JP7697199B2 - Imaging optical system and imaging device - Google Patents

Description

The present invention relates to an imaging optical system and an imaging device equipped with the same.

In recent years, there has been an increasing demand for telephoto lenses, especially for mobile devices such as smartphones. When an optical system becomes telephoto, there is an issue that the amount of lens movement becomes large when focusing on a close-up subject.

Meanwhile, voice coil motors (VCMs) are the mainstream actuators for autofocus (AF) in mobile terminals. For example, in an image pickup device described in Patent Document 1, the entire lens group is moved by the VCM during AF.
When a VCM is used, the lens group to be moved is pressed by a spring member in the opposite direction to the movement direction caused by the VCM. When electricity is applied to the VCM, the lens group moves against the force of the spring member, and when electricity is stopped, the lens group returns to its initial position by the force of the spring member.
However, in a VCM, because the amount of current flow and the amount of deformation of the spring member must have a linear relationship, the design can only ensure a movement of about 0.2 mm.

Therefore, when a lens is designed on the assumption that it will be mounted on a mobile terminal and that a VCM is used, the amount of lens movement during AF is limited to approximately 0.2 mm or less, making it particularly difficult to apply to the telephoto lens mentioned above.
In order to realize AF with such a small amount of movement, there is a method of moving only some of the lenses in the lens group, rather than moving the entire lens group during AF, which is called partial group focusing. However, in order to reduce the amount of movement during AF with the partial group focusing method, it is necessary to strengthen the refractive power of the lens or lens group (AF group) that moves on the optical axis during AF, and if the refractive power of the AF group becomes strong, the attitude error sensitivity of the AF group becomes high. If the attitude error sensitivity is high, the shooting quality will be greatly reduced if the lens tilts or shifts laterally even slightly during AF. In other words, 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, which will deteriorate productivity (mass production).

International Publication No. 2018/130898

The present invention was made in consideration of the above-mentioned circumstances, and aims to reduce the sensitivity of the lens to attitude errors during focusing operations.

In order to achieve the above object, the present invention provides
A single-focus imaging optical system that forms a subject image on a photoelectric conversion unit of an imaging element,
From the object side,
A reflective optical element that bends an incident light beam by 90 degrees;
a fixed optical system including at least one lens;
a movable optical system including only one lens having power and movable on an optical axis;
An imaging element;
It consists of:
The focal length is 120 mm or more in 35 mm equivalent.
It is characterized in that the following conditional expression is satisfied.
0.5≦K≦2.8 (1)
however,
K: Amount of focus shift that changes when the movable optical system moves one position

The present invention also provides an imaging device,
The imaging optical system;
A stepping motor that drives the movable optical system;
The present invention is characterized by comprising:

The present invention makes it possible to reduce the sensitivity of the lens to attitude errors during focusing operations.

1A and 1B are a front view and a rear view of a mobile terminal equipped with an imaging device according to an embodiment of the present invention. 1 is a perspective view of an imaging device according to an embodiment. FIG. 2 is an exploded perspective view of the imaging device according to the embodiment. FIG. 2 is a diagram for explaining a position sensor. 1A and 1B are a perspective view and a side view of an imaging device for explaining a heat transfer member. 5A and 5B are diagrams illustrating a connection structure between a lead screw of a stepping motor and a connection member of a movable lens unit. 3A is a perspective view, FIG. 3B is a front view, and FIG. 3C is a side view of a connecting member of a movable lens unit. 5A and 5B are enlarged front and side views of a connection portion between a lead screw of a stepping motor and a connection member of a movable lens unit. 2 is a block diagram showing a schematic control configuration of the imaging apparatus according to the embodiment; FIG. 1 is a diagram illustrating an imaging optical system according to an embodiment. FIG. 13 is a perspective view of an imaging device according to a modified example of the embodiment. 10A and 10B are a perspective view and a side view of an imaging device according to a modified example of the embodiment. 1A is a cross-sectional view of the imaging optical system of Example 1 when the object distance is infinity, FIG. 1B is a cross-sectional view when the object distance is 1.0 m, and FIG. 1A is a cross-sectional view of an imaging optical system according to a second embodiment when the object distance is infinity, FIG. 1B is a cross-sectional view of an imaging optical system when the object distance is 1.0 m, and FIG. 13A is a cross-sectional view of the imaging optical system of Example 3 when the object distance is infinity, FIG. 13B is a cross-sectional view of the imaging optical system when the object distance is 1.0 m, and FIG.

The following describes an embodiment of the present invention with reference to the drawings.

[General configuration of a mobile terminal]
1A and 1B 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 a mobile terminal 300. In this embodiment, the mobile terminal 300 is a smartphone, and is equipped with a triple-lens camera on the back, including a wide-angle camera C1, a standard camera C2, and a telephoto camera C3, each with a different focal length. This triple-lens camera also uses digital zoom during shooting, allowing seamless zooming from wide angle to telephoto. The imaging device 100 is mounted as a lens unit for the telephoto camera C3.
The mobile terminal 300 is not limited to a smartphone, but may be a mobile phone, a personal handyphone system (PHS), a personal digital assistant (PDA), a tablet computer, a mobile computer, a digital still camera, a video camera, an action camera, etc. The imaging device 100 is not limited to a telephoto camera.

[Configuration of the 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. Some components (such as a cover member 55) are omitted from Figs. 2 and 3.
In the following description, the up-down, front-back, and left-right directions of the imaging device 100 refer to the directions shown in the drawings. Here, the up-down direction corresponds to the thickness direction of the portable terminal 300, the front-back direction corresponds to the width direction of the portable terminal 300, and the left-right direction corresponds to the longitudinal direction of the portable terminal 300, and the upper side (upper side) of the up-down directions corresponds to the rear side (back side) of the portable terminal 300. Also, 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 reflecting 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.

The reflecting member 20 is an example of a reflecting 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 ) included in the imaging device 100 by approximately 90°. The first optical axis Ax1 extends upward from the reflecting member 20 along the up-down direction, and the second optical axis Ax2 extends backward from the reflecting member 20 along the front-rear direction. The reflecting member 20 can be, for example, a prism or a mirror.
The reflecting 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. 1B).
The reflecting member 20 may have a camera shake correction function.

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. As described below, 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 clamped between the reflecting member 20 and the main body 50 from the front to the rear, and is fixed after being adjusted in position to reduce manufacturing errors.

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 housed in the main barrel 50 in a state in which it is movable along the second optical axis Ax2.
The movable lens unit 40 also has a connecting member 43 that is connected to a stepping motor 70 to receive a driving force. The details of the connection structure with the stepping motor 70, including the configuration of the connecting member 43, will be described later.

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 barrel 50 accommodates the movable lens unit 40 therein. Specifically, two guide shafts 51 extending along the front-to-rear direction are provided side by side on both left and right sides within the main barrel 50, and these two guide shafts 51 support the holding member 42 of the movable lens unit 40 so that it can move along the front-to-rear direction.

The stepping motor 70 drives 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 in the front-to-rear direction from the front end of the drive unit 71. The stepping motor 70 is fixed to the right side of the main barrel 50 with the lead screw 72 inserted into the main barrel 50 through an opening 53 formed in the right side of the main barrel 50.
In this embodiment, the lead screw 72 is right-handed and connected (meshed) with the connecting member 43 of the movable lens unit 40. Therefore, when the lead screw 72 is rotated by the driving unit 71, the rotational force is converted into a thrust in the front-rear direction via 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 of the driving 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. In addition, an optical position sensor 54 that detects the front-rear position of the movable lens unit 40 (holding member 42) is electrically connected to the flexible substrate 52. Although not shown, the position sensor 54 is fixed to the main body 50. The stepping motor 70 (driving unit 71) and the position sensor 54 are electrically connected to the processing unit 80 described later via the flexible substrate 52 (see FIG. 9). Note that the type and structure of the position sensor 54 are not particularly limited as long as it can detect the front-rear position of the movable lens unit 40.
Further, the driving unit 71 is located behind the movable lens 41, off to the right of the second optical axis Ax2 in the left-right direction, and is located inside the other parts of the image pickup device 100 in the up-down direction (i.e., does not protrude vertically). In other words, the driving unit 71, which is a heat source during driving, is located away from the fixed lens 31 of the image pickup device 100, which has a relatively high attitude error sensitivity.

5A and 5B, a heat transfer member 73 is disposed on the upper side of a driving unit 71 of a stepping motor 70. The heat transfer member 73 is made of a material that is flexible (elastic) and has excellent heat transfer properties. The heat transfer member 73 only needs to have a thermal conductivity at least higher than that of air, and preferably has a thermal conductivity of 3 W/m·K or more. In this 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 plate 310 is disposed above the imaging device 100 with a gap (air layer) therebetween, and the heat transfer member 73 is disposed between the driving unit 71 and the metal plate 310 and abuts against them. The metal plate 310 is desirably made of a metal with high thermal conductivity (e.g., aluminum material, etc.). In terms of heat dissipation performance, the metal plate 310 is desirably an exterior component of the mobile terminal 300.
As a result, the heat transfer member 73 flexibly deforms to come into surface contact with the driving unit 71 of the stepping motor 70 and the flat metal plate 310, promoting heat transfer between them. This ensures a stable thermal connection between the driving unit 71 and the flat metal plate 310, and allows the driving unit 71 to preferably dissipate heat. This makes it possible to preferably suppress a temperature rise in the imaging device 100, particularly a temperature rise in the resin lenses which are sensitive to thermal deformation.
In addition, an air layer is interposed between the flat metal plate 310 (or an exterior part) with which the heat transfer member 73 is in contact and the portion of the imaging device 100 other than the heat transfer member 73. As a result, the flat metal plate 310 and the imaging device 100 are insulated by the air layer, so that it is possible to suppress the heat of the drive unit 71 from being transferred to the imaging device 100 (particularly the resin lens) through the flat metal plate 310.

6(a) and (b) are diagrams for explaining the connection structure between the lead screw 72 of the stepping motor 70 and the connection member 43 of the movable lens unit 40, and Fig. 8(a) and (b) are front and side views of an enlarged view of the connection portion. Also, Fig. 7(a) to (c) are perspective views, front and side views of the connection 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 a lead screw 72 of a stepping motor 70 .
Specifically, as shown in FIG. 7 , the connecting member 43 has a flat plate portion 431 and two arm portions 432 extending upward from both 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 the right side surface, and these teeth 431a mesh with the lead screw 72 (see FIG. 8).
Cylindrical shafts 432a protruding outward from the outer surfaces on both the front and rear sides are provided concentrically on the upper portions of the two arms 432. The front and rear shafts 432a are journaled on the holding member 42, so that the connecting member 43 is supported rotatably about an axis along the front-rear direction. The rear one of the two arms 432 extends upward from the lower end of the flat plate portion 431 and is easily flexible in the front-rear direction.

A torsion coil spring 44 is attached to the connecting member 43 .
The torsion coil spring 44 is disposed between the two arms 432 of the connecting member 43 and biases the two arms 432 in the front-rear outward direction. This brings the two arms 432 into close contact with the holding member 42, thereby suppressing backlash between the connecting member 43 and the holding member 42 in the front-rear direction.
8, one end 44a of the torsion coil spring 44 is engaged with the flat plate portion 431 of the connecting member 43, and the other end 44b is engaged with the holding member 42. Therefore, the torsion coil spring 44 biases the connecting member 43 around the shaft portion 432a in a direction that rotates the connecting member 43 counterclockwise when viewed from the front (i.e., in a direction that presses the flat plate portion 431 against the lead screw 72). This allows the lead screw 72 and the connecting member 43 to be suitably coupled (engaged), and poor engagement between them is suppressed.

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 barrel 50 in a state where it is mounted on the front surface of the substrate 61. The imaging sensor 60 is adhesively fixed to the main barrel 50 after its position is adjusted to reduce manufacturing errors.
The image sensor 60 is, for example, a CMOS type image sensor. The image sensor 60 has a photoelectric conversion section as an imaging surface I, around which a signal processing circuit (not shown) is formed. In the photoelectric conversion section, pixels, i.e., photoelectric conversion elements, are arranged two-dimensionally. Note that the image sensor 60 is not limited to the above-mentioned CMOS type image sensor, and may incorporate other imaging elements such as a CCD.

[Control configuration of the imaging device]
Next, the control configuration of the image capture device 100 will be described.
FIG. 9 is a block diagram showing a schematic control configuration of the imaging device 100. As shown in FIG.
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 memory unit 84 , an image processing unit 85 , a display unit 86 , and a control unit 87 .

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. This causes the movable lens 41 of the imaging optical system 10 to move along the second optical axis Ax2, thereby performing 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 monitoring the output of the position sensor 54 to move the movable lens 41. Then, the position where the output characteristic of the position sensor 54 changes (from ON to OFF, or from OFF to ON) is set as the initial position.
During a focusing operation, the lens driving unit 81 continuously measures the contrast value of the image at a constant cycle using 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 image is in focus).

The element driving section 82 receives voltages and clock signals for driving the image sensor 60 from the control section 87 and outputs them to circuits associated with the image sensor 60 , thereby operating the image sensor 60 .
The input unit 83 is a section that accepts operations by the user or commands from an external device.
The storage unit 84 is a section that stores information necessary for the operation of the imaging device 100, acquired image data, lens correction data used in image processing, and the like.
The image processing unit 85 performs image processing on the image signal output from the imaging sensor 60. The image processing unit 85 performs distortion correction processing on the image signal based on the lens correction data read out from the storage unit 84, in addition to normal image processing such as color correction, gradation correction, and zooming.
The display unit 86 is a section that displays information to be presented to the user, captured images, etc. The display unit 86 can also function as the input unit 83.
The control unit 87 comprehensively controls the operations of the lens driving unit 81, the element driving unit 82, the input unit 83, the storage unit 84, the image processing unit 85, the display unit 86, and the like.
In addition, the processing unit 80 or a part thereof may be configured integrally with the control device of the mobile terminal 300.

[Optical configuration of imaging optical system]
Next, the optical configuration of the imaging optical system 10 included in the imaging device 100 will be described.
FIG. 10 is a diagram showing an imaging optical system 10 according to 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 an imaging surface (projection surface) I of an imaging sensor 60. The imaging optical system 10 includes the above-mentioned reflecting member 20, fixed lens 31, movable lens 41, and imaging sensor 60. More specifically, the imaging optical system 10 includes, in order from the object side, the reflecting member 20, a first lens L1, a second lens L2, and a third lens L3 as the fixed lens 31, a fourth lens L4 as the movable lens 41, and the imaging sensor 60 (imaging surface I). An aperture stop S is disposed between the reflecting member 20 and the first lens L1.
The number of lenses in the fixed lens 31 is not particularly limited as long as it includes at least one lens.
The number of lenses in the movable lens 41 is not particularly limited, and it is sufficient that the movable lens 41 includes at least one lens.
The focal length of the entire imaging optical system 10 is 120 mm or more in 35 mm equivalent.

A parallel plate F may also be placed between the fourth lens L4 and the imaging sensor 60. The parallel plate F is a parallel plate intended to function as an optical low-pass filter, an IR cut filter, a sealing glass for the imaging sensor 60, or the like. The parallel plate F may be placed as a separate filter member, but its function may also be imparted to any of the lens surfaces of the imaging optical system 10. For example, in the case of an infrared cut filter, an infrared cut coating may be applied to the surface of one or more lenses.

The first lens L1 to the third lens L3 of the fixed lens 31 include the lens with the largest effective diameter among all the lenses included in the fixed lens 31 and the movable lens 41. In other words, the lens with the larger effective diameter is arranged in the fixed lens 31, and the lens with the smaller effective diameter is arranged in the movable lens 41. This allows the lens unit to be made thinner than a configuration in which the entire lens is moved.
In other words, in the past, a configuration was adopted in which the entire lens, including lenses with a large effective diameter, was moved, but in order to achieve telephoto photography, the lens diameter was increased, which resulted in a thicker lens unit and reduced product value.
In this regard, in the imaging optical system 10 of this embodiment, only a portion of the lens is moved during focusing, not the entire lens, and the movable lens 41 has an effective diameter smaller than that of the fixed lens 31. Therefore, the imaging optical system 10 and thus the imaging device 100 can be made thinner than in a conventional configuration in which the entire lens is moved. Also, because the movable lens 41 is smaller and lighter than in the past, the power required to move the movable lens 41 can be reduced, thereby saving power.

The first lens L1 to the fourth lens L4 are so-called I-cut lenses, which are circular lenses with the top and bottom cut off horizontally.
However, it is not necessary for all the lenses to have a non-circular shape such as an I-cut lens, and it is sufficient that 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 mobile terminal 300 will increase. Therefore, by making at least one lens non-circular, for example an I-cut lens, it is possible to reduce the thickness of the imaging device 100 and thus the mobile terminal 300 from top to bottom. Note that the non-circular shape in this case is not limited to an I-cut lens, and may be, for example, a D-cut lens cut in only one direction.

Moreover, the imaging optical system 10 satisfies the following conditional expression (1).
0.5≦K≦2.8 (1)
Here, K is the amount of focus position shift that changes when the fourth lens L4 (movable lens 41) moves by 1 (unit movement amount).

Generally, in a lens unit, the sensitivity of each lens to attitude error increases as the lens moves from wide-angle to telephoto, and precise maintenance of the attitude is required when moving the lens for focus adjustment. In other words, even the slightest tilt of the lens or the slightest deviation perpendicular to the direction of movement can cause degradation of image quality.
In this regard, in the imaging optical system 10 of this embodiment, since K is within the range of conditional expression (1), the lens movement amount during focusing can be increased (to a predetermined value or more). This reduces the attitude error sensitivity of the movable lens 41, and suppresses image quality degradation even if the movable lens 41 is slightly tilted or misaligned. This in turn stabilizes product performance and improves productivity.

Furthermore, it is preferable that the imaging optical system 10 satisfies the following conditional expression (2) in addition to the above conditional expression (1).
0.50< |f _focus /f| <1.00...(2)
Here, f _focus is the focal length of the fourth lens L 4 (movable lens 41 ), and f is the focal length of the entire imaging optical system 10 .

Condition (2) is a condition for appropriately setting the amount of movement of the movable group and the deterioration in performance when an error occurs in the fourth lens L4 (movable lens 41).
By setting |f _focus /f| to be greater than the lower limit of conditional expression (2), the refractive power of the movable lens 41 does not become excessively strong, and deterioration of performance when an error occurs can be suppressed to a small extent. On the other hand, by setting |f _focus /f| to be less than the upper limit of conditional expression (2), the refractive power of the movable lens 41 can be maintained at an appropriate level, and it becomes possible to suppress the amount of movement of the movable lens 41 from becoming too large during a focusing operation to a close distance, for example.

Furthermore, it is preferable that the imaging optical system 10 satisfies the following conditional expression (3).
0.25<f1/f<0.45...(3)
Here, f1 is the focal length of the first lens L1, and f is the focal length of the entire imaging optical system 10.

Conditional expression (3) is a conditional expression for appropriately setting the focal length of the first lens L1 and achieving both a reduction in the overall length of the imaging optical system 10 and favorable correction of aberrations.
When f1/f is greater than the lower limit of conditional expression (3), the refractive power of the first lens L1 does not become too strong, and various aberrations occurring in the first lens L1 can be suppressed. On the other hand, when f1/f is less than the upper limit of conditional expression (3), the refractive power of the first lens L1 can be maintained at an appropriate level, and the overall length of the imaging optical system 10 can be shortened.

[Technical effect of the present embodiment]
As described above, according to this embodiment, by ensuring that K falls within the range of conditional expression (1), the amount of lens movement during focus adjustment can be increased (to a predetermined value or more).
This makes it possible to reduce the sensitivity to attitude errors of the movable lens 41 during focusing operations, and therefore makes it possible to suppress deterioration in image quality even if the movable lens 41 is slightly tilted or misaligned, thereby stabilizing product performance and improving productivity.

Furthermore, according to this embodiment, the fixed lens 31 includes a lens with the largest effective diameter of all the lenses. In other words, a lens with an effective diameter smaller than that of the fixed lens 31 is moved as the movable lens 41 during focusing operation.
This allows the imaging optical system 10, and in turn the imaging device 100, to be thinner than in a conventional configuration in which the entire lens is moved. Also, since the movable lens 41 is smaller and lighter than in the past, the power required to move the movable lens 41 can be reduced, thereby achieving power saving.

Furthermore, according to this embodiment, by |f _focus /f| exceeding the lower limit of conditional expression (2), the refractive power of the movable lens 41 does not become excessively strong, and it is possible to suppress the deterioration of performance when an error occurs. On the other hand, by |f _focus /f| being below the upper limit of conditional expression (2), it is possible to maintain the refractive power of the movable lens 41 at an appropriate level, and it is possible to suppress the amount of movement of the movable lens 41 from becoming too large during a focusing operation to a close distance, etc.

In addition, according to this embodiment, by making f1/f exceed the lower limit of conditional expression (3), the refractive power of the first lens L1 does not become too strong, and various aberrations occurring in the first lens L1 can be suppressed. On the other hand, by making f1/f less than the upper limit of conditional expression (3), the refractive power of the first lens L1 can be maintained at an appropriate level, and the overall length of the imaging optical system 10 can be shortened.

Furthermore, according to this embodiment, at least one of all the lenses has a non-circular shape.
This allows the imaging device 100 and therefore the mobile terminal 300 to be made thinner from top to bottom.

Furthermore, according to this embodiment, the movable lens 41 is driven by the stepping motor 70 .
Generally, a voice coil motor (VCM) that applies driving force in only one direction by biasing it with a spring is used as the driving source for the focusing operation of wide-angle lenses for smartphones. However, due to restrictions on the spring design, etc., the VCM can only ensure a movement of about 0.2 mm.
In this regard, the stepping motor 70 allows the movable distance to be adjusted by the length of the lead screw 72, so that it has a higher degree of design freedom than a VCM and can be suitably adapted to the case where the movable lens 41 is moved by a large distance.

Furthermore, according to this embodiment, the driving portion 71 of the stepping motor 70 is located behind the movable lens 41, off the second optical axis Ax2 in the left-right direction, and is positioned more inward than other portions in the up-down direction.
This allows the drive unit 71, which is a heat source during operation, to be appropriately separated from the fixed lens 31, which has a high sensitivity to attitude errors, without increasing the size of the imaging device 100. Therefore, it is possible to suppress deterioration in image quality caused by thermal deformation of the lens surface of the fixed lens 31.

According to the present embodiment, an elastic heat transfer member 73 is disposed above the driving unit 71. The heat transfer member 73 abuts against the driving unit 71 and the metal plate 310 disposed above the imaging device 100.
As a result, the heat transfer member 73 flexibly deforms to come into surface contact with the driving unit 71 of the stepping motor 70 and the flat metal plate 310, promoting heat transfer between them. This ensures a stable thermal connection between the driving unit 71 and the flat metal plate 310, and allows the driving unit 71 to preferably dissipate heat. This makes it possible to preferably suppress a temperature rise in the imaging device 100, particularly a temperature rise in the resin lenses which are sensitive to thermal deformation.
In addition, an air layer is interposed between the metal plate 310, which the heat transfer member 73 abuts, and the imaging device 100 (portions other than the heat transfer member 73). As a result, the metal plate 310 and the imaging device 100 are insulated by the air layer, so that it is possible to suppress the heat of the drive unit 71 from being transferred through the metal plate 310 to the imaging device 100 (particularly the resin lens).

[Modification]
Next, a modification of the above embodiment will be described.
Fig. 11 is a perspective view of the imaging device 100A of this modification, Fig. 12(a) is a perspective view of the imaging device 100A seen from a different direction than in Fig. 11, and Fig. 12(b) is a side view of the imaging device 100A. Note that some parts (cover member 55, heat transfer member 73) are omitted from illustration in Fig. 11.
The imaging device 100A of this modification differs from the imaging device 100 of the above embodiment mainly in the ratio of the length of the fixed lens unit to the length of the main body in the front-to-rear direction. Below, differences from the above embodiment will be mainly described, and components similar to those in the above embodiment will be given the same reference numerals and their description will be omitted.

The imaging device 100A of this modification includes a fixed lens unit 30A and a main barrel 50A, instead of the fixed lens unit 30 and the main barrel 50 of the above embodiment.
In the fixed lens unit 30A, the interval between the fixed lenses 31 is wider and it is longer in the front-rear direction compared to the fixed lens unit 30 of the above embodiment. That is, compared to the above embodiment, the holding frame 32A is longer in the front-rear direction, and the fixing frame 21A of the reflecting member 20 that fixes it is also longer in the front-rear direction.
The main barrel 50A is shorter in the front-rear direction than the main barrel 50 of the above embodiment. More specifically, the main barrel 50A is shorter in the front-rear direction by retracting the front end portion by approximately the same amount as the fixed lens unit 30A is extended. Accordingly, the mounting position of the stepping motor 70 is also moved rearward.

This modification also provides the same effects as those of the above embodiment.
Furthermore, in this modification, the footprint of the imaging device 100A is smaller than that of the above embodiment, and the sensitivity to attitude errors of the movable lens unit 40 is also lower, which can further improve productivity.

Although one embodiment of the present invention has been described above, embodiments to which the present invention can be applied are not limited to the above-described embodiment and its variations, and can be modified as appropriate without departing from the spirit of the present invention.

ただし、
Ａｉ：ｉ次の非球面係数
Ｒ ：曲率半径
Ｋ ：円錐定数 Examples of the imaging optical system of the present invention will be described below. 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 element R: radius of curvature D: axial surface spacing Nd: refractive index for the d-line of the lens material vd: Abbe number of the lens material In each example, a surface having an "*" after each surface number in the lens surface data is a surface having an aspheric shape, and the shape of the aspheric surface is expressed by the following "Equation 1" with the vertex of the surface as the origin, the X-axis in the direction of the optical axis, and h as the height perpendicular to the optical axis.

however,
Ai: ith aspheric coefficient R: radius of curvature K: conic constant

Example 1
13 shows a cross-sectional view and an aberration diagram of the imaging optical system of Example 1. Of these, (a) is a cross-sectional view of the imaging optical system when the object distance is infinity, (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). When the object (subject) distance is infinity, the fourth lens L4 (movable lens 41) is closest to the fixed lens 31, and when the object distance approaches from this state, the fourth lens L4 moves toward the imaging sensor 60 (imaging surface I).
The imaging optical system of Example 1 corresponds to, but is not limited to, the imaging optical system 10 included in the imaging device 100 of the above embodiment.

The overall specifications of the imaging optical system of the first embodiment are shown below.
f = 29.15 mm
fB = 6.09 mm
F = 3.81
2Y = 5 mm

The lens surface data for Example 1 is shown in Table 1 below.

The aspheric coefficients of the lens surfaces in Example 1 are shown in the following Table 2. Note that hereinafter (including the lens data in the table), powers of 10 (for example, 2.5×10−02) will be represented using E (for example, 2.5E−02).

The single lens data for Example 1 is shown in Table 3 below.

The surface spacing data during focusing operation in Example 1 is shown in Table 4 below. Note that "Variable A" and "Variable B" in the table correspond to the numerical values in the corresponding columns for the on-axis surface spacing D in Table 1 above.

The values of the conditional expressions (1) to (3) in the imaging optical system of the first embodiment are shown below.
Conditional expression (1): K=2.80
Conditional expression (2): |f _focus /f|=0.55
Conditional expression (3): f1/f=0.36

Example 2
14 shows a cross-sectional view and aberration diagrams of the imaging optical system of Example 2. In these diagrams, (a) is a cross-sectional view of the imaging optical system when the object distance is infinity, (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, and distortion aberration).
The imaging optical system of the second embodiment corresponds to, but is not limited to, the imaging optical system included in the imaging device 100A of the modified example.

The overall specifications of the imaging optical system of the second embodiment are shown below.
f = 29.14 mm
fB = 6.06 mm
F = 3.81
2Y = 5 mm

The lens surface data for Example 2 is shown in Table 5 below.

The aspheric coefficients of the lens surfaces in Example 2 are shown in Table 6 below.

The single lens data for Example 2 is shown in Table 7 below.

The surface spacing data during focusing operation in Example 2 is shown in Table 8 below. Note that "Variable A" and "Variable B" in the table correspond to the numerical values in the corresponding columns for the on-axis surface spacing D in Table 5 above.

The values of the conditional expressions (1) to (3) in the imaging optical system of the second embodiment are shown below.
Conditional expression (1): K=0.90
Conditional expression (2): |f _focus /f|=0.88
Conditional expression (3): f1/f=0.40

Example 3
15 shows a cross-sectional view and aberration diagrams of the imaging optical system of Example 3. In these diagrams, (a) is a cross-sectional view of the imaging optical system when the object distance is infinity, (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, and distortion aberration).

The overall specifications of the imaging optical system of the third embodiment are shown below.
f = 29.15 mm
fB = 6.02 mm
F = 3.81
2Y = 5 mm

The lens surface data for Example 3 is shown in Table 9 below.

The aspheric coefficients of the lens surfaces in Example 3 are shown in Table 10 below.

The single lens data for Example 3 is shown in Table 11 below.

The surface spacing data during focusing operation in Example 3 is shown in Table 12 below. Note that "Variable A" and "Variable B" in the table correspond to the numerical values in the corresponding columns for the on-axis surface spacing D in Table 9 above.

The values of the conditional expressions (1) to (3) in the imaging optical system of the third embodiment are shown below.
Conditional expression (1): K=1.80
Conditional expression (2): |f _focus /f|=0.71
Conditional expression (3): f1/f=0.37

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 (imaging element)
70 Stepping motor 71 Drive unit (driving force generating unit)
71a Connection contact 72 Lead screw 73 Heat transfer member 100, 100A Imaging device 300 Portable terminal 310 Metal plate Ax1 First optical axis Ax2 Second optical axis L1 First lens L2 Second lens L3 Third lens L4 Fourth lens F Parallel plate I Imaging surface

Claims (8)

A single-focus imaging optical system that forms a subject image on a photoelectric conversion unit of an imaging element,
From the object side,
A reflective optical element that bends an incident light beam by 90 degrees;
a fixed optical system including at least one lens;
a movable optical system including only one lens having power and movable on an optical axis;
An imaging element;
It consists of:
The focal length is 120 mm or more in 35 mm equivalent.
An imaging optical system characterized by satisfying the following conditional expression:
0.5≦K≦2.8 (1)
however,
K: Amount of focus shift that changes when the movable optical system moves one position The imaging optical system according to claim 1, characterized in that the fixed optical system includes a lens having the largest effective diameter among all lenses included in the fixed optical system and the movable optical system. 3. The imaging optical system according to claim 1, wherein the following condition is satisfied:
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 the fixed optical system includes a first lens that is located closest to an object among all lenses included in the fixed optical system and the movable optical system,
4. The imaging optical system according to claim 1, wherein the following condition is satisfied:
0.25<f1/f<0.45...(3)
however,
f1: focal length of the first lens f: focal length of the entire imaging optical system The imaging optical system according to any one of claims 1 to 4, characterized in that at least one lens among all lenses included in the fixed optical system and the movable optical system has a non-circular shape. 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 comprising: Let us assume that a direction along a first optical axis on the object side of the reflecting optical element is a Y direction, a direction along a second optical axis on the fixed optical system side of the reflecting optical element perpendicular to the Y direction is a Z direction, and a direction perpendicular to both the Y direction and the Z direction is an X direction.
7. The imaging device according to claim 6, wherein the driving force generating unit of the stepping motor is disposed at a position closer to the imaging element than the movable optical system in the Z direction and at a position offset from the second optical axis in the X direction, and does not protrude on either side in the Y direction beyond other parts of the imaging device. the driving force generating unit has an electrical connection contact on a side surface in an X direction,
a heat transfer member having elasticity is disposed on the Y direction side of the driving force generating unit,
8. The imaging device according to claim 7, wherein the heat transfer member is in contact with a metal member disposed on the Y-direction side of the imaging device with an air gap therebetween and the driving force generating unit.

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