Lens device and imaging device

Abstract

To provide a compact lens apparatus capable of a rapid focusing.SOLUTION: A lens apparatus (101) includes: a first focus lens (404); a second focus lens (413); a first actuator (421) configured to drive the first focus lens; and a second actuator (431) configured to drive the second focus lens. When the maximum speed of the first focus lens is defined as VMAX1, the maximum speed of the second focus lens is defined as VMAX2, a stroke which is the operable range of the first focus lens is defined as k1, and a stroke which is the operable range of the second focus lens is defined as k2, the following conditional expressions are satisfied: VMAX1>VMAX2; k1>k2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a lens device and an imaging device. [Background technology]

[0002] Patent Document 1 discloses a lens device in which two focus lenses are driven by two actuators, respectively. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2020 / 170586 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 discloses that stepping motors or voice coil motors can be used as the two actuators, but does not take into consideration the characteristics of the two focus lenses. When a stepping motor is used as the actuator, the drive speed of the focus lens is slow, and it takes a long time to focus. Alternatively, when a voice coil motor is used as the actuator, a large space is required, and the lens device becomes large.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a compact lens device that can achieve focusing in a short time. [Means for solving the problem]

[0006] A lens device according to one aspect of the present invention includes a first focus lens, a second focus lens, a first actuator that drives the first focus lens, and a second actuator that drives the second focus lens, wherein when a maximum speed of the first focus lens is VMAX1, a maximum speed of the second focus lens is VMAX2, a stroke that is an operable range of the first focus lens is k1, and a stroke that is an operable range of the second focus lens is k2, VMAX1>VMAX2 k1>k2 The following condition is satisfied.

[0007] Other objects and features of the present invention are illustrated in the following examples. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a small lens device that can achieve focusing in a short time. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a configuration diagram of an imaging device according to a first embodiment. [Figure 2] 5 is a diagram showing the relationship between the positions of the first focus lens and the second focus lens and time in Example 1. FIG. [Figure 3] 1 is a table showing specification values in the first embodiment. [Figure 4] 10 is a table showing specification values in the second embodiment. [Figure 5] FIG. 10 is a configuration diagram of an imaging device according to a third embodiment. [Figure 6] 10 is a table showing specification values in Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0011] Example 1 First, an imaging device 10 according to a first embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a configuration diagram of the imaging device 10. The imaging device 10 is configured to include a camera body 201 and a lens device 101 that is detachable from the camera body 201. However, this embodiment is not limited to this, and can also be applied to an imaging device in which the camera body and the lens device are configured integrally.

[0012] The lens device 101 has a first-group barrel 444, an image blur correction barrel 445, an aperture unit 405, a first focus barrel 425, a fourth-group barrel 442, a second focus barrel 434, and a sixth barrel (sixth-group barrel) 443. The first-group barrel 444 holds the first lens 401. The image blur correction barrel 445 holds the image blur correction lens 411. The first focus barrel 425 holds the first focus lens 404. The fourth-group barrel 442 holds the fourth lens 410. The second focus barrel 434 holds the second focus lens 413. The sixth barrel 443 holds the sixth lens 412. Note that the lens held in each barrel is not limited to one lens, and may be a lens group consisting of multiple lenses. The lenses, aperture unit 405, and the like constitute an imaging optical system.

[0013] The lens device 101 also includes a gyro sensor 106 as a shake detection unit, and a main CPU (lens control unit) 107 that controls the overall drive of the lens device 101 and performs calculations.

[0014] Main CPU 107 drives aperture unit 405 by issuing an instruction to aperture drive source 109. Main CPU 107 also drives first focus barrel 425 and first focus lens 404 together by issuing an instruction to first focus lens drive source 110. Main CPU 107 also drives second focus barrel 434 and second focus lens 413 together by issuing an instruction to second focus lens drive source 111.

[0015] First focus lens 404 and second focus lens 413 are arranged in a direction along optical axis x. Furthermore, first focus lens 404 and second focus lens 413 move simultaneously in conjunction with each other during focusing.

[0016] The image blur correction lens barrel 445 is held so as to be drivable within a plane perpendicular to the optical axis x relative to the image blur correction base tube 446. When performing image blur correction control, the main CPU 107 calculates the amount of blur correction using the detection value of the gyro sensor 106 and sends an instruction to the image blur correction drive source 108. The image blur correction drive source 108 performs blur correction by driving the image blur correction lens barrel 445 in the y direction (yaw direction) and p direction (pitch direction), which are axes perpendicular to the optical axis x. In this way, the image blur correction lens barrel 445 and the image blur correction drive source 108 function as an image blur correction unit.

[0017] The aperture unit 405 is fixed to an aperture base 441. The lens device 101 is fixed to the camera body 201 via a mount 414, and captures an image of a subject by forming an image on an image sensor 202 held in the camera body 201 through an optical member (image pickup optical system) within the lens device 101.

[0018] The camera body 201 includes a main CPU (camera control unit) 203, a release button 204 as an operating member, a main power supply 205, and an image recording medium 206. The release button 204 has a two-stage depression configuration, with the first stage called SW1 and the second stage called SW2. SW1 issues instructions for preparations to start shooting, such as returning from shooting standby and starting image stabilization, autofocus, and metering. SW2 issues instructions for shooting and recording the image to the image recording medium 206. The main CPU 203 supplies power to the lens device 101 and exchanges other shooting information with the main CPU 107 of the lens device 101 via a contact block (not shown) provided on the mount 414.

[0019] In this embodiment, the lens device 101 is a fixed focal length lens and does not perform a variable magnification operation. The lens device 101 has a fixed barrel (not shown), to which a first group barrel 444, an image blur correction base barrel 446, an aperture base 441, a fourth group barrel 442, and a sixth barrel 443 are fixed. However, this embodiment is not limited to this and can also be applied to a lens device that performs a variable magnification operation.

[0020] The first focus barrel 425 is supported by a guide bar fixed to the fixed barrel so that it can move straight only in the optical axis direction, and the second focus barrel 434 is supported by a guide bar fixed to the fixed barrel so that it can move straight only in the optical axis direction.

[0021] Next, the first actuator 421 will be described. The first actuator 421 is a linear actuator, such as a voice coil motor. However, this embodiment is not limited to this, and the first actuator 421 may be an actuator other than a linear actuator. The yoke 423 is fixed to the fixed barrel. As shown in FIG. 1, the magnet 424 is bipolarly magnetized in a direction perpendicular to the optical axis x and is fixed to the yoke 423. The coil 422 is fixed to the first focus barrel 425 by adhesive or the like, and as shown in FIG. 1, is disposed in a non-contact manner with the yoke 423 so as to surround the yoke 423 in the optical axis direction. In the space in which the coil 422 is disposed, a magnetic flux flows in a direction perpendicular to the optical axis x due to the magnet 424 and the yoke 423.

[0022] When a current is passed through the yoke 423, which is the first focus lens drive source 110, in response to an instruction from the main CPU 107, a Lorentz force is generated, and a drive force toward the object side in the optical axis direction or the image plane side in the optical axis direction is generated in the coil 422. This allows the first focus barrel 425 and the first focus lens 404 held therein to be driven in the optical axis direction.

[0023] Next, the position encoder 426 will be described. The position encoder 426 is, for example, a GMR (Giant Magneto Resistive effect) sensor, but is not limited to this. A sensor head 427 is fixed to the first focus barrel 425. The magnetic scale of the position encoder 426 is fixed to the fixed barrel. An output according to the position of the first focus barrel 425 is sent from the sensor head 427, which is the first focus lens position encoder 112, to the main CPU 107, making it possible to detect the position of the first focus barrel 425. In accordance with this value, the current value to the first focus lens drive source 110 is controlled via the main CPU 107, thereby controlling the position of the first focus lens 404.

[0024] The first focus barrel 425 has an object-side end (object-side mechanical end) 425a and an image-plane-side end (object-side mechanical end) 425b. The aperture base 441 has an end 441a corresponding to the object-side end 425a. The fourth-group barrel 442 has an end 442b corresponding to the image-plane-side end 425b. This limits the drive range (operable range) of the first focus barrel 425, i.e., the first focus lens 404. In this embodiment, the operable range of the first focus lens 404 is defined as the stroke k1 of the first focus lens 404 (first focus lens stroke). In this embodiment, the lens apparatus 101 is a fixed-focus lens and is in a state where the focus is set at infinity. As the first focus lens 404 moves toward the image plane, it transitions to a state where the focus is set at the closest distance, and the position closest to the object is the closest focus position, which is the shortest shooting distance of the lens apparatus 101.

[0025] Next, the second actuator (stepping motor) 431 will be described. The second actuator 431 is, for example, an actuator (stepping motor) that converts rotational force into driving force in the optical axis direction. However, this embodiment is not limited to this, and the second actuator 431 may be an actuator other than a stepping motor.

[0026] The second actuator 431 is configured to include a motor engine 433 and a lead screw 432. The second actuator 431 is fixed to a fixed barrel via a metal plate or the like connected to the motor engine 433. In this embodiment, the lead screw 432 is threaded with a pitch of 0.4. A rack 435 meshes with the threaded portion of the lead screw 432. The rack 435 is held by the second focus barrel 434, and is attached so that its holding portion and the meshing portion of the lead screw 432 absorb any deviation from the ideal position of the second focus barrel 434, i.e., the second actuator 431.

[0027] The main CPU 107 issues a pulse drive command to the motor engine 433, which is the second focus lens drive source 111, to drive the second focus barrel 434, which holds the second focus lens 413. In this embodiment, the motor engine 433 rotates once per 40 pulses. The second focus barrel 434 is driven 0.4 mm toward the object side or the image plane side depending on the direction of rotation. The second focus barrel 434 has a light-shielding fin (not shown), and a photointerrupter attached to the fixed barrel can recognize the reference position of the second focus barrel 434. The main CPU 107 counts pulses from the reference position to control the position of the second focus barrel 434, which holds the second focus lens 413, under open control.

[0028] The second focus barrel 434 has an object side end (object side mechanical end) 434a and an image plane side end (image plane side mechanical end) 434b. The fourth group barrel 442 has an end 442a corresponding to the object side end 434a. The sixth barrel 443 has an end 443b corresponding to the image plane side end 434b. This limits the driveable range (operable range) of the second focus barrel 434, i.e., the second focus lens 413. In this embodiment, the operable range of the second focus lens 413 is defined as a stroke k2 of the second focus lens 413 (second focus lens stroke).

[0029] The lens device 101 is a fixed focal length lens and is in a state where it is focused at infinity. Clearances are provided further toward the object side of the first focus lens 404 and the second focus lens 413 to allow for infinity focusing. As the first focus lens 404 and the second focus lens 413 move toward the image plane, they transition to a state where they are focused on the close-up side. When the first focus lens 404 and the second focus lens 413 are at their most object-side positions, they are in a focus position where they are focused on the close-up side, which is the shortest shooting distance of the lens device 101.

[0030] Here, the image plane movement amount per unit movement amount of first focus lens 404 (first focus sensitivity) is defined as ES1, and the image plane movement amount per unit movement amount of second focus lens 413 (second focus sensitivity) is defined as ES2. The mass of first focus lens 404 (first focus lens mass) is defined as m1, and the mass of second focus lens 413 (second focus lens mass) is defined as m2.

[0031] The maximum speed of the first focus lens 404 driven by the first actuator 421 (maximum first focus lens speed) is defined as VMAX1. The maximum speed of the second focus lens 413 driven by the second actuator 431 (maximum second focus lens speed) is defined as VMAX2. Here, maximum speed means the fastest drive speed among all drives performed by commands from the main CPU 107 for the combination of the lens apparatus 101 and the camera body 201. In this embodiment, the magnetic circuit of the first actuator 421 is designed so that VMAX1 is 70 mm / s. This design takes into consideration the mass of the moving group including the first focus lens 404, the sliding load between the first focus barrel 425, which is a sliding part, and the guide bar, the back electromotive force, the available power, and the like.

[0032] The second actuator 431 can be driven at a maximum of 3000 PPS (30,000 pulses per second) without losing synchronization. 40 pulses advances the actuator 0.4 mm per rotation, so VMAX2 is 30 mm / s. In this embodiment, it is preferable to satisfy the condition VMAX1>VMAX2. More preferably, there is a maximum speed difference between VMAX1 and VMAX2 of at least two (satisfying VMAX1>2×VMAX2).

[0033] Figure 2 shows the movement trajectory of each actuator in this embodiment over 0.1 seconds when driven at maximum output. In Figure 2, the vertical axis represents the position (mm) of each focus lens, and the horizontal axis represents time (s). In Figure 2, VCM represents the first actuator 421, and STM represents the second actuator 431.

[0034] The values calculated are based on the characteristics of the first actuator 421, with a movable group mass of 0.2 kg, a maximum output of 0.1 N, and a velocity resistance coefficient of 1.143 N·s / m, which is the sum of the viscous resistance of the grease and the back electromotive force. Here, L1 is the distance traveled per unit time (e.g., 0.1 seconds) when the first focus lens 404 starts moving from a stopped state with the maximum driving force of the first actuator 421 (first maximum movable distance). In this embodiment, L1 is 5.85 mm.

[0035] The second actuator 431 requires the following accelerations to reach a maximum speed of 3000 PPS: 2 pulses at 500 PPS, 2 pulses at 1000 PPS, and 2 pulses at 2000 PPS. Here, the distance traveled per unit time (e.g., 0.1 seconds) when the second focus lens 413 starts moving from a stopped state with the maximum driving force of the second actuator 431 is defined as L2 (second maximum movable distance). In this embodiment, L2 is 2.85 mm.

[0036] In this embodiment, it is preferable that the relationship L1>L2 is satisfied. More preferably, L1 and L2 have a difference of at least two times (satisfying L1>2×L2). Here, the reason for comparing the maximum movable distance in "0.1 seconds" is that, with shortening the focusing time being an important issue in the development of imaging devices, extending the driving distance in a short time of about 0.1 seconds is important.

[0037] The maximum acceleration of first focus lens 404 is AMAX1, and the maximum acceleration of second focus lens 413 is AMAX2. In this case, satisfying L1>L2 is equivalent to satisfying AMAX1>AMAX2.

[0038] FIG. 3 is a table showing the specifications of this embodiment. The contents of each value are as described above. The first focus lens stroke k1 is 22 mm, and the second focus lens stroke k2 is 16 mm. The first focus sensitivity ES1 is 3.3, and the second focus sensitivity ES2 is 2.6 (|ES1|>|ES2|). The first focus lens mass m1 is 12 g, and the second focus lens mass m2 is 6 g (m1>m2). The actual moving group mass is this value plus the moving parts of the focus barrel and actuator.

[0039] The product ES1×k1 of the first focus sensitivity ES1 and the first focus lens stroke k1 is 72.6. The product ES2×k2 of the second focus sensitivity ES2 and the second focus lens stroke k2 is 41.6. That is, in this embodiment, it is preferable to satisfy |ES1×k1|>|ES2×k2|. Here, the product of the focus sensitivity and the focus lens stroke indicates the amount of image plane movement caused by the focus lens.

[0040] The product m1×k1 of the first focus lens mass m1 and the first focus lens stroke k1 is 264. The product m2×k2 of the second focus lens mass m2 and the second focus lens stroke k2 is 96. In this embodiment, it is preferable that m1×k1 > m2×k2 be satisfied. Here, the product of the focus lens mass and the focus lens stroke indicates, for example, the amount of work required when driving the lens device in the lifting direction.

[0041] Next, the effects of this embodiment described so far will be explained. In this embodiment, for example, a voice coil motor is used as first actuator 421, and a stepping motor is used as second actuator 431. Furthermore, in this embodiment, at least one of the conditional expressions VMAX1>VMAX2 and k1>k2 or the conditional expressions AMAX1>AMAX2 and k1>k2 is satisfied.

[0042] For example, when a stepping motor is used as the first actuator 421, the focusing speed is slower than when a voice coil motor is used, resulting in a slower focusing time. In particular, with regard to the speed of the search drive that moves the entire focus stroke from infinity to close subject distances, the difference in maximum speed affects the drive time.

[0043] In a configuration in which two focus lenses are driven to achieve focus, as in this embodiment, the focus lenses must be moved at a speed approximately equal to the ratio of the first focus lens stroke k1 to the second focus lens stroke k2. Therefore, when using actuators with approximately the same maximum speed for both lenses, the side that must be moved faster—in this embodiment, the first focus lens 404—is limited, and the second focus lens 413 must be moved slowly. This lengthens the focusing time. Even when the entire stroke is not moved, the focus lenses must be moved at a speed approximately equal to the ratio of the first focus lens stroke k1 to the second focus lens stroke k2.

[0044] Therefore, even when driving a short distance, it is necessary to move the first focus lens 404, which has a large stroke, quickly. As described above, the first maximum movable distance L1 and the second maximum movable distance L2 from the stop position in 0.1 seconds have the relationship L1>L2, so it is possible to focus more quickly even when driving the focus over a narrow range.

[0045] The first focus lens stroke k1 is preferably 10 mm or more. For example, the first focus lens stroke k1 in this embodiment is 22 mm, which is a relatively long distance. When the first focus lens stroke k1 is short, even if the maximum speed of the first actuator 421 is slow, the focusing time is short, so there is no significant difference. On the other hand, in the case of a large stroke of 10 mm or more, as in this embodiment, the configuration of this embodiment greatly contributes to shortening the focusing time.

[0046] Conventionally, a known configuration employs a voice coil motor for both the first actuator 421 and the second actuator 431. In this case, the voice coil motor requires a position encoder for control, which takes up space and costs, resulting in an increase in the size and cost of the lens device.

[0047] In the case of a voice coil motor, power consumption increases because the coil must be constantly energized to maintain position. Furthermore, when a voice coil motor is driven, high-frequency magnetic noise is generated from the coil, which may affect the image sensor 202 and result in poor image capture. To address this issue, an LC filter consisting of a coil and a capacitor must be incorporated into the circuit to cut out unnecessary high-frequency magnetic noise. However, because the LC filter coil generates magnetic noise, it must be placed in front of the lens, away from the image sensor. This requires space in front of the lens for the LC filter, including the wiring, which tends to increase the size of the lens device. Furthermore, the first actuator 421 is generally more expensive than the second actuator 431.

[0048] In this embodiment, in accordance with the characteristics of the focus lens, for example, a voice coil motor is used as the first actuator 421 and a stepping motor is used as the second actuator 431. This makes it possible to realize a low-cost, compact lens device while maintaining a short focusing time. Furthermore, by reducing power consumption, it contributes to increasing the number of images that can be taken with the camera and reducing the environmental impact.

[0049] In this embodiment, first actuator 421 has been described as a voice coil motor serving as a linear actuator, but may be another linear actuator such as a linear ultrasonic motor or an electromagnetic linear motor. Also, in this embodiment, second actuator 431 has been described as a stepping motor serving as an actuator that converts rotational force into driving force in the optical axis direction, but may be another type of actuator that converts rotational force into driving force in the optical axis direction.

[0050] Example 2 Next, a second embodiment of the present invention will be described. Fig. 4 is a table showing the specifications of this embodiment. Note that the basic configuration of the imaging device in this embodiment is the same as that of the imaging device in the first embodiment described with reference to Fig. 1, and therefore a common description will be omitted.

[0051] If the second focus lens stroke k2 can be made even smaller than in the first embodiment, the overall focusing time can be further shortened. In the optical system assumed here, to make the second focus lens stroke k2 even smaller, the second focus sensitivity ES2 needs to be increased. This is because the value of the second focus sensitivity ES2 x the second focus lens stroke k2, which is the amount of image plane movement required for the second focus lens 413, does not change significantly. Therefore, if the second focus sensitivity ES2 is increased, the second focus lens stroke k2 becomes smaller.

[0052] To increase the second focus sensitivity ES2, it is necessary to increase the power of the second focus lens 413. To increase the power of the second focus lens 413, it is necessary to increase the number of lenses in the second focus lens 413. In that case, the mass m2 of the second focus lens tends to increase. If the mass m2 of the second focus lens is increased and a second actuator 431 with the same driving force is used, the maximum speed of the stepping motor must be reduced. In a stepping motor configuration in which rotational force is converted into axial drive by a lead screw, the main load is rotational sliding loss, so even if the mass of the moving group increases, the maximum speed does not decrease proportionally.

[0053] In this embodiment, the maximum speed is 2600 PPS, and the maximum speed VMAX2 of the second focus lens is 26 mm / s. The second actuator 431 requires the following accelerations to reach the maximum speed of 2600 PPS: two pulses at 500 PPS, two pulses at 1000 PPS, and two pulses at 2000 PPS. Here, the movement distance (second maximum movable distance) per unit time (e.g., 0.1 seconds) when the second focus lens 413 starts moving from a stopped state with the maximum driving force of the second actuator 431 is defined as L2. In this embodiment, L2 is 2.48 mm.

[0054] 4, in this embodiment, the first focus lens maximum speed VMAX1>the second focus lens maximum speed VMAX2 is satisfied. Also, the relationship between the first maximum movable distance L1 and the second maximum movable distance L2 is L1>L2, which corresponds to satisfying AMAX1>AMAX2.

[0055] Also, the relationship between the first focus lens stroke k1 and the second focus lens stroke k2 satisfies k1 > k2. The first focus lens stroke k1 is more than twice as large as the second focus lens stroke k2 (k1 ≥ 2 × k2). Also, in this embodiment, |ES1| < |ES2| and m1 < m2 are satisfied. Also, in this embodiment, |ES1 × k1| > |ES2 × k2| is satisfied. Here, the product of the focus sensitivity and the focus lens stroke indicates the amount of image plane movement by the focus lens.

[0056] Also, in this embodiment, m1 × k1 > m2 × k2. Here, the product of the focus lens mass and the focus lens stroke indicates, for example, the amount of work required when the lens device is driven upward in the lifting direction.

[0057] Similar to Example 1 and Example 2, when performing a search drive over the entire stroke, the drive time of the entire system is limited by the drive on the side of the second actuator 431. When calculating the search time including acceleration and deceleration, the search time of Example 1 is 0.54 seconds, and the search time of Example 2 is as short as 0.345 seconds. Thus, even when |ES1| < |ES2|, it is preferable to set the actuator with a large product of the focus sensitivity and the focus lens stroke to a voice coil motor with a high maximum speed, and set the actuator with a small product to a stepping motor. Thereby, a lens device with a short focusing time can be realized.

[0058] Even if m1 < m2, it is preferable to set the actuator with a large product of the focus lens mass and the focus lens stroke to a voice coil motor with a high maximum speed, and set the actuator with a small product to a stepping motor. Thereby, a lens with a short focusing time can be realized.

[0059] (Example 3) Next, Example 3 of the present invention will be described. FIG. 5 is a configuration diagram of the imaging device 20 in this embodiment. In this embodiment, the description of the parts common to the imaging device 10 of Example 1 is omitted.

[0060] The imaging device 20 is configured to include a camera body 201 and a lens device 102 that is detachable from the camera body 201. The lens device 102 has a first-group barrel 544, an image blur correction barrel 545, an aperture unit 505, a first focus barrel 525, a second-group barrel 542, a second focus barrel 534, and a second-group barrel 543. Each barrel holds a first lens 501, an image blur correction lens 511, a first focus lens 504, a second-group lens 510, a second focus lens 513, and a second-group lens 512, respectively. The image blur correction barrel 545 is held drivably in a plane perpendicular to the optical axis x with respect to an image blur correction base barrel 546. The aperture unit 505 is fixed to an aperture base 541.

[0061] The lens device 102 of this embodiment has a zoom lens and is capable of variable magnification (changing the focal length). The lens device 102 has a guide barrel and a cam ring (not shown). Rollers provided on the first-group barrel 544 engage with cam grooves in the cam ring and linear grooves in the guide barrel. This causes the first-group barrel 544 to move back and forth in the optical axis direction in response to the rotation of a zoom ring that is linked to the cam ring.

[0062] Next, the second unit 547 will be described. The second unit 547 has a second unit base (movable barrel) 548 that moves in the optical axis direction in response to changes in focal length. A 2a group lens 510, an aperture base 541, an image blur correction base barrel 546, and a 2b group lens 512 are fixed to the second unit base 548.

[0063] The first focusing lens barrel 525 is supported by a guide bar fixed to the second unit base 548 so as to be able to move straight only in the optical axis direction. The second focusing lens barrel 534 is supported by a guide bar fixed to the second unit base 548 so as to be able to move straight only in the optical axis direction.

[0064] The rollers provided on the second unit base 548 engage with the cam grooves of the cam ring and the linear grooves of the guide barrel, causing the second unit 547 to advance and retreat in the optical axis direction as the zoom ring, which is linked to the cam ring, is rotated.

[0065] Next, the first actuator 551 will be described. In this embodiment, the first actuator 551 is, for example, a linear vibration motor (ultrasonic motor). The first actuator 551 is held by the second unit base 548. The slider 552 is fixed to the second unit base 548. The vibrator 553 is made up of a piezoelectric element, and is driven by bringing a contact portion into pressure contact with the slider 552 and applying an ultrasonic voltage to generate a traveling wave. The rack 554 plays a role in connecting the vibrator 553 and the first focus barrel 525 while absorbing any deviation from the ideal position between them.

[0066] Next, the position encoder 526 will be described. The sensor head 557 is fixed to the second unit base 548. The optical scale 558 is fixed to the first focus barrel 525. An output according to the position of the first focus barrel 525 is sent from the sensor head 557, which is the first focus lens position encoder 112, to the main CPU 107, making it possible to detect the position of the first focus barrel 525. The main CPU 107 controls the value of the current to the first focus lens drive source 110 according to this value, thereby controlling the position of the first focus lens 504.

[0067] The first focus barrel 525 has an object-side end 525a and an image-plane-side end 525b. The aperture base 541 has an end 541a corresponding to the object-side end 525a. The image blur correction base barrel 546 has an end 546b corresponding to the image-plane-side end 525b. This limits the drive range of the first focus barrel 525, which holds the first focus lens 504, and this range is defined as the first focus lens stroke k1. The lens device 102 in FIG. 5 is a zoom lens, and is in a state where the focus is set to infinity at the WIDE end (wide-angle end). The first focus lens stroke k1 is ensured so that the focus is maintained from infinity to close up across the entire zoom range.

[0068] Next, the second actuator 531 will be described. The second actuator is, for example, a stepping motor, and is held by the second unit base 548. The second actuator 531 is composed of a motor engine 533 and a lead screw 532. The second actuator 531 is fixed to a fixed barrel via a metal plate or the like connected to the motor engine 533. In this embodiment, the lead screw 532 is threaded with a pitch of 0.4. A rack 535 meshes with the threaded portion of the lead screw 532. The rack 535 is held by the second focus barrel 534, and is attached so that the meshing portion of this holding portion and the lead screw 532 absorbs any deviation from the ideal positions of the second actuator 531 and the second focus barrel 534.

[0069] The second focus barrel 534 has an object side end 534a and an image plane side end 534b. The second unit base 548 has an end 548a corresponding to the object side end 534a. The 2a group barrel 542 has an end 542b corresponding to the image plane side end 534b. This limits the drive range of the second focus barrel 534 that holds the second focus lens 513, and this range is defined as the second focus lens stroke k2.

[0070] 5 is a zoom lens, and is in focus at infinity at the WIDE end. The second focus lens stroke k2 is ensured so that the lens can be in focus from infinity to close range over the entire zoom range.

[0071] Here, the image plane movement amount per unit movement amount of first focus lens 504 (first focus sensitivity) is defined as ES1, and the image plane movement amount per unit movement amount of second actuator 431 (second focus sensitivity) is defined as ES2. Also, the mass of first focus lens 504 (first focus lens mass) is defined as m1, and the mass of second focus lens 513 (second focus lens mass) is defined as m2.

[0072] The maximum speed of first focus lens 504 driven by first actuator 551 (maximum first focus lens speed) is defined as VMAX1. Also, the maximum speed of second focus lens 513 driven by second actuator 531 (maximum second focus lens speed) is defined as VMAX2. Here, maximum speed refers to the fastest drive speed among all drives performed by commands from main CPU 107 for the combination of lens device 102 and camera body 201.

[0073] In this embodiment, the output characteristics of the first actuator 551 are designed and controlled so that VMAX1 is 100 mm / s. Generally, a linear ultrasonic motor is capable of higher output and higher speed driving than a stepping motor. This design requires consideration of the moving group mass including the first actuator 551, the sliding load between the first focus lens barrel 525, which is the sliding part, and the guide bar, and the available power.

[0074] The second actuator 531 can be driven at a maximum of 3000 PPS (30,000 pulses per second) without losing synchronization. Forty pulses advances 0.4 mm per rotation, so VMAX2 is 30 mm / s. In this case, VMAX1 > VMAX2, and the maximum speed difference between the two actuators is more than twice (VMAX1 ≥ 2 × VMAX2).

[0075] In this embodiment, the first actuator 551 has the characteristic of moving a movable group including the second focus barrel 534 holding the second focus lens 513 at a speed of 12700 mm / s. 2 At maximum output, the second focus barrel 534 reaches a maximum speed of 100 mm / s in 0.0079 seconds from a stopped state. The distance traveled (first maximum movable distance) per unit (e.g., 0.1 seconds) when the second focus barrel 534 starts moving from a stopped state with the maximum driving force of the first actuator 551 is defined as L1. In this embodiment, L1 is 9.21 mm.

[0076] STM in the graph of FIG. 2 represents the second actuator 531. The second actuator 531 requires the following accelerations to reach a maximum speed of 3000 PPS: two pulses at 500 PPS, two pulses at 1000 PPS, and two pulses at 2000 PPS. Here, the distance traveled (second maximum movable distance) per unit (e.g., 0.1 seconds) when the second focus lens 413 starts moving from a stopped state with the maximum driving force of the second actuator 531 is defined as L2. In this embodiment, L2 is 2.85 mm.

[0077] In this embodiment, L1>L2 (i.e., AMAX1>AMAX2) is satisfied, and the difference between the two maximum movable distances is more than twice (L1≧2×L2). The reason for comparing the maximum movable distances in "0.1 seconds" here is that shortening the focusing time is an important issue in the development of imaging devices, and extending the driving distance in a short time such as 0.1 seconds is important.

[0078] FIG. 6 is a table showing the specifications of this embodiment. The contents of each value are as described above. The first focus lens stroke k1 is 5.9 mm, and the second focus lens stroke k2 is 3.6 mm. The first focus sensitivity ES1 is 1.98, and the second focus sensitivity ES2 is 1.81. The first focus lens mass m1 is 14.2 g, and the second focus lens mass m2 is 4.4 g. The actual moving group mass is this value plus the moving parts of the focus barrel and actuator.

[0079] The product ES1×k1 of the first focus sensitivity ES1 and the first focus lens stroke k1 is 11.7. The product ES2×k2 of the second focus sensitivity ES2 and the second focus lens stroke k2 is 6.5, so |ES1×k1|>|ES2×k2|. Here, the product of the focus sensitivity and the focus lens stroke indicates the amount of image plane movement caused by the focus lens.

[0080] The product m1×k1 of the first focus lens mass m1 and the first focus lens stroke k1 is 83.8. The product m2×k2 of the second focus lens mass m2 and the second focus lens stroke k2 is 15.8, so m1×k1>m2×k2. Here, the product of the focus lens mass and the focus lens stroke indicates the amount of work required, for example, when driving the lens apparatus upward in a lifting direction.

[0081] The effects of this embodiment described above will now be explained. In this embodiment, a linear vibration motor is used for the first actuator, and a stepping motor is used for the second actuator. In this embodiment, the relationships k1>k2 and VMAX1>VMAX2 are satisfied. For example, when a stepping motor is used for the first actuator, the focusing speed is slower than when a linear vibration motor is used, and therefore the focusing time is slower.

[0082] In another conventional example, a linear vibration motor is used for both the first and second actuators. In this case, the linear vibration motor requires a position encoder for control, which takes up space and costs money, resulting in an increase in the size and cost of the lens device.

[0083] A linear vibration motor requires a transformer, which is an electrical element for voltage boosting. It also requires an inductor, which is an electrical element for suppressing electrical noise. Both the transformer and the inductor have a coil portion. When the linear vibration motor is driven, magnetic noise is generated from the coil, which may affect the image sensor 202 and thus the image capture results. To address this, the transformer and inductor must be placed in front of the lens, away from the image sensor. For this reason, space for the transformer and inductor, including their wiring, is required on the second unit base 548, which holds the first and second actuators.

[0084] Because the second unit base 548 is a group that moves with zooming, it is necessary to secure space for arranging the transformer and inductor, including their wiring, in a limited space, which requires the second unit base 548, including the optical system, to be large. This can result in an increase in the size of the lens device. On the other hand, in this embodiment, by using a stepping motor as the second actuator, it is possible to reduce the space required for arranging the transformer and inductor, including their wiring, on the second unit base 548, thereby achieving a more compact lens device.

[0085] Furthermore, the first actuator 551 is generally more expensive than the second actuator 531. On the other hand, in this embodiment, the second actuator is a stepping motor, thereby making it possible to suppress costs.

[0086] In the zoom lens of this embodiment, a linear vibration motor is used as the first actuator and a stepping motor is used as the second actuator to match the characteristics of the focus lens, thereby realizing a low-cost, compact lens device while maintaining a short focusing time.

[0087] The disclosure of each embodiment includes the following configurations and methods. (Configuration 1) A first focus lens; A second focus lens; a first actuator that drives the first focus lens; a second actuator that drives the second focus lens, When the maximum speed of the first focus lens is VMAX1, the maximum speed of the second focus lens is VMAX2, the stroke that is the movable range of the first focus lens is k1, and the stroke that is the movable range of the second focus lens is k2, VMAX1>VMAX2 k1>k2 A lens device characterized by satisfying the following conditional expressions: (Configuration 2) A first focus lens; A second focus lens; a first actuator that drives the first focus lens; a second actuator that drives the second focus lens, When the maximum acceleration of the first focus lens is AMAX1, the maximum acceleration of the second focus lens is AMAX2, the stroke which is the movable range of the first focus lens is k1, and the stroke which is the movable range of the second focus lens is k2, AMAX1>AMAX2 k1>k2 A lens device characterized by satisfying the following conditional expressions: (Configuration 3) the first actuator has a driving force that causes the first focus lens to start moving from a stopped state and the maximum movable distance per unit time is L1; the second actuator has a driving force that causes the second focus lens to start moving from a stopped state and the maximum movable distance per unit time is L2; L1>L2 3. The lens device according to configuration 2, wherein the following condition is satisfied: (Configuration 4) the first actuator is a direct acting actuator, 4. The lens device according to any one of configurations 1 to 3, wherein the second actuator is an actuator that converts a rotational force into a driving force in the optical axis direction. (Configuration 5) the first actuator is a voice coil motor or a vibration motor, 5. The lens device according to configuration 4, wherein the second actuator is a stepping motor. (Configuration 6) When the mass of the first focus lens is m1 and the mass of the second focus lens is m2, m1×k1>m2×k2 6. The lens device according to any one of configurations 1 to 5, wherein the following condition is satisfied: (Configuration 7) When the focus sensitivity of the first focus lens is ES1 and the focus sensitivity of the second focus lens is ES2, |ES1×k1|>|ES2×k2| 7. The lens device according to any one of configurations 1 to 6, wherein the following condition is satisfied: (Configuration 8) 8. The lens device according to any one of configurations 1 to 7, further comprising a position encoder for detecting the position of the second focus lens. (Configuration 9) 9. The lens device according to any one of configurations 1 to 8, wherein the first focus lens and the second focus lens move simultaneously in conjunction with each other during focusing. (Configuration 10) When the focus sensitivity of the first focus lens is ES1 and the focus sensitivity of the second focus lens is ES2, |ES1|>|ES2| 10. The lens device according to any one of configurations 1 to 9, wherein the following condition is satisfied: (Configuration 11) When the mass of the first focus lens is m1 and the mass of the second focus lens is m2, m1>m2 11. The lens device according to any one of configurations 1 to 10, wherein the following condition is satisfied: (Configuration 12) 12. The lens device according to any one of configurations 1 to 11, wherein the stroke of the first focus lens is 10 mm or more. (Configuration 13) k1 ≥ 2 × k2 13. The lens device according to any one of configurations 1 to 12, wherein the following condition is satisfied: (Configuration 14) 14. The lens device according to any one of configurations 1 to 13, wherein the first focus lens and the second focus lens are arranged in a direction along the optical axis. (Configuration 15) a movable cylinder that moves in the optical axis direction in response to a change in the focal length; 15. The lens device according to any one of configurations 1 to 14, wherein the first actuator and the second actuator are held by the movable barrel. (Configuration 16) An imaging device comprising the lens device according to any one of configurations 1 to 15 and an imaging element.

[0088] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0089] 101, 102 Lens device 404, 504 First focus lens 413, 513 Second focus lens 421, 551 First actuator 431, 531 Second actuator

Claims

1. A first focus lens; A second focus lens; a first actuator that drives the first focus lens; a second actuator that drives the second focus lens, When the maximum speed of the first focus lens is VMAX1, the maximum speed of the second focus lens is VMAX2, the stroke that is the movable range of the first focus lens is k1, and the stroke that is the movable range of the second focus lens is k2, VMAX1>VMAX2 k1>k2 A lens device characterized by satisfying the following conditional expressions:

2. A first focus lens; A second focus lens; a first actuator that drives the first focus lens; a second actuator that drives the second focus lens, When the maximum acceleration of the first focus lens is AMAX1, the maximum acceleration of the second focus lens is AMAX2, the stroke which is the movable range of the first focus lens is k1, and the stroke which is the movable range of the second focus lens is k2, AMAX1>AMAX2 k1>k2 A lens device characterized by satisfying the following conditional expressions:

3. the first actuator has a driving force that causes the first focus lens to start moving from a stopped state and the maximum movable distance per unit time is L1; the second actuator has a driving force that causes the second focus lens to start moving from a stopped state and the maximum movable distance per unit time is L2; L1>L2 3. The lens device according to claim 2, wherein the following condition is satisfied:

4. the first actuator is a linear actuator, 4. The lens device according to claim 1, wherein the second actuator is an actuator that converts a rotational force into a driving force in the optical axis direction.

5. the first actuator is a voice coil motor or a vibration motor, 5. The lens device according to claim 4, wherein the second actuator is a stepping motor.

6. When the mass of the first focus lens is m1 and the mass of the second focus lens is m2, m1 × k1 > m2 × k2 4. The lens device according to claim 1, wherein the following condition is satisfied:

7. When the focus sensitivity of the first focus lens is ES1 and the focus sensitivity of the second focus lens is ES2, |ES1×k1|>|ES2×k2| 4. The lens device according to claim 1, wherein the following condition is satisfied:

8. 4. The lens device according to claim 1, further comprising a position encoder for detecting a position of the second focus lens.

9. 4. The lens device according to claim 1, wherein the first focus lens and the second focus lens move simultaneously in conjunction with each other during focusing.

10. When the focus sensitivity of the first focus lens is ES1 and the focus sensitivity of the second focus lens is ES2, |ES1|>|ES2| 4. The lens device according to claim 1, wherein the following condition is satisfied:

11. When the mass of the first focus lens is m1 and the mass of the second focus lens is m2, m1>m2 4. The lens device according to claim 1, wherein the following condition is satisfied:

12. 4. The lens device according to claim 1, wherein the stroke of the first focus lens is 10 mm or more.

13. k1 ≧ 2 × k2 4. The lens device according to claim 1, wherein the following condition is satisfied:

14. 4. The lens device according to claim 1, wherein the first focus lens and the second focus lens are arranged in a direction along an optical axis.

15. a movable cylinder that moves in the optical axis direction in response to a change in the focal length; 4. The lens device according to claim 1, wherein the first actuator and the second actuator are held by the movable barrel.

16. An imaging device comprising: a lens device according to claim 1; and an imaging element.

Images