JP2019168493A - Optical system, lens unit and image capturing device - Google Patents

Abstract

To provide an optical system which is compact and offers good optical performance.SOLUTION: An image capturing optical system 10 substantially consists of a first lens L1 having negative refractive power, a second lens L2 having negative refractive power, a third lens L3 having positive refractive power, an aperture stop ST, a fourth lens L4 having negative refractive power, a fifth lens L5 having positive refractive power, and a sixth lens L6 in order from the object side, the second lens L2 having a convex surface on the object side, and the sixth lens L6 having a concave surface of the object side. The optical system satisfies the following conditional expression (1): 40≤νd3 ...(1), where νd3 represents an Abbe number of the third lens L3.SELECTED DRAWING: Figure 1

Description

  The present invention particularly relates to an optical system used in an imaging apparatus such as an in-vehicle camera, a portable terminal camera, and a surveillance camera, a lens unit including the optical system, and an imaging apparatus.

  2. Description of the Related Art In recent years, small imaging lenses used for imaging devices such as in-vehicle cameras, portable terminal cameras, and surveillance cameras are known (see, for example, Patent Documents 1 to 3). An image sensor such as a CCD (Charge Coupled Device) type image sensor or a CMOS (Complementary Metal Oxide Semiconductor) type image sensor used in such an image pickup apparatus is designed to have higher pixels and smaller size. Along with this, an image pickup device body including these image pickup devices has been reduced in size, and an image pickup lens mounted thereon is required to be reduced in size and weight in addition to bright and good optical performance.

  In the optical system of Patent Document 1, a low-cost design is realized by using many plastic lenses. However, the F value is as dark as 2.0, and the optical system that has been required in recent years is not a bright optical system. Further, the total length is large with respect to the focal length of the entire system, and the miniaturization of the optical system has not been realized.

  Even in the optical system of Patent Document 2, a low-cost design is realized by using many plastic lenses. However, the optical performance is lowered by using a lot of plastic lenses, and the performance of the optical system has not been improved.

  Even in the optical system of Patent Document 3, a low-cost design is realized by using many plastic lenses. However, the F value is as dark as 2.3, and an optical system having a bright F value required in recent years is not available.

JP 2017-037119 A JP 2017-047431 A JP 2017-167253 A

  The present invention has been made in view of the above-described background art, and an object of the present invention is to provide an optical system that is small in size and can ensure good optical performance.

  Another object of the present invention is to provide a lens unit and an imaging apparatus incorporating the above optical system.

In order to achieve the above object, an optical system according to the present invention includes, in order from the object side, a first lens having negative refractive power, a second lens having negative refractive power, and a third lens having positive refractive power. A lens, a stop, a fourth lens having a negative refractive power, a fifth lens having a positive refractive power, and a sixth lens, and the object side surface of the second lens has a convex surface shape. And the object side surface of the sixth lens has a concave surface shape and satisfies the following conditional expression.
40 ≦ νd3 (1)
Here, the value νd3 is the Abbe number of the third lens.

  According to the optical system, by disposing the diaphragm between the third lens and the fourth lens, the diaphragm is disposed near the center of the optical system, and the front lens (that is, the first lens) and The rear lens (that is, the sixth lens) can be reduced in diameter. If the stop is arranged on the object side from between the third lens and the fourth lens, the exit pupil position can be moved away from the imaging surface, so that the telecentricity required when using an imaging element such as a CMOS or CCD is provided. This can be ensured and the diameter of the front ball can be reduced, but there is a problem that the diameter of the rear ball is increased. On the other hand, if the aperture is arranged closer to the image side, the rear lens can be reduced in diameter, but the exit pupil position is closer to the image side, making it difficult to ensure telecentricity, and the front lens diameter is smaller. The problem of increasing the size arises. For this reason, in the present invention, the diaphragm is disposed between the third lens and the fourth lens.

  In the optical system, two negative lenses are arranged on the object side as seen in a retrofocus type. Thereby, since the entrance pupil position can be brought closer to the object side, it is possible to realize a wide angle while reducing the front lens diameter. In addition, since the power can be divided compared to the case where there is a single negative lens, coma, astigmatism, field curvature, and distortion are reduced in the first and second lenses. Can do. In addition, by dividing the power, aberration variation with respect to the eccentricity error when the first and second lenses are incorporated into the lens barrel can be reduced as compared with the case where one lens is incorporated into the lens barrel. Therefore, mass productivity can be improved.

  In addition, spherical aberration and coma generated in the first and second lenses can be corrected by using a third lens that is positioned immediately before the stop and through which a thick light beam passes as a positive lens. In addition, when the fourth and fifth lenses located on the image side of the stop are configured with a negative lens and a positive lens, it is possible to effectively correct axial chromatic aberration and lateral chromatic aberration. In addition, by arranging the lens positioned on the image side from the stop as described above, the height from the optical axis of the off-axis light beam after the fifth lens which is a positive lens can be reduced. Can be miniaturized.

  In addition, since the sixth lens can suppress the occurrence of field curvature and distortion at a high image height, it is possible to ensure good optical performance.

  In the second lens, since the high image height light beam passes through the high position of the lens following the first lens, the contribution of the second lens to the high image height light beam becomes large. For this reason, by making the second lens a negative meniscus lens having a convex shape on the object side, the angle formed between the high image height light beam and the normal of the lens surface can be reduced. Since field curvature and distortion occurring on the side surface can be suppressed, good optical performance can be ensured.

  Further, by making the object side surface of the sixth lens concave, it is possible to reduce the angle formed by the light ray having a high image height and the normal of the lens surface, and the field curvature that occurs on the object side surface of the sixth lens. In addition, since the distortion aberration can be reduced, good optical performance can be ensured.

  The third lens is positioned immediately before the stop, and a thick light beam passes at each image height. However, since the light beam passing height from the optical axis of each image height is low, the contribution to the on-axis light beam is particularly high. growing. By setting the value νd3 of conditional expression (1) to be equal to or greater than the lower limit, axial chromatic aberration can be suppressed to a small value, and good optical performance can be ensured.

In a specific aspect of the present invention, the optical system satisfies the following conditional expression.
1.5 <f123 / f456 (2)
Here, the value f123 is the combined focal length from the first lens to the third lens, and the value f456 is the combined focal length from the fourth lens to the sixth lens.

  Conditional expression (2) defines the ratio of the combined focal length from the first lens to the third lens to the combined focal length from the fourth lens to the sixth lens. When the value f123 / f456 of conditional expression (2) exceeds the lower limit, the combined focal length from the first lens to the third lens with respect to the combined focal length from the fourth lens to the sixth lens does not become too small. For this reason, the image-side principal point position from the image side surface of the sixth lens, which is constituted by the first lens to the sixth lens, is not placed closer to the object side, and the back focus is not too short. Therefore, a space for inserting an optical element such as an optical filter can be secured after the sixth lens, which is the most image side lens. Further, when dust adheres to the lens surface closest to the image, it is possible to make it difficult for the dust to be reflected in the image.

In another aspect of the present invention, the optical system satisfies the following conditional expression.
4.5 <f123 / f (3)
Here, the value f is the focal length of the entire system.

  Conditional expression (3) defines the ratio of the combined focal length from the first lens to the third lens with respect to the focal length of the entire system. When the value f123 / f of conditional expression (3) exceeds the lower limit, the combined focal length from the first lens to the third lens does not become too small. Therefore, the combined power from the first lens to the third lens does not become too strong, various aberrations generated from the first lens to the third lens can be suppressed, and good optical performance can be ensured. Further, since the combined power from the first lens to the third lens does not become too strong, an increase in the front lens diameter can be prevented.

In still another aspect of the present invention, the optical system satisfies the following conditional expression.
3.5 <L / f <5.5 (4)
Here, the value L is the total length of the entire system (that is, the distance from the most object-side surface of the optical system to the imaging surface).

  Conditional expression (4) defines the ratio of the total length to the focal length of the entire system. Conventionally, there are many optical systems that adopt a configuration in which a strong negative lens is arranged on the object side like the retrofocus type, and the entrance pupil position is moved to the object side, so it is possible to reduce the front lens diameter while widening the angle. However, there is a problem in that the principal point position is easily placed on the image side and the total length becomes longer with respect to the focal length. By satisfying conditional expression (4), it is possible to realize a small optical system having a short overall length despite a long focal length. When the value L / f of conditional expression (4) is below the upper limit, the total length can be shortened with respect to the focal length. On the other hand, when the value L / f of conditional expression (4) exceeds the lower limit, the total length is not too short with respect to the focal length, and the power of each lens of the optical system does not become too strong. Various aberrations can be suppressed, and good optical performance can be ensured.

In still another aspect of the present invention, the optical system satisfies the following conditional expression.
f2 / f <−2.5 (5)
Here, the value f2 is the focal length of the second lens.

  Conditional expression (5) defines the ratio of the focal length of the second lens to the focal length of the entire system. When the value f2 / f of conditional expression (5) is less than the upper limit, the focal length of the second lens does not become too short. Therefore, it is possible to suppress curvature of field and distortion at a high image height, which are generated when the power of the second lens becomes too strong. Further, since the focal length of the second lens does not become too short, it is possible to suppress aberration fluctuations due to eccentricity errors when the second lens is incorporated into the lens barrel. As described above, satisfying conditional expression (5) makes it possible to reduce the size of the optical system and ensure good optical characteristics.

  In still another aspect of the present invention, the sixth lens has a negative refractive power. In this case, since the image side principal point position from the image side surface of the sixth lens can be positioned more on the object side, the overall length can be reduced. Further, since the off-axis light beam that has passed through the sixth lens can be refracted in the high direction from the optical axis, the height of the off-axis light beam that passes through the sixth lens can be reduced, and the sixth lens has a small diameter Can be

In still another aspect of the present invention, the optical system satisfies the following conditional expression.
54 ≦ νd1 (6)
Here, the value νd1 is the Abbe number of the first lens.

  The first lens located closest to the object side has a large contribution to these light rays because light rays with a high image height pass through the highest position. By using a glass material that satisfies the conditional expression (6) in the first lens, it is possible to suppress lateral chromatic aberration that occurs at a high image height of the first lens, and it is possible to ensure good optical performance.

In still another aspect of the present invention, the optical system satisfies the following conditional expression.
35 ≦ νd6 (7)
Here, the value νd6 is the Abbe number of the sixth lens.

  Similarly to the first lens, the sixth lens located closest to the image side also has a large contribution to these light rays because the high image height light rays pass through the highest position. By using a glass material that satisfies the conditional expression (7) in the sixth lens, it is possible to suppress lateral chromatic aberration that occurs at the high image height of the sixth lens, and it is possible to ensure good optical performance.

In still another aspect of the present invention, the optical system satisfies the following conditional expression.
35 <νd5-νd4 (8)
Here, the value νd4 is the Abbe number of the fourth lens, and the value νd5 is the Abbe number of the fifth lens.

  Since the fourth and fifth lenses are located immediately after the stop and a thick light beam passes at each image height, the influence on the axial chromatic aberration and lateral chromatic aberration by these lenses is large. When the value νd5-νd4 of conditional expression (8) exceeds the lower limit, axial chromatic aberration generated in the fourth lens having negative power is generated in the reverse direction by the fifth lens having positive power. Therefore, axial chromatic aberration can be canceled by the fourth and fifth lenses. Thereby, axial chromatic aberration can be suppressed.

  In still another aspect of the present invention, the first lens has a spherical shape. By using a spherical lens as the first lens whose diameter tends to increase, the cost can be reduced compared to an aspherical lens.

  In yet another aspect of the invention, at least one of the second and third lenses has an aspheric shape, and at least one of the fourth, fifth, and sixth lenses has an aspheric shape. In this case, various aberrations can be effectively corrected, and good optical performance can be ensured.

  In still another aspect of the present invention, the first lens is a glass lens. In this case, it is possible to prevent scratches on the lens surface and ensure good optical performance while improving environmental resistance.

  In still another aspect of the present invention, the second, third, fourth, fifth, and sixth lenses are glass lenses. A glass lens has a smaller change in refractive index due to a temperature change than a plastic lens. Therefore, by using all the lenses constituting the optical system including the second to sixth lenses as glass lenses, it is possible to realize an optical system having a small change in optical performance even in a severe environment.

  In order to achieve the above object, a lens unit according to the present invention includes the above-described optical system and a lens barrel that holds the optical system.

  The lens unit includes the above-described optical system, and can achieve downsizing and ensuring good optical performance.

  In order to achieve the above object, an imaging apparatus according to the present invention includes the above-described optical system and an imaging element that detects an image obtained from the optical system.

  The imaging apparatus includes the above-described optical system, and can achieve downsizing and securing good optical performance.

It is a figure explaining a lens unit and an imaging device provided with an imaging optical system of one embodiment of the present invention. (A) is sectional drawing, such as an imaging optical system of Example 1, (B)-(D) are aberration diagrams. (A) is sectional drawing, such as an imaging optical system of Example 2, (B)-(D) are aberration diagrams. (A) is sectional drawing, such as an imaging optical system of Example 3, (B)-(D) are aberration diagrams. (A) is sectional drawing, such as an imaging optical system of Example 4, (B)-(D) are aberration diagrams. (A) is sectional drawing, such as an imaging optical system of Example 5, (B)-(D) are aberration diagrams. (A) is sectional drawing, such as an imaging optical system of Example 6, (B)-(D) are aberration diagrams. (A) is sectional drawing, such as an imaging optical system of Example 7, (B)-(D) are aberration diagrams. (A) is sectional drawing, such as an imaging optical system of Example 8, (B)-(D) are aberration diagrams. (A) is sectional drawing, such as an imaging optical system of Example 9, (B)-(D) are aberration diagrams. (A) is sectional drawing, such as an imaging optical system of Example 10, (B)-(D) are aberration diagrams.

  FIG. 1 is a cross-sectional view illustrating an imaging apparatus 100 that is an embodiment of the present invention. The imaging apparatus 100 includes a camera module 30 that forms an image signal, and a processing unit 60 that exhibits the functions of the imaging apparatus 100 by operating the camera module 30.

  The camera module 30 includes a lens unit 40 including the imaging optical system 10 and a sensor unit 50 that converts a subject image formed by the imaging optical system 10 into an image signal.

  The lens unit 40 includes an imaging optical system 10 that is an optical system, and a lens barrel 41 that supports the imaging optical system 10. The imaging optical system 10 includes first to sixth lenses L1 to L6. The lens barrel 41 is formed of resin, metal, a mixture of resin and glass fiber, etc., and stores and holds a lens or the like therein. When the lens barrel 41 is formed of a metal or a resin in which glass fiber is mixed, the imaging optical system 10 can be stably fixed with less thermal expansion than the resin. The lens barrel 41 has an opening OP through which light from the object side is incident.

  The total angle of view of the imaging optical system 10 is 120 ° or more. The first to sixth lenses L1 to L6 constituting the imaging optical system 10 are directly or indirectly held on the inner surface side of the lens barrel 41 at the flange portion or the outer peripheral portion thereof, and the optical axis AX direction and light Positioning in the direction perpendicular to the axis AX is performed. The lens barrel 41 also supports optical elements other than the lenses L1 to L6, such as an aperture (aperture stop) ST and a filter F1.

  The sensor unit 50 includes a solid-state imaging device 51 that photoelectrically converts a subject image formed by the imaging optical system 10, a substrate 52 that supports the solid-state imaging device 51, and a sensor that holds the solid-state imaging device 51 via the substrate 52. A holder 53. The solid-state image sensor 51 is, for example, a CMOS image sensor. The substrate 52 includes wiring for operating the solid-state imaging device 51, peripheral circuits, and the like. The sensor holder 53 is formed of a resin or other material, and positions the solid-state image sensor 51 with respect to the optical axis AX. The lens barrel 41 of the lens unit 40 is fixed in a state of being positioned so as to be fitted to the sensor holder 53.

  The solid-state imaging device (imaging device) 51 has a photoelectric conversion unit 51a as the imaging surface I, and a signal processing circuit (not shown) is formed in the vicinity thereof. Pixels, that is, photoelectric conversion elements are two-dimensionally arranged in the photoelectric conversion unit 51a. The solid-state imaging device 51 is not limited to the above-described CMOS type image sensor, and may be a device incorporating another imaging device such as a CCD.

  A filter or the like can be disposed between the lenses constituting the lens unit 40 or between the lens unit 40 and the sensor unit 50. In the example of FIG. 1, the filter F <b> 1 is disposed between the sixth lens L <b> 6 of the imaging optical system 10 and the solid-state imaging element 51. The filter F1 is a parallel plate assuming an optical low-pass filter, an IR cut filter, a seal glass of the solid-state image sensor 51, and the like. The filter F1 can be arranged as a separate filter member, but it can be given to any lens surface constituting the imaging optical system 10 without being arranged separately. For example, in the case of an infrared cut filter, an infrared cut coat may be applied on the surface of one or a plurality of lenses.

  The processing unit 60 includes an element driving unit 61, an input unit 62, a storage unit 63, a display unit 64, and a control unit 68. The element driving unit 61 operates the solid-state image sensor 51 by outputting a control signal to a circuit or the like associated with the solid-state image sensor 51. The element driving unit 61 receives a voltage and a clock signal for driving the solid-state imaging device 51 from the control unit 68, and outputs YUV and other digital pixel signals corresponding to the output signal of the solid-state imaging device 51 to an external circuit. You can also do it. The input unit 62 is a part that accepts user operations, the storage unit 63 is a part that stores information necessary for the operation of the imaging apparatus 100, image data acquired by the camera module 30, and the like. This is a part for displaying information to be presented to the user, captured images, and the like. The control unit 68 comprehensively controls operations of the element driving unit 61, the input unit 62, the storage unit 63, and the like, and can perform various image processing on image data obtained by the camera module 30, for example. . When the imaging apparatus 100 is used as, for example, an in-vehicle camera, appropriate image processing is performed and an image is displayed to the driver.

  Although detailed description is omitted, the specific function of the processing unit 60 is appropriately adjusted according to the application of the device in which the imaging apparatus 100 is incorporated. The imaging device 100 can be mounted on devices for various uses such as an in-vehicle camera and a surveillance camera.

  Hereinafter, the imaging optical system 10 of the first embodiment will be described with reference to FIG. The imaging optical system 10 illustrated in FIG. 1 has substantially the same configuration as an imaging optical system 10A of Example 1 described later.

  The illustrated imaging optical system 10 includes, in order from the object side, a first lens L1 having a negative refractive power, a second lens L2 having a negative refractive power, a third lens L3 having a positive refractive power, and a diaphragm. It is substantially composed of ST, a fourth lens L4 having negative refractive power, a fifth lens L5 having positive refractive power, and a sixth lens L6.

  In the imaging optical system 10, the stop ST is disposed between the third lens L3 and the fourth lens L4, so that the stop ST is disposed near the center of the optical system. Thereby, it is possible to make both the front lens (that is, the first lens L1) and the rear lens (that is, the sixth lens L6) smaller in diameter. If the aperture stop ST is arranged closer to the object side, the exit pupil position can be moved away from the imaging surface I, so that the telecentricity necessary when using the solid-state imaging device 51 such as CMOS or CCD can be ensured. Although the front lens diameter can be reduced, there arises a problem that the rear lens diameter increases. On the other hand, if the aperture stop ST is arranged closer to the image side, the rear lens diameter can be reduced. However, since the exit pupil position is closer to the image side, it becomes difficult to ensure telecentricity, and the front lens The problem arises that the diameter increases.

  In the imaging optical system 10, two negative lenses are arranged on the object side so as to be seen as a retrofocus type. Thereby, since the entrance pupil position can be brought closer to the object side, it is possible to realize a wide angle while reducing the front lens diameter. In addition, since the power can be divided as compared with the case of a single negative lens, coma aberration, astigmatism, field curvature, and distortion occurring in the first and second lenses L1 and L2 can be reduced. Can be small. Also, by dividing the power, aberration variation with respect to the eccentricity error when the first and second lenses L1 and L2 are incorporated into the lens barrel 41 as compared with the case where one lens is incorporated into the lens barrel 41. Therefore, mass productivity can be improved.

  Further, the spherical lens and the coma aberration generated in the first and second lenses L1 and L2 can be corrected by making the third lens L3, which is located immediately before the stop ST and through which a thick light beam passes, be a positive lens. . In addition, the fourth and fifth lenses L4 and L5 located on the image side of the aperture stop ST have a large contribution to the light beam by the fourth and fifth lenses L4 and L5 because a thick light beam passes through the entire image height. Therefore, the fourth and fifth lenses L4 and L5 positioned on the image side of the stop ST are configured by a negative lens and a positive lens, so that the axial chromatic aberration and the lateral chromatic aberration can be effectively corrected. In addition, by arranging the lens positioned on the image side from the stop ST as described above, the height of the off-axis light beam from the optical axis AX of the fifth lens L5 and the subsequent positive lenses can be reduced. The rear ball diameter can be reduced.

  In addition, by having the sixth lens L6, it is possible to suppress the occurrence of curvature of field and distortion at a high image height, and thus it is possible to ensure good optical performance.

  The sixth lens L6 may have either a negative refractive index or a positive refractive index, but more preferably has a negative refractive power. When the sixth lens L6 has a negative refractive power, the image-side principal point position from the image side surface of the sixth lens L6 can be positioned closer to the object side, and thus the overall length can be reduced. In addition, since the off-axis light beam that has passed through the sixth lens L6 can be refracted in a higher direction from the optical axis AX, the height of the off-axis light beam that passes through the sixth lens L6 can be reduced. The diameter of the lens L6 can be reduced.

  The first lens L1 has a spherical shape. The first lens L1 arranged on the most object side passes a high position of a light beam having a high image height with respect to the optical axis AX. Therefore, the diameter of the first lens L1 tends to increase. By using the first lens L1 as a spherical lens, the cost can be reduced as compared with an aspherical lens.

  The object side surface of the second lens L2 has a convex surface shape. In general, the smaller the angle formed between the normal of the lens surface and the light beam, the smaller the occurrence of aberration. In the second lens L2, the contribution of the second lens L2 to the high image height light beam is large. By making the second lens L2 a negative meniscus lens having a convex shape on the object side, the angle formed between the high image height light beam and the normal of the lens surface can be reduced, and the object side surface of the second lens L2 can be reduced. Can suppress the curvature of field and distortion that occur in the optical field, so that good optical performance can be ensured.

  The object side surface of the sixth lens L6 has a concave surface shape. Thereby, in particular, the angle formed between the high image height light beam and the normal of the lens surface can be reduced, and the field curvature and distortion occurring on the object side surface of the sixth lens L6 can be suppressed to a low level. Good optical performance can be ensured.

  At least one of the second and third lenses L2 and L3 has an aspheric shape, and at least one of the fourth to sixth lenses L4 to L6 has an aspheric shape. Thereby, various aberrations can be effectively corrected, and good optical performance can be ensured.

  The first lens L1 is a glass lens. In the optical system used in the in-vehicle lens and the monitoring lens, the first lens L1 is exposed to the outside world, so that the lens surface is easily damaged, and there is a possibility that the optical performance is deteriorated. By using the first lens L1 as a glass lens, it is possible to prevent scratches on the lens surface and ensure good optical performance while improving environmental resistance.

  The second to sixth lenses L2 to L6 are also preferably glass lenses. A glass lens has a smaller change in refractive index due to a temperature change than a plastic lens. Although a low cost can be realized by using a lot of plastic lenses, it may cause a change in optical performance in a severe environment where a temperature change and a humidity change are large. Therefore, by using all the lenses constituting the optical system including the second to sixth lenses L2 to L6 as glass lenses, it is possible to realize an optical system with small change in optical performance even under severe environments.

The imaging optical system 10 satisfies the following conditional expression.
40 ≦ νd3 (1)
Here, the value νd3 is the Abbe number of the third lens L3.

  The third lens L3 is positioned immediately before the stop ST, and a thick light beam passes at each image height. However, since the light beam passing height from the optical axis AX of each image height is low, the contribution to the on-axis light beam in particular. Becomes larger. By setting the value νd3 of conditional expression (1) to be equal to or greater than the lower limit, axial chromatic aberration can be suppressed to a small value, and good optical performance can be ensured.

The imaging optical system 10 satisfies the following conditional expression.
1.5 <f123 / f456 (2)
Here, the value f123 is the combined focal length from the first lens L1 to the third lens L3, and the value f456 is the combined focal length from the fourth lens L4 to the sixth lens L6.

The imaging optical system 10 more preferably satisfies the following conditional expression.
1.5 <f123 / f456 <15 (2) ′

  Conditional expression (2) defines the ratio of the combined focal length from the first lens L1 to the third lens L3 to the combined focal length from the fourth lens L4 to the sixth lens L6. When the value f123 / f456 of conditional expression (2) exceeds the lower limit, the combined focal length from the first lens L1 to the third lens L3 with respect to the combined focal length from the fourth lens L4 to the sixth lens L6 becomes too small. Absent. For this reason, the image-side principal point position from the image side surface of the sixth lens L6 constituted by the first lens L1 to the sixth lens L6 is not further placed on the object side, and the back focus does not become too short. Therefore, a space for inserting an optical element such as an optical filter can be secured after the sixth lens L6, which is the most image side lens. Further, when dust adheres to the lens surface closest to the image, it is possible to make it difficult for the dust to be reflected in the image.

The imaging optical system 10 satisfies the following conditional expression.
4.5 <f123 / f (3)
Here, the value f is the focal length of the entire system.

The imaging optical system 10 more preferably satisfies the following conditional expression.
4.5 <f123 / f <25 (3) ′

  Conditional expression (3) defines the ratio of the combined focal length from the first lens L1 to the third lens L3 to the focal length of the entire system. When the value f123 / f of conditional expression (3) exceeds the lower limit, the combined focal length from the first lens L1 to the third lens L3 does not become too small. Therefore, the combined power from the first lens L1 to the third lens L3 does not become too strong, and various aberrations generated from the first lens L1 to the third lens L3 can be suppressed, and good optical performance can be ensured. it can. In addition, since the combined power from the first lens L1 to the third lens L3 does not become too strong, an increase in the diameter of the front lens can be prevented.

The imaging optical system 10 satisfies the following conditional expression.
3.5 <L / f <5.5 (4)
Here, the value L is the total length of the entire system (that is, the distance from the most object-side surface of the optical system to the imaging surface).

  Conditional expression (4) defines the ratio of the total length to the focal length of the entire system. Conventionally, many optical systems have a configuration in which a strong negative lens is arranged on the object side like the retrofocus type, and the entrance pupil position is moved to the object side, so the front lens diameter can be reduced while widening the angle. However, there is a problem that the principal point position is easily placed on the image side, and the total length becomes longer with respect to the focal length. By satisfying conditional expression (4), it is possible to realize a small optical system having a short overall length despite a long focal length. When the value L / f of conditional expression (4) is below the upper limit, the total length can be shortened with respect to the focal length. On the other hand, when the value L / f of conditional expression (4) exceeds the lower limit, the total length is not too short with respect to the focal length, and the power of each lens of the optical system does not become too strong. Various aberrations can be suppressed, and good optical performance can be ensured.

The imaging optical system 10 satisfies the following conditional expression.
f2 / f <−2.5 (5)
Here, the value f2 is the focal length of the second lens L2.

The imaging optical system 10 more preferably satisfies the following conditional expression.
−25 <f2 / f <−2.5 (5) ′

  Conditional expression (5) defines the ratio of the focal length of the second lens L2 to the focal length of the entire system. In the second lens L2, particularly, a high image height light beam passes at a high position with respect to the optical axis AX, so that the influence on the high image height light beam becomes large. When the value f2 / f of conditional expression (5) is below the upper limit, the focal length of the second lens L2 does not become too short. Therefore, it is possible to suppress curvature of field and distortion at a high image height, which are generated when the power of the second lens L2 becomes too strong. In addition, since the focal length of the second lens L2 does not become too short, fluctuations in aberration due to decentration errors when the second lens L2 is incorporated into the lens barrel 41 can be suppressed. As described above, satisfying conditional expression (5) makes it possible to reduce the size of the optical system and ensure good optical characteristics.

The imaging optical system 10 satisfies the following conditional expression.
54 ≦ νd1 (6)
Here, the value νd1 is the Abbe number of the first lens L1.

  The first lens L1 located closest to the object side is a lens through which a light beam having a high image height passes through the highest position. For this reason, the first lens L1 has a great influence on the light beam having a high image height, and particularly the chromatic aberration has a great influence on the lateral chromatic aberration. Therefore, by using a glass material that satisfies the conditional expression (6) in the first lens L1, lateral chromatic aberration that occurs at the high image height of the first lens L1 can be suppressed, and good optical performance can be ensured. .

The imaging optical system 10 satisfies the following conditional expression.
35 ≦ νd6 (7)
Here, the value νd6 is the Abbe number of the sixth lens L6.

  The sixth lens L6 located closest to the image side is a lens through which a high image height ray passes the highest position. Therefore, the influence of the sixth lens L6 on the light beam having a high image height is large, and particularly the chromatic aberration has a great influence on the lateral chromatic aberration. Therefore, by using a glass material that satisfies the conditional expression (7) in the sixth lens L6, it is possible to suppress lateral chromatic aberration that occurs at the high image height of the sixth lens L6, and it is possible to ensure good optical performance. .

The imaging optical system 10 satisfies the following conditional expression.
35 <νd5-νd4 (8)
Here, the value νd4 is the Abbe number of the fourth lens L4, and the value νd5 is the Abbe number of the fifth lens L5.

  The fourth and fifth lenses L4 and L5 are located immediately after the stop ST, and a thick light beam passes at each image height. Therefore, the fourth and fifth lenses L4 and L5 have a great influence on the longitudinal chromatic aberration and the lateral chromatic aberration. When the value νd5-νd4 of conditional expression (8) exceeds the lower limit, axial chromatic aberration generated in the fourth lens L4 having negative power is generated in the reverse direction in the fifth lens L5 having positive power. Therefore, axial chromatic aberration can be canceled by the fourth and fifth lenses L4 and L5. Thereby, axial chromatic aberration can be suppressed.

  The imaging optical system 10 may further include other optical elements that have substantially no power (for example, a lens, a filter member, etc.).

  Since the imaging optical system 10 described above has the lens configuration as described above, it has good optical performance while being small.

ただし、
Ａｉ：ｉ次の非球面係数
Ｒ ：曲率半径
Ｋ ：円錐定数 〔Example〕
Examples of the imaging optical system of the present invention will be described below. Symbols used in each example are as follows.
f: Focal length of entire system Fno: F number 2w: Maximum total angle of view ENTP: Entrance pupil position (distance from first surface to entrance pupil position)
EXTP: exit pupil position (distance from imaging surface to exit pupil position)
R: radius of curvature D: axial spacing Nd: refractive index of lens material with respect to d-line vd: Abbe number of lens material ED: effective diameter In each example, a surface with “*” written after each surface number The surface having an aspherical shape, and the aspherical shape is expressed by the following “Equation 1” with the vertex of the surface as the origin, the X axis in the optical axis direction, and the height in the direction perpendicular to the optical axis as h. .

However,
Ai: i-order aspheric coefficient R: radius of curvature K: conic constant

Example 1
The overall specifications of the imaging optical system of Example 1 are shown below.
f = 5.11 (mm)
Fno = 1.60
2w = 120.00 (°)
ENTP = 5.19 (mm)
EXTP = -4.77 (mm)

The lens surface data of the imaging optical system of Example 1 is shown in Table 1 below. In Table 1 below, the surface number is represented by “Surf. N”, the diaphragm (aperture diaphragm) is represented by “ST”, and the infinity is represented by “INF”.
[Table 1]
Surf. NR (mm) D (mm) Nd vd ED (mm)
1 250.000 0.700 1.6180 63.39 9.522
2 9.042 0.200 7.585
3 * 5.500 0.969 1.7680 49.24 7.429
4 * 3.787 2.965 6.220
5 82.382 4.100 1.6180 63.39 5.922
6 -6.463 1.311 5.596
ST INF 0.220 5.204
8 6.551 2.000 1.9459 17.98 5.146
9 3.500 0.010 1.5140 42.83 4.732
10 3.500 3.322 1.7292 54.67 4.736
11 -9.491 1.395 4.833
12 * -6.114 1.764 1.6935 53.20 5.054
13 * -230.000 0.100 6.286
14 INF 0.300 1.5168 64.20 6.503
15 INF 1.496 6.563

The aspheric coefficients of the lens surfaces of Example 1 are shown in Table 2 below. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻⁰² ) is expressed using E (for example, 2.5E-02).
[Table 2]
Third side
K = 1.074532E-01, A4 = -1.624884E-03, A6 = -2.328955E-04,
A8 = 5.001098E-06, A10 = 0.000000E + 00
4th page
K = -8.986798E-01, A4 = 1.470839E-03, A7 = -2.647765E-04,
A8 = 1.291450E-05, A10 = 0.000000E + 00
12th page
K = 0.000000E + 00, A4 = -5.290430E-03, A8 = 4.261773E-04,
A8 = -3.650813E-05, A10 = 1.608478E-06
Side 13
K = 0.000000E + 00, A4 = -8.969457E-03, A6 = 3.647311E-04,
A8 = -9.201162E-06, A10 = 1.730727E-07

The single lens data of Example 1 is shown in Table 3 below.
[Table 3]
Lens Focal length (mm)
L1 -15.197
L2 -21.002
L3 9.872
L4 -11.659
L5 3.931
L6 -9.087

  FIG. 2A is a cross-sectional view of the imaging optical system 10A and the like of the first embodiment. The imaging optical system 10A includes a meniscus type first lens L1 having negative refractive power and convex toward the object side, a meniscus type second lens L2 having negative refractive power and convex toward the object side, and a positive A biconvex third lens L3 having refractive power, a meniscus fourth lens L4 having negative refractive power and convex toward the object side, and a biconvex fifth lens L5 having positive refractive power; A meniscus sixth lens L6 having negative refractive power and concave on the object side. The first, third to fifth lenses L1, L3 to L5 have spherical surfaces as optical surfaces. The second and sixth lenses L2 and L6 have aspheric surfaces as optical surfaces. The fourth and fifth lenses L4 and L5 are cemented lenses joined by an adhesive. The first to sixth lenses L1 to L6 are all made of glass. A diaphragm (aperture diaphragm) ST is disposed between the third lens L3 and the fourth lens L4. A filter F1 having an appropriate thickness is disposed between the sixth lens L6 and the solid-state imaging element 51. The filter F1 is a parallel plate assuming an optical low-pass filter, an IR cut filter, a seal glass of the solid-state image sensor 51, and the like. Reference numeral I denotes an imaging surface that is a projection surface of the solid-state imaging device 51. Note that the symbols F1 and I are the same in the following embodiments.

  2B to 2D show aberration diagrams (spherical aberration, astigmatism, and distortion aberration) of the imaging optical system 10A of Example 1. FIG.

(Example 2)
The overall specifications of the imaging optical system of Example 2 are shown below.
f = 4.87 (mm)
Fno = 1.60
2w = 120.00 (°)
ENTP = 5.14 (mm)
EXTP = -4.93 (mm)

The lens surface data of the imaging optical system of Example 2 is shown in Table 4 below.
[Table 4]
Surf. NR (mm) D (mm) Nd vd ED (mm)
1 250.000 0.700 1.6180 63.39 9.531
2 9.531 0.204 7.640
3 * 5.525 1.864 1.7680 49.24 7.485
4 * 2.992 2.702 5.647
5 * 8.348 4.053 1.5444 55.91 4.960
6 * -7.250 0.000 5.005
ST INF 1.224 4.968
8 6.372 1.325 1.9459 17.98 4.930
9 3.636 0.010 1.5140 42.83 4.708
10 3.636 2.775 1.7292 54.67 4.714
11 -7.991 1.555 4.961
12 * -5.495 1.733 1.7308 40.50 4.981
13 * -230.000 0.100 6.353
14 INF 0.300 1.5168 64.20 6.543
15 INF 1.497 6.596

The aspherical coefficient of the lens surface of Example 2 is shown in Table 5 below.
[Table 5]
Third side
K = 8.490109E-02, A4 = -2.889466E-03, A6 = -1.038759E-04,
A8 = 1.558407E-06, A10 = 0.000000E + 00
4th page
K = -1.079921E + 00, A4 = -1.493043E-03, A6 = -1.889487E-04,
A8 = 1.146423E-05, A10 = 0.000000E + 00
5th page
K = 0.000000E + 00, A4 = -1.137313E-03, A6 = 2.594269E-06,
A8 = 0.000000E + 00, A10 = 0.000000E + 00
6th page
K = 0.000000E + 00, A4 = 4.903884E-05, A6 = 3.578433E-05,
A8 = 0.000000E + 00, A10 = 0.000000E + 00
12th page
K = 0.000000E + 00, A4 = -8.493088E-03, A6 = 1.093650E-03,
A8 = -1.632637E-04, A10 = 8.691583E-06
Side 13
K = 0.000000E + 00, A4 = -8.208992E-03, A6 = 5.511346E-04,
A8 = -4.489897E-05, A10 = 1.472478E-06

The single lens data of Example 2 is shown in Table 6 below.
[Table 6]
Lens Focal length (mm)
L1 -16.051
L2 -12.491
L3 7.847
L4 -11.709
L5 3.811
L6 -7.729

  FIG. 3A is a cross-sectional view of the imaging optical system 10B and the like of the second embodiment. The imaging optical system 10B includes a meniscus type first lens L1 having negative refractive power and convex toward the object side, a meniscus type second lens L2 having negative refractive power and convex toward the object side, and a positive A biconvex third lens L3 having refractive power, a meniscus fourth lens L4 having negative refractive power and convex toward the object side, and a biconvex fifth lens L5 having positive refractive power; A meniscus sixth lens L6 having negative refractive power and concave on the object side. The first, fourth, and fifth lenses L1, L4, and L5 have spherical surfaces as optical surfaces. The second, third, and sixth lenses L2, L3, and L6 have aspheric surfaces as optical surfaces. The fourth and fifth lenses L4 and L5 are cemented lenses joined by an adhesive. The first to sixth lenses L1 to L6 are all made of glass. A diaphragm (aperture diaphragm) ST is disposed between the third lens L3 and the fourth lens L4. A filter F1 having an appropriate thickness is disposed between the sixth lens L6 and the solid-state imaging element 51.

  3B to 3D show aberration diagrams (spherical aberration, astigmatism, and distortion aberration) of the imaging optical system 10B of Example 2. FIG.

Example 3
The overall specifications of the imaging optical system of Example 3 are shown below.
f = 3.57 (mm)
Fno = 1.60
2w = 170.00 (°)
ENTP = 4.28 (mm)
EXTP = -4.75 (mm)

Data on the lens surface of the imaging optical system of Example 3 is shown in Table 7 below.
[Table 7]
Surf. NR (mm) D (mm) Nd vd ED (mm)
1 250.000 0.700 1.6968 55.46 9.521
2 7.691 0.313 7.192
3 * 6.121 1.138 1.5891 61.25 7.006
4 * 2.639 1.893 5.155
5 * -1225.760 4.100 1.8208 42.71 4.942
6 * -5.664 2.556 4.909
ST INF 0.008 4.289
8 7.740 0.500 1.9459 17.98 4.266
9 3.923 0.100 4.054
10 4.338 2.334 1.7292 54.67 4.087
11 -6.144 1.820 3.932
12 * -11.504 2.000 1.6935 53.20 4.265
13 * -230.000 0.100 5.580
14 INF 0.300 1.5168 64.20 5.730
15 INF 1.690 5.778

The aspherical coefficients of the lens surfaces of Example 3 are shown in Table 8 below.
[Table 8]
Third side
K = 7.190465E-01, A4 = -1.049769E-03, A6 = -2.005107E-04,
A8 = 0.000000E + 00, A10 = 0.000000E + 00
4th page
K = -2.022474E + 00, A4 = 1.107115E-02, A6 = -6.137177E-04,
A8 = 0.000000E + 00, A10 = 0.000000E + 00
5th page
K = 0.000000E + 00, A4 = -2.903510E-03, A6 = -1.276619E-04,
A8 = 0.000000E + 00, A10 = 0.000000E + 00
6th page
K = 0.000000E + 00, A4 = -4.992387E-04, A6 = 1.483626E-05,
A8 = 0.000000E + 00, A10 = 0.000000E + 00
12th page
K = 0.000000E + 00, A4 = -7.969897E-03, A6 = 8.653563E-04,
A8 = -1.477482E-04, A10 = 0.000000E + 00
Side 13
K = 0.000000E + 00, A4 = -8.819385E-03, A6 = 2.070926E-04,
A8 = -1.757791E-05, A10 = 0.000000E + 00

The single lens data of Example 3 is shown in Table 9 below.
[Table 9]
Lens Focal length (mm)
L1 -11.401
L2 -8.962
L3 6.923
L4 -8.980
L5 3.848
L6 -17.527

  FIG. 4A is a cross-sectional view of the imaging optical system 10C and the like of the third embodiment. The imaging optical system 10C includes a meniscus type first lens L1 having negative refractive power and convex toward the object side, a meniscus type second lens L2 having negative refractive power and convex toward the object side, and a positive A meniscus third lens L3 having a refractive power and concave on the object side, a meniscus fourth lens L4 having a negative refractive power and convex on the object side, and a biconvex lens having a positive refractive power. A fifth lens L5 and a meniscus sixth lens L6 having negative refractive power and concave on the object side are provided. The first, fourth, and fifth lenses L1, L4, and L5 have spherical surfaces as optical surfaces. The second, third, and sixth lenses L2, L3, and L6 have aspheric surfaces as optical surfaces. The first to sixth lenses L1 to L6 are all made of glass. A diaphragm (aperture diaphragm) ST is disposed between the third lens L3 and the fourth lens L4. A filter F1 having an appropriate thickness is disposed between the sixth lens L6 and the solid-state imaging element 51.

  4B to 4D show aberration diagrams (spherical aberration, astigmatism, and distortion aberration) of the imaging optical system 10C of Example 3. FIG.

Example 4
The overall specifications of the imaging optical system of Example 4 are shown below.
f = 4.95 (mm)
Fno = 1.60
2w = 120.00 (°)
ENTP = 5.23 (mm)
EXTP = -6.06 (mm)

Data on the lens surface of the imaging optical system of Example 4 is shown in Table 10 below.
[Table 10]
Surf. NR (mm) D (mm) Nd vd ED (mm)
1 250.000 0.700 1.6180 63.39 9.516
2 10.075 0.200 7.676
3 * 5.609 2.200 1.7680 49.24 7.344
4 * 3.038 1.613 5.200
5 * -47.058 4.100 1.5920 67.02 5.045
6 * -5.242 0.753 5.020
ST INF 1.070 5.014
8 6.791 2.000 1.9459 17.98 5.140
9 3.801 0.010 1.5140 42.83 5.072
10 3.801 2.901 1.7292 54.67 5.079
11 -8.796 2.140 5.438
12 * -8.975 1.563 1.6935 53.20 5.481
13 * -230.000 0.100 6.732
14 INF 0.300 1.5168 64.20 6.833
15 INF 1.495 6.852

The aspherical coefficients of the lens surfaces of Example 4 are shown in Table 11 below.
[Table 11]
Third side
K = 2.017233E-01, A4 = -1.987446E-03, A6 = -1.209980E-04,
A8 = 0.000000E + 00, A10 = 0.000000E + 00
4th page
K = -8.159516E-01, A4 = -3.217344E-04, A6 = -3.401830E-04,
A8 = 1.939074E-05, A10 = 0.000000E + 00
5th page
K = 0.000000E + 00, A4 = -1.789504E-03, A6 = 0.000000E + 00,
A8 = 0.000000E + 00, A10 = 0.000000E + 00
6th page
K = 0.000000E + 00, A4 = -1.289295E-04, A6 = 0.000000E + 00,
A8 = 0.000000E + 00, A10 = 0.000000E + 00
12th page
K = 0.000000E + 00, A4 = -7.637974E-03, A6 = 3.137057E-04,
A8 = -4.227067E-05, A10 = 0.000000E + 00
Side 13
K = 0.000000E + 00, A4 = -7.966052E-03, A6 = 1.707259E-04,
A8 = -6.891223E-06, A10 = 0.000000E + 00

The single lens data of Example 4 is shown in Table 12 below.
[Table 12]
Lens Focal length (mm)
L1 -17.007
L2 -13.740
L3 9.613
L4 -13.528
L5 4.032
L6 -13.507

  FIG. 5A is a cross-sectional view of the imaging optical system 10D and the like of the fourth embodiment. The imaging optical system 10D includes a meniscus type first lens L1 having negative refractive power and convex toward the object side, a meniscus type second lens L2 having negative refractive power and convex toward the object side, and a positive A meniscus third lens L3 having a refractive power and concave on the object side, a meniscus fourth lens L4 having a negative refractive power and convex on the object side, and a biconvex lens having a positive refractive power. A fifth lens L5 and a meniscus sixth lens L6 having negative refractive power and concave on the object side are provided. The first, fourth, and fifth lenses L1, L4, and L5 have spherical surfaces as optical surfaces. The second, third, and sixth lenses L2, L3, and L6 have aspheric surfaces as optical surfaces. The fourth and fifth lenses L4 and L5 are cemented lenses joined by an adhesive. The first to sixth lenses L1 to L6 are all made of glass. A diaphragm (aperture diaphragm) ST is disposed between the third lens L3 and the fourth lens L4. A filter F1 having an appropriate thickness is disposed between the sixth lens L6 and the solid-state imaging element 51.

  5B to 5D show aberration diagrams (spherical aberration, astigmatism, and distortion aberration) of the imaging optical system 10D of Example 4. FIG.

(Example 5)
The overall specifications of the imaging optical system of Example 5 are shown below.
f = 4.93 (mm)
Fno = 1.60
2w = 120.00 (°)
ENTP = 5.15 (mm)
EXTP = -6.37 (mm)

Data on the lens surface of the imaging optical system of Example 5 is shown in Table 13 below.
[Table 13]
Surf. NR (mm) D (mm) Nd vd ED (mm)
1 250.000 0.700 1.5935 67.00 9.516
2 10.408 0.200 7.672
3 * 5.709 2.175 1.7680 49.24 7.326
4 * 2.975 1.649 5.135
5 * -45.619 4.100 1.5920 67.02 4.943
6 * -5.322 0.588 5.064
ST INF 1.270 5.039
8 6.538 2.000 1.9459 17.98 5.202
9 3.690 0.010 1.5140 42.83 5.070
10 3.690 2.973 1.7292 54.67 5.078
11 -8.884 1.957 5.405
12 * -9.459 1.850 1.7290 54.04 5.471
13 * -230.000 0.100 6.869
14 INF 0.300 1.5168 64.20 6.917
15 INF 1.516 6.927

The aspheric coefficients of the lens surfaces of Example 5 are shown in Table 14 below.
[Table 14]
Third side
K = 3.316209E-01, A4 = -2.113593E-03, A6 = -1.210219E-04,
A8 = 0.000000E + 00, A10 = 0.000000E + 00
4th page
K = -3.331985E-01, A4 = -2.956339E-03, A6 = -3.522070E-04,
A8 = 0.000000E + 00, A10 = 0.000000E + 00
5th page
K = 0.000000E + 00, A4 = -1.567304E-03, A6 = 0.000000E + 00,
A8 = 0.000000E + 00, A10 = 0.000000E + 00
6th page
K = 0.000000E + 00, A4 = -1.525632E-04, A6 = 0.000000E + 00,
A8 = 0.000000E + 00, A10 = 0.000000E + 00
12th page
K = 0.000000E + 00, A4 = -6.802468E-03, A6 = 2.121134E-04,
A8 = -3.608763E-05, A10 = 0.000000E + 00
Side 13
K = 0.000000E + 00, A4 = -6.768958E-03, A6 = 9.308062E-05,
A8 = -3.375939E-06, A10 = 0.000000E + 00

The single lens data of Example 5 is shown in Table 15 below.
[Table 15]
Lens Focal length (mm)
L1 -18.319
L2 -12.365
L3 9.805
L4 -13.592
L5 3.971
L6 -13.579

  FIG. 6A is a cross-sectional view of the imaging optical system 10E and the like according to the fifth embodiment. The imaging optical system 10E includes a meniscus type first lens L1 having negative refractive power and convex toward the object side, a meniscus type second lens L2 having negative refractive power and convex toward the object side, and a positive A meniscus third lens L3 having a refractive power and concave on the object side, a meniscus fourth lens L4 having a negative refractive power and convex on the object side, and a biconvex lens having a positive refractive power. A fifth lens L5 and a meniscus sixth lens L6 having negative refractive power and concave on the object side are provided. The first, fourth, and fifth lenses L1, L4, and L5 have spherical surfaces as optical surfaces. The second, third, and sixth lenses L2, L3, and L6 have aspheric surfaces as optical surfaces. The fourth and fifth lenses L4 and L5 are cemented lenses joined by an adhesive. The first to sixth lenses L1 to L6 are all made of glass. A diaphragm (aperture diaphragm) ST is disposed between the third lens L3 and the fourth lens L4. A filter F1 having an appropriate thickness is disposed between the sixth lens L6 and the solid-state imaging element 51.

  6B to 6D show aberration diagrams (spherical aberration, astigmatism, and distortion aberration) of the imaging optical system 10E of Example 5. FIG.

(Example 6)
The overall specifications of the imaging optical system of Example 6 are shown below.
f = 5.18 (mm)
Fno = 1.60
2w = 120.00 (°)
ENTP = 5.17 (mm)
EXTP = -5.86 (mm)

Data on the lens surface of the imaging optical system of Example 6 is shown in Table 16 below.
[Table 16]
Surf. NR (mm) D (mm) Nd vd ED (mm)
1 250.000 0.700 1.6180 63.39 9.525
2 8.344 0.200 7.511
3 * 5.500 1.794 1.7680 49.24 7.365
4 * 3.342 2.707 5.623
5 830.438 4.100 1.7292 54.67 5.381
6 -6.546 0.767 5.770
ST INF 0.318 5.605
8 6.881 2.000 1.9229 20.88 5.558
9 3.500 0.010 1.5140 42.83 4.942
10 3.500 2.919 1.6180 63.39 4.944
11 -8.045 2.294 5.049
12 * -11.810 1.646 1.7290 54.04 5.833
13 * -230.000 0.100 6.684
14 INF 0.300 1.5168 64.20 6.800
15 INF 1.758 6.832

Table 17 below shows the aspheric coefficients of the lens surfaces of Example 6.
[Table 17]
Third side
K = 4.813686E-01, A4 = -1.475065E-03, A6 = -2.003896E-04,
A8 = 0.000000E + 00, A10 = 0.000000E + 00
4th page
K = -2.362824E-01, A4 = 2.391717E-04, A6 = -3.831023E-04,
A8 = 0.000000E + 00, A10 = 0.000000E + 00
12th page
K = 0.000000E + 00, A4 = -4.221206E-03, A6 = 1.592116E-04,
A8 = 4.528629E-06, A10 = 0.000000E + 00
Side 13
K = 0.000000E + 00, A4 = -7.286229E-03, A6 = 2.157199E-04,
A8 = 0.000000E + 00, A10 = 0.000000E + 00

The single lens data of Example 6 is shown in Table 18 below.
[Table 18]
Lens Focal length (mm)
L1 -13.984
L2 -17.361
L3 8.925
L4 -10.778
L5 4.368
L6 -17.131

  FIG. 7A is a cross-sectional view of the imaging optical system 10F and the like of the sixth embodiment. The imaging optical system 10F includes a meniscus type first lens L1 having negative refractive power and convex toward the object side, a meniscus type second lens L2 having negative refractive power and convex toward the object side, and a positive A biconvex third lens L3 having refractive power, a meniscus fourth lens L4 having negative refractive power and convex toward the object side, and a biconvex fifth lens L5 having positive refractive power; A meniscus sixth lens L6 having negative refractive power and concave on the object side. The first, third to fifth lenses L1, L3 to L5 have spherical surfaces as optical surfaces. The second and sixth lenses L2 and L6 have aspheric surfaces as optical surfaces. The fourth and fifth lenses L4 and L5 are cemented lenses joined by an adhesive. The first to sixth lenses L1 to L6 are all made of glass. A diaphragm (aperture diaphragm) ST is disposed between the third lens L3 and the fourth lens L4. A filter F1 having an appropriate thickness is disposed between the sixth lens L6 and the solid-state imaging element 51.

  7B to 7D show aberration diagrams (spherical aberration, astigmatism, and distortion aberration) of the imaging optical system 10F according to Example 6. FIG.

(Example 7)
The overall specifications of the imaging optical system of Example 7 are shown below.
f = 5.05 (mm)
Fno = 1.60
2w = 120.00 (°)
ENTP = 4.88 (mm)
EXTP = -5.62 (mm)

Data on the lens surface of the imaging optical system of Example 7 is shown in Table 19 below.
[Table 19]
Surf. NR (mm) D (mm) Nd vd ED (mm)
1 250.000 0.700 1.5688 56.04 9.525
2 5.018 0.808 6.820
3 * 5.557 2.175 1.7680 49.24 6.713
4 * 4.231 1.907 5.330
5 234.381 4.100 1.7292 54.67 5.064
6 -6.485 0.413 5.608
ST INF 0.268 5.440
8 6.352 2.000 1.9459 17.98 5.386
9 3.500 0.010 1.5140 42.83 4.738
10 3.500 2.765 1.6180 63.39 4.740
11 -8.496 2.010 4.816
12 * -10.923 2.100 1.7680 49.24 5.432
13 * -230.000 0.100 6.609
14 INF 0.300 1.5168 64.20 6.726
15 INF 1.501 6.758

Table 20 below shows the aspheric coefficients of the lens surfaces of Example 7.
[Table 20]
Third side
K = 8.444764E-01, A4 = -2.614988E-03, A6 = -1.738652E-04,
A8 = -5.218844E-06, A10 = 0.000000E + 00
4th page
K = 1.217372E-01, A4 = -1.466915E-03, A6 = -3.640626E-04,
A8 = 1.384098E-05, A10 = 0.000000E + 00
12th page
K = 0.000000E + 00, A4 = -3.774998E-03, A6 = 3.237505E-04,
A8 = -3.419817E-05, A10 = 1.583963E-06
Side 13
K = 0.000000E + 00, A4 = -7.444015E-03, A6 = 3.210729E-04,
A8 = -1.166117E-05, A10 = 2.547001E-07

The single lens data of Example 7 is shown in Table 21 below.
[Table 21]
Lens Focal length (mm)
L1 -9.012
L2 -80.315
L3 8.717
L4 -12.503
L5 4.398
L6 -14.995

  FIG. 8A is a cross-sectional view of the imaging optical system 10G and the like according to the seventh embodiment. The imaging optical system 10G includes a meniscus type first lens L1 having negative refractive power and convex toward the object side, a meniscus type second lens L2 having negative refractive power and convex toward the object side, and a positive A biconvex third lens L3 having refractive power, a meniscus fourth lens L4 having negative refractive power and convex toward the object side, and a biconvex fifth lens L5 having positive refractive power; A meniscus sixth lens L6 having negative refractive power and concave on the object side. The first, third to fifth lenses L1, L3 to L5 have spherical surfaces as optical surfaces. The second and sixth lenses L2 and L6 have aspheric surfaces as optical surfaces. The fourth and fifth lenses L4 and L5 are cemented lenses joined by an adhesive. The first to sixth lenses L1 to L6 are all made of glass. A diaphragm (aperture diaphragm) ST is disposed between the third lens L3 and the fourth lens L4. A filter F1 having an appropriate thickness is disposed between the sixth lens L6 and the solid-state imaging element 51.

  8B to 8D show aberration diagrams (spherical aberration, astigmatism, and distortion aberration) of the imaging optical system 10G of Example 7. FIG.

(Example 8)
The overall specifications of the imaging optical system of Example 8 are shown below.
f = 5.07 (mm)
Fno = 1.60
2w = 120.00 (°)
ENTP = 5.19 (mm)
EXTP = -5.17 (mm)

Data on the lens surface of the imaging optical system of Example 8 is shown in Table 22 below.
[Table 22]
Surf. NR (mm) D (mm) Nd vd ED (mm)
1 250.000 0.700 1.6968 55.46 9.524
2 6.194 0.613 7.281
3 * 5.500 1.761 1.7680 49.24 7.178
4 * 4.442 2.271 6.119
5 138.522 4.100 1.6180 63.39 6.000
6 -6.605 1.425 5.807
ST INF 0.179 5.430
8 6.342 2.000 1.9459 17.98 5.429
9 3.500 0.010 1.5140 42.83 4.816
10 3.500 2.677 1.7292 54.67 4.818
11 -12.521 1.933 4.723
12 * -8.136 2.100 1.6935 53.20 5.050
13 * -230.000 0.100 6.366
14 INF 0.300 1.5168 64.20 6.550
15 INF 1.497 6.603

Table 23 below shows the aspheric coefficients of the lens surfaces of Example 8.
[Table 23]
Third side
K = 6.235838E-01, A4 = -2.071776E-03, A6 = -2.321987E-04,
A8 = 0.000000E + 00, A10 = 0.000000E + 00
4th page
K = -6.841718E-01, A4 = 2.395688E-04, A6 = -3.383195E-04,
A8 = 1.620589E-05, A10 = 0.000000E + 00
12th page
K = 0.000000E + 00, A4 = -3.846583E-03, A6 = 0.000000E + 00,
A8 = 0.000000E + 00, A10 = 0.000000E + 00
Side 13
K = 0.000000E + 00, A4 = -7.189751E-03, A6 = 1.702006E-04,
A8 = 0.000000E + 00, A10 = 0.000000E + 00

The single lens data of Example 8 is shown in Table 24 below.
[Table 24]
Lens Focal length (mm)
L1 -9.126
L2 -108.597
L3 10.313
L4 -12.549
L5 4.036
L6 -12.209

  FIG. 9A is a cross-sectional view of the imaging optical system 10H and the like according to the eighth embodiment. The imaging optical system 10H includes a meniscus type first lens L1 having negative refractive power and convex toward the object side, a meniscus type second lens L2 having negative refractive power and convex toward the object side, and a positive A biconvex third lens L3 having refractive power, a meniscus fourth lens L4 having negative refractive power and convex toward the object side, and a biconvex fifth lens L5 having positive refractive power; A meniscus sixth lens L6 having negative refractive power and concave on the object side. The first, third to fifth lenses L1, L3 to L5 have spherical surfaces as optical surfaces. The second and sixth lenses L2 and L6 have aspheric surfaces as optical surfaces. The fourth and fifth lenses L4 and L5 are cemented lenses joined by an adhesive. The first to sixth lenses L1 to L6 are all made of glass. A diaphragm (aperture diaphragm) ST is disposed between the third lens L3 and the fourth lens L4. A filter F1 having an appropriate thickness is disposed between the sixth lens L6 and the solid-state imaging element 51.

  FIGS. 9B to 9D show aberration diagrams (spherical aberration, astigmatism, and distortion aberration) of the imaging optical system 10H of Example 8. FIGS.

Example 9
The overall specifications of the imaging optical system of Example 9 are shown below.
f = 5.01 (mm)
Fno = 1.60
2w = 160.00 (°)
ENTP = 4.82 (mm)
EXTP = -4.89 (mm)

The data of the lens surface of the imaging optical system of Example 9 is shown in Table 25 below.
[Table 25]
Surf. NR (mm) D (mm) Nd vd ED (mm)
1 250.000 0.700 1.7292 54.67 9.526
2 6.976 0.435 7.165
3 * 5.500 2.200 1.7680 49.24 7.007
4 * 3.668 1.737 5.152
5 21.875 4.100 1.6968 55.46 4.756
6 -6.868 0.463 5.203
ST INF 0.191 5.102
8 6.821 2.000 1.9459 17.98 5.066
9 3.556 0.010 1.5140 42.83 4.601
10 3.556 2.665 1.7292 54.67 4.604
11 -8.551 1.679 4.693
12 * -7.398 2.050 1.7680 49.24 4.988
13 * -230.000 0.100 6.580
14 INF 0.300 1.5168 64.20 6.901
15 INF 1.495 6.984

Table 26 below shows the aspheric coefficients of the lens surfaces of Example 9.
[Table 26]
Third side
K = 6.507905E-01, A4 = -2.343577E-03, A6 = -2.230943E-04,
A8 = 0.000000E + 00, A10 = 0.000000E + 00
4th page
K = -3.111814E-01, A4 = -5.469224E-04, A6 = -4.670266E-04,
A8 = 2.277932E-05, A10 = 0.000000E + 00
12th page
K = 0.000000E + 00, A4 = -4.771348E-03, A6 = 1.349028E-04,
A8 = -9.672968E-06, A10 = 0.000000E + 00
Side 13
K = 0.000000E + 00, A4 = -7.175196E-03, A6 = 1.869686E-04,
A8 = -2.115236E-06, A10 = 0.000000E + 00

The single lens data of Example 9 is shown in Table 27 below.
[Table 27]
Lens Focal length (mm)
L1 -9.854
L2 -29.988
L3 7.968
L4 -11.182
L5 3.797
L6 -9.993

  FIG. 10A is a cross-sectional view of the imaging optical system 10I and the like according to the ninth embodiment. The imaging optical system 10I includes a meniscus type first lens L1 having negative refractive power and convex toward the object side, a meniscus type second lens L2 having negative refractive power and convex toward the object side, and a positive A biconvex third lens L3 having refractive power, a meniscus fourth lens L4 having negative refractive power and convex toward the object side, and a biconvex fifth lens L5 having positive refractive power; A meniscus sixth lens L6 having negative refractive power and concave on the object side. The first, third to fifth lenses L1, L3 to L5 have spherical surfaces as optical surfaces. The second and sixth lenses L2 and L6 have aspheric surfaces as optical surfaces. The fourth and fifth lenses L4 and L5 are cemented lenses joined by an adhesive. The first to sixth lenses L1 to L6 are all made of glass. A diaphragm (aperture diaphragm) ST is disposed between the third lens L3 and the fourth lens L4. A filter F1 having an appropriate thickness is disposed between the sixth lens L6 and the solid-state imaging element 51.

  FIGS. 10B to 10D show aberration diagrams (spherical aberration, astigmatism, and distortion aberration) of the imaging optical system 10I of Example 9. FIGS.

(Example 10)
The overall specifications of the imaging optical system of Example 10 are shown below.
f = 5.19 (mm)
Fno = 1.60
2w = 120.00 (°)
ENTP = 5.36 (mm)
EXTP = -4.84 (mm)

Data on the lens surface of the imaging optical system of Example 10 is shown in Table 28 below.
[Table 28]
Surf. NR (mm) D (mm) Nd vd ED (mm)
1 250.000 0.700 1.5891 61.25 9.497
2 10.073 0.200 7.625
3 * 5.500 2.200 1.7680 49.24 7.320
4 * 3.011 2.051 5.154
5 25.275 4.100 1.6968 55.46 4.820
6 -6.808 0.243 5.068
ST INF 0.000 5.006
8 6.799 2.000 1.9459 17.98 5.000
9 3.540 0.010 1.5140 42.83 4.559
10 3.540 2.696 1.6968 55.46 4.562
11 -7.893 1.762 4.741
12 * -8.194 1.834 1.7680 49.24 5.139
13 * -230.000 0.100 6.421
14 INF 0.300 1.5168 64.20 6.627
15 INF 1.477 6.681

Table 29 below shows the aspheric coefficients of the lens surfaces of Example 10.
[Table 29]
Third side
K = 5.069768E-01, A4 = -2.315056E-03, A6 = -1.674065E-04,
A8 = 0.000000E + 00, A10 = 0.000000E + 00
4th page
K = -2.548912E-01, A4 = -2.033487E-03, A6 = -4.422167E-04,
A8 = 0.000000E + 00, A10 = 0.000000E + 00
12th page
K = 0.000000E + 00, A4 = -6.354468E-03, A6 = 6.041170E-04,
A8 = -7.952514E-05, A10 = 3.961534E-06
Side 13
K = 0.000000E + 00, A4 = -8.577607E-03, A6 = 4.489956E-04,
A8 = -2.473129E-05, A10 = 7.184231E-07

The single lens data of Example 10 is shown in Table 30 below.
[Table 30]
Lens Focal length (mm)
L1 -17.834
L2 -14.068
L3 8.124
L4 -11.126
L5 3.883
L6 -11.103

  FIG. 11A is a cross-sectional view of the imaging optical system 10J and the like of the tenth embodiment. The imaging optical system 10J includes a meniscus type first lens L1 having negative refractive power and convex toward the object side, a meniscus type second lens L2 having negative refractive power and convex toward the object side, and a positive A biconvex third lens L3 having refractive power, a meniscus fourth lens L4 having negative refractive power and convex toward the object side, and a biconvex fifth lens L5 having positive refractive power; A meniscus sixth lens L6 having negative refractive power and concave on the object side. The first, third to fifth lenses L1, L3 to L5 have spherical surfaces as optical surfaces. The second and sixth lenses L2 and L6 have aspheric surfaces as optical surfaces. The fourth and fifth lenses L4 and L5 are cemented lenses joined by an adhesive. The first to sixth lenses L1 to L6 are all made of glass. A diaphragm (aperture diaphragm) ST is disposed between the third lens L3 and the fourth lens L4. A filter F1 having an appropriate thickness is disposed between the sixth lens L6 and the solid-state imaging element 51.

  11B to 11D show aberration diagrams (spherical aberration, astigmatism, and distortion aberration) of the imaging optical system 10J of Example 10. FIG.

Table 31 below summarizes the values of Examples 1 to 10 corresponding to the conditional expressions (1) to (8) for reference.
[Table 31]

  As described above, the imaging optical system and the like have been described according to the embodiment. However, the imaging optical system according to the present invention is not limited to the above-described embodiment or example, and various modifications can be made.

  Moreover, in the said Example, the filter F1 divides | segments the filter F1 into two sheets, and each has another role at the time of imaging with visible light or near-infrared light in uses, such as a vehicle-mounted camera and a surveillance camera. It is also possible to take the configuration as described above.

AX: optical axis, F1: filter, I: imaging surface, L1 to L6: lens, OP: aperture, 10, 10A to 10J: imaging optical system, 30: camera module, 40: lens unit, 41: lens barrel, 50 DESCRIPTION OF SYMBOLS Sensor part 51 ... Image pick-up element 53 ... Sensor holder 60 ... Processing part 61 ... Element drive part 62 ... Input part 63 ... Memory | storage part 64 ... Display part 68 ... Control part 100 ... Imaging device

Claims (15)

From the object side,
A first lens having negative refractive power;
A second lens having negative refractive power;
A third lens having positive refractive power;
Aperture,
A fourth lens having negative refractive power;
A fifth lens having positive refractive power;
A sixth lens;
Essentially
The object side surface of the second lens has a convex surface shape,
The object side surface of the sixth lens has a concave surface shape;
An optical system characterized by satisfying the following conditional expression.
40 ≦ νd3 (1)
here,
νd3: Abbe number of the third lens The optical system according to claim 1, wherein the following conditional expression is satisfied.
1.5 <f123 / f456 (2)
here,
f123: Composite focal length from the first lens to the third lens f456: Composite focal length from the fourth lens to the sixth lens The optical system according to claim 1, wherein the following conditional expression is satisfied.
4.5 <f123 / f (3)
here,
f123: composite focal length from the first lens to the third lens f: focal length of the entire system The optical system according to any one of claims 1 to 3, wherein the following conditional expression is satisfied.
3.5 <L / f <5.5 (4)
here,
L: Total length of the entire system f: Focal length of the entire system The optical system according to any one of claims 1 to 4, wherein the following conditional expression is satisfied.
f2 / f <−2.5 (5)
here,
f2: focal length of the second lens f: focal length of the entire system   The optical system according to claim 1, wherein the sixth lens has a negative refractive power. The optical system according to any one of claims 1 to 6, wherein the following conditional expression is satisfied.
54 ≦ νd1 (6)
here,
νd1: Abbe number of the first lens The optical system according to any one of claims 1 to 7, wherein the following conditional expression is satisfied.
35 ≦ νd6 (7)
here,
νd6: Abbe number of the sixth lens The optical system according to claim 1, wherein the following conditional expression is satisfied.
35 <νd5-νd4 (8)
here,
νd4: Abbe number of the fourth lens νd5: Abbe number of the fifth lens   The optical system according to any one of claims 1 to 9, wherein the first lens has a spherical shape. At least one of the second and third lenses has an aspherical shape;
The optical system according to claim 10, wherein at least one of the fourth, fifth, and sixth lenses has an aspherical shape.   The optical system according to claim 10, wherein the first lens is a glass lens.   The optical system according to claim 12, wherein the second, third, fourth, fifth, and sixth lenses are glass lenses. An optical system according to any one of claims 1 to 13,
A lens barrel holding the optical system;
A lens unit comprising: An optical system according to any one of claims 1 to 13,
An image sensor for detecting an image obtained from the optical system;
An imaging apparatus comprising:

Images