Patent Publication Number: US-2013242421-A1

Title: Position detection device, image pickup apparatus, and magnet

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. JP 2012-058214 filed in the Japanese Patent Office on Mar. 15, 2012, the entire content of which is incorporated herein by reference. 
     BACKGROUND 
     The present disclosure relates to a position detection device suitable for detecting a position of a lens in an optical axis direction, an image pickup apparatus equipped with the position detection device, and a magnet provided in the position detection device. 
     In general, lens drivers included in, for example, video cameras or digital still cameras having an autofocus function or a motorized zoom function are provided with a position detection device that detects a position of a moving focus lens or a moving zoom lens. For a position detection device of this type, in relatively many cases, a magneto resistive (MR) device such as an MR sensor is used, which converts the change in magnetic force of a magnet into an electrical signal. 
     Such a position detection device includes a magnet for positional detection and a magneto-resistive effect device, for example, as described in Japanese Unexamined Patent Application Publication No. 2002-169073. Specifically, the magnet for positional detection is magnetized to have the magnetic poles alternating along a travel direction of a moving part. The magneto-resistive effect device is configured to vary its resistance, according to the change in magnetism, and is secured to a fixed member so as to face an area over which the magnet for positional detection moves. 
     SUMMARY 
     Unfortunately, since magnets for positional detection, as described above, are magnetized to have the magnetic poles alternating along a travel direction of a moving part, there are cases where the magnetized widths of each N pole and each S pole vary from each other. These variations may become a factor of deteriorating the precision of detection. 
     There is a need for a position detection device that makes it possible to enhance the precision of detection, an image pickup apparatus equipped with the position detection device, and a magnet provided in the position detection device. 
     According to an embodiment of the present disclosure, there is provided a position detection device including a magnet and a magnetic detection device arranged opposite to each other to be relatively movable in a straight-line direction. The magnet has a first surface facing the magnetic detection device, and has periodic projections and recesses arrayed on the first surface in a relative movement direction. 
     In the position detection device according to the embodiment of the present disclosure, one of the magnet and the magnetic detection device moves relative to the other in the straight-line direction, together with a target for positional detection. This enables the magnetic detection device to detect a magnetic field on the first surface of the magnet which faces the magnetic detection device. 
     Since the periodic projections and recesses arrayed in the relative movement direction are provided on the first surface of the magnet which faces the magnetic detection device, the lowering of the detection precision due to the variation in the magnetized width is suppressed, as opposed to techniques in related art. Therefore, the detection precision is enhanced. 
     According to an embodiment of the present disclosure, there is provided an image pickup apparatus including: a lens configured to be movable in an optical axis direction; and a position detection device for the lens, and the position detection device includes a magnet and a magnetic detection device arranged opposite to each other to be relatively movable in a straight-line direction. The magnet has a first surface facing the magnetic detection device, and has periodic projections and recesses arrayed on the first surface in a relative movement direction. 
     In the image pickup apparatus according to the embodiment of the present disclosure, when the lens moves in the optical axis direction, the position detection device detects a position of the lens in the optical axis direction. 
     According to an embodiment of the present disclosure, there is provided a magnet to be provided in a position detection device. The position detection device performs positional detection by relatively moving a magnet and a magnetic detection device in a straight-line direction. The magnet and the magnetic detection device are arranged opposite to each other. The magnet includes periodic projections and recesses arrayed on a first surface in a relative movement direction, the first surface facing the magnetic detection device. 
     According to the position detection device, the image pickup apparatus, or the magnet according to the embodiment of the present disclosure, the first surface of the magnet which faces the magnetic detection device is provided with the periodic projections and recesses arrayed thereon in the relative movement direction. Consequently, the lowering of the detection precision due to the variation in the magnetized width is suppressed, as opposed to techniques in related art, so that the detection precision is enhanced. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the technology as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and, together with the specification, serve to explain the principles of the technology. 
         FIG. 1  is a perspective view illustrating an appearance of an image pickup apparatus according to a first embodiment of the present disclosure, as seen from the front. 
         FIG. 2  is a perspective view illustrating the appearance of the image pickup apparatus illustrated in  FIG. 1 , as seen from the rear. 
         FIG. 3  is a block diagram illustrating a control system in the image pickup apparatus illustrated in  FIG. 1 . 
         FIG. 4A  is a perspective view illustrating a lens barrel illustrated in  FIG. 1 , and  FIG. 4B  is a cross-sectional view schematically illustrating an internal structure of the lens barrel. 
         FIG. 5  is an explanatory view of a configuration of a lens guide mechanism, a lens movement mechanism, and a position detection device which are all related to a second moving lens illustrated in  FIG. 4 . 
         FIG. 6  is a schematic chart of respective detection results of two magnetic detection devices. 
         FIGS. 7A ,  7 B, and  7 C are a top view, a side view, and a bottom view, respectively, of a configuration of the magnet illustrated in  FIG. 5 . 
         FIG. 8  is a cross-sectional view of the magnet taken along a line VIII-VIII of  FIG. 7A . 
         FIGS. 9A ,  9 B, and  9 C are a top view, a side view, and a bottom view, respectively, of a configuration of a modification example of the magnet illustrated in  FIGS. 7A ,  7 B, and  7 C. 
         FIGS. 10A ,  10 B, and  10 C are a top view, a side view, and a bottom view, respectively, of a configuration of another modification example of the magnet illustrated in  FIGS. 7A ,  7 B, and  7 C. 
         FIGS. 11A ,  11 B, and  11 C are a top view, a side view, and a bottom view, respectively, of a configuration of still another modification example of the magnet illustrated in  FIGS. 7A ,  7 B, and  7 C. 
         FIG. 12  is a graph showing a relationship between a position scale of the magnet illustrated in  FIGS. 7A ,  7 B, and  7 C and an output of a magnetic detection device. 
       Parts (A), (B), and (C) of  FIG. 13  are a top view, a side view, and a bottom view, respectively, of a configuration of a magnet in a position detection device according to a second embodiment of the present disclosure. 
         FIG. 14  is a graph showing a relationship between a position scale of the magnet illustrated in  FIG. 13  and an output of a magnetic detection device. 
       Parts (A), (B), and (C) of  FIG. 15  are a top view, a side view, and a bottom view, respectively, of a configuration of a magnet in a position detection device according to a third embodiment of the present disclosure. 
         FIG. 16  is a graph showing a relationship between a position scale of the magnet illustrated in  FIG. 15  and an output of a magnetic detection device. 
         FIG. 17A  is a side view illustrating the configuration of the magnet of the second embodiment, and  FIG. 17B  is a side view illustrating a configuration of a magnet in a position detection device according to Modification example 1. 
         FIG. 18  is a graph showing a relationship between a position scale of the magnet illustrated in  FIG. 17B  and an output of a magnetic detection device. 
         FIG. 19A  is a side view illustrating the configuration of the magnet of the second embodiment, and  FIG. 19B  is a side view illustrating a configuration of magnets according to Modification examples 2-1 to 2-3. 
         FIG. 20  is a graph showing a relationship between a position scale of the magnet according to Modification example 2-1 and an output of a magnetic detection device. 
         FIG. 21  is a graph showing a relationship between a position scale of the magnet according to Modification example 2-2 and an output of a magnetic detection device. 
         FIG. 22  is a graph showing a relationship between a position scale of the magnet according to Modification example 2-3 and an output of a magnetic detection device. 
         FIG. 23A  is a side view illustrating the configuration of the magnet of the second embodiment, and  FIG. 23B  is a side view illustrating a configuration of a magnet according to Modification example 3. 
         FIG. 24  is a graph showing a relationship between a position scale of the magnet illustrated in  FIG. 23B  and an output of a magnetic detection device. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present disclosure will be described in detail, with reference to the accompanying drawings. It is to be noted that the description will be given in the following order. 
     1. First embodiment (an example in which: projections and recesses are alternately provided, as periodic projections and recesses, on a first surface of a magnet which faces a magnetic detection device; ribs are provided on both side edges of the first surface of the magnet; and rectangular holes are provided as the recesses) 
     2. Second embodiment (an example in which in the first embodiment, an inclined section and a flat section are provided in each longitudinal outer region on a second surface of the magnet) 
     3. Third embodiment (an example in which: grooves are provided as the recesses; and the inclined section and the flat section are provided in each longitudinal outer region on the second surface of the magnet) 
     4. Modification example 1 (an example in which in the second embodiment, the length of the middle region is increased) 
     5. Modification examples 2-1 to 2-3 (an example of a linear inclination structure in which in the second embodiment, only the inclined section is provided in each longitudinal outer region) 
     6. Modification example 3 (an example of a double inclination structure in which in the second embodiment, two inclined sections and a flat intermediate section therebetween are provided) 
     First Embodiment 
       FIGS. 1 and 2  illustrate an appearance of an image pickup apparatus  1  (digital still camera) according to a first embodiment of the present disclosure, as seen from the front and rear, respectively. The image pickup apparatus  1  has a configuration, for example, where a lens barrel  11  having a collapsible mechanism is attached to a surface of a housing  10  (an exterior member) which faces a subject, namely, to the front surface of the housing  10 . A flash  12  that emits assist light for capturing, and a self-timer lamp  13  are arranged in the vicinity of the lens barrel  11 . An image pickup optical system  14  and an image pickup device  15  (not illustrated in  FIG. 1 , see  FIG. 3  or  4 ) are arranged inside the lens barrel  11 . 
     Herein, the “front” refers to a side facing an object or a subject in a direction along an optical axis Z of the image pickup optical system  14 . The “rear” refers to a side on which an image is created or an image pickup device  15  is disposed. 
     The image pickup optical system  14  is configured to be moved by a lens drive section  25 A (not illustrated in  FIG. 1 , see  FIG. 3 ) built into the housing  10 . Specifically, the image pickup optical system  14  is movable along the optical axis Z between a capturing position (a wide-angle state, a telephoto state, or an intermediate state therebetween) and an accommodated position (collapsed position). In the capturing position, the image pickup optical system  14  protrudes forwardly from the front surface of the housing  10 , and in the accommodated position, the image pickup optical system  14  is embedded in the front surface of the housing  10 . The image pickup device  15  captures an image of a subject formed by the image pickup optical system  14 , and includes, for example, charge coupled devices (CCD) or CMOS image sensors. 
     The upper surface of the housing  10  is provided with, for example, a shutter button  16  used to capture an image, a zoom operation lever  17  used to adjust a zoom of the image pickup optical system  14 , and a power button  18 . 
     The rear surface of the housing  10  is provided with, for example, a display section  19  having a touch panel function for menu selection. Optionally, an operation switch for menu selection (not illustrated) may be provided independently of the display section  19 , in place of the touch panel function of the display section  19 . 
       FIG. 3  illustrates a control system of the image pickup apparatus  1 . The image pickup apparatus  1  includes, for example, the lens barrel  11 , the display section  19 , an image recording/reproducing circuit  21 , an internal memory  22 , an external memory  23 , an image signal processing section  24 , a lens barrel control section  25 , a monitor drive section  26 , an amplifier  27 , a first interface  28 , and a second interface  29 . 
     The image recording/reproducing circuit  21  has, for example, an arithmetic circuit with a microcomputer (central processing unit (CPU)). In addition, the image recording/reproducing circuit  21  controls the image signal processing section  24 , the monitor drive section  26 , and the lens barrel control section  25 , according to an operation with the shutter button  16 , the zoom operation lever  17 , the power button  18 , the touch panel of the display section  19 , or the like. The image recording/reproducing circuit  21  is connected to the internal memory  22 , the image signal processing section  24 , the lens barrel control section  25 , the monitor drive section  26 , the amplifier  27 , the first interface (I/F)  28 , and the second interface (I/F)  29 . 
     The internal memory  22  includes, for example, in addition to a program memory and a data memory that are used to drive the image recording/reproducing circuit  21 , a random access memory (RAM) and a read only memory (ROM). The external memory  23  is used to expand the total memory capacity. 
     The image signal processing section  24  generates image data, based on a captured image signal outputted from the image pickup device  15 , and enters the generated image data into the image recording/reproducing circuit  21 . The image signal processing section  24  is connected to the image pickup device  15  attached to the lens barrel  11  through the amplifier  27 . 
     The lens barrel control section  25  controls the driving of the lens barrel  11 . The lens barrel control section  25  is connected to the lens drive section  25 A and a position detection device  30 . The lens drive section  25 A performs zoom operation and focus operation of the lens barrel  11 . The position detection device  30  detects a position of a lens in the image pickup optical system  14 , and supplies the detection result to the lens barrel control section  25 . The detail of the position detection device  30  will be described later. 
     The display section  19  is connected to the image recording/reproducing circuit  21  through the monitor drive section  26 . The monitor drive section  26  displays image data on the display section  19 . 
     The first interface  28  is connected to a connector  28 A, and the external memory  23  is detachably connectable to the first interface  28 . The second interface  29  is connected to a connection terminal  29 A provided in the housing  10 . 
       FIG. 4A  illustrates an appearance of the lens barrel  11  illustrated in  FIG. 1  in a protruding state, and  FIG. 4B  illustrates an internal configuration of the lens barrel  11 . The lens barrel  11  includes a decorative ring  11 A, a barrier unit  11 B, a first lens frame  11 C, a first moving frame  11 D, a second moving frame  11 E, a linear movement guide ring  11 F, a rotation ring  11 G, a fixed ring  11 H, and a rear barrel  11 I, in this order of closeness to a subject. The image pickup optical system  14  includes, for example, a first lens group  14 A, a second lens group  14 B, and a third lens group  14 C along the optical axis Z, in this order from the front (subject side) to the rear. 
     The fixed ring  11 H is fixed to the housing  10 . The rear barrel  11 I is detachably fixed to the rear of the fixed ring  11 H with a plurality of fastening screws (not illustrated). The rear barrel  11 I is provided with a substantially quadrangular through-hole at the center thereof, and the image pickup device  15  is attached to the through-hole. 
     The rotation ring  11 G is rotatable around the optical axis Z relative to the fixed ring  11 H, and is linearly movable in the direction along the optical axis Z relative thereto. In more detail, the rotation ring  11 G has a gear train (not illustrated) on the outer periphery thereof, and is rotatable around the optical axis Z by the driving of a drive motor (not illustrated) fixed between the fixed ring  11 H and the rear barrel  11 I. In addition, the rotation ring  11 G is provided with three cam pins (not illustrated), and the cam pins engage with three corresponding cam grooves (not illustrated) provided on the inner periphery of the fixed ring  11 H. Accordingly, the rotation ring  11 G is movable in the direction along the optical axis Z along tracks formed by the cam grooves of the fixed ring  11 H, along with the relative rotation of the rotation ring  11 G to the fixed ring  11 H. 
     The linear movement guide ring  11 F is permitted only to linearly move relative to the fixed ring  11 H in the direction along the optical axis Z without rotating relative thereto. In more detail, the linear movement guide ring  11 F has five projections (not illustrated) to fit into the fixed ring  11 H, and the projections engage with five corresponding straight grooves (not illustrated) provided in the fixed ring  11 H. As a result, the linear movement guide ring  11 F is permitted only to move in the direction along the optical axis Z relative to the fixed ring  11 H, and movement of the linear movement guide ring  11 F is restricted in a rotational direction. 
     When the rotation ring  11 G and the linear movement guide ring  11 F are bayonet-coupled to each other in the above-described manner, the linear movement guide ring  11 F is permitted to linearly move without any suppression from the rotation of the rotation ring  11 G. Moreover, when the rotation ring  11 G moves in the direction along the optical axis Z, the linear movement guide ring  11 F moves integrally with the rotation ring  11 G. 
     The first lens frame  11 C holds the first lens group  14 A, and is held by the first moving frame  11 D. The first moving frame  11 D moves the first lens frame  11 C. The second moving frame  11 E moves the second lens group  14 B while holding it. 
     Each of the first moving frame  11 D and the second moving frame  11 E is permitted only to linearly move in the direction along the optical axis Z relative to the fixed ring  11 H without rotating relative thereto. Specifically, each of the first moving frame  11 D and the second moving frame  11 E is provided with three cam pins (not illustrated). The cam pins engage with three corresponding cam grooves (not illustrated) provided on the inner periphery of the rotation ring  11 G. Furthermore, each of the first moving frame  11 D and the second moving frame  11 E also engages with straight grooves (not illustrated) of the linear movement guide ring  11 F, so as not to rotate in conjunction with the rotation of the rotation ring  11 G. 
     The barrier unit  11 B closes an optical path, or a photographing opening, when photographs are not taken, in order to protect the image pickup optical system  14 . 
     The cosmetic ring  11 A is fixed to the first moving frame  11 D, in order to improve the appearance of the lens barrel  11  and protect the barrier unit  11 B. Any kind of metal, such as aluminum alloy and stainless steel is suitable for a material of the cosmetic ring  11 A, but an engineering plastic may also be used therefor. 
       FIG. 5  is an explanatory view of a configuration of the lens guide mechanism  40 , the lens movement mechanism  50 , and the position detection device  30 , which are all related to the third lens group  14 C illustrated in  FIG. 4 . 
     The lens guide mechanism  40  supports the third lens group  14 C on a base  11 J fixed to the fixed ring  11 H, so as to allow the third lens group  14 C to be movable in the direction along the optical axis Z. The lens guide mechanism  40  includes, for example, a lens holding frame  41 , a sleeve section  42 , a groove section  43 , a first guide spindle (not illustrated), and a second guide spindle (not illustrated). The lens holding frame  41  is a ring-shaped member that holds the third lens group  14 C. Both the sleeve section  42  and the groove section  43  are provided in the outer region of the lens holding frame  41 . The first and second guide spindles (not illustrated) are disposed to pass through the sleeve section and the groove section  43 , respectively while being parallel to the optical axis Z. This enables the third lens group  14 C held by the lens holding frame  41  to linearly reciprocate along the optical axis Z. 
     The lens movement mechanism  50  includes, for example, a driving coil  51 , an opposed yoke  52 , a driving magnet  53 , and a ground yoke  54 . The driving coil  51  is formed by winding a wire around an imaginary axis parallel to the optical axis Z, and is secured to the lens holding frame  41  with, for example, an adhesive. The inner periphery of the driving coil  51  is opened in front-and-rear directions. The opposed yoke  52  has a rectangular-plate shape, and is loosely inserted into the inner periphery of the driving coil  51 , so as to be disposed parallel to the optical axis Z. The driving magnet  53  has a rectangular-plate shape, and is disposed on the outer periphery of the driving coil  51  while being parallel to the opposed yoke  52 . The ground yoke  54  has a rectangular-plate shape which is substantially the same as that of the driving magnet  53 , and is provided between the driving magnet  53  and the base  11 J. 
     The lens movement mechanism  50  is driven by the lens drive section  25 A (see  FIG. 3 ). The lens drive section  25 A includes a D/A convertor  25 A 1  and a motor driver  25 A 2 , as illustrated in  FIG. 5 . The D/A convertor  25 A 1  D/A-converts a drive signal in a digital format that is supplied from the lens barrel control section  25  (see  FIG. 3 ). The motor driver  25 A 2  supplies a drive current to the driving coil  51 , based on a drive signal in an analog format that is supplied from the D/A convertor  25 A 1 . This enables the lens movement mechanism  50  to move the lens holding frame  41  in a direction along the optical axis Z, by a magnetic interaction between a magnetic field generated by the driving magnet  53  and a magnetic field generated by the driving coil  51  based on the drive current from the lens drive section  25 A. 
     The position detection device  30  includes, for example, a positional detection magnet  31  (hereinafter, referred to as simply “magnet  31 ”), a magnetic detection device  32 , and a positional information generating section  33 . 
     The magnet  31  and the magnetic detection device  32  are arranged opposite to each other, so as to be relatively movable in a straight-line direction. In more detail, the magnet  31  is held by, for example, a holding member (not illustrated) secured to the sleeve section  42 , and is linearly movable in the direction along the optical axis Z, together with the third lens group  14 C, or a target for positional detection, and the lens holding frame  41 . On the other hand, the magnetic detection device  32  is fixed to the base  11 J by a holding member (not illustrated) while facing the magnet  31 . 
     The magnetic detection device  32  generates a detection signal (position signal) Ss of a level corresponding to the strength of a magnetic force generated between the poles of the magnet  31 . For example, the magnetic detection device  32  may be a Hall device. Since a Hall device generates a voltage proportional to a magnetic flux density, the detection signal Ss outputted from the Hall device has a voltage corresponding to (or proportional to) the strength of an exerted magnetic force (or the magnitude of the magnetic flux density). If a distance between the magnet  31  and the magnetic detection device  32  is adjusted appropriately, the detection signal Ss outputted from the magnetic detection device  32  becomes a substantially sinusoidal signal. It is to be noted that the magnetic detection device  32  is not limited to a Hall device. The magnetic detection device  32  may be any given device as long as it detects the strength of a magnetic force and generates the detection signal Ss. For example, the magnetic detection device  32  may be an MR device. 
     Although it is not illustrated, it is preferable that the magnetic detection device  32  be composed of two device units arranged along a relative movement direction A 1  in which the magnetic detection device  32  and the magnet  31  move relative to each other. As illustrated in  FIG. 6 , by outputting respective substantially sinusoidal signals with different phases (first phase S 1  and second phase S 2 ), from the two device units of the magnetic detection device  32 , it is possible to determine a direction in which the third lens group  14 C moves. 
     The positional information generating section  33  includes, for example, an amplifier circuit  33 A and an A/D convertor  33 B. The amplifier circuit  33 A amplifies the detection signal Ss from the magnetic detection device  32 . The A/D convertor  33 B converts the detection signal Ss in an analog format which has been amplified by the amplifier circuit  33 A into a detection signal Ss in a digital format, and then supplies the converted detection signal Ss to the lens barrel control section  25  as positional information regarding the third lens group  14 C. As a result, the lens barrel control section  25  detects a position of the third lens group  14 C in the direction along the optical axis Z, based on the detection signal Ss. Then, the lens barrel control section  25  supplies a drive signal to the lens drive section  25 A, according to the detection result, thereby controlling the position of the third lens group  14 C in the direction along the optical axis Z and the closed loop of, for example, a servomechanism. 
       FIGS. 7A ,  7 B, and  7 C illustrate a configuration of the magnet  31  illustrated in  FIG. 5 .  FIG. 8  illustrates a cross section of the magnet  31  taken along a line VIII-VIII of  FIG. 7A . The magnet  31  is a rectangular parallelepiped, bar-shaped member that linearly extends in the relative movement direction A 1 . The magnet  31  has a first surface  31 A facing the magnetic detection device  32 , and on the first surface  31 A, periodic projections and recesses  34  are arrayed in the relative movement direction A 1 . With the periodic projections and recesses  34  in the image pickup apparatus  1 , the lowering of the detection precision due to the variation in the magnetized width is suppressed, as opposed to techniques in related art. Therefore, the detection precision is enhanced. 
     It is preferable that the magnet  31  be formed of, for example, a resin magnet. In this case, it is possible to mold the magnet  31  precisely at a low cost by employing an injection molding method. Further, a variation in the period of the sinusoidal output signal is reduced, thereby being able to provide more precise positional detection than a magnet formed with a magnetization method of the related art does. Furthermore, a complex, expensive magnetizing device, such as that for use in related art, is made unnecessary, and thus the cost reduction in the magnet  31  is achievable. Alternatively, the magnet  31  may be formed of a ferrite magnet. 
     It is preferable that the magnet  31  be magnetized in a single direction from a second surface  31 B to the first surface  31 A as an arrow A 2  illustrated in  FIG. 7B  or  8 , or from the first surface  31 A to the second surface  31 B (not illustrated). This enables the magnetization process to be performed easier than that in the case in which the magnetic poles of a magnet alternating along the movement direction as in related art. Thus, if the first surface  31 A is an N pole, the second surface  31 B becomes an S pole, as illustrated in  FIGS. 7B and 8 . Otherwise, if the first surface  31 A is an S pole, the second surface  31 B becomes an N pole (not illustrated). As described above, the magnetizing direction A 2  of the magnet  31  is parallel to the direction in which the magnet  31  faces the magnetic detection device  32 , and is vertical to the relative movement direction A 1 . 
     The magnet  31  has projections  34 A and recesses  34 B arranged alternately, as the periodic projections and recesses  34 . The recesses  34 B are depressions, more specifically, rectangular holes formed at regular intervals in the relative movement direction A 1 , for example, as illustrated in  FIGS. 7A , and  8 . The longer side of each of the projections  34 A and the recesses  34 B is vertical to the relative movement direction A 1 . Alternatively, each of the recesses  34 B may be a through-hole (namely, the depth of each of the recesses  34 B is equal to the thickness of the magnet  31 ), for example, as illustrated in  FIG. 9 . 
     The planar shape of each of the periodic projections and recesses  34  is not limited to rectangular as illustrated in  FIGS. 7A , and  8 , but may be circular, elliptic, or other shapes as illustrated in  FIG. 10  or  11 . 
     It is preferable that the periodic projections and recesses  34  include a starting projection at the end of the magnet in the relative movement direction A 1 . With this arrangement, the waveform is less distorted at the ends thereof. In the cases of  FIGS. 7A to 11C , for example, nine and a half periods of periodic projection and recess  34  and nine recesses  34 B are provided. However, there is no limitation on the number of periods of the periodic projection and recess  34  and the number of the recesses  34 B. They may be varied as appropriate, according to a distance over which the image pickup optical system  14  moves. 
     It is preferable that the magnet  31  be provided with ribs  35  on both side edges of the first surface  31 A. Providing the ribs  35  reduces the warping of the magnet  31  due to the expansion and contraction of the resin upon molding, thus achieving the more precise positional detection. It is preferable that the ribs  35  be provided on both side edges of the first surface  31 A, as illustrated in  FIG. 7A , but the single rib  35  may be provided on either of the two side edges of the first surface  31 A. Alternatively, holes with a depth the same as that of each of the recesses  34 B may be provided on the second surface  31 B, in place of the ribs  35 . Even in this case, the same effect is attained. 
     The magnet  31 , as described above, may be manufactured through the following processes. First, a magnetic powder is set in a die (not illustrated), and is molded and sintered by an injection molding method. Subsequently, the resulting body is magnetized with an air core coil. In the first embodiment, the magnet  31  is manufactured through a molding process using a die, and the magnetizing process is easily performed. Therefore, it is possible to produce the positional detection magnet  31  at a lower cost and with a smaller range of variation than a magnet, as in related art, which is magnetized to have the magnetic poles alternating along the relative movement direction. 
     In the image pickup apparatus  1 , the lens barrel control section  25  drives the lens drive section  25 A according to an operation with the zoom operation lever  17 . Then, the third lens group  14 C of the image pickup optical system  14  is moved in the direction along the optical axis Z. Accordingly, the magnet  31  of the position detection device  30  linearly moves relative to the magnetic detection device  32  in the direction along the arrow A 1 , together with the third lens group  14 C that is a target for positional detection. Then, the magnetic detection device  32  detects a magnetic field on the first surface  31 A of the magnet  31  which faces the magnetic detection device  32 . 
     In this case, the first surface  31 A of the magnet  31  is provided with the periodic projections and recesses  34  arrayed thereon in the relative movement direction A 1 . With the periodic projections and recesses  34 , the lowering of the detection precision due to the variation in the magnetized width is suppressed, as opposed to techniques of the related art. Therefore, the detection precision is enhanced. 
       FIG. 12  schematically shows a measurement result of a magnetic field on the first surface  31 A of the magnet  31 . In this measurement, a Hall device was used as the magnetic detection device  32 , and a magnetic flux density that was vertical to the first surface  31 A was detected. 
     As seen from  FIG. 12 , a proper, substantially sinusoidal output was obtained from a middle region  31 C of the magnet  31  in the relative movement direction A 1 . In contrast, the output waveform was distorted at each outer region  31 D outside the middle region  31 C. However, when a sufficient margin is provided in each outer region  31 D, it is possible to use only the middle region  31 C, in which the output is a substantially sinusoidal waveform, for positional detection. 
     As described above, in the first embodiment, the first surface  31 A of the magnet  31  is provided with the periodic projections and recesses  34  arrayed in the relative movement direction A 1 . With the periodic projections and recesses  34 , the lowering of the detection precision due to the variation in the magnetized width is suppressed, as opposed to techniques of the related art. Consequently, the detection precision is enhanced. 
     Second Embodiment 
     Parts (A), (B), and (C) of  FIG. 13  illustrate a configuration of a magnet  31  in a position detection device  30  according to a second embodiment of the present disclosure. In the second embodiment, the thickness of the magnet  31  in the middle thereof is set larger than that at each end thereof, in the relative movement direction A 1 . Aside from this, the magnet  31  according to the second embodiment has the same configuration as the first embodiment does. In addition, the magnet  31  of the second embodiment may be manufactured through the same process as that of the first embodiment. Accordingly, in the following description, the same reference numerals are assigned to components corresponding to those of the first embodiment. 
     The magnet  31  includes a middle region  31 C disposed in the middle of the magnet  31  along the relative movement direction A 1 , and outer regions  31 D arranged on the respective outer sides of the middle region  31 C. A thickness d 2  of the middle region  31 C is uniform. 
     The thickness d 2  of the magnet  31  in the middle thereof along the relative movement direction A 1  (namely, the thickness d 2  of the middle region  31 C) is larger than a thickness d 1  at each end  31 E thereof along the relative movement direction A 1 . With this configuration, in the second embodiment, increase in permeance in each outer region  31 D is suppressed, when the magnet  31  and the magnetic detection device  32  move relative to each other. This makes it possible to obtain the proper, substantially sinusoidal output from not only the middle region  31 C but also each of the outer regions  31 D. 
     Specifically, each of the outer regions  31 D on the second surface  31 B includes an inclined section  31 F inclined with respect to the relative movement direction A 1 . It is preferable that a thickness d 3  of each inclined section  31 F be increased toward the middle region  31 C. With this inclined section  31 F, an effect of improving the distortion of an output waveform from each outer region  31 D is further enhanced. 
     Herein, each of the thicknesses d 1 , d 2 , and d 3  refers to a thickness of the magnet  31  in the magnetizing direction A 2 , namely, a distance between the second surface  31 B and the projection  34 A of the periodic projection and recess  34 . 
     It is preferable that each outer region  31 D on the second surface  31 B have the inclined section  31 F and a flat section  31 G in this order of closeness to the middle region  31 C. Providing the flat sections  31 G facilitates the positioning of the magnet  31  during an attachment process and to improve the precision with which the magnet  31  is molded. 
     The magnetic detection device  32  and the positional information generating section  33  are configured to be the same as those in the above-described first embodiment. 
     In the image pickup apparatus  1 , the lens barrel control section  25  drives the lens drive section  25 A according to an operation with the zoom operation lever  17 . Then, the third lens group  14 C of the image pickup optical system  14  is moved in the direction along the optical axis Z. Accordingly, the magnet  31  of the position detection device  30  linearly moves relative to the magnetic detection device  32  in a direction of the arrow A 1 , together with the third lens group  14 C that is a target for positional detection. As a result, the magnetic detection device  32  detects a magnetic field on the first surface  31 A of the magnet  31  which faces the magnetic detection device  32 . 
     In this case, since the thickness d 2  of the magnet  31  in the middle thereof (the middle region  31 C) is larger than the thickness d 1  at each end  31 E thereof, increase in permeance in each outer region  31 D is suppressed, when the magnet  31  and the magnetic detection device  32  move relative to each other. This makes it possible to obtain the proper, substantially sinusoidal output from not only the middle region  31 C but also each outer region  31 D. 
       FIG. 14  schematically shows a measurement result of a magnetic field on the first surface  31 A of the magnet  31 . In this measurement, a Hall device was used as the magnetic detection device  32 , and a magnetic flux density that was vertical to the first surface  31 A was detected. Moreover, the periodic projections and recesses  34  included a starting projection  34 A at the end of the magnet  31  in the relative movement direction A 1 . Each flat section  31 G was provided so as to face a projection  34 A and a recess  34 B of a first period and a projection  34 A of a second period, with respect to the corresponding starting projection  34 A. In addition, each inclined section  31 F was provided so as to face a recess  34 B of the second period and a projection  34 A of a third period, with respect to the corresponding starting projection  34 A. It is to be noted that  FIG. 14  also shows the measurement result of the first embodiment illustrated in  FIG. 12 . 
     It is found from  FIG. 14  that in the first embodiment, the amplitude and a midpoint of the amplitude of the output waveform in the vicinity of the third period from each end starts being varied in comparison with those of the middle region  31 C. In contrast, it is found that in the second embodiment, the amplitudes and midpoints of the amplitudes of the output waveform are substantially constant between the 0.5th periods from the respective ends. Consequently, the second embodiment enables the total length of the magnet  31  to be decreased by a length corresponding to five periods (2.5 periods×both ends=5 periods). 
     Incidentally, a rotational angle detection method is known, which utilizes a variation in magnetism generated by the projections and recesses of a toothed wheel, as described in Japanese Unexamined Patent Application Publication No. 2003-180672 (FIG. 4). However, in the case where linear movement is detected using the projections and recesses of the toothed wheel described in this document, in place of rotational movement, a fragment of the ring-shaped toothed wheel is extracted and flattened to be used as a magnet or a magnetic unit of a limited length. In this case, disadvantageously, the magnetic field on the magnet or the magnetic unit of a limited length may be distorted in both outer regions thereof. Therefore, there are cases where an output signal from a sensor equipped with such a magnet or such a magnetic unit is distorted in both outer regions of the stroke. As a result, a margin with a sufficient length is provided in each outer region of the magnet or the magnetic unit, and only a region of the magnet or the magnetic unit in which the output waveform is not distorted is utilized. In this case, it may be necessary to increase the magnet or the magnetic unit in length, and if a lens barrel is equipped with this position detection device, the lens barrel is prone to being enlarged in a direction along an optical axis. 
     In contrast, in the second embodiment, the thickness d 2  of the magnet  31  in the middle thereof (the middle region  31 C) is larger than the thickness d 1  at each end  31 E thereof, in the relative movement direction A 1 , thereby reducing the distortion of the output waveform from each outer region  31 D of the magnet  31 . Consequently, it is possible to decrease the total length of the magnet  31  by reducing the margin of each outer region  31 D of the magnet  31 , and therefore it is possible to reduce the size of the magnet  31  in the relative movement direction A 1 . Furthermore, since the respective total lengths of the position detection device  30  and the lens barrel  11  equipped with the above position detection device  30  are decreased in a direction along an optical axis, it is also possible to provide the compact and thin image pickup apparatus  1 . 
     As described above, in the second embodiment, the thickness d 2  of the magnet  31  in the middle thereof (the middle region  31 C) is larger than the thickness d 1  at each end  31 E thereof, by providing each outer region  31 D in the second surface  31 B with the inclined section  31 F and the flat section  31 G. This makes it possible to obtain proper, substantially sinusoidal output from not only the middle region  31 C of the magnet  31  but also each outer region  31 D thereof. Furthermore, it is achieved that the total length of the magnet  31  is decreased. This configuration is advantageous in terms of miniaturizing both the position detection device  30  and the lens barrel  11 , more specifically, decreasing the thickness of the image pickup apparatus  1 . 
     The description of the second embodiment has been given regarding to the case where the inclined section  31 F and the flat section  31 G are provided in the outer region  31 D of the second surface  31 B, so that the thickness d 2  of the magnet  31  in the middle thereof (the middle region  31 C) is larger than the thickness d 1  at each end  31 E thereof in the relative movement direction A 1 . However, another configuration, such as that where the recesses  34 B in each outer region  31 D are formed more deeply, may be employed, in order to cause the thickness d 2  of the magnet  31  in the middle thereof (the middle region  31 C) to be larger than the thickness d 1  at each end  31 E thereof in the relative movement direction A 1 . 
     Third Embodiment 
     Parts (A), (B), and (C) of  FIG. 15  illustrate a configuration of a magnet  31  of a position detection device  30  according to a third embodiment of the present disclosure. Except that the periodic projections and recesses  34  include, as recesses, grooves provided across the first surface  31 A in a direction along the width of the first surface  31 A, the magnet  31  according to the third embodiment has a similar configuration to that of the second embodiment. In addition, the magnet  31  according to the third embodiment may be manufactured through the same process as the first embodiment. Accordingly, in the following description, the same reference numerals are assigned to components corresponding to those of the first or second embodiment. 
       FIG. 16  schematically shows a measurement result of a magnetic field on the first surface  31 A of the magnet  31 . In this case, a Hall device was used as the magnetic detection device  32 , and a magnetic flux density that was vertical to the first surface  31 A was detected. Moreover, the periodic projections and recesses  34  included a starting projection  34 A at the end of the magnet  31  in the relative movement direction A 1 . Each flat section  31 G was provided so as to face projections  34 A and recesses  34 B of first and second periods, with respect to the corresponding starting projection  34 A, and each inclined section  31 F was provided so as to face a projection  34 A of the third period. It is to be noted that  FIG. 16  also shows the measurement result of the first embodiment illustrated in  FIG. 12 . 
     It is found from  FIG. 16  that in the first embodiment, the amplitude and a midpoint of the amplitude of the output waveform in the vicinity of the third period from each end starts being varied in comparison with those of the middle region  31 C. In contrast, it is found that in the third embodiment, the amplitudes and midpoints of the amplitudes of the output waveform are substantially constant between the 0.5th periods from the respective ends. Consequently, the third embodiment enables the total length of the magnet  31  to be decreased by a length corresponding to five periods (2.5 periods×both ends=5 periods). Thus, since the respective total lengths of the position detection device  30  and the lens barrel  11  equipped with the above position detection device  30  are decreased in a direction along an optical axis, it is possible to provide the compact and thin image pickup apparatus  1 . 
     As described above, in the third embodiment, the thickness d 2  of the magnet  31  in the middle thereof (the middle region  31 C) is larger than the thickness d 1  at each end  31 E thereof, similar to the second embodiment. This makes it possible to obtain proper, substantially sinusoidal output from not only the middle region  31 C of the magnet  31  but also each outer region  31 D thereof. Accordingly, it is achieved that the total length of the magnet  31  is decreased. This configuration is advantageous in terms of miniaturizing both the position detection device  30  and the lens barrel  11 , more specifically, decreasing the thickness of the image pickup apparatus  1 . 
     Hereinafter, description will be given of Modification examples 1 to 3 of the present disclosure. All of Modification examples 1 to 3 are based on the magnet  31  of the above-described second embodiment. 
     Modification Example 1 
       FIG. 17A  illustrates the configuration of the magnet of the second embodiment, and  FIG. 17B  illustrates a configuration of a magnet  31  according to Modification example 1. Except that the length of the middle region  31 C is increased by approximately half from the length of the magnet  31  of the second embodiment, this modification example has a similar configuration as that of the second embodiment. In addition, the magnet  31  according to the modification example may be manufactured through the same process as the first embodiment is. Accordingly, in the following description, the same reference numerals are assigned to components corresponding to those of the first or second embodiment. 
       FIG. 18  schematically shows a measurement result of a magnetic field on the first surface  31 A of the magnet  31 . In this measurement, a Hall device was used as the magnetic detection device  32 , and a magnetic flux density that was vertical to the first surface  31  was detected. Moreover, the periodic projections and recesses  34  included a starting projection  34 A at the end of the magnet  31  in the relative movement direction A 1 . Each flat section  31 G was provided so as to face a projection  34 A and a recess  34 B of a first period and a projection  34 A of a second period, with respect to the corresponding starting projection  34 A, and each inclined section  31 F was provided so as to face a recess  34 B of the second period and a projection  34 A of a third period. It is to be noted that  FIG. 18  also shows the measurement result of the first embodiment illustrated in  FIG. 12 . 
     It is found from  FIG. 18  that in the first embodiment, the amplitude and a mid point of the amplitude of the output waveform in the vicinity of the third period from each end starts being varied in comparison with those of the middle region  31 C. In contrast, it is found that in this modification example, the amplitudes and midpoints of the amplitudes of the output waveform are substantially constant between the first periods from the respective ends. 
     Consequently, this modification example enables the total length of the magnet  31  to be decreased by a length corresponding to four periods (2 periods×both ends=4 periods). 
     Consequently, it is evident that the proper, substantially sinusoidal output is obtainable from not only the middle region  31 C but also each outer region  31 D even when the length of the middle region  31 C is increased, as long as the thickness d 2  of the magnet  31  in the middle thereof (the middle region  31 C) is set larger than the thickness d 1  at each end  31 E thereof in the relative movement direction A 1  by providing each outer region  31 D on the second surface  31 B with the inclined section  31 F and the flat section  31 G. 
     Modification Example 2-1 to 2-3 
       FIG. 19A  illustrates the configuration of the magnet  31  of the second embodiment, and  FIG. 19B  illustrates a configuration of a magnet  31  according to Modification examples 2-1 to 2-3. Except that only the inclined section  31 F is provided in each of the outer regions  31 D on the second surface  31 B and the flat section  31 G is removed in the magnet  31  of the second embodiment, each of the modification examples has a similar configuration to that of the second embodiment. In addition, each of the magnets  31  according to Modification examples 2-1 to 2-3 may be manufactured through a similar process to that of the first embodiment. Accordingly, in the following description, the same reference numerals are assigned to components corresponding to those of the first or second embodiment. 
       FIGS. 20 to 22  schematically show measurement results of a magnetic field on the first surface  31 A of the magnet  31 . In this measurement, a Hall device was used as the magnetic detection device  32 , and a magnetic flux density that was vertical to the first surface  31  was detected. Moreover, the periodic projections and recesses  34  included a starting projection  34 A at the end of the magnet  31  in the relative movement direction A 1 . Each inclined section  31 F was provided so as to face the projections  34 A and the recesses  34 B of first and second periods and the projection  34 A of a third period, with respect to the corresponding starting projection  34 A. 
     In Modification examples 2-1 to 2-3, the respective gradients of the inclined sections  31 F were set to differ from one another. In Modification example 2-1, the magnet  31  was configured to have downward inclination that inclines by approximately 1.7% of the thickness of the end  31 E of the magnet  31  upon every proceeding by about 0.5 mm in the relative movement direction A 1 . In Modification example 2-2, the magnet  31  was configured to have a downward inclination that inclines by approximately 2.5% of the thickness of the end  31 E of the magnet  31  upon every proceeding by about 0.5 mm in the relative movement direction A 1 . In Modification example 2-3, the magnet  31  was configured to have a downward inclination that inclines by approximately 3.3% of the thickness of the end  31 E of the magnet  31  upon every proceeding by about 0.5 mm in the relative movement direction A 1 . 
     It is to be noted that each of  FIGS. 20 to 22  also shows the measurement results of the first and second embodiments illustrated in  FIGS. 12 and 14 . 
     As seen from  FIGS. 20 to 22 , all of Modification examples 2-1 to 2-3 suppress the distortion of the output waveform more strongly than the first embodiment without the inclined sections  31 F does. It is evident that a proper, substantially sinusoidal output is obtainable from not only the middle region  31 C of the magnet  31  but also each outer region  31 D thereof, by providing each outer region  31 D on the second surface  31 B with only the inclined section  31 F. 
     As the gradient of the inclined section  31 E increases, the output waveform from each outer region  31 D is less distorted. In fact, the output waveform of Modification example 2-3 exhibits substantially the same distortion level as that of the second embodiment. Consequently, it is evident that the more advantageous effect is obtained by adjusting the gradient of each inclined section  31 F. 
     Modification Example 3 
       FIG. 23A  illustrates the configuration of the magnet  31  of the second embodiment, and  FIG. 23B  illustrates a configuration of a magnet  31  according to Modification example 
     3. Except that each outer region  31 D on the second surface  31 B is provided with two inclined sections  31 F 1  and  31 F 2  and a flat intermediate section  31 H therebetween in the magnet  31  of the second embodiment, this Modification example 3 has a similar configuration to that of the above-described second embodiment. In addition, the magnet  31  according to Modification example 3 may be manufactured through a similar process to that of the first embodiment. Accordingly, in the following description, the same reference numerals are assigned to components corresponding to those of the first or second embodiment. 
       FIG. 24  schematically shows a measurement result of a magnetic field on the first surface  31 A of the magnet  31 . In this measurement, a Hall device was used as the magnetic detection device  32 , and a magnetic flux density that was vertical to the first surface  31  was detected. Moreover, each outermost one of the projections and recesses  34  in the magnet  31  along the relative movement direction A 1  was the projection  34 A. The first inclined section  31 F 1  was provided to face a projection  34 A and a recess  34 B of a first period with respect to the corresponding starting projection  34 A; the flat intermediate section  31 H was provided to face a projection  34 A of a second period; and the second inclined section  31 F 2  was provided to face a recess  34 B of the second period and a projection  34 A of a third period. The gradient of each of the first inclined section  31 F 1  and the second inclined section  31 F 2  was set such that the magnet  31  had a downward inclination that inclines by approximately 4.2% of the maximum thickness of the magnet  31  upon every proceeding by about 0.5 mm in the relative movement direction A 1 . It is to be noted that  FIG. 24  also shows the measurement results of the first and second embodiments illustrated in  FIGS. 12 and 14 . 
     As seen from  FIG. 24 , Modification example 3 suppresses the distortion of the output waveform more strongly than the first embodiment without the inclined sections  31 F does. In fact, the output waveform of Modification example 3 exhibits substantially the same distortion level as that of the second embodiment. Consequently, it is evident that a proper, substantially sinusoidal output is also obtainable from not only the middle region  31 C of the magnet  31  but also each outer region  31 D thereof, when each outer region  31 D on the second surface  31 B is provided with the two inclined sections  31 F 1  and  31 F 2  and the flat intermediate section  31 H therebetween. 
     Up to this point, the embodiments and the like of the present disclosure have been described. However, the present disclosure is not limited to the embodiments and the like as described above, and various other modifications are possible. 
     For example, a method of providing the gradient for each inclined section  31 F is not limited to that described in the above embodiments and the like. For example, the location of each inclined section  31 F, and a difference between the thickness d 2  of the middle region  31 C and the thickness d 1  of end  31 E may be changed, depending on the number of periods of periodic projections and recesses  34  on the first surface  31 A of the magnet  31  or the length or width of the magnet  31 . This method is applicable to the magnet  31  with any given size, and also makes it possible to decrease the total length of the magnet  31  by producing the same advantageous effect as that of the above-described embodiments and the like. 
     Moreover, there is no limitation regarding, for example, the materials, thicknesses, and manufacturing methods of the components described in the above embodiments and the like. Alternatively, other materials, thicknesses, or manufacturing method thereof may be employed. For example, the periodic projection and recess  34  may be formed with a cutting process. 
     The above embodiments and the like have been described by concretely exemplifying the configuration of the image pickup apparatus  1 . However, it is not necessary for the image pickup apparatus  1  to have all the components, and any other component may be added thereto. 
     The position detection device according to any of the embodiments and the like of the present disclosure is suitable for sensing long-distance movement (2 mm or longer). Specifically, the position detection device is applicable to a wide variety of fields, including printers, industrial machines, and portable electronic apparatuses equipped with an optical zoom function, such as portable phones and smartphones, in addition to positional detection of a lens of the image pickup apparatus  1 . 
     Note that an embodiment of the present technology may also include the following configuration. 
     (1) A position detection device including: 
     a magnet and a magnetic detection device arranged opposite to each other to be relatively movable in a straight-line direction, 
     wherein the magnet has a first surface facing the magnetic detection device, and has periodic projections and recesses arrayed on the first surface in a relative movement direction. 
     (2) The position detection device according to (1), wherein 
     the magnet has the first surface and a second surface, the second surface being opposite to the first surface, and 
     a distance between the first surface and the second surface at a middle of the magnet along the relative movement direction is longer than a distance between the first surface and the second surface at an end of the magnet along the relative movement direction. 
     (3) The position detection device according to (2), wherein 
     an outer region of the magnet includes, on the second surface, an inclined section inclined with respect to the relative movement direction, and 
     the distance between the first surface and the second surface in the inclined section increases toward the middle of the magnet in the relative movement direction. 
     (4) The position detection device according to (3), wherein 
     the periodic projections and recesses include a starting projection at the end of the magnet in the relative movement direction. 
     (5) The position detection device according to (4), wherein 
     the outer region of the magnet includes, on the second surface, the inclined section and a flat section in this order of closeness to the middle of the magnet in the relative movement direction. 
     (6) The position detection device according to any one of (1) to (5), wherein 
     the magnet includes a rib on a side edge of the first surface. 
     (7) The position detection device according to (6), wherein 
     the flat section is provided to face projection and recess of a first period and a projection of a second period, with respect to the starting projection, and 
     the inclined section is provided to face a recess of the second period and a projection of a third period. 
     (8) The position detection device according to any one of (1) to (5), wherein 
     the periodic projections and recesses include, as recesses, grooves provided across the first surface in the direction along the width of the first surface. 
     (9) The position detection device according to (8), wherein 
     the flat section is provided to face projections and recesses of a first and a second periods, with respect to the starting projection, and 
     the inclined section is provided to face a projection of a third period. 
     (10) The position detection device according to (5), wherein 
     an outer region of the magnet includes, on the second surface, two inclined sections and a flat intermediate section between the two inclined sections. 
     (11) The position detection device according to any one of (1) to (10), wherein 
     the magnet includes projections and recesses alternately, as the periodic projections and recesses. 
     (12) The position detection device according to any one of (1) to (11), wherein 
     the magnet is magnetized in a single direction. 
     (13) An image pickup apparatus including: 
     a lens configured to be movable in an optical axis direction; and 
     a position detection device for the lens, the position detection device including a magnet and a magnetic detection device arranged opposite to each other to be relatively movable in a straight-line direction, 
     wherein the magnet has a first surface facing the magnetic detection device, and has periodic projections and recesses arrayed on the first surface in a relative movement direction. 
     (14) A magnet to be provided in a position detection device, the position detection device performing positional detection by relatively moving a magnet and a magnetic detection device in a straight-line direction, the magnet and the magnetic detection device arranged opposite to each other, the magnet including: 
     periodic projections and recesses arrayed on a first surface in a relative movement direction, the first surface facing the magnetic detection device. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations, and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.