the vertical axis represents the image height (Y), the solid line is the characteristic on the sagittal image plane (S) for the d line (wavelength 587.56 nm), and the dotted line is the characteristic on the meridional image plane (T) for the d line.

  In the distortion diagram, the vertical axis represents the image height (Y) and represents the characteristics at the d-line (wavelength 587.56 nm).

  FIG. 3 shows a lateral aberration diagram of the imaging optical system when focused on infinity. Each lateral aberration diagram shows coma aberration at 0.70 FA and 0.00FA. FA is the maximum image height. In each lateral aberration diagram, the horizontal axis represents the distance from the principal ray on the pupil plane, the solid line is the d line (wavelength 587.56 nm), the long broken line is the C line (wavelength 656.27 nm), and the short broken line is the F line ( Wavelength 486.13 nm). Since the matters relating to these aberration diagrams are the same in the respective drawings shown in the other examples, the description thereof will be omitted below.

In the imaging optical system of Example 1, the temperature coefficient (dn3, dn4) of relative refractive index at the temperature of 20 ° C. to 40 ° C. with respect to the d-line of the third lens and the fourth lens (unit: 10 ⁻⁶ / K) is as follows. Note that the third lens and the fourth lens, which are positive lenses disposed closest to the stop in the front group and the rear group, respectively, have such a relative refractive index temperature coefficient, so that even when the ambient temperature changes. It becomes easier to suppress the focus shift and maintain high resolution. The same applies to the following embodiments.
dn3 = −5.9
dn4 = 3.4

(1) Configuration of Optical System FIG. 4 shows a lens configuration at the time of focusing on infinity of the imaging optical system according to the second embodiment of the present invention.

  The imaging optical system of Example 2 includes a front group G1, an aperture (aperture stop) S, and a rear group G2, which are arranged in order, and forms a subject image on the image plane I of the image sensor. The front group includes, in order from the subject side, a first lens that is a negative lens, a second lens that is a positive lens, and a third lens that is a positive lens. The rear group includes, in order from the subject side, a fourth lens that is a positive lens, a fifth lens that is a negative lens, and a sixth lens that is a positive lens. It consists of 6 lenses.

  The first lens is an aspherical surface that has a convex surface on the subject side and weakens the convex power when separated from the optical axis. The second lens has a concave surface on the subject side and a convex surface on the image side. These surface shapes are as shown in Tables 4 and 5 described later.

(2) Numerical Examples Next, numerical examples to which specific numerical values of the imaging optical system are applied will be described. Table 4 shows surface data of the imaging optical system, Table 5 shows aspherical data, and Table 6 shows specification data of the imaging optical system. Table 28 shows numerical values of the conditional expressions (1) to (6) of the imaging optical system.

  FIG. 5 is a longitudinal aberration diagram when the imaging optical system is focused at infinity, and FIG. 6 is a transverse aberration diagram when the imaging optical system is focused at infinity.

In the imaging optical system of Example 2, the temperature coefficients (dn3, dn4) of the relative refractive index at the temperature of 20 ° C. to 40 ° C. with respect to the d-line of the third lens and the fourth lens are as follows. .
dn3 = −0.7
dn4 = 3.4

(1) Configuration of Optical System FIG. 7 shows a lens configuration at the time of focusing on infinity of the imaging optical system of Example 3 according to the present invention.

  In the imaging optical system of Example 3, a front group G1, a stop (aperture stop) S, and a rear group G2 are arranged in order, and an object image is formed on the image plane I of the image sensor. The front group includes, in order from the subject side, a first lens that is a negative lens, a second lens that is a positive lens, and a third lens that is a positive lens. The rear group includes, in order from the subject side, a fourth lens that is a positive lens, a fifth lens that is a negative lens, and a sixth lens that is a positive lens. It consists of 6 lenses.

  The first lens is an aspherical surface that has a convex surface on the subject side and weakens the convex power when separated from the optical axis. The second lens has a concave surface on the subject side and a convex surface on the image side. These surface shapes are as shown in Tables 7 and 8 to be described later.

(2) Numerical Examples Next, numerical examples to which specific numerical values of the imaging optical system are applied will be described. Table 7 shows surface data of the imaging optical system, Table 8 shows aspherical data, and Table 9 shows specification data of the imaging optical system. Table 28 shows numerical values of the conditional expressions (1) to (6) of the imaging optical system.

  FIG. 8 is a longitudinal aberration diagram when the imaging optical system is focused at infinity, and FIG. 9 is a transverse aberration diagram when the imaging optical system is focused at infinity.

In the imaging optical system of Example 3, the temperature coefficient (dn3, dn4) of the relative refractive index at a temperature of 20 ° C. to 40 ° C. with respect to the d line of the third lens and the fourth lens is as follows. .
dn3 = −5.9
dn4 = 3.4

(1) Configuration of Optical System FIG. 10 shows a lens configuration at the time of focusing on infinity of the imaging optical system of Example 4 according to the present invention.

  The imaging optical system of Example 4 includes a front group G1, a stop (aperture stop) S, and a rear group G2, which are arranged in order, and forms a subject image on the image plane I of the image sensor. The front group includes, in order from the subject side, a first lens that is a negative lens, a second lens that is a positive lens, and a third lens that is a positive lens. The rear group includes a fourth lens that is a positive lens, a fifth lens that is a negative lens, and a sixth lens that is a positive lens, and the imaging optical system is substantially composed of six lenses. Become.

  The first lens is an aspherical surface that has a convex surface on the subject side and weakens the convex power when separated from the optical axis. The second lens has a concave surface on the subject side and a convex surface on the image side. These surface shapes are as shown in Table 10 and Table 11 described later.

(2) Numerical Examples Next, numerical examples to which specific numerical values of the imaging optical system are applied will be described. Table 10 shows surface data of the imaging optical system, Table 11 shows aspherical data, and Table 12 shows specification data of the imaging optical system. Table 28 shows numerical values of the conditional expressions (1) to (6) of the imaging optical system.

  FIG. 11 is a longitudinal aberration diagram when the imaging optical system is focused at infinity, and FIG. 12 is a transverse aberration diagram when the imaging optical system is focused at infinity.

In the imaging optical system of Example 4, the temperature coefficients (dn3, dn4) of the relative refractive index at the temperature of 20 ° C. to 40 ° C. with respect to the d-line of the third lens and the fourth lens are as follows. .
dn3 = −5.9
dn4 = 3.4

(1) Configuration of Optical System FIG. 13 shows the lens configuration of the imaging optical system of Example 5 according to the present invention when focusing on infinity.

  In the imaging optical system of Example 5, a front group G1, a stop (aperture stop) S, and a rear group G2 are arranged in order, and an object image is formed on the image plane I of the image sensor. The front group includes, in order from the subject side, a first lens that is a negative lens, a second lens that is a positive lens, and a third lens that is a positive lens. The rear group includes, in order from the subject side, a fourth lens that is a positive lens, a fifth lens that is a negative lens, and a sixth lens that is a positive lens. It consists of 6 lenses.

  The first lens is an aspherical surface that has a convex surface on the subject side and weakens the convex power when separated from the optical axis. The second lens has a concave surface on the subject side and a convex surface on the image side. These surface shapes are as shown in Table 13 and Table 14 described later.

(2) Numerical Examples Next, numerical examples to which specific numerical values of the imaging optical system are applied will be described. Table 13 shows surface data of the imaging optical system, Table 14 shows aspherical data, and Table 15 shows specification data of the imaging optical system. Table 28 shows numerical values of the conditional expressions (1) to (6) of the imaging optical system.

  FIG. 14 is a longitudinal aberration diagram when the imaging optical system is focused at infinity, and FIG. 15 is a transverse aberration diagram when the imaging optical system is focused at infinity.

In the imaging optical system of Example 5, the temperature coefficient (dn3, dn4) of the relative refractive index at a temperature of 20 ° C. to 40 ° C. with respect to the d-line of the third lens and the fourth lens is as follows. .
dn3 = −6.5
dn4 = 1.1

(1) Configuration of Optical System FIG. 16 shows the lens configuration of the imaging optical system of Example 6 according to the present invention when focusing on infinity.

  In the imaging optical system of Example 6, a front group G1, a stop (aperture stop) S, and a rear group G2 are arranged in order, and an object image is formed on the image plane I of the image sensor. The front group includes, in order from the subject side, a first lens that is a negative lens, a second lens that is a positive lens, and a third lens that is a positive lens. The rear group includes, in order from the subject side, a fourth lens that is a positive lens, a fifth lens that is a negative lens, and a sixth lens that is a positive lens. It consists of 6 lenses.

  The first lens is an aspherical surface that has a convex surface on the subject side and weakens the convex power when separated from the optical axis. The second lens has a concave surface on the subject side and a convex surface on the image side. These surface shapes are as shown in Table 16 and Table 17 described later.

(2) Numerical Examples Next, numerical examples to which specific numerical values of the imaging optical system are applied will be described. Table 16 shows surface data of the imaging optical system, Table 17 shows aspherical data, and Table 18 shows specification data of the imaging optical system. Table 28 shows numerical values of the conditional expressions (1) to (6) of the imaging optical system.

  FIG. 17 is a longitudinal aberration diagram when the imaging optical system is focused at infinity, and FIG. 18 is a transverse aberration diagram when the imaging optical system is focused at infinity.

In the imaging optical system of Example 6, the temperature coefficient (dn3, dn4) of the relative refractive index at the temperature of 20 ° C. to 40 ° C. with respect to the d-line of the third lens and the fourth lens is as follows. .
dn3 = −6.5
dn4 = −0.7

(1) Configuration of Optical System FIG. 19 shows the lens configuration of the imaging optical system of Example 7 according to the present invention when focusing on infinity.

  In the imaging optical system of the seventh embodiment, a front group G1, an aperture (aperture stop) S, and a rear group G2 are sequentially arranged, and an object image is formed on the image plane I of the image sensor. The front group includes, in order from the subject side, a first lens that is a negative lens, a second lens that is a positive lens, and a third lens that is a positive lens. The rear group includes, in order from the subject side, a fourth lens that is a positive lens, a positive lens, a fifth lens that is a negative lens, and a sixth lens that is a positive lens. Consists essentially of seven lenses. The imaging optical system of Example 7 is different from the imaging optical system of Examples 1 to 6 in that a positive lens is provided between the fourth lens and the fifth lens.

  The first lens is an aspherical surface that has a convex surface on the subject side and weakens the convex power when separated from the optical axis. The second lens has a concave surface on the subject side and a convex surface on the image side. These surface shapes are as shown in Table 19 and Table 20 described later.

(2) Numerical Examples Next, numerical examples to which specific numerical values of the imaging optical system are applied will be described. Table 19 shows surface data of the imaging optical system, Table 20 shows aspherical data, and Table 21 shows specification data of the imaging optical system. Table 28 shows numerical values of the conditional expressions (1) to (6) of the imaging optical system.

  FIG. 20 is a longitudinal aberration diagram when the imaging optical system is focused at infinity, and FIG. 21 is a transverse aberration diagram when the imaging optical system is focused at infinity.

In the imaging optical system of Example 7, the temperature coefficient (dn3, dn4) of the relative refractive index at the temperature of 20 ° C. to 40 ° C. with respect to the d-line of the third lens and the fourth lens is as follows. .
dn3 = −5.1
dn4 = 1.3

(1) Configuration of Optical System FIG. 22 shows the lens configuration of the imaging optical system of Example 8 according to the present invention when focusing on infinity.

  In the imaging optical system of Example 8, a front group G1, a stop (aperture stop) S, and a rear group G2 are arranged in this order, and an object image is formed on the image plane I of the image sensor. The front group includes, in order from the subject side, a first lens that is a negative lens, a negative lens, a second lens that is a positive lens, and a third lens that is a positive lens. The rear group includes, in order from the subject side, a fourth lens that is a positive lens, a fifth lens that is a negative lens, and a sixth lens that is a positive lens. It consists of seven lenses. The imaging optical system of Example 8 includes a negative lens between the first lens and the second lens, unlike the imaging optical system of Examples 1 to 6.

  The first lens is an aspherical surface that has a convex surface on the subject side and weakens the convex power when separated from the optical axis. The second lens has a concave surface on the subject side and a convex surface on the image side. These surface shapes are as shown in Table 22 and Table 23 described later.

(2) Numerical Examples Next, numerical examples to which specific numerical values of the imaging optical system are applied will be described. Table 22 shows surface data of the imaging optical system, Table 23 shows aspherical data, and Table 24 shows specification data of the imaging optical system. Table 28 shows numerical values of the conditional expressions (1) to (6) of the imaging optical system.

  FIG. 23 is a longitudinal aberration diagram when the imaging optical system is focused at infinity, and FIG. 24 is a transverse aberration diagram when the imaging optical system is focused at infinity.

In the imaging optical system of Example 8, the temperature coefficients (dn3, dn4) of the relative refractive index at the temperature of 20 ° C. to 40 ° C. with respect to the d-line of the third lens and the fourth lens are as follows. .
dn3 = −5.9
dn4 = −0.7

(1) Configuration of Optical System FIG. 25 shows a lens configuration of the imaging optical system of Example 9 according to the present invention when focusing on infinity.

  The imaging optical system according to the ninth embodiment includes a front group G1, an aperture (aperture stop) S, and a rear group G2, which are arranged in order, and forms an object image on the image plane I of the image sensor. The front group includes, in order from the subject side, a first lens that is a negative lens, a negative lens, a second lens that is a positive lens, and a third lens that is a positive lens. The rear group includes, in order from the subject side, a fourth lens that is a positive lens, a positive lens, a fifth lens that is a negative lens, and a sixth lens that is a positive lens. Consists essentially of eight lenses. The imaging optical system of Example 9 is different from the imaging optical system of Examples 1 to 6 in that a negative lens is provided between the first lens and the second lens, and the fourth lens and the fifth lens. With a positive lens.

  The first lens is an aspherical surface that has a convex surface on the subject side and weakens the convex power when separated from the optical axis. The second lens has a concave surface on the subject side and a convex surface on the image side. These surface shapes are as shown in Table 25 and Table 26 described later.

(2) Numerical Examples Next, numerical examples to which specific numerical values of the imaging optical system are applied will be described. Table 25 shows surface data of the imaging optical system, Table 26 shows aspherical data, and Table 27 shows specification data of the imaging optical system. Table 28 shows numerical values of the conditional expressions (1) to (6) of the imaging optical system.

  FIG. 26 shows a longitudinal aberration diagram when the imaging optical system is focused at infinity, and FIG. 27 shows a lateral aberration diagram when the imaging optical system is focused at infinity.

In the imaging optical system of Example 9, the temperature coefficients (dn3, dn4) of the relative refractive index at the temperature of 20 ° C. to 40 ° C. with respect to the d-line of the third lens and the fourth lens are as follows. .
dn3 = −6.7
dn4 = −0.7

  According to the present invention, it is possible to provide a compact imaging optical system and imaging apparatus that are wide-angled and can maintain high resolution regardless of changes in ambient temperature.

G1 ... front group G2 ... rear group S ... aperture stop IRCF ... infrared cut filter I ... image plane

Claims (10)

An imaging optical system in which a front group, a stop, and a rear group are sequentially arranged from the subject side,
The front group includes a first lens arranged closest to the subject side, and a second lens and a third lens arranged in order on the image side of the first lens,
The first lens is a negative lens;
The second lens is a positive lens having a concave surface on the subject side and a convex surface on the image side,
The third lens has a concave surface on the subject side,
The image-side surface of the second lens and the object-side surface of the third lens are adjacent to each other so that there is an air space on the optical axis and both lenses are in contact with each other outside the effective diameter range of each lens. An imaging optical system characterized by being arranged. The imaging optical system according to claim 1, wherein the second lens and the third lens satisfy the following conditional expression (1).
(1) 1.05 <(| L2R2 | + d23) / | L3R1 | <2.49
However,
L2R2: radius of curvature of the image side surface of the second lens L3R1: radius of curvature of the subject side surface of the third lens d23: air space on the optical axis of the second lens and the third lens   3. The imaging optical system according to claim 1, wherein the first lens has a convex surface on the subject side and an aspheric surface that weakens the convex power when the first lens is away from the optical axis.   The imaging optical system according to any one of claims 1 to 3, wherein the third lens is a positive lens. The front group includes at least one positive lens other than the second lens,
The imaging optical system according to any one of claims 1 to 4, wherein the following conditional expression (2) and conditional expression (3) are satisfied.
(2) ν2 <47
(3) ν3> 65
However,
ν2: Abbe number of the positive lens having the smallest Abbe number with respect to the d line among the positive lenses included in the front group ν3: Of the positive lens included in the front group, the positive lens having the largest Abbe number with respect to the d line Abbe number The front group includes at least one positive lens other than the second lens,
The imaging optical system according to any one of claims 1 to 5, wherein the following conditional expression (4) is satisfied.
(4) 0.15 <N2-N3
However,
N2: The refractive index of the positive lens having the largest refractive index with respect to the d-line among the positive lenses included in the front group N3: The positive lens having the smallest refractive index with respect to the d-line among the positive lenses included in the front group Refractive index The front group includes, in order from the subject side, the first lens, the second lens, and the third lens.
The rear group includes, in order from the subject side, a fourth lens that is a positive lens, a fifth lens that is a negative lens, and a sixth lens that is a positive lens.
The imaging optical system according to any one of claims 1 to 6, wherein the imaging optical system substantially includes these six lenses. The imaging optical system according to claim 1, wherein the imaging optical system satisfies the following conditional expression (5).
(5) 1.3 <| f12 / f | <9.5
However,
f: focal length of the imaging optical system f12: focal length of the second lens The imaging optical system according to any one of claims 1 to 8, wherein the imaging optical system satisfies the following conditional expression (6).
(6) 2.2 <| f13 / f | <8.9
However,
f: Focal length of the imaging optical system f13: Focal length of the third lens   The imaging optical system according to any one of claims 1 to 9, and the optical image formed by the imaging optical system on the image side of the imaging optical system is converted into an electrical signal. An imaging apparatus comprising: an imaging element.

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