Imaging optical system, imaging device, and mobile body

Abstract

To provide an image capturing optical system capable of suppressing the change in optical performance before and after a temperature change.SOLUTION: An image capturing optical system of the present invention is configured to form an object image on an image sensor, and satisfies the following conditional expressions: 30<W ...(1), 0.9<|gi / g0|<1.1 ...(2), where W represents a half view angel, Wi represents an arbitrary view angle within the half view angle W, gi represents an exit pupil distance at the view angle Wi, and g0 represents an exit pupil distance on an optical axis.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to an imaging optical system , pick up an imaging device, and a moving body.

Background Art

[0002] In an imaging optical system mounted on an imaging device such as a digital camera or a video camera, generally in addition to high resolution and low distortion, in order to enable good imaging recognition even in a dark environment such as at night, various conditions are required, such as a small F-number and a large aperture, and being small in size. Among such imaging optical systems, in particular, an imaging optical system used for so-called sensing such as in-vehicle use or surveillance use is often used outdoors, and is used in a harsh environment where the temperature change is large or where repeated temperature changes occur. In an imaging optical system used for sensing, it is required that the fluctuation of the optical performance is small even due to such changes in the surrounding environment. Further, for example, in a lens unit, due to a change in the temperature environment, the lenses constituting the lens unit may be displaced in a direction perpendicular to the optical axis, and the relative positional relationship of the lenses may change (hereinafter referred to as lens decentration). This lens decentration causes a deviation in the imaging position of light rays across the entire imaging surface. In an imaging optical system used for sensing, in addition to maintaining the resolution during temperature fluctuations, in order to suppress such lens decentration and accurately acquire the size and shape of an object to be sensed, it is required to maintain the imaging position of the target object before and after the temperature change (suppress the change in the imaging position in the direction perpendicular to the optical axis).

Summary of the Invention

Problems to be Solved by the Invention

[0003] The present invention has been made in view of the above problems, and an object thereof is to provide an imaging optical system that suppresses changes in optical performance before and after a temperature change.

Means for Solving the Problems

[0004] In order to solve the above-described problems, an imaging optical system according to the present invention is an imaging optical system that forms a subject image on an imaging element. The imaging optical system includes, in order from the object side, a first lens having a meniscus shape with a negative refractive power, a second lens having a meniscus shape with a negative refractive power, a third lens having a positive refractive power, and a fourth lens and a fifth lens which are cemented lenses formed by cementing a lens having a positive refractive power and a lens having a negative refractive power integrally, and a sixth lens which is disposed on the image plane side most among the lenses constituting the imaging optical system and has a positive refractive power , held in a lens barrel with their optical axes aligned When the semi-field angle is W, any field angle within the semi-field angle W is Wi, the exit pupil distance at the field angle Wi is gi, and the exit pupil distance on the optical axis is g0, 55≦ W ··· (1) 0.9 < |gi / g0| < 1.1 ··· (2) satisfies the conditional expression, and at least one of the first lens and the second lens has a relative refractive index temperature coefficient dn / dt in air at 0°C to 20°C with respect to light in the wavelength range of 580 nm to 640 nm, when -6 <dn / dt ··· (3) is satisfied, and the lens disposed closest to the image plane Sixth has -5.7×10 -6 >dn / dt ··· (4) satisfied.

Effect of the Invention

[0005] According to the present invention, it is possible to provide an imaging optical system that suppresses changes in optical performance before and after a temperature change.

Brief Description of the Drawings

[0006]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Embodiments for Carrying Out the Invention

[0007] As an example of the imaging device of the present invention, the digital camera 100 is illustrated in FIGS. 1 and 2. FIG. 1 schematically shows the appearance of the digital camera 100 as viewed from the front side, which is the object side, i.e., the subject side. Similarly, FIG. 2 schematically shows the appearance of the digital camera 100 as viewed from the back side, which is the shooting side.

[0008] The digital camera 100 is a digital camera in the present embodiment, but may also be a camera device for sensing applications such as a surveillance camera, a process monitoring camera for a manufacturing line, an in-vehicle camera, or a stereo camera device.

[0009] The digital camera 100 includes a housing 5 that is a camera body, an imaging optical system 1 composed of a plurality of lenses, an optical viewfinder 2, an electronic flash type strobe 3, a shutter button 4, a power switch 6, a liquid crystal monitor 7, operation buttons 8, and a memory card slot 9. As shown in FIG. 3, the digital camera 100 also has, inside the housing 5, a CPU 11 which is a central processing unit of the control unit, an image processing unit 12, a light receiving element 13, a signal processing unit 14, a semiconductor memory 15, and a communication card 16.

[0010] The digital camera 100 has an imaging optical system 1 and a light receiving element 13 configured as an image sensor using a CMOS (Complementary Metal Oxide Semiconductor) image sensor or a CCD (Charge Coupled Device) image sensor, etc., and reads the subject optical image formed by the imaging optical system 1 with the light receiving element 13 which is an image sensor.

[0011] The subject optical image read by the light receiving element 13 is appropriately processed by the signal processing unit 14 controlled by the CPU 11 and converted into digital image information. Further, predetermined image processing is performed by the image processing unit 12 and stored in the semiconductor memory 15 as a storage unit such as a non-volatile memory. As another example of a storage unit or storage medium for storing such an image, in addition to storing it in the semiconductor memory 15, it may be transmitted to an external information processing terminal using the communication card 16, or a memory card inserted into the memory card slot 9 may be used.

[0012] The liquid crystal monitor 7 can display not only the photographed image data but also the image data stored in the semiconductor memory 15. Also, setting changes for image processing by the operation buttons 8 are also displayed on such a liquid crystal monitor 7. In this embodiment, the liquid crystal monitor 7 is used as a display device, but the configuration is not limited thereto, and an organic EL display or other display devices may be used.

[0013] The imaging optical system 1 is composed of a plurality of lenses that form the imaging optical system as described later. The lens on the frontmost (object side) is covered by a lens barrier provided in the housing 5 when the digital camera 100 is carried. In this embodiment, when the operator operates the power switch 6 to turn on the power, the lens barrier opens and the object surface of the lens on the object side of the imaging optical system 1 is exposed from the housing 5.

[0014] The semiconductor memory 15 and the communication card 16 are loaded and used in a dedicated or general-purpose slot such as the memory card slot 9.

[0015] The imaging optical system 1 of the digital camera 100 will be described. The imaging optical system 1 used in the digital camera 100 is an optical system similar to the so-called retrofocus type in this embodiment.

[0016] In a retrofocus type imaging optical system, a lens group with negative power is arranged in the front group on the object side, and a lens group with positive power is arranged in the rear group on the image side. Both the front group and the rear group have the effect of separating the exit pupil from the image plane. Also, a space is secured to arrange filters such as an optical low-pass filter and an infrared cut filter between the imaging element, aiming to achieve optical performance suitable for sensing applications.

[0017] In this embodiment, as shown in FIG. 4, the imaging optical system 1 sequentially includes a first lens L1 having a meniscus shape with negative refractive power, a second lens L2 having a meniscus shape with negative refractive power, a third lens L3 having positive refractive power, a fourth lens L4 having positive refractive power, a fifth lens L5 having negative refractive power, a cemented lens L45 formed by cementing the fourth and fifth lenses, and a sixth lens L6 having positive refractive power. In the array configuration of the imaging optical system 1, an aperture stop S is disposed between the third lens L3 and the cemented lens L45, and a glass filter F1 such as an infrared cut filter and a low-pass filter is disposed on the image plane side of the sixth lens L6. Further, a cover glass CG is disposed on the image plane side thereof. Also, on the most image plane side is, as a matter of course, the light receiving surface IMG of the light receiving element 13. The imaging optical system 1 is an imaging optical system that forms a subject image on the light receiving surface IMG of the light receiving element 13 with such a configuration.

[0018] The first lens L1 is a meniscus lens having a concave surface on the image plane side. With such a first lens L1, while maintaining a negative refractive power, it is possible to adjust the distortion aberration. Also, in order to secure a wide angle of view and a back focus of the imaging optical system 1, a certain amount of large negative refractive power is required for the first lens L1 in order to bend an off-axis chief ray over a wide range of angles of view.

[0019] However, generally, as the refractive power of the lens becomes stronger, as a result, the sensitivity to the optical axis deviation due to the decentration of the lens tends to increase. By adjusting the distortion aberration in the first lens L1, it is possible to adjust the occurrence of the distortion aberration of each lens constituting the imaging optical system 1, and it is possible to reduce the sensitivity of the optical axis deviation distribution due to the decentration of the lens. It is known that such adjustment of the distortion aberration is effective by adjusting the angle at which the off-axis chief ray enters the lens surface, but it is difficult to provide the negative refractive power as described above. Therefore, in the first lens L1, while maintaining a certain amount of negative refractive power, the imaging position deviation of the light rays is minimized by a meniscus shape having a convex surface on the object side so that the imaging position deviation of the light rays is minimized over the entire imaging surface.

[0020] The second lens L2 is a meniscus lens having a concave surface on the object side.

[0021] The third lens L3 is a biconvex lens having a positive refractive power, and corrects the spherical aberration generated in the first lens L1.

[0022] The fourth lens L4 and the fifth lens L5 are joined to form an integral joined lens L45. The joined lens L45 is effective in suppressing chromatic aberration and controlling higher-order aberrations. Also, when the fourth lens L4 and the fifth lens L5 are joined, even when the decentration sensitivity in each individual lens is high, the arrangement error can be suppressed, which contributes to an improvement in the accuracy during assembly.

[0023] The sixth lens L6 is a lens having at least one aspherical lens surface. While correcting various aberrations such as distortion, spherical aberration, field curvature, and coma, the overall lens length is made shorter than that of an imaging optical system composed only of spherical lenses, and the refractive power of the final lens is prevented from becoming extremely strong.

[0024] In the imaging optical system 1, by using an aspherical surface on either the object side or the image side surface of either the first lens L1 or the second lens L2, while maintaining a wide angle of view and good imaging performance, the displacement of the light ray position within the imaging plane during lens decentration is reduced. In this way, by limiting the number of aspherical lenses, imaging performance can be ensured without relying on expensive aspherical lenses, which contributes to cost reduction.

[0025] Also, in the imaging optical system 1, when the semi-field angle is W, an arbitrary field angle Wi within the semi-field angle W, the exit pupil distance gi at the field angle Wi, and the exit pupil distance g0 on the optical axis, the following conditional expressions (1) and (2) are satisfied.

[0026]

Equation

[0027]

Equation

[0028] Such conditional expression (1) means that it is used in a wide-angle lens whose half field angle of the imaging optical system 1 is larger than 30°. Also, by restricting the ratio of the exit pupil distance within the field angle to be greater than 0.9 and less than 1.1 in the imaging plane, the image height shift in the imaging plane due to the change in the environmental temperature can be suppressed by conditional expression (2).

[0029] The exit pupil distance is the distance between the intersection of the incident light ray on the image plane and the optical axis and the intersection of the image plane and the optical axis. When the ratio of the exit pupil distance is too large within the field angle, the amount of change in the optical axis deviation in the image plane will be large and a difference will occur when the lens is decentered. In this case, even if the power of each lens is sufficiently suppressed, it is difficult to sufficiently satisfy the performance of the optical axis deviation. Therefore, in the present invention, the imaging optical system 1 using a wide-angle lens that satisfies conditional expression (1) also satisfies conditional expression (2) and is provided such that the ratio of the exit pupil distance falls within a predetermined range within the field angle. With such a configuration, the image height shift in the imaging plane caused by the change in the environmental temperature can be suppressed.

[0030] In order to ensure a wide field angle and a back focus, it is necessary to give the lens on the object side, such as the first lens L1 or the second lens L2, the action of bending the off-axis chief ray. Therefore, in the present embodiment, meniscus lenses having a negative refractive power are arranged in the first lens L1 and the second lens L2, and in order to further increase the refractive power, any one of the surfaces of the first lens L1 and the second lens L2 has an aspherical shape. With such a configuration, the imaging optical system 1 maintains a wide field angle as shown in conditional expression (1).

[0031] Now, as already described, in a lens with a relatively large refractive power, the sensitivity of the optical axis deviation due to the decentering of the lens tends to be high. That is, it is known that the deviation of the focal position caused by the change in the environmental temperature tends to be large. This is caused not only by changes in the optical path length due to thermal expansion or the like caused by temperature changes, or so-called shifts and tilts due to thermal expansion of the lens mounting portion, but also by changes in the refractive index of the optical material. Therefore, in the present embodiment, for at least one of the first lens L1, the second lens L2, and the sixth lens L6, which have relatively large refractive powers among the plurality of lenses constituting the imaging optical system 1, the following conditional expression (3) is satisfied. Note that the relative refractive index temperature coefficient dn / dt in air at 0°C to 20°C with respect to light having a wavelength λ in the wavelength range of 580 nm to 640 nm was used.

[0032]

Equation

[0033] Further, in the present embodiment, for at least one of the first lens L1, the second lens L2, and the sixth lens L6, which have relatively large refractive powers among the plurality of lenses constituting the imaging optical system 1, the following conditional expression (4) is satisfied.

[0034]

Equation

[0035] The conditional expression (3) and the conditional expression (4) will be described. When the temperature rises in a lens having a positive refractive power and the relative refractive index temperature coefficient is positive, the focal position shifts to the negative side. Similarly, when the relative refractive index temperature coefficient is negative, the focal position shifts to the positive side. When the temperature rises in a lens having a negative refractive power, conversely, when the relative refractive index temperature coefficient is positive, the focal position shifts to the positive side. Similarly, when the relative refractive index temperature coefficient is negative, the focal position shifts to the negative side.

[0036] Thus, if a negative lens having a relatively large refractive power has a positive relative refractive index temperature coefficient that satisfies the conditional expression (3), the focal position shifts to the positive side due to a temperature change.

[0037] Also, if a positive lens having a relatively large refractive power has a negative relative refractive index temperature coefficient that satisfies the conditional expression (4), the focal position shifts to the positive side due to a temperature change.

[0038] Thus, by having at least one lens formed of a glass material that satisfies the conditional expression (3) and at least one lens formed of a glass material that satisfies the conditional expression (4), the imaging optical system 1 can suppress fluctuations in the focal position during a temperature change. Note that, in practice, it is more preferable to configure such a structure to correct a shift in the focal position caused by a change in the air gap (surface interval) due to thermal expansion between the lens barrel 20 and each lens that occurs due to a temperature change, as will be described later. Therefore, in the present embodiment, particularly, a shift in the focus position caused by the material constituting the lens is suppressed by a pair of lenses that satisfy the conditional expressions (3) and (4), respectively, during a temperature change.

[0039] Now, fluctuations in the focal position of such a lens may naturally occur also due to the mounting accuracy during manufacturing and the physical position fluctuations (lens decentration) of the lens due to thermal expansion. Therefore, in the present embodiment, with respect to the first lens L1, in order to suppress fluctuations in the position during lens decentration, as shown in FIG. 5, it is held by the lens barrel 20, which is a support structure, and the retainer ring 23. Note that, in the present embodiment, the lens barrel 20 is configured to attach and fix the first lens L1 between the separately attachable retainer ring 23, but is not limited to such a configuration. Also, in the present embodiment, the lens barrel 20 and the retainer ring 23 function as a "support structure" for supporting the lenses of the imaging optical system 1.

[0040] As shown in FIG. 5, the first lens L1 has a first side surface L1a on the outer peripheral side surface extending in the optical axis direction of the lens, where the lens side surface portion has a stepped structure and does not contact the inner wall surface 21 of the lens barrel 20, and a second side surface L1b that contacts the inner wall surface 21 of the lens barrel 20. Furthermore, the second side surface L1b of the first lens L1 is provided to be smaller than the diameter of the first side surface L1a.

[0041] The second side surface L1b is mounted in the internal space of the lens barrel 20 and positions and holds the lens in the radial direction. In other words, the first lens L1 has a protruding portion protruding from the side surface that abuts and is positioned against the lens barrel 20, and a gap portion 22 is provided so that the side surface on the outer peripheral side of the protruding portion does not contact the lens barrel 20 and the pressing ring 23.

[0042] On the object surface side of the first lens L1, it is necessary to ensure a large diameter in order to secure a sufficient optical effective diameter and optical outer diameter required to obtain a wide-angle field of view. On the other hand, if the first lens L1 is positioned at a large diameter position, when there is a slight difference in mounting accuracy or when the lens tilts from a plane perpendicular to the optical axis direction of the lens, there will also be a problem that the lens eccentricity will increase.

[0043] Therefore, in the present embodiment, a second side surface L1b having a smaller diameter than the first side surface L1a is provided, and positioning is performed by contacting the inner wall surface 21 of the lens barrel 20 at such a second side surface L1b. At this time, since the first side surface L1a is shaped so as not to be mounted in the internal space of the lens barrel 20, the lens side surface L1a is not pushed by the inner wall surface 21 of the lens barrel 20. Furthermore, when the first lens L1 is mounted, the second side surface L1b of the first lens L1 is inserted along the optical axis direction so as to be mounted in the internal space of the lens barrel 20 and fixed in a manner of being pressed from the front by the pressing ring 23, so it is easy to ensure the accuracy during assembly. In this way, since the diameter φ1b of the second side surface L1b whose positioning in the radial direction of the lens is held is made smaller than the diameter φ1a of the first side surface L1a, lens shift can be suppressed as compared with the case where positioning is held by the first side surface without having the second side surface. That is, in the present embodiment, when the diameter φb of the second side surface Lb and the diameter φa of the first side surface La, which are positioned and held in the radial direction of the lens L, are set respectively, the lens satisfies the conditional expression (5).

[0044]

Equation

[0045] When the temperature changes, the lens is pushed against the inner wall surface 21 of the lens barrel 20, which is a support structure, and thus lens shift occurs. The amount of lens shift is proportional to the outer diameter of the lens side surface that contacts the support structure and the difference in the linear expansion coefficients of the support structure and the lens. Therefore, it is effective in suppressing lens shift to reduce the outer diameter size of the lens side surface that contacts the support structure so as to satisfy the conditional expression (5).

[0046] In addition, since there is a gap 22 between the first side surface L1a that is not mounted in the internal space of the support structure and the internal space of the retainer ring that presses and supports the lens, the first side surface L1a is prevented from being pushed by the inner wall 23a of the retainer ring 23, and further lens shift can be suppressed.

[0047] In addition, in the present embodiment, on the outer side of the object-side optical surface having the larger optical surface among the object-side optical surface and the image-side optical surface of the first lens L1, there is a flat portion L1c extending in a direction perpendicular to the optical axis, and the contact position Q of the retainer ring 23 on the flat portion L1c is farther from the optical axis than the second side surface L1b of the stepped lens. With such a configuration, it is possible to achieve both ensuring the light ray region necessary for wide-angle conversion and suppressing lens shift.

[0048] Hereinafter, as a specific numerical example 1 of such an imaging optical system 1, the optical performance of each lens is shown in Table 1. In each of the following embodiments, the parallel flat plate disposed on the image plane side is assumed to be various filters F1 such as an optical low-pass filter and an infrared cut filter, or a cover glass (sealing glass) CG of a light receiving element 13 such as a CCD sensor. The meanings of the common symbols in each embodiment are as follows. f: Focal length of the entire system f Li : Focal length of the i-th lens g0: Exit pupil position on the optical axis g w / 2 : Exit pupil position at half field angle W / 2 g w : Exit pupil position at field angle W Fno: F-number L: Overall optical length W: Half field angle (degrees) R: Radius of curvature D: Spacing between surfaces Nd: Refractive index νd: Abbe number

[0049]

Table 1

[0050] Also, for the aspherical lens, the aspherical coefficients were set as shown in Table 2 using the known formula (Equation 6).

[0051]

Equation

[0052] However, for the aspherical shape, x is the optical axis with the direction of light propagation being positive, and y is the direction perpendicular to the optical axis. Also, E: Effective diameter of the lens R: Paraxial radius of curvature K: Conic coefficient, A4, A6, A8, A10, A 12 、A 14 are the aspherical coefficients of the 4th, 6th, 8th, 10th, 12th, and 14th orders, respectively.

[0053]

Table 2

[0054] Next, Table 3 shows the parameters indicating the respective optical performances of the F-number, half field angle, overall length, and focal length of the imaging optical system 1, and Table 4 shows the calculation results (conditional formula numerical values) of the conditional formulas regarding the focal length.

[0055]

Table 3

[0056]

Table 4

[0057]

Table 5

[0058] As shown in Table 5, in Numerical Example 1, when the half field angle is W, any field angle Wi within the half field angle W, the exit pupil distance gi at the field angle Wi, and the exit pupil distance g0 on the optical axis, Conditional Formulas (1) and (2) are satisfied. With such a configuration, the imaging optical system 1 can sufficiently suppress the change in optical performance before and after the temperature change.

[0059] The aberration diagrams of spherical aberration, astigmatism, distortion, and coma for an infinite object in Numerical Example 1 are shown in FIG. 8. In FIG. 7, d indicates the respective aberrations at the d-line (wavelength λ = 587.6 nm), and g indicates the respective aberrations at the g-line (wavelength λ = 435.8 nm). In the astigmatism diagram, the solid line indicates the sagittal aberration, and the dashed line indicates the meridional aberration. As is apparent from FIG. 7, the aberration of Numerical Example 1 is corrected at a high level, and the spherical aberration and the axial chromatic aberration are so small as not to cause problems. The astigmatism, field curvature, and lateral chromatic aberration are also sufficiently small, the coma aberration and its chromatic aberration disturbance are well suppressed up to the outermost periphery, and the distortion aberration is also less than 2.0% in absolute value.

[0060] FIG. 8 shows the optical axis deviation when each lens group is decentered by 1 μm. In the figure, "SUM_A" is the value obtained by summing the absolute values of the optical axis deviation amounts when each of the first to sixth lenses is decentered by 1 μm, and means the optical axis deviation of the entire lens unit (the entire imaging optical system 1) when each lens group moves in a direction that intensifies the optical axis deviation. Also, "SUM_A / Y'" indicates the ratio of the axial deviation distribution of the entire lens unit with respect to the maximum image height. In Numerical Example 1, even when each lens group moves in a direction that intensifies the optical axis deviation, as shown by "SUM_A / Y'" in FIG. 8, the optical axis deviation of the entire lens unit is 0.06% with respect to the maximum image height Y', and the sensitivity of the optical axis deviation is sufficiently suppressed.

[0061] Also, in the present embodiment, as shown in Table 1, for the relative refractive index temperature coefficient: dn / dt, it has the first lens L1 and the second lens L2 that satisfy the conditional expression (3). Furthermore, it has the sixth lens L6 that satisfies the conditional expression (4). With such a configuration, since the focal position at the time of temperature change is displaced in a direction where the conditional expression (3) and the conditional expression (4) suppress each other, the imaging optical system 1 can sufficiently suppress the change in optical performance before and after the temperature change.

[0062] Also, in the present embodiment, the imaging optical system 1 has the first lens L1 located on the most object side and the second lens L2 located second from the object side, and at least one of the surfaces of the first lens L1 and the second lens L2 on the object side or the image side is an aspherical lens with an aspherical shape. With such a configuration, it is possible to perform sufficient wide-angle conversion and aberration correction with an imaging optical system of six lenses while limiting the number of expensive aspherical lenses.

[0063] In this embodiment, there are also a lens barrel 20 which is a support structure for holding lenses with the optical axes of a plurality of lenses substantially aligned, a pressing ring 23 for pressing and supporting the first lens L1, and a spacer ring 24 which is disposed between the lenses to support the lenses and adjust the surface interval. In addition, the first lens L1 is a stepped glass lens having a first side surface L1a that does not contact the inner wall surface 21 of the lens barrel 20 on the outer peripheral side surface extending in the optical axis direction of the lens, and a second side surface L1b that has a diameter smaller than that of the first side surface L1a and contacts the inner wall surface 21 of the lens barrel 20. That is, "at least one of the lenses of the imaging optical system 1 is a stepped glass lens having a first side surface that does not contact the support structure on the outer peripheral side surface extending in the optical axis direction of the lens, and a second side surface that has a diameter smaller than that of the first side surface and contacts the support structure". With such a configuration, the outer diameter size of the lens side surface in contact with the support structure can be reduced, and lens shift can be suppressed.

[0064] Furthermore, in the first lens L1 of this embodiment, when the diameter of the first side surface L1a is φa and the diameter of the second side surface L1b is φb, the conditional expression (5) is satisfied. With such a configuration, even if the surface on the object side has a larger diameter, the lens shift can be reduced by making the second side surface for positioning smaller, so that it is possible to secure the light ray region necessary for wide-angleization and suppress the lens shift at the same time.

[0065] As a second numerical example of the present invention, the imaging optical system 1 in FIG. 9 will be described. Also in Numerical Example 2, similar to Numerical Example 1, the first lens L1 is a meniscus lens convex on the object side, the second lens L2 is a meniscus lens concave on the object side, the third lens L3 is a convex lens having a positive refractive power, a cemented lens L45 in which the fourth lens L4 and the fifth lens L5 are cemented, and a sixth lens L6 having a positive refractive power. In Numerical Example 2, as shown in Tables 6 and 7, the object side surface and the image side surface of the second lens L2 are aspherical surfaces.

[0066]

Table 6

[0067] Also, in the aspherical lens, the aspherical coefficients were set as shown in Table 7 using the same known formula (Equation 6) as in Numerical Example 1. However, for the aspherical shape, x is the optical axis with the direction of light propagation being positive, and y is the direction orthogonal to the optical axis. Also, E: Effective diameter of the lens R: Paraxial radius of curvature K: Conic coefficient, A4, A6, A8, A10, A 12 , A 14 are the aspherical coefficients of the 4th, 6th, 8th, 10th, 12th, and 14th orders, respectively.

[0068]

Table 7

[0069] Next, Table 8 shows the parameters indicating the respective optical performances of the F-number, half field angle, overall length, and focal length of the imaging optical system 1, and Table 9 shows the calculation results (conditional formula values) of the conditional formulas related to the focal length.

[0070]

Table 8

[0071]

Table 9

[0072]

Table 10

[0073] As shown in Table 10, Numerical Example 2 satisfies Conditional Expression (1) and Conditional Expression (2) when the semi-angle: W, any angle within the semi-angle W: Wi, the exit pupil distance at the angle Wi: gi, and the exit pupil distance on the optical axis: g0 are set as such. With such a configuration, the imaging optical system 1 can sufficiently suppress changes in optical performance before and after a temperature change.

[0074] Aberration diagrams of spherical aberration, astigmatism, distortion, and coma for an infinite object in Numerical Example 2 are shown in FIG. 10. In FIG. 10, d indicates the respective aberrations at the d-line (wavelength λ = 587.6 nm), and g indicates the respective aberrations at the g-line (wavelength λ = 435.8 nm). In the astigmatism diagram, the solid line indicates the sagittal aberration, and the dashed line indicates the meridional aberration. As is clear from FIG. 10, the aberrations of Numerical Example 2 are corrected at a high level, and the spherical aberration and axial chromatic aberration are so small as not to be a problem. The astigmatism, field curvature, and lateral chromatic aberration are also sufficiently small, the coma and its chromatic aberration disturbance are well suppressed up to the outermost periphery, and the distortion is also less than 2.0% in absolute value.

[0075] FIG. 11 shows the optical axis deviation when each lens group is decentered by 1 μm. Also, since "SUM_A" and "SUM_A / Y'" in the figure are the same as those in Numerical Example 1, the description thereof is omitted. Even in Numerical Example 2, when each lens group moves in a direction that intensifies the optical axis deviation, as shown by "SUM_A / Y'" in FIG. 11, the optical axis deviation of the entire lens unit system is 0.07% with respect to the maximum image height Y', and the sensitivity of the optical axis deviation is sufficiently suppressed.

[0076] Also, in the present embodiment, as shown in Table 1, for the relative refractive index temperature coefficient: dn / dt, it has a second lens L2 that satisfies Conditional Expression (3). Furthermore, it has a sixth lens L6 that satisfies Conditional Expression (4). With such a configuration, since the focal position at the time of temperature change is displaced in a direction where they mutually suppress each other by Conditional Expression (3) and Conditional Expression (4), the imaging optical system 1 can sufficiently suppress changes in optical performance before and after a temperature change.

[0077] In addition, in the present embodiment, the imaging optical system 1 includes a first lens L1 located closest to the object side and a second lens L2 located second from the object side, and at least one of the object-side surface and the image-side surface of the second lens L2 is an aspherical lens with an aspherical shape. With such a configuration, it is possible to achieve sufficient wide-angle conversion and aberration correction with an imaging optical system having six lenses while limiting the number of expensive aspherical lenses.

[0078] As a third numerical example of the present invention, the imaging optical system 1 in FIG. 12 will be described. Also in Numerical Example 3, similar to Numerical Example 1, the first lens L1 is a meniscus lens convex on the object side, the second lens L2 is a meniscus lens concave on the object side, the third lens L3 is a meniscus lens having a positive refractive power, a cemented lens L45 formed by cementing the fourth lens L4 and the fifth lens L5, and a sixth lens L6 having a positive refractive power. In Numerical Example 3, as shown in Tables 11 and 12, the object-side surface and the image-side surface of the second lens L2 are aspherical surfaces, and the third lens L3 is a meniscus lens.

[0079]

Table 11

[0080] Also, in the aspherical lens, as in Numerical Example 1, the aspherical coefficients were set as shown in Table 12 using a known formula (Equation 6). However, for the aspherical shape, x is the optical axis with the direction of light propagation being positive, and y is the direction orthogonal to the optical axis. Also, E: Effective diameter of the lens R: Paraxial curvature radius K: Conic coefficient, A4, A6, A8, A10, A 12 、A 14 are the aspherical coefficients of the fourth, sixth, eighth, tenth, twelfth, and fourteenth orders, respectively.

[0081]

Table 12

[0082] Next, Table 13 shows the parameters indicating the respective optical performances of the F-number, half field angle, overall length, and focal length of the imaging optical system 1, and Table 14 shows the calculation results (conditional formula numerical values) of the conditional formulas regarding the focal length.

[0083]

Table 13

[0084]

Table 14

[0085]

Table 15

[0086] As shown in Table 15, in Numerical Example 3, when the half field angle is W, any field angle Wi within the half field angle W, the exit pupil distance gi at the field angle Wi, and the exit pupil distance g0 on the optical axis, Conditional formulas (1) and (2) are satisfied. With such a configuration, the imaging optical system 1 can sufficiently suppress the change in optical performance before and after the temperature change.

[0087] Aberration diagrams of spherical aberration, astigmatism, distortion, and coma for an infinite object in Numerical Example 3 are shown in FIG. 13. In FIG. 13, d indicates the respective aberrations at the d line (wavelength λ = 587.6 nm), and g indicates the respective aberrations at the g line (wavelength λ = 435.8 nm). In the astigmatism diagram, the solid line indicates the sagittal aberration, and the dashed line indicates the meridional aberration. As is apparent from FIG. 13, the aberrations of Numerical Example 3 are corrected at a high level, and the spherical aberration and axial chromatic aberration are so small as not to pose a problem. The astigmatism, field curvature, and lateral chromatic aberration are also sufficiently small, and the coma aberration and its chromatic aberration disturbance are well suppressed up to the outermost periphery. In addition, the distortion aberration is less than 2.0% in absolute value.

[0088] FIG. 14 shows the optical axis deviation when each lens group is decentered by 1 μm. Also, since "SUM_A" and "SUM_A / Y'" in the figure are the same as those in Numerical Examples 1 and 2, the explanation is omitted. Even in Numerical Example 3, even if each lens group moves in a direction that intensifies the optical axis deviation from each other, as shown by "SUM_A / Y'" in FIG. 14, the optical axis deviation of the entire lens unit system is 0.06% with respect to the maximum image height Y', and the sensitivity of the optical axis deviation is sufficiently suppressed.

[0089] In addition, in the present embodiment, as shown in Table 11, for the relative refractive index temperature coefficient: dn / dt, it has a second lens L2 that satisfies the conditional expression (3). Furthermore, it has a sixth lens L6 that satisfies the conditional expression (4). With such a configuration, since the focal position at the time of temperature change is displaced in a direction where the conditional expression (3) and the conditional expression (4) suppress each other, the imaging optical system 1 can sufficiently suppress the change in optical performance before and after the temperature change.

[0090] In addition, in the present embodiment, the imaging optical system 1 has a first lens L1 located on the most object side and a second lens L2 located second from the object side, and at least one of the object side or image side surfaces of the second lens L2 is an aspherical lens with an aspherical shape. With such a configuration, it is possible to perform sufficient wide-angle conversion and aberration correction with an imaging optical system using six lenses while limiting the number of expensive aspherical lenses.

[0091] Regarding the attachment method of the lens barrel 20 and the first lens L1, although FIGS. 5 and 6 were used to explain only the lens shape of Numerical Example 1, the same configuration can be used for attachment for other Numerical Examples 2 and 3 as well. Also, in that case, it is preferable to satisfy the conditional expression (5).

[0092] As described above, the configuration of the "digital camera 100" using the imaging optical system 1 of the present invention has been described. However, such an invention relates to an imaging optical system, and in addition to the imaging device described above, it can be used for various imaging devices such as "camera devices for photography", "camera devices for inspection", "stereo camera devices", "in-vehicle camera devices", and "monitoring camera devices".

[0093] For example, as shown in FIG. 15, an embodiment as an "inspection camera device" will be described. The inspection camera device 101 described below is an inspection device for performing so-called "product inspection".

[0094] There can be various inspections and inspection items in product inspection. For the sake of simplicity, a case of inspecting the "presence or absence of scratches" of products manufactured in large quantities will be taken as an example for explanation. In FIG. 15(a), reference numeral 200 indicates an "imaging unit", reference numeral 230 indicates an "inspection process execution unit", and reference numeral 240 indicates a "display unit". Also, reference numeral W indicates a "product", and reference numeral 260 indicates a "product conveyance belt (hereinafter simply referred to as the 'conveyance belt 260'). The imaging unit 200 is a camera function unit in the inspection device and has the imaging optical system 1 and the image processing unit 220.

[0095] Products W to be inspected are placed at equal intervals on the conveyance belt 260 and are conveyed at a constant speed in the direction of the arrow (to the right in the figure) by the conveyance belt 260. The imaging optical system 1 forms an image of the product W to be inspected, and any one of the imaging optical systems 1 of the present invention, specifically, Numerical Examples 1 to 3 described above can be used. Product inspection is performed according to each of the "preparation process", "inspection process", and "result display process" shown in FIG. 15(b). Among these processes, the "inspection process and result display process" are the "inspection process".

[0096] In the "preparation process", inspection conditions are set. That is, according to the size, shape of the product W conveyed by the conveyor belt 260, the part to be inspected for the presence or absence of scratches, etc., the shooting position and shooting posture of the imaging optical system 1 (the orientation of the imaging lens and the distance from the shooting object, that is, the object distance) are determined. Then, according to the position and size of the "scratch" whose presence or absence is to be detected, the position of the imaging optical system 1 is set.

[0097] On the one hand, a "model product confirmed to have no scratches" is placed at the inspection position on the conveyor belt 260 and photographed by the imaging unit 200. The photographing is performed by imaging with an image sensor arranged in the image processing unit 220, and the image captured by the image sensor is regarded as "image information" and image processing for digitization is performed. The digitized data after image processing is sent to the inspection process execution unit 230, and the inspection process execution unit 230 stores the digital data as "model data".

[0098] In the "inspection process", the product W is placed on the conveyor belt 260 in the "same posture as the model product" and sequentially conveyed by the conveyor belt 260. When each conveyed product W passes through the "inspection position", it is photographed by the imaging optical system 1, digitized by the image processing unit 220, and sent to the inspection process execution unit 230. The inspection process execution unit 230 is configured as a "computer or CPU", controls the image processing unit 220, and also controls the photographing of the imaging optical system 1 via the image processing unit 220.

[0099] When the inspection process execution unit 230 receives the "image data of the product W" digitized by the image processing unit 220, it performs matching between this image data and the stored model data. If there is a "scratch" on the photographed product W, the image data and the model data do not match. In this case, the product is determined to be a "defective product". Also, if there is no scratch on the product W, the image data of the product matches the model data. In this case, the product is determined to be a "non-defective product". The "result display step" is a step of displaying the determination results of "good product, defective product" of individual products by the inspection process execution unit 230 on the display unit 240. Note that in terms of the configuration of the apparatus, the inspection process execution unit 230 and the display unit 240 constitute "inspection process execution means".

[0100] Next, as a third embodiment of the present invention, a stereo camera device 300 including an imaging optical system 1 will also be described with reference to FIG. 16. FIG. 16 shows an external view of a stereo camera device 300 having a right camera device 100a having the imaging optical system 1 as an optical system and a left camera device 100b. As shown in FIG. 17, both the right camera device 100a and the left camera device 100b have imaging optical systems 1a and 1b similar to those of the digital camera 100, and light receiving elements 13a and 13b corresponding to the respective imaging optical systems 1. The right camera device 100a and the left camera device 100b may each have a configuration similar to that of the digital camera 100, but are not limited to such a configuration.

[0101] The stereo camera device 300 has an image processing unit 220 for performing correction and image processing on the image information captured by the right camera device 100a and the left camera device 100b, respectively. The image processing unit 220 performs processing on, for example, an object P that is a subject shown in two images captured by the right camera device 100a and the left camera device 100b. Specifically, in the image Qa captured by the right camera device 100a and the image Qb captured by the left camera device 100b, a parallax Z occurs because the position of the object P in the captured image is different. Here, a case of estimating the position of the object P shown in the left camera device 100b based on the position of the right camera device 100a will be described. When the parallax Z and the baseline length B, which is the distance between the right camera device 100a and the left camera device 100b, are considered, there is a correlation relationship expressed by Equation (7) between the overall focal length f of the imaging optical system 1 and the measurement distance D based on the principle of triangulation.

[0102]

Number

[0103] Therefore, if the image processing unit 220 stores the baseline length B and the value of the focal length f, it can obtain the measurement distance D by obtaining the parallax Z from the two images respectively acquired by the right camera device 100a and the left camera device 100b.

[0104] However, in such a stereo camera device 300, if the focal position fluctuates due to temperature changes, the imaging position of the light from the object P will shift, and it will be observed as a shift in the parallax Z. Since this shift can result in a measurement error in the measurement distance D, it is important for the stereo camera device 300 to use the imaging optical system 1 with little variation in the angle of view even with temperature changes.

[0105] Therefore, also in this embodiment, it is desirable to use the imaging optical system 1 as described in Numerical Examples 1 to 3 for the left camera device 100b and the right camera device 100a respectively. By incorporating the imaging optical system 1 into the stereo camera device 300 in this way, it is possible to suppress an increase in the measurement error due to the focal position fluctuation even with changes in the ambient temperature.

[0106] FIG. 18 is a schematic diagram showing an embodiment in which the stereo camera device 300 shown in FIG. 17 is used as an in-vehicle camera device. In FIG. 18, the stereo camera device 300 is mounted on the vehicle AU as an "in-vehicle camera device" to acquire image information outside the vehicle. As shown in FIG. 18, the stereo camera device 300 includes an imaging optical system 1 and a control arithmetic unit 301. The imaging optical system 1 may use any of the numerical examples 1 to 3 described above, or may use an optical system that satisfies conditions such as conditional expressions (1) and (2). The stereo camera device 300 mounted on the vehicle AU acquires image information outside the vehicle and converts it into digital information. The digitized image information is subjected to digital processing such as image processing by the control arithmetic unit 301 and is displayed by an appropriate method. That is, the stereo camera device shown in FIG. 17 can be mounted on a moving body such as a vehicle as an in-vehicle camera device. The digital camera 100 shown in FIG. 1, the inspection camera device 101 described with reference to FIG. 15, the stereo camera device 300 described with reference to FIGS. 16 and 17, and the in-vehicle camera device described with reference to FIG. 18 all use the imaging optical system of the present invention. Therefore, they can capture bright images with a wide angle of view and are also less affected by wide-ranging changes in environmental temperature, so they can be used in a wide range of usage environments.

[0107] The preferred embodiments of the invention have been described above. However, the present invention is not limited to the specific embodiments described above, and various modifications and changes are possible within the scope of the gist of the invention described in the claims, unless otherwise specifically limited in the above description. For example, the camera device can also be used as a mainly shooting-only camera device including a video camera mainly for video shooting, a film camera using a conventional so-called silver halide film, and the like. In addition to such camera devices, imaging functions corresponding to digital cameras and the like are often incorporated into various information devices including mobile phone handsets, portable information terminal devices called PDAs (personal data assistants), and further portable terminal devices such as so-called smartphones and tablet terminals including these functions. The imaging optical system of the present invention can also be used for such information devices.

[0108] The effects described in the embodiments of this invention are merely a list of preferable effects resulting from the invention, and the effects of the invention are not limited to "those described in the embodiments."

Explanation of Signs

[0109] 1 Imaging optical system 13 Image sensor (light-receiving element) 20 Lens barrel (support structure) 21 Inner wall surface 22 Gap portion 23 Pressing ring 24 Spacer ring 100 Imaging device (digital camera) 200 Imaging unit 300 Stereo camera device L1~L6 Lenses constituting the imaging optical system g0 Exit pupil distance gi Exit pupil distance IMG Light-receiving surface of the image sensor and light-receiving element W Half field angle Wi Field angle L1a First side surface L1b Second side surface φa Diameter of the first side surface φb Diameter of the second side surface AU Moving body

Prior Art Documents

Patent Documents

[0110]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Claims

1. An imaging optical system that forms a subject image on an imaging element, wherein the imaging optical system includes, in order from the object side, a first lens having a meniscus shape with a negative refractive power, a second lens having a meniscus shape with a negative refractive power, a third lens having a positive refractive power, a fourth lens and a fifth lens which are cemented lenses formed by cementing a lens having a positive refractive power and a lens having a negative refractive power integrally, and a sixth lens which is disposed on the image plane side most among the lenses constituting the imaging optical system and has a positive refractive power, held in a lens barrel with their optical axes aligned, when the semi-field angle is W, an arbitrary field angle within the semi-field angle W is Wi, the exit pupil distance at the field angle Wi is gi, and the exit pupil distance on the optical axis is g0, 55 ≤ W... (1) 0.9 < |gi / g0| < 1.1... (2) satisfies the conditional expression represented thereby, at least one of the first lens and the second lens, when the relative refractive index temperature coefficient dn / dt in air at 0°C to 20°C with respect to light in the wavelength range of 580 nm to 640 nm is considered, 5.3×10 －６ <dn / dt...(3) satisfies, the sixth lens disposed on the image plane side most, -5.7×10 －６ >dn / dt...(4) satisfies, and an imaging optical system characterized by this.

2. The imaging optical system according to Claim 1, wherein at least one of the first lens and the second lens has at least one surface on the object side or the image side that is an aspherical shape, and an imaging optical system characterized by this.

3. The imaging optical system according to Claim 1 or 2, wherein at least one surface of the sixth lens disposed on the image plane side most of the imaging optical system is an aspherical shape, and an imaging optical system characterized by this.

4. An imaging device having the imaging optical system according to any one of Claims 1 to 3.

5. A moving body having the imaging device according to Claim 4.

Images