JP2015184614A - Automatic focus adjustment device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automatic focus adjustment device that allows for easy and precise focusing relative to a celestial body.SOLUTION: An automatic focus adjustment device causing a focus adjustment unit of an imaging optical system to move to an in-focus position comprises: a movement unit that moves the focus adjustment unit in an optical axis direction; an image pickup element that images a subject image formed by the imaging optical system; an image recognition unit that recognises a specific celestial body image from image imaged by the image pickup element; an image size detection unit that detects a size on the image pickup element of the celestial body image recognised by the image recognition unit; a minimum value detection unit that detects a minimum value from an image size of the celestial body image detected by the image size detection unit in each position when the focus adjustment unit is moved to a plurality of positions different in an optical axis direction by the movement unit; and a movement control unit that causes the focus adjustment unit to be moved to a position where the minimum value is obtained and then control the position.

Description

  The present invention relates to an automatic focus adjustment device suitable for astrophotography.

  Conventionally, when photographing astronomical objects with a camera equipped with an automatic focus adjustment device, it has been difficult to adjust the focus with the focus adjustment device because the celestial body that is the subject is dark. For this reason, in the past, autofocus adjustment was performed by selecting a distant shooting mode mounted on the camera, or the focus was adjusted manually by rotating the focus ring to a position at infinity. It was not possible to confirm whether or not.

  Various astronomical imaging methods have been proposed (Patent Documents 1 and 2). Japanese Patent Laid-Open No. 2004-151867 continuously performs a plurality of preliminary shootings while moving the focus adjustment optical system by a predetermined pitch when the low-luminance focusing mode is set, and adjusts the focus obtained at the time of the preliminary shooting. The stored preliminary image is stored in association with the position of the optical system, and when one of the displayed images is selected by the user, the image is stored in association with the selected image. The focus adjustment optical system is driven to the position of the focus adjustment optical system.

  Patent Document 2 proposes a focus adjustment device for enabling focusing on an object at low brightness and at infinity. For example, when shooting a night celestial object with a predetermined focal length accurately, the user presses the zoom button on a subject at a sufficiently long distance so that it can be regarded as infinity in the daytime. Then, a desired focal length is set, and then the infinity detection button is pressed to focus on an infinite subject at the focal length, and the in-focus position and the focal length are stored. When photographing a celestial object at night, the user presses the infinity movement button of the focus adjustment device to automatically set the focal length and the focus position stored in advance in the focus adjustment device.

JP 2003-322789 A JP 2006-201283 A

  However, the focus adjustment device disclosed in Patent Document 1 has to shoot a plurality of times, display an image written in a memory on a display device, and determine which is better for the user by viewing the image displayed on the display device. So it takes time. In the focus adjustment device of Patent Document 2, the focal length and the focus position must be set in the daytime. Further, since the in-focus position changes depending on the temperature, when there is a temperature difference between daytime and nighttime, the in-focus position may be shifted from the daytime in-focus position during astronomical photography at night.

  The present invention has been made in view of the above problem awareness, and an object of the present invention is to provide an automatic focus adjustment apparatus that can easily and accurately focus on a subject such as an astronomical object.

  The present invention is an automatic focus adjustment apparatus that moves a focus adjustment unit of a photographing optical system to a focus position, and a subject that is formed by a moving unit that moves the focus adjustment unit in an optical axis direction and the photographing optical system. An image sensor that captures an image, an image recognition unit that recognizes a specific celestial image from an image captured by the image sensor, and an image size detection that detects the size of the celestial image recognized by the image recognition unit on the image sensor When the focus adjustment unit is moved to a plurality of different positions in the optical axis direction by the moving unit and the moving unit, a minimum value is detected from the image size of the specific celestial image detected by the image size detection unit at each position. A minimum value detection unit and a movement control unit that controls the movement of the focus adjustment unit to the position of the focus adjustment unit when the minimum value is obtained are provided.

  Another aspect of the present invention is an automatic focus adjustment device that moves a focus adjustment unit of a photographing optical system to a focus position, and a moving unit that moves the focus adjustment unit in an optical axis direction, and the photographing optical system. An image sensor that captures a subject image formed by the image sensor, an image recognition unit that recognizes a specific celestial image from an image captured by the image sensor, and a luminance detection unit that detects the brightness of the celestial image recognized by the image recognition unit When the focus adjustment unit is moved to a plurality of different positions in the optical axis direction by the moving unit, a maximum value is detected from the luminance of the specific celestial image detected by the luminance detection unit at each position. A value detection unit; and a movement control unit that moves the focus adjustment unit to a position of the focus adjustment unit when the maximum value is obtained.

  The size detector preferably detects the diameter of the celestial image as the size of the celestial image. It is practical that the size detection unit detects the size of a specific celestial image while moving the focus adjustment unit from the infinity side movable end to the shortest movable end side by the moving unit.

  It is preferable that the luminance detection unit detects a central luminance of the celestial image. It is practical that the luminance detection unit detects the luminance of a specific celestial image while moving the focus adjusting unit from the infinity side movable end to the shortest movable end side by the moving unit.

  The said image recognition part can recognize the image used as a circular light spot from an image signal as a specific astronomical image.

  According to the present invention, it is possible to obtain an automatic focusing apparatus that can easily and accurately focus on a subject such as a celestial body.

It is a block diagram which shows the principal part of embodiment of the mirror-less interchangeable lens digital camera to which this invention is applied. 6 is a timing chart for explaining the movement locus of the focus adjustment lens group and the state of the captured celestial image in the celestial AF operation when shooting the celestial object in the astrophotography mode at night with the same digital camera. 3 is a flowchart illustrating a first embodiment of an AF operation in the digital camera. It is a flowchart which shows 2nd Embodiment of AF operation | movement in the digital camera.

  FIG. 1 is an embodiment in which the present invention is applied to a mirrorless interchangeable-lens digital camera, and shows the main configuration in block form. The interchangeable lens digital camera 10 includes a camera body 11 and a photographing lens 51 that can be attached to and detached from the camera body 11.

  The camera body 11 includes a body CPU 31 (automatic focus adjustment unit) as a control unit that comprehensively controls the functions of the camera body 11 and the photographing lens 51.

  On the other hand, the photographic lens 51 constitutes a part of the photographic optical system and drives the focus adjustment lens group 52 functioning as a focus adjustment unit and the focus adjustment lens group 52 in the optical axis direction (direction parallel to the optical axis O). A gear block 53, a joint 55 detachably connected to the joint 35 of the camera body 11, and a lens CPU 57 for controlling the lens function. In addition to the focus adjustment lens group 52, the photographing optical system includes a variator and a compensator lens group that constitute a zoom lens, and a stop (not shown in detail). The joint 55 is connected to the gear block 53 via a one-way input / output rotation transmission mechanism 54. Further, the photographing lens 51 includes a focus ring (manual operation unit) 59 that is manually rotated. The focus ring 59 is formed to be rotatable about the optical axis O of the focus adjustment lens group 52 as a virtual central axis, and is connected to the gear block 53 via a one-way input / output rotation transmission mechanism (manual operation unit) 58.

  In this photographic lens 51, one one-way input / output rotation transmission mechanism 54 transmits the rotation of the joint 55 to the gear block 53 and rotates a lens driving ring (not shown) to move the focusing lens group 52 in the optical axis direction. However, the rotation of the gear block 53 is a known mechanism that does not transmit to the joint 55. The other one-way input / output rotation transmission mechanism 58 transmits the rotation of the focus ring 59 to the gear block 53 and rotates the lens driving ring to move the focus adjustment lens group 52 in the optical axis direction. The rotation is a known mechanism that is not transmitted to the focus ring 59. Such a mechanism is known as a seamless lens drive switching mechanism.

  The photographic lens 51 can adjust the focus by moving the focus adjustment lens group 52 by manually operating the focus ring 59 independently of the automatic focus adjustment unit of the mounted camera body 11. . For example, after the user rotates the focus ring 59 to move the focus adjustment lens group 52 to a position where the focus adjustment lens group 52 is focused on a specific subject, the focus adjustment lens group is moved by the automatic focus adjustment unit of the camera body 11. It is possible to move 52 to a position for focusing on a specific subject and vice versa.

  The body CPU 31 rotationally drives the AF motor 33 via the AF motor driver 32. The rotation of the AF motor 33 is decelerated by the gear block 34 and is transmitted to the joint 55 provided at the mount portion of the photographing lens 51 via the joint 35 provided at the mount portion of the camera body 11. The rotation of the joint 55 is transmitted to the gear block 53 via the one-way input / output rotation transmission mechanism 54, and moves the focus adjustment lens group 52 forward and backward in the optical axis direction via the gear block 53. The AF motor 33 includes an encoder 37 that outputs an AF pulse in conjunction with the rotation. The body CPU 31 counts the AF pulse output from the encoder 37 by the built-in counter 31a according to the rotation direction of the AF motor 33, and detects the driving amount of the focus adjustment lens group 52 from the optical axis direction position or the reference position. This is a known configuration. The body CPU 31, the AF motor driver 32, the AF motor 33, the joint 35, the image sensor 45, the AFE 46, and the DSP 41 constitute an automatic focus adjustment device.

  The lens CPU 57 is connected to the peripheral control circuit 21 of the camera body 11 through the connection of the electrical contact groups 56 and 36, and the lens type information and release between the lens CPU 57 and the body CPU 31 through the peripheral control circuit 21. (Minimum) F value / maximum F value information, focal length information, shooting distance information, and the like are communicated by predetermined data communication.

  The camera body 11 further includes a diaphragm mechanism 22 that controls opening and closing of a diaphragm device (not shown) in the photographing lens 51.

  The body CPU 31 has a focus mode switch SWFMo for switching the celestial AF mode and the normal AF mode among the manual focus (MF) mode, the auto focus (single AF / continuous AF) mode, and the auto focus mode. AF operation switch SWAF for starting focus operation (automatic focus adjustment operation), release switch SWR for starting still image shooting and still image recording processing, main switch SWM for turning on / off power to peripheral control circuit 21, etc., shooting mode Mode switch SWMo that switches between astronomical photography mode and normal photography mode, and an enlarged display switch that enlarges and displays a focus detection area or a partial area including a focused subject image. Chi SWMag is connected. The celestial AF mode is an AF mode optimized for celestial shooting, and the celestial shooting mode is a shooting mode optimized for celestial shooting. Details will be described later.

  The camera body 11 is provided with an imaging element 45 as an imaging unit. The subject luminous flux that has entered the camera body 11 from the photographing lens 51 forms a subject image on the light receiving surface of the image sensor 45. The image sensor 45 converts the received subject image into an electrical image signal for each pixel and outputs the electrical image signal. The image signal output from the image sensor 45 is digitized by an AFE (analog front end) 46, signal processing such as white balance by the DSP 41, conversion processing to a display image signal that can be displayed on the monitor (display unit) 42, and the like. The subject image is displayed on the monitor 42 by the display image signal. The monitor 42 is attached to the back surface of the camera body 11. The monitor 42 further displays various shooting information such as the set AF mode (single AF / continuous AF), shooting mode / playback mode / setting mode, shutter speed, aperture value, and the like. In FIG. 1, the image sensor 45 indicated by a two-dot chain line and the image sensor 45 connected to the AFE 46 indicated by a solid line are shown, but these are the same image sensor.

  The DSP 41 communicates image signals and information regarding photographing with the body CPU 31 and operates in accordance with the operation state of the body CPU 31. For example, when the body CPU 31 operates in the shooting mode, the DSP 41 and the monitor 42 operate as a live view display unit that performs live view display on the monitor 42 of the image signal output from the image sensor 45. The DSP 41 converts the image signal output from the image sensor 45 into an image signal that can be processed by the body CPU 31 and outputs the image signal to the body CPU 31 when the body CPU 31 is performing an automatic focus adjustment operation (AF process). When the body CPU 31 is performing a still image shooting operation, the DSP 41 causes the imaging device 45 to perform an imaging operation under the conditions set by the body CPU 31 and performs predetermined processing on the subject image signal captured by the imaging device 45 to perform flash memory 38. Write to. The flash memory 38 is a known memory card that is detachable from the camera body 11.

  When the main switch SWM is turned on, the body CPU 31 turns on power to other members in the camera body 11 such as the peripheral control circuit 21 and the DSP 41 and causes the monitor 42 to display initial information. The peripheral control circuit 21 communicates with the lens CPU 57 to communicate information such as lens type information. When the shooting mode is selected, the body CPU 31 causes the image pickup device 45 to start live view display image pickup processing (moving image pickup processing) via the DSP 41, and causes the DSP 41 to capture the subject image picked up by the image pickup device 45. The live view is displayed on the monitor 42.

  The body CPU 31 detects the subject luminance from the subject image signal output from the DSP 41, and the exposure time (mechanical shutter speed, electronic shutter speed) of the image sensor 45 or the image signal output from the image sensor 45 via the DSP 41. Adjust the gain (ISO sensitivity).

  The camera body 11 (body CPU 31) has a known normal AF (automatic focus adjustment) function. The normal AF in this embodiment is a known so-called image contrast detection method that uses an image signal captured by the image sensor 45 while moving the focus adjustment lens group 52 in the optical axis direction. The body CPU 31 starts the automatic focus adjustment process when the AF operation switch SWAF is turned on. The body CPU 31 calculates the contrast based on the subject image signal captured by the image sensor 45 while moving the focus adjustment lens group 52 between the movable ranges (the closest end and the infinity end) via the AF motor 33. Then, a contrast search operation for detecting the position (focus position) of the focus adjustment lens group 52 at which the contrast reaches a peak is executed. When the body CPU 31 detects a position where the contrast reaches a peak, the body CPU 31 drives the AF motor 33 to move the focus adjustment lens group 52 to the position (focus position) of the focus adjustment lens group 52 at that time. The AF motor 33, the gear block 34, and the joint 35 constitute a moving unit that moves the focusing lens group 52, which is a focusing unit, in the optical axis direction.

  When the camera body 11 operates in the astrophotography mode, the camera body 11 performs automatic focus adjustment by the celestial AF operation. In the astronomical AF operation, the body CPU 31 first moves the focus adjustment lens group 52 to the infinity end (infinitely movable end), and then performs a specific light spot that becomes a circular light spot from the image signal captured by the image sensor 45. The celestial image is recognized (extracted), and the diameter R of the recognized celestial image or the center luminance Bv of the celestial image is detected. After that, the focus adjustment lens group 52 is moved in steps from the infinity end to the near end (from the infinity side movable end to the shortest movable end side) by a predetermined length unit. A specific celestial image serving as a light spot is recognized (followed), and the diameter R of the recognized celestial image or the center luminance Bv of the celestial image is detected. Then, the minimum value of the diameter R or the maximum value of the central luminance Bv is detected from the plurality of diameters R or the central luminance Bv detected at each position by moving a plurality of steps. The position of the focus adjustment lens group 52 when the minimum value of the diameter R or the maximum value of the center luminance Bv is detected is set as the celestial focus position, and the focus adjustment lens group 52 is moved to the celestial focus position.

  Here, the body CPU 31 recognizes a specific celestial image from the image signal captured by the image sensor 45, a size detection unit 31d that detects the size of the celestial image recognized by the image recognition unit, and the same celestial object. A luminance detection unit 31e that detects the luminance of the image, a minimum value detection unit 31f that detects a minimum value of the size, a maximum value detection unit 31g that detects a maximum value of the luminance, and the minimum value or maximum value. The position of the focus adjustment lens group 52 at the time of detection is set as a focus position, and a movement control unit 31h is configured to move the focus adjustment lens group 52 to this focus position.

  FIG. 2 is a timing chart for explaining the movement trajectory (search direction) of the focus adjustment lens group 52 and the state of the captured celestial image in the celestial AF operation when shooting celestial objects at night. Here, changes in the celestial image when the focus adjustment lens group 52 is moved in steps from the infinity end to the near end are shown. In FIG. 2, a square cell represents each pixel 45 a of the image sensor 45. In this embodiment, the diameter R is detected as the size of the specific celestial image, and the central luminance Bv is detected as the luminance Bv of the celestial image.

  In the example shown in FIG. 2, it is determined in the fourth step that the minimum value of the diameter R and the maximum value of the central luminance Bv have been obtained in the second step from the infinity end of the focusing lens group 52, and the maximum value is obtained. The focus adjustment lens group 52 is moved to the in-focus position, with the position of the focus adjustment lens group 52 when obtained as the in-focus position. In this embodiment, the extreme value (inflection point) when the diameter R or the center luminance Bv of the celestial image is continuously reduced or increased twice and then increased or decreased continuously twice is set to the minimum value or the maximum value. That is, it is determined that the object is in focus. The infinity end of the focus adjustment lens group 52 is a infinity side movable end and also a mechanical contact end.

  The AF operation at the time of celestial photography (celestial AF operation) will be described with reference to FIGS. FIG. 3 is a flowchart regarding the AF operation. The AF operation of FIG. 3 is executed by the overall control by the body CPU 31 when the AF operation switch SWAF is turned on. The photographer preferably determines the composition so that the brightest celestial body (star) is positioned at the center of the screen.

  When the body CPU 31 enters the AF operation, the body CPU 31 first checks whether or not the astrophotography mode is set (S101). When the astrophotography mode is not set (S101: NO), the body CPU 31 executes the normal AF operation and ends the AF operation (S119, AF end). When the astronomical shooting mode is set (S101: YES), the astronomical AF operation is started. First, the AF motor 33 is driven toward the infinity end, and the focus adjustment lens group 52 is moved to the infinity end (the contact end). Move (S103).

  Subsequently, the body CPU 31 causes the imaging element 45 to perform an imaging operation, and recognizes (detects and extracts) an astronomical image that is a circular light spot from the captured image signal (S105). When the circular image cannot be recognized (S107: NO), the body CPU 31 moves the focus adjustment lens group 52 stepwise to the near distance side (S109), and makes a circular shape from the image signal captured by causing the image sensor 45 to perform an image capturing operation. An astronomical image serving as the light spot of is recognized (S105).

  When the body CPU 31 can recognize the circular image (S107: YES), the body CPU 31 detects the diameter R of the circular image, and writes the detected diameter R and the position of the focusing lens group 52 at this time in the RAM 31b (S111). It is checked whether a minimum value of the diameter R has been obtained (S113). When the minimum value is not obtained (S113: NO), the body CPU 31 moves the focus adjustment lens group 52 stepwise to the near distance side (S115) and causes the imaging element 45 to perform an imaging operation to obtain a circle from the captured image signal. The image is recognized (tracking the circular image) (S117), the diameter R of the recognized circular image is detected, and the detected diameter R and the position of the focusing lens group 52 at this time are written in the RAM 31b (S111).

  The body CPU 31 detects the minimum value of the diameter R by repeating the processes in steps S111 to S117.

  When the body CPU 31 detects the minimum value of the diameter R (S113: YES), the body CPU 31 reads the position of the focus adjustment lens group 52 when the minimum value is obtained from the RAM 31b and sets it as the in-focus position. The focus adjustment lens group 52 is moved to the position (S119), and the astronomical AF mode is ended (AF end). The position of the focus adjustment lens group 52 when the minimum value of the diameter R of the celestial image is obtained is the celestial focus position with respect to the celestial image.

  After moving the focus adjustment lens group 52 to the celestial focus position, the body CPU 31 locks the focus adjustment lens group 52 to the celestial focus position. For example, even if the photometric switch SWS is turned on, the focus adjustment lens group 52 is not moved. Thus, when the release switch SWR is turned on, the body CPU 31 performs a photographing operation in the astronomical photographing mode.

  As described above, the first embodiment of the present invention detects the position of the focus adjustment lens group 52 at which the diameter R of the celestial image is minimized when the AF operation is performed in the astrophotography mode. It becomes possible to focus. Therefore, according to the first embodiment of the present invention, the in-focus state is detected by the change in the size of a single celestial image captured by moving the focus adjustment lens group 52 to a plurality of different positions. The focus state can be detected easily and accurately.

Recognition of the celestial image and detection of the diameter R of the recognized celestial image can be performed by a known image processing method. It is preferable to recognize the celestial image with priority on the central area of the screen.
Since the specific celestial image moves on the shooting screen due to the rotation of the earth, it is preferable to track the movement trajectory of the specific celestial image in step S117.
The minimum value of the diameter R of the celestial image can be detected when the diameter R of the celestial image decreases continuously for a plurality of times and then increases continuously for a plurality of times. When the minimum value cannot be detected, for example, the focus adjustment lens group 52 may be moved to the position of the focus adjustment lens group 52 when the smallest diameter R is obtained.

  In the above embodiment, the diameter R is detected as the size of the celestial image, but the area of the celestial image may be detected. The position of the focus adjustment lens group 52 when the area of the celestial image is minimized is the celestial focus position.

  Whether or not the celestial image is in focus can also be detected by the center luminance Bv of the celestial image. The brightness of the celestial image is highest when it is in focus, and decreases as the defocus amount increases. Therefore, in the second embodiment, instead of detecting the diameter R of the celestial image, the center luminance Bv of the celestial image is detected. In the timing chart shown in FIG. 2, the center luminance Bv is detected by image data for one pixel.

  FIG. 4 is a flowchart showing an operation when the celestial focus position is detected based on the center luminance Bv. The same processes as those in FIG. 3 are denoted by the same step S numbers, and description thereof is omitted. Since the processing until the circular image is recognized (steps S101 to S109) is the same as the flowchart of FIG. 3, the processing of steps S211 to S219 after the recognition of the circular image (S107: YES) will be described.

  The body CPU 31 detects the center brightness Bv of the circular image, and writes the detected center brightness Bv and the position of the focus adjustment lens group 52 at this time in the RAM 31b (S211). Then, the body CPU 31 checks whether or not the maximum value of the center luminance Bv is obtained (S213). If the maximum value is not obtained (S213: NO), the body adjustment lens group 52 is moved closer to the short distance side. Step movement is performed (S215). The body CPU 31 recognizes a circular image (tracks the circular image) from the image signal captured by causing the imaging device 45 to perform an imaging operation (S217), detects the central luminance Bv of the recognized circular image, and detects the detected central luminance Bv. The position of the focus adjustment lens group 52 at this time is written in the RAM 31b (S211).

  The body CPU 31 repeats the processes in steps S211 to S217 to detect the maximum value of the center luminance Bv (S213: NO).

  When the body CPU 31 detects the maximum value of the central brightness Bv (S213: YES), the body CPU 31 reads the position of the focus adjustment lens group 52 when the maximum value is obtained from the RAM 31b, sets it as the in-focus position, and sets the focus. The focus adjustment lens group 52 is moved to the position (S219), and the astronomical AF mode is ended (AF end). The position of the focus adjustment lens group 52 when the maximum value of the center luminance Bv of the celestial image is obtained is the celestial focus position with respect to the celestial image.

  As described above, the second embodiment of the present invention detects the position of the focusing lens group 52 at which the center luminance Bv of the celestial image becomes maximum when performing the AF operation in the astrophotography mode. It becomes possible to focus on. Therefore, according to the second embodiment of the present invention, the in-focus state is detected by a change in luminance of a single celestial image taken by moving the focus adjustment lens group 52 to a plurality of different positions. The focus state can be detected easily and accurately.

  The center luminance Bv of the celestial image is obtained by using image data for one pixel in the embodiment of FIG. 3, but the center luminance Bv of four pixels adjacent to each other, or nine adjacent pixels or more. You may obtain | require using the average value of image data.

  The maximum value of the center luminance Bv of the celestial image can be detected when the center luminance Bv of the celestial image increases continuously several times and then decreases continuously several times. If the maximum value cannot be detected, for example, the focus adjustment lens group 52 may be moved to the position of the focus adjustment lens group 52 when the largest (high) center luminance Bv is obtained.

  An area for recognizing the celestial image is set in advance as screen coordinates, and an astronomical frame that surrounds the celestial image recognition area is displayed on the monitor screen, so that the user can compose the celestial image within this astronomical frame. You may make it the structure to decide. According to this embodiment, since the digital camera 10 only needs to recognize the celestial image from the image data in the celestial ranging frame, the amount of image data is small, and the celestial image can be easily recognized. It can be detected with accuracy. Since the photographer knows that the celestial image in the celestial ranging frame is in focus, it becomes easy to capture and select the celestial object to be focused.

When the AF operation switch SWAF is turned on, if the image in the frame is enlarged and displayed on the monitor, the photographer can easily see which celestial body is in the frame, and more accurately see the focus state of the celestial image. it can.
When a plurality of celestial images are included in the celestial ranging frame, it is preferable to recognize the celestial image having the highest luminance as a specific celestial image.

  In the first and second embodiments described above, in the photographing operation (S105, S117, S227) by the image sensor 45, the aperture of the photographing lens 51 is opened, and the exposure time is set to an appropriate value for the brightness of the celestial image. It is preferable to set so that The ISO sensitivity (gain) may be increased by several steps from the normal ISO sensitivity.

  Further, the predetermined amount when the AF motor 33 is stepped to the short distance side varies depending on the focal length of the photographing lens, the resolving power, and the like, and is preferably one or several AF pulses. When the focus adjustment lens group 52 is moved stepwise by a movement length longer than the shortest movement length, it is preferable to obtain a more accurate lens position between the step movements by interpolation calculation. The movement of the focus adjustment lens group 52 is not a step movement, but may be continuously moved and imaged at a predetermined time interval or at a predetermined lens position interval to detect the size or brightness of the celestial image. The moving direction of the focus adjustment lens group 52 may be from the shortest movable end to the infinity movable end.

  In the astrophotography mode, when the focus adjustment lens group 52 is moved to the celestial focus position in response to the ON operation of the AF operation switch SWAF, the focus adjustment lens group 52 is held at the celestial focus position (AF lock), and then photometry is performed. It is preferable not to perform the AF operation even when the switch SWS is turned on. In other words, when the astrophotography mode is set, the celestial AF operation is performed upon receiving the ON operation of the AF operation switch SWAF, but the AF operation is preferably not performed even when the photometry switch SWS is turned on.

  The above is an embodiment applied to a so-called mirrorless digital camera, but the present invention can also be applied to a photographing apparatus such as a single-lens reflex digital camera, a so-called compact digital camera, and a video camera. In the case of a single-lens reflex digital camera, the normal AF operation can also be performed by a phase difference detection method.

  The present invention also provides an astronomical tracking imaging device that drives an optical system or an image sensor so that an astronomical image formed on the light receiving surface of the image sensor does not move relative to the light receiving surface (for example, Japanese Patent Application Laid-Open No. 2010-122672). When the celestial body tracking operation is performed during the celestial AF driving, the celestial body tracking operation can be performed for a long time, and more accurate and accurate focus adjustment can be performed.

11 Camera body 21 Peripheral control circuit 31 Body CPU
31a Counter 31b RAM
31c Image recognition unit 31d Size detection unit 31e Luminance detection unit 31f Minimum value detection unit 31g Maximum value detection unit 31h Movement control unit 32 AF motor driver (movement unit)
33 AF motor (moving part)
34 Gear block (moving part)
35 Joint (moving part)
38 Flash memory 41 DSP
42 Monitor (display unit)
45 Image sensor 45a Pixel 46 AFE
51 Shooting lens (shooting optical system)
52 Focus Adjustment Lens Group (Focus Adjuster)
53 Gear block 54 One-way input / output rotation transmission mechanism 55 Joint 57 Lens CPU
58 One-way input / output rotation transmission mechanism 59 Focus ring SWAF AF operation switch SWFMo Focus mode switch SWMo Mode switch

Claims (7)

An automatic focus adjustment device that moves a focus adjustment unit of a photographing optical system to a focus position,
A moving unit for moving the focus adjusting unit in the optical axis direction;
An image sensor that captures a subject image formed by the imaging optical system;
An image recognition unit for recognizing a specific celestial image from an image captured by the image sensor;
An image size detection unit for detecting the size of the celestial image recognized by the image recognition unit on the image sensor;
Minimum value detection that detects a minimum value from the image size of a specific celestial image detected by the image size detection unit at each position when the focus adjustment unit is moved to a plurality of positions in different optical axis directions by the moving unit. And
A movement control unit that controls the movement of the focus adjustment unit to the position of the focus adjustment unit when the minimum value is obtained;
An automatic focusing apparatus characterized by comprising: An automatic focus adjustment device that moves a focus adjustment unit of a photographing optical system to a focus position,
A moving unit for moving the focus adjusting unit in the optical axis direction;
An image sensor that captures a subject image formed by the imaging optical system;
An image recognition unit for recognizing a specific celestial image from an image captured by the image sensor;
A luminance detection unit for detecting the luminance of the celestial image recognized by the image recognition unit;
When the focus adjustment unit is moved to a plurality of different positions in the optical axis direction by the moving unit, a maximum value detection that detects a maximum value from the luminance of a specific celestial image detected by the luminance detection unit at each position And
A movement control unit that moves the focus adjustment unit to the position of the focus adjustment unit when the maximum value is obtained;
An automatic focusing apparatus characterized by comprising: The automatic focus adjustment apparatus according to claim 1, wherein the size detection unit detects a diameter of the celestial image as a size of the celestial image. The automatic focus adjustment apparatus according to claim 2, wherein the luminance detection unit detects a central luminance of the celestial image. 4. The automatic focus adjustment apparatus according to claim 3, wherein the size detection unit detects a size of a specific celestial image while the moving unit moves the focus adjustment unit from the infinity side movable end to the shortest movable end side. Automatic focusing device. 5. The automatic focus adjustment apparatus according to claim 4, wherein the brightness detection unit automatically detects the brightness of a specific celestial image while the moving unit moves the focus adjustment unit from the infinity side movable end to the shortest movable end side. Focus adjustment device. 7. The automatic focus adjustment apparatus according to claim 1, wherein the image recognition unit recognizes an image that becomes a circular light spot from the image signal as a specific celestial image.

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