JP2010145495A - Camera system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate instability upon reversing in hill-climbing AF (hunting prevention). <P>SOLUTION: A camera system includes: a hill-climbing system focus control means; a first output means for outputting a backlash amount of a driving system; and a second output means for outputting an overrun amount caused by the inertia of the driving system. The focus control means controls a focus lens so that the lens may move from a position where the focus evaluation peak value is detected, may surely go beyond a value obtained by adding the backlash amount and the overrun amount, thereafter, may move back to the position where the peak value is detected. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical apparatus having an automatic focusing device.

  In an autofocus single-lens reflex camera, a focusing mechanism such as TTL (Through The Lens) phase difference autofocus (hereinafter referred to as phase difference AF) is generally used. On the other hand, a hill-climbing autofocus (hereinafter referred to as hill-climbing AF) that detects contrast using a high-frequency component of a signal obtained from an image sensor is used in a video camera or the like.

  A comparison of the two autofocus methods has the following characteristics. The phase difference AF enables high-speed focus adjustment because the amount of movement to the in-focus position is known, but due to the structure of the single-lens reflex camera, focus adjustment cannot be performed when the mirror is retracted (mirror-up) from the optical path. On the other hand, in hill-climbing AF, focus detection is performed using the signal from the image sensor, so focus adjustment after mirror up is possible, but in order to know the focus position, the focus evaluation value is compared while moving the focus lens. Need to find the peak value. In addition, because of the principle of hill-climbing AF, the focus adjustment is such that it passes through the peak and then returns to the peak. Therefore, in a lens having a drive system with a relatively large backlash, the following problems occur during inversion. That is, when the amount of overshoot from the peak is small, the drive command is absorbed in the backlash and the lens does not move at all. There is a problem of going too far. As described above, there are cases where the behavior at the time of reversal becomes unstable, for example, a load fluctuation due to backlash or backlash of the drive system, or inertia (inertia) causing excessive or insufficient travel beyond the target position.

For this reason, various methods for eliminating instability at the time of reversal (so-called hunting prevention) have been disclosed. For example, Patent Document 1 discloses a method of causing the lens drive system to go back beyond the target position by at least the backlash amount of the lens driving system and then back the same amount during reversal. Further, Patent Document 2 discloses a method of moving a lens at a lower speed than the lens moving speed before the reversal at the time of reversal to approach the target position. Further, Patent Document 3 discloses a method in which, when it is determined that the backlash correction at the time of inversion is excessive, no correction is performed at the time of inversion again.
Japanese Patent Laid-Open No. 01-280712 JP 05-264889 A Japanese Patent Laid-Open No. 2001-305419

  When the method disclosed in Patent Document 1 is used, the backlash of the drive system can be offset, so that the influence of backlash can be reduced. However, in hill-climbing AF, the target position (in-focus position) can be found only after passing through the peak position. Therefore, when the method of Patent Document 1 is applied, the time until in-focus is delayed. This is because the focus adjustment operation reverses after passing the peak position, and further passes through the target position by the amount of backlash, and then returns by the same amount. Further, in the method disclosed in Patent Document 2, the influence of inertia can be reduced by slowing the driving speed at the time of inversion, but there is a problem that the focusing time is delayed accordingly. Although the method disclosed in Patent Document 3 can reduce the overshoot amount from the target position when going to the in-focus position after reversal, it does not reduce the load fluctuation due to backlash and the influence of inertia.

  Actually, since the backlash amount and inertia of the drive system differ depending on the type of interchangeable lens, the optimum overshoot amount from the peak position differs for each interchangeable lens. Furthermore, since the backlash amount varies depending on the arrangement of the driving mechanism, for example, the focus position and the zoom position, the overshoot amount needs to be controlled accordingly.

  Accordingly, an object of the present invention is to enable high-precision automatic focus adjustment that eliminates instability at the time of reversal in a camera system having at least a focus control means of a hill-climbing detection method.

  In order to achieve the above object, as one aspect, the camera system of the present invention includes a focus lens, a drive unit that drives the focus lens, and a first output unit that outputs information about a backlash amount of the drive system. Is provided. Furthermore, a second output means for outputting information on the amount of overrun caused by the inertia of the drive system, a signal processing means for generating a focus evaluation signal from a signal obtained from the image sensor, and an output of the signal processing means A focusing control means for controlling the focusing operation accordingly is provided. In the camera system as described above, the focus control means always outputs the backlash amount output from the first output means and the second output means from the position where the peak value of the focus evaluation signal is detected. Overshoot the amount of overrun. Thereafter, the focus lens is controlled to be reversed and moved to a position where the peak value is detected.

  According to the present invention, at the time of hill-climbing AF, the focus evaluation value peak position is excessively exceeded by considering backlash and inertia, and then reversed and driven to the peak position, thereby reducing the influence of load fluctuation due to backlash, Unstable inversion can be eliminated. The present invention not only eliminates instability at the time of reversal in a lens having a relatively large backlash amount, but also shortens the focusing time by reducing the overshoot amount in a lens having a small backlash amount. I can do it.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a cross-sectional view of a lens interchangeable digital single-lens reflex camera representing an embodiment of the present invention. Here, the direction of the lens optical axis (photographing optical axis) AXL is defined as the Z direction, the direction orthogonal to the lens optical axis AXL and the horizontal direction of the two directions parallel to the imaging surface is the X direction and the vertical direction. Let the direction be the Y direction.

  Reference numeral 1 denotes a camera body (hereinafter simply referred to as a camera), 2 denotes an interchangeable lens mounted on the camera 1, and 3 denotes a main mirror. In the state shown in FIG. 1, the main mirror 3 is disposed on the optical path of the light beam from the interchangeable lens 2, reflects a part of the light beam, guides it to the finder optical system (7, 8), and the remaining light beam. Permeate. A sub mirror 4 is disposed behind the main mirror 3, and the light beam transmitted through the main mirror 3 is reflected and guided to the focus detection unit 5. The main mirror 3 and the sub mirror 4 can be retracted from the optical path by a drive mechanism (not shown).

  The phase difference type focus detection unit 5 includes an AF sensor and has a function of performing focus detection (detection of the focus state of the interchangeable lens 2) by a so-called phase difference detection method. The AF sensor includes a condenser lens that splits an incident light beam into two, two separator lenses that re-image each split light beam, and a line sensor such as a CCD sensor that photoelectrically converts two imaged subject images. Composed. The line sensor is arranged in a cross shape so as to detect the image position of the subject in the vertical direction (Y direction) and the horizontal direction (X direction).

  Reference numeral 6 denotes an image sensor composed of a CCD sensor or a CMOS sensor, and a light beam from the interchangeable lens 2 forms an image on a light receiving surface (image surface) of the image sensor 6. The imaging element 6 photoelectrically converts the formed subject image and outputs an imaging signal. The exposure amount of the image sensor 6 is controlled by an electronically controlled focal plane shutter (not shown).

  Note that due to the above structure, when the main mirror 3 and the sub mirror 4 are retracted from the optical path, focus detection (phase difference AF) by the phase difference detection method cannot be performed. In this case, so-called hill-climbing detection type focus adjustment (hill-climbing AF) is performed, in which contrast information is output from a signal processing unit (not shown) that receives a signal from the image sensor 6 and is adjusted. Is called. It should be noted that switching between phase difference AF and hill-climbing AF can be performed by a focus detection means selection unit (not shown).

  The finder optical system includes a pentaprism 7 and an eyepiece lens 8.

  In the interchangeable lens 2, in order from the subject side, 11 is a first lens unit, 12 is a second lens unit as a focus lens, 13 is a third lens unit as a variable power lens, and 14 is a fourth lens unit. In addition, a diaphragm unit 15 is disposed between the third and fourth lens units 13 and 14, and adjusts the amount of light passing through the interchangeable lens 2 and reaching the camera 1 side. The lens units 11 to 14 and the aperture unit 15 constitute a photographing optical system.

  The second lens unit (focus lens) 12 receives the driving force from the AF motor 16 and moves on the optical axis AXL to adjust the focus.

  The third lens unit (magnification lens) 13 moves on the lens optical axis AXL by the operation force of the photographer being transmitted by a transmission mechanism (not shown), and performs magnification.

  Reference numeral 17 denotes a display panel, which has a function of displaying an image output from a signal processing unit (not shown) that receives a signal from the image sensor 6 and various other shooting information.

  FIG. 2 is a block diagram showing an electric circuit configuration of the interchangeable lens digital single-lens reflex camera system shown in FIG.

  In this figure, 100 is an electric circuit on the camera 1 side (hereinafter referred to as camera-side electric circuit), and 200 is an electric circuit on the interchangeable lens 2 side (hereinafter referred to as lens-side electric circuit).

  In the camera-side electric circuit, reference numeral 101 denotes a camera CPU composed of a microcomputer. The camera CPU 101 controls the operation of each component on the camera 1 side, and is provided on the interchangeable lens 2 via the camera contact 102 and the lens contact 202 on the interchangeable lens 2 side (hereinafter simply referred to as the lens 2 side). Communication with the CPU 201 is performed. Information communicated to the lens 2 side includes drive information of the focus lens 12 and the like, and signals received from the lens 2 side include focus position, zoom position information, and the like.

  The camera contact 102 includes a signal transmission contact for transmitting a signal to the lens 2 side and a power contact for supplying power to the interchangeable lens 2.

  A power switch 103 that can be operated from the outside is a switch that activates the camera CPU 101 to enable power supply to each actuator, sensor, and the like in the system and operation of the system.

  A focus detection unit selection unit 104 has a function of switching focus detection units based on a phase difference detection method or a hill-climbing detection method. The arrangement of the main mirror 3, the sub mirror 4, and the shutter is switched according to the selection of the focus detection means selection unit 104. That is, when focus detection by the hill-climbing detection method is selected, the main mirror 3 and the sub mirror 4 are retracted from the optical path and the shutter is opened, and light from the subject reaches the image sensor. On the other hand, when the phase difference detection method is selected, the main mirror 3 and the sub mirror 4 are on the optical path, and the shutter is closed.

  Reference numeral 105 denotes a two-stroke release switch that can be operated from the outside, and has a first stroke switch (SW1) and a second stroke switch (SW2). A signal from the release switch 105 is input to the camera CPU 101. The camera CPU 101 enters a shooting preparation state in response to an ON signal input from the first stroke switch (SW1). Note that the processing of the camera CPU 101 and the like with respect to the input of ON signals from SW1 and SW2 differs depending on the selection of the focus detection means selection unit 104, and will be described separately below.

  When the phase difference detection method is selected in the focus detection means selection unit 104, when the ON signal from SW1 is input, the subject luminance measurement by the photometry unit 106 and the phase difference detection method by the focus detection unit 107 are performed. Start focus detection. The camera CPU 101 calculates the aperture value of the aperture unit 15, the exposure amount of the image sensor 6 (in the shutter speed), and the like based on the photometric result. Further, the camera CPU 101 drives the focus lens 12 required to focus on the subject to be photographed based on the focus detection information (defocus amount and defocus direction) that is the focus state detection result. And determine the drive direction. Information on the driving amount and the driving direction is transmitted to the lens CPU 201. The lens CPU 201 controls the operation of each component in the lens 2. Further, when an ON signal is input from the second stroke switch (SW2), the camera CPU 101 transmits an aperture drive command to the lens CPU 201 to set the aperture unit 15 to the previously calculated aperture value. In addition, the camera CPU 101 transmits an exposure start command to the exposure unit 110 to perform a retracting (up) operation of the mirrors 3 and 4 and an opening operation of the shutter, and the imaging unit 111 including the imaging device 6 captures the subject image. Photoelectric conversion, that is, photographing is performed.

  When the hill-climbing detection method is selected in the focus detection means selection unit 104, when the ON signal from SW1 is input, the signal processing unit 112 processes the output signal of the image sensor 6 and extracts the contrast information of the image. . The focus evaluation unit 113 determines the focus position by determining the history of contrast information obtained from the signal processing unit when the focus lens 12 is moved. A specific determination method will be described below. The focus evaluation unit 113 drives the lens in a direction in which the evaluation value increases from the change in the focus evaluation value when the focus lens 12 is driven, and determines the position where the evaluation value has a peak as the focus position. . Since the peak position has already been passed when the in-focus position is determined, the driving direction is reversed and the focus lens 12 is moved to the peak position. Note that the driving direction of the lens is not reversed unless the reversal start determining unit 206 described later determines that reversal is started. That is, control is performed such that the drive direction is reversed only after it is determined that the reversal is started and the evaluation value is maximized (focus position).

  Further, when an ON signal is input from the second stroke switch (SW2), the camera CPU 101 transmits an aperture drive command to the lens CPU 201 to set the aperture unit 15 to the previously calculated aperture value. In addition, the camera CPU 101 transmits an exposure start command to the exposure unit 110, performs a release operation after closing the shutter once, and performs photoelectric conversion of the subject image, that is, imaging, in the imaging unit 111 including the imaging element 6.

  An image pickup signal from the image pickup unit 111 (image pickup element 6) is converted into a digital signal by the signal processing unit 112, further subjected to various correction processes, and output as an image signal. The image signal (data) is recorded and stored in a recording medium such as a semiconductor memory such as a flash memory, a magnetic disk, and an optical disk in the image recording unit 114.

  When the hill-climbing detection method is selected in the focus detection means selection unit 104, an image acquired by the image sensor 6 can be displayed on the display panel 17 in real time.

  The lens contact 202 includes a signal transmission contact for exchanging signals with the camera 1 side, and a power contact for receiving power supply from the camera 1 side.

  203 is a backlash amount output means, which reads out and outputs a backlash amount corresponding to a focus position and a focus position obtained from the zoom position detection unit 209, which will be described later, from a table in which values are set in advance.

  Reference numeral 204 denotes an overrun amount output means, which reads out an overrun amount corresponding to a focus position, a zoom position or a lens driving speed obtained from a focus position and zoom position detection unit 209, which will be described later, from a table in which values are set in advance. Output.

  Reference numeral 205 denotes an overshoot amount calculation unit for the focus lens 12, which outputs a difference from a position where the focus evaluation value determined by the focus evaluation unit 113 takes a peak to the current position.

  Reference numeral 206 denotes inversion start determination means, which outputs an inversion start signal only when the following conditions are satisfied.

Output B of backlash output means 203
Output C of overrun amount output means 204
Output of overshoot amount calculation means 205 D
When
D> B + C or D = B + C
Reference numeral 207 denotes a focusing drive unit that drives the focus lens 12 by driving the AF motor 16 in accordance with the drive amount and drive direction information of the focus lens 12 transmitted from the camera CPU 101.

  Reference numeral 208 denotes an aperture drive unit, which is controlled by the lens CPU 201 that has received an aperture drive command from the camera CPU 101, and operates the aperture unit 15 shown in FIG. 1 to an aperture state corresponding to the aperture value specified by the command.

  Reference numeral 209 denotes a focus position / zoom position detection unit. The first detection unit detects the position of the second lens unit (focus lens) 12 and the second detection detects the position of the third lens unit 13 that is a variable power lens. It consists of parts.

  Next, the main operation of the system shown in FIG. 2 will be described with reference to the flowchart of FIG. 3 limited to the hill-climbing detection method. First, when the power switch 103 in the camera-side electric circuit 100 is turned on, power supply to the lens-side electric circuit 200 is started, and communication between the camera CPU 101 and the lens CPU 201 is started (step S in the figure). > 1001). In step 1001, the focus adjustment number flag n for determining whether or not the focus adjustment is the first time after the SW1 ON signal is generated and the variable Amax for storing the peak value of the focus evaluation value are initialized.

  Next, the camera CPU 101 determines whether or not the SW1 ON signal is generated in the release switch 105 (step 1002). When the ON signal is generated, the process proceeds to step 1003. Otherwise, the process returns to step 1001. In step 1003, the camera CPU 101 determines whether the focus adjustment number flag n is 0. When the focus adjustment count flag n is 0, that is, when the first focus adjustment is performed after SW1 is turned ON, the process proceeds to step 1004. When n = 0 is not satisfied, the process proceeds to step 1019.

  In step 1004, the focus evaluation unit 113 sets the drive direction of the focus lens 12. A specific method will be described below. First, the focus lens 12 is driven in a predetermined direction (for example, the closest direction), and the focus evaluation value output from the signal processing unit 112 is compared before and after driving. If the focus evaluation value after driving is greater or equal, the driving direction is set to the same direction as a predetermined direction. On the other hand, when the focus evaluation value after driving is smaller, the driving direction is set to a direction opposite to the predetermined direction.

  In step 1005, the focus evaluation unit 113 captures the focus evaluation value A from the signal processing unit 112.

  Next, the focus evaluation unit 113 compares the focus evaluation value A acquired in step 1005 with the peak value stored in Amax (step 1006). If the focus evaluation value A is smaller than the peak value Amax, the process proceeds to step 1010, and if greater or equal, the process proceeds to step 1007.

  In step 1007, it is determined whether or not the focus lens 12 has reached the end. If not, the process proceeds to step 1008, and if it has reached the end, the process proceeds to step 1017.

  In step 1008, the focus evaluation value A captured in the immediately preceding step 1005 is stored in Amax as a peak value, and the focus lens 12 is driven in the same direction as the previous driving direction by a predetermined amount of movement.

  Steps 1005 to 1009 are repeated until the acquired focus evaluation value A is smaller than the peak value Amax (corresponding to a state of climbing a mountain). In step 1006, if the acquired focus evaluation value A is smaller than the peak value Amax (a state where the mountain has been fully climbed), the process proceeds to step 1010. In step 1010, the focus position and zoom position detection unit 209 detects the focus position and zoom position. From these values, the backlash amount B in the current lens arrangement is acquired from the backlash output means 203 (step 1011). Further, the overrun amount C of the focus lens 12 due to inertia is acquired from the overrun amount output means 204 (step 1012). In step 1013, the overshoot amount D from the peak position is calculated by the overshoot amount calculation means 205. In step 1014, the inversion start determination unit 206 compares the overshoot amount D with a value obtained by adding the backlash amount B and the overrun amount C due to the inertia. If the overshoot amount D from the peak position is greater or equal, the process proceeds to step 1015, and if smaller, the process proceeds to step 1007. In step 1015, the focus lens 12 is driven to the position where the focus evaluation value is Amax, and the focus evaluation value at the target position is stored as the peak evaluation value Amax (step 1016).

  In step 1018, the focus adjustment number flag n is set to 1. Next, in Step 1019, it is determined whether or not the ON signal from SW2 is input by the second stroke operation of the release button 105, and Step 1002 to Step 1019 are repeated until the ON signal is input. When the ON signal from SW2 is input, the process proceeds to step 1020.

  In step 1020, the camera CPU 101 performs an exposure operation of the image sensor 6. In step 1021, the camera CPU 101 records captured image data on a recording medium and returns to step 1001.

  When the focus lens 12 reaches the end in step 1007, the process proceeds to step 1017 and is processed as a search NG. If it is determined in step 1003 that the focus adjustment count flag n is other than 0, that is, it is determined that hill-climbing AF has already been performed after SW1 is turned on, the process proceeds to step 1019, and the lens is not driven until SW1 is turned off.

  The camera CPU 101 and the lens CPU 201 repeat the above series of operations until the power switch 103 is turned off. When the power switch 103 is turned off, the communication between the camera CPU 101 and the lens CPU 201 is terminated, and the power supply to the lens-side electric circuit 200 is also terminated.

  In the embodiment, the focus detection means is switched depending on whether the main mirror and the sub mirror are retracted from the optical path, but the present invention is not limited to this. For example, the present invention can be applied to a camera system that can always switch between phase difference AF and mountain climbing AF using a half mirror.

  In the present embodiment, the method of displaying the signal from the image sensor on the display panel in real time when performing hill-climbing AF has been described, but the present invention is not limited thereto. For example, a liquid crystal panel may be arranged in the finder so that an image from the image sensor can be viewed on the finder.

  Further, although the present embodiment has been described with respect to a lens interchangeable digital single-lens reflex camera, the present invention can also be applied to a digital camera on a lens-integrated side, and further to a video camera.

1 is a cross-sectional view showing a lens interchangeable digital single-lens reflex camera that is an embodiment of the present invention. The block diagram which shows the electric circuit structure of the said camera system. 7 is a flowchart showing main operations in the camera system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Camera body 2 Interchangeable lens 3 Main mirror 4 Sub mirror 5 Phase difference type focus detection unit 6 Image sensor 7 Penta prism 8 Eyepiece 11 First lens unit 12 Second lens unit (focus lens)
13 Third lens unit (variable magnification lens)
14 Fourth lens unit 15 Aperture unit 16 AF motor 17 Display panel

Claims (1)

A focus lens; drive means for driving the focus lens; first output means for outputting information on a backlash amount of the drive system; and second information for outputting information on an overrun amount resulting from inertia of the drive system. In a camera system comprising: output means; signal processing means for generating a focus evaluation signal from a signal obtained from an image sensor; and focus control means for controlling a focusing operation according to an output of the signal processing means. ,
The focus control means always adds the backlash amount output from the first output means and the overrun amount output from the second output means from the position where the peak value of the focus evaluation signal is detected. Overshoot the value,
Thereafter, the camera system is controlled to reverse and move the focus lens to a position where the peak value is detected.

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