Imaging Optical System and Imaging Device

Abstract

To reduce the attitude error sensitivity of a lens during a focusing operation.SOLUTION: An imaging optical system (10) comprises, in order from an object side, a reflection member (20) that bends an incident beam by 90°, a stationary lens (31) that includes at least one lens, a movable lens (41) that includes at least one lens and is movable on a second optical axis Ax2, and an imaging sensor (60). The imaging optical system (10) has a focal length of 120 mm or more in terms of 35 mm format, and satisfies the following conditional expression. (1) 0.5≤K≤2.8, wherein K is a focus position deviation amount that changes when the movable lens (31) moves.SELECTED DRAWING: Figure 10

Description

Technical Field

[0001] The present invention relates to an imaging optical system and an imaging device including the same.

Background Art

[0002] In recent years, the demand for telephoto lenses has been increasing, particularly for mobile terminals such as smartphones. When the optical system becomes telephoto, there is a problem that the amount of movement of the lens during the focusing operation on a close subject or the like becomes large.

[0003] By the way, as an autofocus (AF) actuator for mobile terminals, a voice coil motor (VCM) is the mainstream. For example, in the imaging device described in Patent Document 1, the entire lens group is moved by the VCM during AF. When applying the VCM, the lens group to be moved is pressed by a spring member in a direction opposite to the moving direction by the VCM. When the VCM is energized, the lens group moves against the force of the spring member, and when the energization of the VCM is stopped, the lens group returns to the initial position by the force of the spring member. However, in the VCM, since the amount of energization and the amount of deformation of the spring member need to have a linear relationship, etc., only a movement amount of about 0.2 mm can be ensured in terms of design.

[0004] Therefore, when designing the lens on the premise of applying the VCM assuming mounting on a mobile terminal, the lens movement amount during AF is restricted to about 0.2 mm or less, and it is particularly difficult to apply to the above-described telephoto lens or the like. In order to achieve AF with such a small amount of movement, instead of moving the entire lens group during AF, there is a method called partial group focusing in which only a part of the lenses in the lens group are moved. However, in order to reduce the amount of movement during AF in the partial group focusing method, it is necessary to increase the refractive power of the lens or lens group (AF group) that moves on the optical axis during AF. When the refractive power of the AF group increases, the posture error sensitivity of the AF group increases. When the posture error sensitivity is high, if the lens tilts or shifts horizontally even slightly during AF, the image quality will deteriorate significantly. That is, in order to realize a high-sensitivity lens that can focus greatly with a small movement distance, it is necessary to manufacture the lens with high precision, resulting in deterioration of productivity (mass productivity).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to reduce the posture error sensitivity of the lens during the focusing operation.

Means for Solving the Problems

[0007] To achieve the above object, the present invention provides a single-focus imaging optical system that forms a subject image on the photoelectric conversion unit of an imaging device, in order from the object side, a reflective optical element that bends incident light rays by 90°, a fixed optical system including at least one lens, Having power including lenses Only one a movable optical system that can move on the optical axis, an imaging device, and consists of The focal length is 120 mm or more in terms of 35 mm conversion, and is characterized by satisfying the following conditional expression. 0.5 ≦ K ≦ 2.8 ···(1) However, K: Amount of focus position deviation that changes when the movable optical system moves once

[0008] Further, the present invention is an imaging device, the above imaging optical system, a stepping motor that drives the movable optical system, and is characterized by including the same.

Effects of the Invention

[0009] According to the present invention, it is possible to reduce the sensitivity of the lens attitude error during the focusing operation.

Brief Description of the Drawings

[0010]

Figure 1

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Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0012] [Schematic Configuration of Mobile Terminal] Figs. 1(a) and (b) are a front view and a rear view of a mobile terminal 300 including an imaging device 100 according to an embodiment of the present invention. As shown in this figure, the imaging device 100 is mounted on the mobile terminal 300. The mobile terminal 300 is a smartphone in this embodiment, and is equipped with a three-eye camera including a wide-angle camera C1, a standard camera C2, and a telephoto camera C3 having different focal lengths on the back surface. In this three-eye camera, digital zoom is used in combination during shooting, enabling seamless zooming from wide-angle to telephoto. The imaging device 100 is mounted as a lens unit for the telephoto camera C3 among these. Note that the mobile terminal 300 is not limited to a smartphone, and may be a mobile phone, a PHS (Personal Handyphone System), a PDA (Personal Digital Assistant), a tablet computer, a mobile computer, a digital still camera, a video camera, an action camera, or the like. Further, the imaging device 100 is not limited to that for a telephoto camera.

[0013] [Configuration of Imaging Device] FIG. 2 is a perspective view of the imaging device 100, and FIG. 3 is an exploded perspective view of the imaging device 100. FIG. 4 is a diagram for explaining a position sensor 54 described later, and FIGS. 5(a) and 5(b) are a perspective view and a side view of the imaging device 100 for mainly explaining a heat transfer member 73 described later. In FIGS. 2 and 3, illustration of some components (such as a lid member 55) is omitted. In the following description, the up-down, front-back, and left-right directions in the imaging device 100 refer to the directions shown in the figures. Here, the up-down direction corresponds to the thickness direction of the mobile terminal 300, the front-back direction corresponds to the width direction of the mobile terminal 300, and the left-right direction corresponds to the longitudinal direction of the mobile terminal 300. Among the up-down directions, the upper side (upper) corresponds to the back side (rear side) of the mobile terminal 300. Further, the X, Y, and Z directions according to the present invention correspond to the left-right direction, the up-down direction, and the front-back direction. As shown in FIGS. 2 and 3, the imaging device 100 includes a reflection member 20, a fixed lens unit 30, a movable lens unit 40, a main body 50, an imaging sensor 60, and a stepping motor 70.

[0014] The reflection member 20 is an example of a reflection optical element according to the present invention, and bends the first optical axis Ax1 and the second optical axis Ax2 of the imaging optical system 10 (see FIG. 10) provided in the imaging device 100 by approximately 90°. The first optical axis Ax1 extends upward from the reflection member 20 along the up-down direction, and the second optical axis Ax2 extends rearward from the reflection member 20 along the front-back direction. For example, a prism, a mirror, or the like can be applied to the reflection member 20. The reflection member 20 is attached to a fixed frame 21. The fixed frame 21 is fixed to the front surface of the main body 50. The upper surface of the reflecting member 20 faces the light-transmitting portion 330 of the telephoto camera C3 of the mobile terminal 300 (see Fig. 1(b)). Note that the reflecting member 20 may have an anti-shake function.

[0015] The fixed lens unit 30 is disposed behind the reflecting member 20. The fixed lens unit 30 has a fixed lens 31 disposed on the second optical axis Ax2 and a holding frame 32 that holds the periphery of the fixed lens 31. The fixed lens 31 includes a first lens L1, a second lens L2, and a third lens L3 arranged along the second optical axis Ax2 (see Fig. 10). The fixed lens unit 30 is fixed after being position-adjusted to reduce manufacturing errors while being sandwiched back and forth between the reflecting member 20 and the main body 50.

[0016] The movable lens unit 40 is disposed behind the fixed lens unit 30. The movable lens unit 40 has a movable lens 41 disposed on the second optical axis Ax2 and a holding member 42 that holds the periphery of the movable lens 41. The movable lens unit 40 is accommodated in the main body 50 in a state where it can move along the second optical axis Ax2. In addition, the movable lens unit 40 has a connecting member 43 that is connected to the stepping motor 70 and receives a driving force. Details of the connection structure with the stepping motor 70 including the configuration of the connecting member 43 will be described later.

[0017] The main body 50 is formed in a rectangular box shape that opens upward, and the upper opening is closed by a lid member 55 (see Fig. 5(a)). The main body 50 houses the movable lens unit 40 inside. Specifically, two guide shafts 51 extending along the front-rear direction are arranged in parallel on the left and right sides inside the main body 50, and these two guide shafts 51 support the holding member 42 of the movable lens unit 40 so as to be movable along the front-rear direction.

[0018] The stepping motor 70 is for driving the movable lens unit 40. The stepping motor 70 has a drive unit 71 that generates a driving force, and a lead screw 72 that extends along the front-rear direction from the front end of the drive unit 71. The stepping motor 70 is fixed to the right side surface of the main body 50 with the lead screw 72 inserted into the main body 50 through an opening 53 formed on the right side surface of the main body 50. In the present embodiment, the lead screw 72 has a right-handed thread, and the right-handed thread is connected (meshed) with the connecting member 43 of the movable lens unit 40. Therefore, when the drive unit 71 rotates the lead screw 72, the rotational force is converted into a thrust force in the front-rear direction through the connecting member 43, and the holding member 42 (movable lens unit 40) moves in the front-rear direction. A plurality of connection contacts 71a are provided on the right side portion of the drive unit 71. The plurality of connection contacts 71a are electrically connected to the flexible substrate 52. As shown in FIG. 4, the main part of the flexible substrate 52 is disposed below the main body 50. Also, an optical position sensor 54 for detecting the front-rear direction position of the movable lens unit 40 (holding member 42) is electrically connected to the flexible substrate 52. The position sensor 54 is fixed to the main body 50, although not shown in the figure. The stepping motor 70 (drive unit 71) and the position sensor 54 are electrically connected to a processing unit 80 described later through the flexible substrate 52 (see FIG. 9). Note that the sensor type, structure, etc. of the position sensor 54 are not particularly limited as long as it can detect the front-rear direction position of the movable lens unit 40. Also, the drive unit 71 is located at a position rearward of the movable lens 41, deviated to the right from the second optical axis Ax2 in the left-right direction, and located inside the other parts of the imaging device 100 in the up-down direction (that is, it does not protrude up and down). That is, the drive unit 71, which is a heat generation source during driving, is arranged at a position separated from the fixed lens 31, which has a relatively high sensitivity to posture error among the imaging device 100.

[0019] As shown in FIGS. 5(a) and 5(b), a heat transfer member 73 is disposed above a drive unit 71 of a stepping motor 70. The heat transfer member 73 is made of a material having flexibility (elasticity) and excellent heat transfer properties. The heat transfer member 73 only needs to have a thermal conductivity greater than that of air, and preferably has a thermal conductivity of 3 W / m·K or more. In the present embodiment, a silicon sheet (for example, TC-400CAT-20 manufactured by Shin-Etsu Chemical Co., Ltd., thermal conductivity 4.5 W / m·K) is used as the heat transfer member 73. A metal flat plate 310 is disposed above the imaging device 100 with a gap (air layer) interposed therebetween, and the heat transfer member 73 is disposed between the drive unit 71 and the metal flat plate 310 and is in contact with them. The metal flat plate 310 is preferably made of a metal having a high thermal conductivity (for example, an aluminum material). Also, in terms of heat dissipation performance, the metal flat plate 310 is preferably an exterior component of the mobile terminal 300. Thereby, the heat transfer member 73 flexibly deforms to be in surface contact with the drive unit 71 of the stepping motor 70 and the metal flat plate 310, while promoting heat transfer between them. Therefore, a stable thermal connection is ensured between the drive unit 71 and the metal flat plate 310, and the drive unit 71 can be suitably dissipated. Therefore, the temperature rise of the imaging device 100, particularly the temperature rise of the resin lens that dislikes thermal deformation, can be suitably suppressed. Also, an air layer is interposed between the metal flat plate 310 (or the exterior component) with which the heat transfer member 73 is in contact and other parts of the imaging device 100 other than the heat transfer member 73. Thereby, since the metal flat plate 310 and the imaging device 100 are thermally insulated by the air layer, it is possible to suppress the heat of the drive unit 71 from being transmitted to the imaging device 100 (particularly the resin lens) through the metal flat plate 310.

[0020] FIGS. 6(a) and 6(b) are diagrams for explaining the connection structure between a lead screw 72 of a stepping motor 70 and a connecting member 43 of a movable lens unit 40, and FIGS. 8(a) and 8(b) are enlarged front views and side views of the connection portion. FIGS. 7(a) to 7(c) are perspective views, front views, and side views of the connecting member 43. As shown in FIG. 6, the connecting member 43 is attached to the right end of the holding member 42 and is connected to the lead screw 72 of the stepping motor 70. Specifically, as shown in FIG. 7, the connecting member 43 has a flat plate portion 431 and two arm portions 432 that extend upward from both the front and rear ends of the flat plate portion 431. The flat plate portion 431 has three rows of mountain-shaped teeth 431a formed on its right side surface, and these teeth 431a mesh with the lead screw 72 (see FIG. 8). On the upper parts of the two arm portions 432, cylindrical shaft portions 432a that protrude forward and rearward outward from the outer side surfaces on both the front and rear sides are provided concentrically with each other. By pivotally supporting the shaft portions 432a on both the front and rear sides by the holding member 42, the connecting member 43 is rotatably supported about an axis along the front-rear direction. Further, the rear one of the two arm portions 432 extends upward from the lower end of the flat plate portion 431 and is easily bent in the front-rear direction.

[0021] A torsion coil spring 44 is attached to the connecting member 43. The torsion coil spring 44 is disposed between the two arm portions 432 of the connecting member 43 and biases the two arm portions 432 in the front-rear outward direction. Thereby, the two arm portions 432 are brought into close contact with the holding member 42, and the play in the front-rear direction between the connecting member 43 and the holding member 42 is suppressed. Further, as shown in FIG. 8, one end 44a of the torsion coil spring 44 is locked to the flat plate portion 431 of the connecting member 43, and the other end 44b is locked to the holding member 42. Therefore, the torsion coil spring 44 biases the connecting member 43 in a direction of rotating counterclockwise in a front view about the shaft portion 432a (that is, a direction of pressing the flat plate portion 431 against the lead screw 72). Thereby, the lead screw 72 and the connecting member 43 are preferably connected (meshed), and poor meshing between them is suppressed.

[0022] As shown in FIGS. 2 and 3, the imaging sensor 60 is an imaging element (solid-state imaging element) that photoelectrically converts the subject image formed by the imaging optical system 10. The imaging sensor 60 is disposed on the second optical axis Ax2 and behind the movable lens 41, and is fixed to the rear end of the main body 50 in a state of being mounted on the front surface of the substrate 61. The imaging sensor 60 is adhesively fixed to the main body 50 after being position-adjusted to reduce manufacturing errors. The imaging sensor 60 is, for example, a CMOS type image sensor. The imaging sensor 60 has a photoelectric conversion unit as an imaging surface I, and signal processing circuits (not shown) are formed around it. Pixel elements, that is, photoelectric conversion elements, are two-dimensionally arranged in the photoelectric conversion unit. Note that the imaging sensor 60 is not limited to the above-described CMOS type image sensor, and other imaging elements such as a CCD may be incorporated.

[0023] [Control Configuration of Imaging Device] Subsequently, the control configuration of the imaging device 100 will be described. FIG. 9 is a block diagram showing a schematic control configuration of the imaging device 100. As shown in this figure, the imaging device 100 includes a processing unit 80. The processing unit 80 includes a lens driving unit 81, an element driving unit 82, an input unit 83, a storage unit 84, an image processing unit 85, a display unit 86, and a control unit 87.

[0024] The lens driving unit 81 controls the operation of the stepping motor 70 based on the position information of the movable lens 41 acquired from the position sensor 54. Thereby, the movable lens 41 of the imaging optical system 10 is moved along the second optical axis Ax2 to perform operations such as focusing (focus adjustment) of the imaging optical system 10. Specifically, as an initialization operation, the lens driving unit 81 first energizes the stepping motor 70 (driving unit 71), and then drives the stepping motor 70 in a predetermined direction while observing the output of the position sensor 54 to move the movable lens 41. Then, the position at which the output characteristics of the position sensor 54 change (from ON to OFF, or from OFF to ON) is set as the initial position. During the focusing operation, the lens driving unit 81 continuously takes the contrast value of the image at a constant period by the imaging sensor 60 while driving the stepping motor 70. Then, the stepping motor 70 is stopped at the position where the contrast is maximum (i.e., the position where the focus is in focus).

[0025] The element driving unit 82 operates the imaging sensor 60 by receiving the supply of voltage and clock signals for driving the imaging sensor 60 from the control unit 87 and outputting them to the circuit associated with the imaging sensor 60. The input unit 83 is a part that receives user operations or commands from an external device. The storage unit 84 is a part that stores information necessary for the operation of the imaging device 100, acquired image data, lens correction data used for image processing, and the like. The image processing unit 85 performs image processing on the image signal output from the imaging sensor 60. In addition to normal image processing such as color correction, tone correction, and zooming, the image processing unit 85 executes distortion correction processing on the image signal based on the lens correction data read from the storage unit 84. The display unit 86 is a part that displays information to be presented to the user, captured images, and the like. Note that the display unit 86 can also serve as the function of the input unit 83. The control unit 87 comprehensively controls the operations of the lens driving unit 81, element driving unit 82, input unit 83, storage unit 84, image processing unit 85, display unit 86, and the like. Note that the processing unit 80 or a part thereof may be integrally configured with the control device of the mobile terminal 300.

[0026] [Optical Configuration of Imaging Optical System] Subsequently, the optical configuration of the imaging optical system 10 provided in the imaging device 100 will be described. FIG. 10 is a diagram showing the imaging optical system 10 of the present embodiment. As shown in this figure, the imaging device 100 includes a single-focus imaging optical system 10 for forming a subject image on the imaging surface (projection surface) I of the imaging sensor 60. The imaging optical system 10 includes the reflection member 20, the fixed lens 31, the movable lens 41, and the imaging sensor 60 described above. More specifically, the imaging optical system 10 includes, in order from the object side, the reflection member 20, the first lens L1, the second lens L2, and the third lens L3 as the fixed lens 31, the fourth lens L4 as the movable lens 41, and the imaging sensor 60 (imaging surface I). An aperture stop S is disposed between the reflection member 20 and the first lens L1. The number of lenses of the fixed lens 31 is not particularly limited, and may include at least one lens. The number of lenses of the movable lens 41 is not particularly limited, and may include at least one lens. The focal length of the entire imaging optical system 10 is 120 mm or more in terms of 35 mm.

[0027] Also, a parallel plate F may be disposed between the fourth lens L4 and the imaging sensor 60. The parallel plate F is a parallel plate assuming an optical low-pass filter, an IR cut filter, a seal glass of the imaging sensor 60, etc. The parallel plate F can be disposed as a separate filter member, or its function can be imparted to any lens surface of the imaging optical system 10. For example, in the case of an infrared cut filter, an infrared cut coat may be applied on the surface of one or more lenses.

[0028] The first lens L1 to the third lens L3 of the fixed lens 31 include the lens having the largest effective diameter among all the lenses included in the fixed lens 31 and the movable lens 41. That is, a lens with a larger effective diameter is disposed in the fixed lens 31, and a lens with a smaller effective diameter is disposed in the movable lens 41. Thereby, the lens unit can be made thinner than a configuration in which the entire lens is moved. That is, conventionally, a configuration in which the entire lens including a lens with a large effective diameter is moved was adopted. However, in order to increase the telephoto ratio, the lens diameter is increased, resulting in a problem that the lens unit becomes thick and the value of the product decreases. In this regard, in the imaging optical system 10 of the present embodiment, instead of moving all the lenses during the focusing operation, only some of the lenses are moved, and the movable lens 41 is made a lens having a smaller effective diameter than the fixed lens 31. Therefore, the thickness of the imaging optical system 10 and thus the imaging device 100 can be made thinner than the conventional configuration in which all the lenses are moved. Further, since the movable lens 41 is smaller and lighter than in the conventional case, the power required for moving the movable lens 41 can be suppressed, and power saving can be achieved.

[0029] The first lens L1 to the fourth lens L4 are so-called I-cut lenses obtained by horizontally cutting the upper and lower parts of a circle. However, it is not necessary for all the lenses to have a non-circular shape such as an I-cut lens. It is sufficient if at least one of all the lenses has a non-circular shape. If the lenses mounted on the imaging device 100 are circular, the thickness of the portable terminal 300 will increase. Therefore, by making at least one lens have a non-circular shape, for example, an I-cut lens, the thickness of the imaging device 100 and thus the portable terminal 300 in the vertical direction can be made thinner. Note that the non-circular shape in this case is not limited to the I-cut lens, and may be, for example, a D-cut lens cut only in one direction.

[0030] Further, the imaging optical system 10 satisfies the following conditional expression (1). 0.5 ≦ K ≦ 2.8 ···(1) However, K is the amount of defocus position shift that changes when the fourth lens L4 (movable lens 41) moves by 1 (unit displacement amount).

[0031] Generally, in a lens unit, as the angle of view changes from wide-angle to telephoto, the sensitivity of the posture error of each lens increases, and high posture maintenance is required when moving the lens for focus adjustment. That is, a minute inclination of the lens or a minute deviation in a direction perpendicular to the moving direction causes image quality degradation. In this regard, in the imaging optical system 10 of the present embodiment, by having K within the range of the conditional expression (1), it is possible to increase (make it equal to or greater than a predetermined value) the lens movement amount during the focusing operation. As a result, the sensitivity to the posture error of the movable lens 41 can be reduced, and even when there is some inclination or deviation in the movable lens 41, deterioration of the image quality can be suppressed. Consequently, the product performance can be stabilized and the productivity can be improved.

[0032] Furthermore, in addition to the above conditional expression (1), the imaging optical system 10 preferably satisfies the following conditional expression (2). 0.50 < |f focus / f| < 1.00 ···(2) However, f focus is the focal length of the fourth lens L4 (movable lens 41), and f is the focal length of the entire imaging optical system 10.

[0033] The conditional expression (2) is a conditional expression for appropriately setting the performance deterioration at the time of error occurrence of the fourth lens L4 (movable lens 41) and the movement amount of the movable group. |f focus / f| exceeding the lower limit of the conditional expression (2) can prevent the refractive power of the movable lens 41 from becoming excessively strong and can suppress the performance deterioration at the time of error occurrence to a small level. On the other hand, |f focus / f| being below the upper limit of the conditional expression (2) can maintain the refractive power of the movable lens 41 appropriately and can prevent the movement amount of the movable lens 41 from becoming too large, for example, during the focusing operation to a short distance.

[0034] Furthermore, the imaging optical system 10 preferably satisfies the following conditional expression (3). 0.25 < f1 / f < 0.45 ···(3) However, f1 is the focal length of the first lens L1, and f is the focal length of the entire imaging optical system 10.

[0035] The conditional expression (3) is a conditional expression for appropriately setting the focal length of the first lens L1 and achieving both miniaturization of the overall length of the imaging optical system 10 and good aberration correction. When f1 / f exceeds the lower limit of conditional expression (3), the refractive power of the first lens L1 does not become too strong, and various aberrations generated in the first lens L1 can be suppressed. On the other hand, when f1 / f is below the upper limit of conditional expression (3), the refractive power of the first lens L1 can be moderately maintained, so the overall length of the imaging optical system 10 can be shortened.

[0036] [Technical effects of the present embodiment] As described above, according to the present embodiment, since K is within the range of conditional expression (1), the lens movement amount during focusing adjustment can be increased (to be equal to or greater than a predetermined value). Thereby, the sensitivity of the attitude error of the movable lens 41 during the focusing operation can be reduced. Therefore, even when there is some inclination or deviation in the movable lens 41, image quality degradation can be suppressed, and thus the product performance can be stabilized and the productivity can be improved.

[0037] Also, according to the present embodiment, the fixed lens 31 includes the lens with the largest effective diameter among all the lenses. That is, a lens with an effective diameter smaller than that of the fixed lens 31 is moved as the movable lens 41 during the focusing operation. Thereby, the thickness of the imaging optical system 10 and thus the imaging device 100 can be made thinner than the conventional configuration in which the entire lens is moved. Also, since the movable lens 41 is smaller and lighter than in the prior art, the power required for the movement of the movable lens 41 can be suppressed to achieve power saving.

[0038] Also, according to the present embodiment, when |f focus / f| exceeds the lower limit of conditional expression (2), the refractive power of the movable lens 41 does not become excessively strong, and the performance degradation during error occurrence can be suppressed to a small extent. On the other hand, when |f focus / f| is below the upper limit of conditional expression (2), the refractive power of the movable lens 41 can be moderately maintained, and it becomes possible to suppress the movement amount of the movable lens 41 from becoming too large during the focusing operation at a short distance.

[0039] Further, according to the present embodiment, by f1 / f exceeding the lower limit of the conditional expression (3), the refractive power of the first lens L1 does not become too strong, and various aberrations generated in the first lens L1 can be suppressed. On the other hand, by f1 / f being below the upper limit of the conditional expression (3), the refractive power of the first lens L1 can be appropriately maintained, so that the overall length of the imaging optical system 10 can be shortened.

[0040] Further, according to the present embodiment, at least one of all the lenses has a non-circular shape. Thereby, the vertical thickness of the imaging device 100 and thus the mobile terminal 300 can be reduced.

[0041] Further, according to the present embodiment, the movable lens 41 is driven by the stepping motor 70. Generally, as a drive source used for the focusing operation of a wide-angle lens for a smartphone, a voice coil motor (VCM) that is offset by a spring and applies a driving force in only one direction is used. However, in a VCM, due to restrictions on spring design and the like, the movable amount can only be ensured to be about 0.2 mm. In this regard, since the stepping motor 70 can adjust the movable distance according to the length of the lead screw 72, it has a higher degree of design freedom than a VCM and can also suitably cope with the case of moving the movable lens 41 greatly.

[0042] Further, according to the present embodiment, the drive unit 71 of the stepping motor 70 is located behind the movable lens 41, is deviated from the second optical axis Ax2 in the left-right direction, and is arranged at a position inside the other parts in the up-down direction. Thereby, without increasing the size of the imaging device 100, the drive unit 71, which is a heat generation source during driving, can be suitably separated from the fixed lens 31 with a high posture error sensitivity. Therefore, it is possible to suppress a decrease in the imaging quality due to thermal deformation of the lens surface of the fixed lens 31.

[0043] Further, according to the present embodiment, an elastic heat transfer member 73 is disposed above the drive unit 71. The heat transfer member 73 is in contact with a metal flat plate 310 disposed above the imaging device 100 and the drive unit 71. Thereby, the heat transfer member 73 deforms flexibly and makes surface contact with the drive unit 71 of the stepping motor 70 and the metal flat plate 310, while promoting heat transfer therebetween. Therefore, a stable thermal connection is ensured between the drive unit 71 and the metal flat plate 310, and the drive unit 71 can be suitably radiated. Accordingly, the temperature rise of the imaging device 100, particularly the temperature rise of the resin lens that dislikes thermal deformation, can be suitably suppressed. In addition, an air layer is interposed between the metal flat plate 310 with which the heat transfer member 73 is in contact and the imaging device 100 (parts other than the heat transfer member 73). Thereby, since the metal flat plate 310 and the imaging device 100 are thermally insulated by the air layer, it is possible to suppress the heat of the drive unit 71 from being transmitted to the imaging device 100 (particularly the resin lens) through the metal flat plate 310.

[0044] [Modification Example] Subsequently, a modification example of the above embodiment will be described. FIG. 11 is a perspective view of the imaging device 100A of this modification example, FIG. 12(a) is a perspective view of the imaging device 100A viewed from a direction different from FIG. 11, and FIG. 12(b) is a side view of the imaging device 100A. In FIG. 11, illustration of some components (the lid member 55, the heat transfer member 73) is omitted. The imaging device 100A of this modification example is mainly different from the imaging device 100 of the above embodiment in the ratio of the length in the front-rear direction of the fixed lens unit and the main body. Hereinafter, mainly the differences from the above embodiment will be described, and the same components as those in the above embodiment will be denoted by the same reference numerals and the description thereof will be omitted.

[0045] The imaging device 100A of this modification example includes a fixed lens unit 30A and a main body 50A instead of the fixed lens unit 30 and the main body 50 of the above embodiment. The fixed lens unit 30A has a wider interval between the fixed lenses 31 and is longer in the front-rear direction compared to the fixed lens unit 30 of the above-described embodiment. That is, compared to the above-described embodiment, the holding frame 32A is longer in the front-rear direction, and the fixed frame 21A of the reflecting member 20 for fixing it is also longer in the front-rear direction. The main body 50A is shorter in the front-rear direction compared to the main body 50 of the above-described embodiment. More specifically, the main body 50A is shorter in the front-rear direction by retreating the front end portion by approximately the amount by which the fixed lens unit 30A extends. Accordingly, the mounting position of the stepping motor 70 has also moved rearward.

[0046] Even with this modification example, the same effects as those of the above-described embodiment can be obtained. Also, in this modification example, compared to the above-described embodiment, the footprint of the imaging device 100A is smaller, and the attitude error sensitivity of the movable lens unit 40 is also lower. Therefore, productivity can be further improved.

[0047] Although one embodiment of the present invention has been described above, the embodiments to which the present invention is applicable are not limited to the above-described embodiment and its modification examples, and can be appropriately changed without departing from the spirit of the present invention.

Example

[0048] Hereinafter, examples of the imaging optical system of the present invention will be shown. The symbols used in each example are as follows. f: Focal length of the entire imaging optical system fB: Back focus F: F-number 2Y: Diagonal length of the imaging surface of the solid-state imaging device R: Radius of curvature D: Interval between axial surfaces Nd: Refractive index with respect to the d-line of the lens material νd: Abbe number of the lens material In each embodiment, the surface with an asterisk (*) described after each surface number of the lens surface data has an aspherical shape. The shape of the aspherical surface is represented 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.

Equation

[0049] (Embodiment 1) FIG. 13 shows a cross-sectional view and an aberration diagram of the imaging optical system of Embodiment 1. Among them, (a) is a cross-sectional view of the imaging optical system when the object distance is infinite, (b) is a cross-sectional view of the imaging optical system when the object distance is 1.0 m, and (c) is a longitudinal aberration diagram (spherical aberration, astigmatism, distortion). When the object (subject) distance is infinite, the fourth lens L4 (movable lens 41) is in the state closest to the fixed lens 31. As the object distance approaches from this state, the fourth lens L4 moves toward the imaging sensor 60 (imaging surface I). Note that the imaging optical system of Embodiment 1 is not particularly limited, but corresponds to the imaging optical system 10 included in the imaging device 100 of the above embodiment.

[0050] The overall specifications of the imaging optical system of Embodiment 1 are shown below. f = 29.15 mm fB = 6.09 mm F = 3.81 2Y = 5 mm

[0051] The lens surface data of Embodiment 1 is shown in Table 1 below.

Table 1

[0052] The aspherical coefficients of the lens surfaces of Embodiment 1 are shown in Table 2 below. Hereinafter (including the lens data in the table), powers of 10 (for example, 2.5×10-02) shall be represented using E (for example, 2.5E-02).

Table 2

[0053] The single-lens data of Example 1 are shown in Table 3 below.

Table 3

[0054] The surface interval data during the focusing operation of Example 1 are shown in Table 4 below. Note that "Variable A" and "Variable B" in the table correspond to the numerical values in the corresponding columns of the axial surface interval D in Table 1 above.

Table 4

[0055] The numerical values of conditional expressions (1) to (3) in the imaging optical system of Example 1 are shown below. Conditional expression (1): K = 2.80 Conditional expression (2): |f focus / f| = 0.55 Conditional expression (3): f1 / f = 0.36

[0056] (Example 2) Fig. 14 shows a cross-sectional view and aberration diagram of the imaging optical system of Example 2. Among them, (a) is a cross-sectional view of the imaging optical system when the object distance is infinite, (b) is a cross-sectional view of the imaging optical system when the object distance is 1.0 m, and (c) is a longitudinal aberration diagram (spherical aberration, astigmatism, distortion aberration). Note that the imaging optical system of Example 2 is not particularly limited, but corresponds to the imaging optical system provided in the imaging device 100A of the above modification example.

[0057] The overall specifications of the imaging optical system of Example 2 are shown below. f = 29.14 mm fB = 6.06 mm F = 3.81 2Y = 5 mm

[0058] The lens surface data of Example 2 are shown in Table 5 below.

Table 5

[0059] The aspherical coefficients of the lens surfaces in Example 2 are shown in Table 6 below.

Table 6

[0060] The single lens data of Example 2 are shown in Table 7 below.

Table 7

[0061] The data of the surface interval during the focusing operation in Example 2 are shown in Table 8 below. Note that "Variable A" and "Variable B" in the table correspond to the numerical values in the corresponding columns of the axial surface interval D in Table 5 above.

Table 8

[0062] The numerical values of the conditional expressions (1) to (3) in the imaging optical system of Example 2 are shown below. Conditional expression (1): K = 0.90 Conditional expression (2): |f focus / f| = 0.88 Conditional expression (3): f1 / f = 0.40

[0063] (Example 3) Fig. 15 shows a cross-sectional view and aberration diagram of the imaging optical system of Example 3. Among them, (a) is a cross-sectional view of the imaging optical system when the object distance is infinite, (b) is a cross-sectional view of the imaging optical system when the object distance is 1.0 m, and (c) is a longitudinal aberration diagram (spherical aberration, astigmatism, distortion aberration).

[0064] The overall specifications of the imaging optical system of Example 3 are shown below. f = 29.15 mm fB = 6.02 mm F = 3.81 2Y = 5 mm

[0065] The data of the lens surfaces of Example 3 are shown in Table 9 below.

Table 9

[0066] The aspherical coefficients of the lens surfaces of Example 3 are shown in Table 10 below.

Table 10

[0067] The single-lens data of Example 3 are shown in Table 11 below.

Table 11

[0068] The data of the interval between surfaces during the focusing operation of Example 3 are shown in Table 12 below. Note that "Variable A" and "Variable B" in the table correspond to the numerical values in the corresponding columns of the axial surface interval D in Table 9 above.

Table 12

[0069] The numerical values of the conditional expressions (1) to (3) in the imaging optical system of Example 3 are shown below. Conditional expression (1): K = 1.80 Conditional expression (2): |f focus / f| = 0.71 Conditional expression (3): f1 / f = 0.37

Explanation of symbols

[0070] 10 Imaging optical system 20 Reflecting member (reflective optical element) 30, 30A Fixed lens unit 31 Fixed lens (fixed optical system) 40 Movable lens unit 41 Movable lens (movable optical system) 43 Connecting member 50, 50A Main Body 60 Imaging Sensor (Image Sensor Element) 70 Stepping Motor 71 Driving Unit (Driving Force Generation Unit) 71a Connection Contact 72 Lead Screw 73 Heat Transfer Member 100, 100A Imaging Device 300 Mobile Terminal 310 Metal Flat Plate Ax1 First Optical Axis Ax2 Second Optical Axis L1 First Lens L2 Second Lens L3 Third Lens L4 Fourth Lens F Parallel Flat Plate I Imaging Surface

Claims

1. A single-focus imaging optical system that forms a subject image on the photoelectric conversion unit of an imaging element, comprising: In order from the object side, A reflective optical element that bends incident light rays by 90°, A fixed optical system including at least one lens, A movable optical system including only one lens having power and movable on the optical axis, An imaging element, Consisting of, The focal length is 120 mm or more in terms of 35 mm, An imaging optical system characterized by satisfying the following conditional expression. 0.5 ≦ K ≦ 2.8... (1) However, K: Amount of focus position shift that changes when the movable optical system moves once

2. The imaging optical system according to claim 1, wherein the fixed optical system includes a lens having the largest effective diameter among all the lenses included in the fixed optical system and the movable optical system.

3. The imaging optical system according to claim 1 or 2, characterized by satisfying the following conditional expression. 0.50 < |ffocus / f| < 1.00... (2) However, ffocus: Focal length of the movable optical system f: Focal length of the entire imaging optical system

4. The fixed optical system includes a first lens that is located closest to the object side among all the lenses included in the fixed optical system and the movable optical system, The imaging optical system according to any one of claims 1 to 3, characterized by satisfying the following conditional expression. 0.25 < f1 / f < 0.45... (3) However, f1: Focal length of the first lens f: Focal length of the entire imaging optical system

5. The imaging optical system according to any one of claims 1 to 4, wherein at least one of all the lenses included in the fixed optical system and the movable optical system has a non-circular shape.

6. An imaging optical system according to any one of claims 1 to 5, A stepping motor that drives the movable optical system, An imaging device characterized by comprising.

7. When the direction along the first optical axis on the object side of the reflective optical element is the Y direction, the direction along the second optical axis on the fixed optical system side and orthogonal to the Y direction is the Z direction, and the direction orthogonal to both the Y direction and the Z direction is the X direction, The driving force generating unit of the stepping motor is located on the imaging element side of the movable optical system in the Z direction, is disposed at a position deviated from the second optical axis in the X direction, and does not protrude beyond both sides in the Y direction more than other parts of the imaging device. The imaging device according to claim 6.

8. The driving force generating unit has electrical connection contacts on the side surface in the X direction, On the Y-direction side of the driving force generating unit, a heat transfer member having elasticity is disposed, The imaging device according to claim 7, wherein the heat transfer member is in contact with a metal member disposed via an air layer on the Y-direction side of the imaging device and the driving force generating unit.

Images