JP4906590B2 - Imaging device - Google Patents

Description

  The present invention relates to exposure control during still image shooting in a single-lens reflex digital camera capable of observing a subject image on a display device.

  A cross-sectional view of a single-lens reflex digital camera is shown in FIG. In FIG. 5, the members to which the luminous flux of the subject image reaches are mainly described.

  Reference numeral 200 denotes a digital camera body, and 201 denotes an interchangeable lens that can be attached to and detached from the digital camera body 200. Reference numeral 202 denotes a mirror that reflects a part of the light flux of the subject image formed by the photographing lens group inside the interchangeable lens 201, and has a semi-transparency that can switch between a state of entering the photographing optical path and a state of retracting from the photographing optical path. Have. FIG. 5 shows a state in which the mirror 202 has entered the photographing optical path, and guides a part of the light beam of the subject image to the sub mirror 203 described later and reflects the remaining light beam to the focus plate 215. Reference numeral 203 denotes a sub-mirror that reflects the light beam transmitted through the mirror 202 to the focus detection circuit 204. Reference numeral 204 denotes a focus detection circuit that detects the in-focus state from the light flux of the subject image reflected by the sub mirror 203.

  Reference numeral 205 denotes a focal plane shutter for controlling the exposure time of the image sensor 213 during still image shooting. Reference numeral 206 denotes a base plate of the focal plane shutter 205, and reference numeral 207 denotes a cover plate of the focal plane shutter 205. Reference numeral 208 denotes a rear curtain of the focal plane shutter 205, and in the state of FIG. 5, exists at a position retracted from the aperture that is the opening of the base plate 206. Reference numeral 209 denotes a front curtain of the focal plane shutter 205, which exists in a position where the aperture is blocked in the state shown in FIG.

  Reference numeral 210 denotes a low-pass filter that separates the luminous flux of the subject image into point images. Reference numeral 211 denotes a cover glass of the image sensor 213, and 212 denotes a package of the image sensor 213. An image sensor 213 having a photoelectric conversion function converts the light flux of the subject image into image data composed of electrical signals.

  Reference numeral 214 denotes a video display circuit such as a liquid crystal monitor device or an organic EL (electroluminescence) display device, which displays a camera control menu and image data obtained by the image sensor 213. Reference numeral 215 denotes a focusing plate, 216 denotes a pentaprism, and 217 denotes a finder optical system provided for observing a subject image formed on the focusing plate 215. Reference numeral 218 denotes a photometric lens for guiding the light beam that has passed through the focusing plate to the photometric element, and reference numeral 219 denotes a photometric sensor that measures the amount of light of the subject image from the light beam to which the photometric lens 218 is added.

  Also in such a single-lens reflex digital camera, there has been proposed one that can display a subject image in real time on the video display circuit 214 on the rear surface and can use the video display circuit 214 as a substitute for the finder optical system 217 for observing the subject. (See Patent Document 1).

As a specific configuration, for example, the mirror 202 disposed on the photographing optical path for guiding the subject image to the finder optical system 217 is retracted from the photographing optical path, and the tip of the focal plane shutter 205 disposed in front of the image sensor is arranged. Only the curtain 209 is run. Then, the subject image collected by the photographing lens is obtained by continuously converting it into image data by the image sensor, and this continuously obtained image data is subjected to image processing and sequentially applied to the video display circuit 214 on the rear surface. indicate.
JP 2001-125173 A

  Here, the exposure time of the single-lens reflex digital camera described above is determined by the travel interval between the front curtain 209 and the rear curtain 208. Therefore, if still image shooting is performed in a state in which the subject can be observed by displaying an image on the video display circuit 214 on the back side, the front curtain 209 needs to be charged again. That is, when the photographer operates the release switch to instruct still image shooting while observing the subject on the video display circuit 214, the rear curtain 208 of the focal plane shutter 205 is first run. Then, it is necessary to charge the front curtain 209 and the rear curtain 208 by a charge lever (not shown). When this charging is completed, the front curtain 209 and the rear curtain 208 are sequentially driven with an interval corresponding to the shutter speed, and shooting is performed.

  Here, it is also conceivable that the camera is configured to charge only the front curtain 209 without running the rear curtain 208 after the release switch is operated. In this case, since the conventionally used focal plane shutter 205 is a mechanism that charges the front curtain 209 and the rear curtain 208 simultaneously, it is necessary to newly manufacture a mechanism that can charge only the front curtain 209. Arise. Further, even if the mechanism charges only the front curtain 209 or the mechanism charges both the front curtain 209 and the rear curtain 208, the time required to charge the front curtain 209 occurs as a release time lag. .

  In order to shorten the release time lag, it may be possible to charge the front curtain 209 before operating the release switch. However, since the subject image does not reach the image sensor by performing the charging operation of the front curtain 209, the subject cannot be observed using the video display circuit 214, and the user grasps the release timing and the composition of the subject. Will not be able to.

  As described above, when the subject is observed with the image displayed on the video display circuit 214, it is necessary to charge the front curtain 209. For this reason, there has been a problem that the release time lag becomes longer than when the subject is observed using the finder optical system.

In order to solve the above-described problems, an imaging apparatus according to the present invention includes an imaging element that receives a subject luminous flux , accumulates charges, and outputs an image signal , a mechanical shutter including a front curtain and a rear curtain, and the imaging element. Display means for displaying an image based on the output image signal, control means for controlling reset scanning of the image sensor, and an image based on the image signal continuously output from the image sensor by the display means The charge accumulation time of the image sensor is controlled by either reset scanning of the image sensor by the control means or traveling of the front curtain of the mechanical shutter at the time of still image shooting in response to a still image shooting instruction made during Selection means for selecting whether or not, and the display means sequentially displays images based on image signals continuously output from the imaging device By the rear curtain of the mechanical shutter and better selected by made the still image shooting instruction the selection means during still image shooting according to, and controlling the accumulation time of the charge of the imaging element.

According to the present invention, it is possible to immediately shift from the live view state to still image shooting, and the release time lag can be greatly reduced. If it is considered that exposure unevenness is likely to occur due to changes over time or environmental changes, exposure unevenness can be suppressed in advance by selecting to use a mechanical front curtain.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the components described in the following embodiments are merely examples, and are not intended to limit the scope of the present invention only to them.

(First embodiment)
First, the structure which comprises the imaging device concerning this embodiment is demonstrated using FIG. Although some members are not shown in FIG. 1, it is assumed that all the configurations shown in FIG. 5 are included. The imaging apparatus according to the present embodiment includes a camera main body 100 and an interchangeable lens 101 as an optical unit attached to the camera main body 100.

  When the imaging apparatus is in a non-photographing state (the state shown in FIG. 1), a part of the subject light flux that has passed through the photographing lens 114 is reflected by the mirror 102 located in the photographing optical path to be a finder optical system. 103. Thus, the photographer can observe the subject image via the finder optical system 103.

  When the release button is pressed and the imaging apparatus shifts from the non-photographing state to the photographing state, the mirror 102 is retracted from the photographing optical path. As a result, the subject luminous flux from the photographic lens 114 travels toward the image sensor 104 that is a CMOS sensor that is an XY address type photoelectric conversion element. Here, a focal plane shutter (hereinafter, mechanical shutter) 105 is arranged on the object side (lens side) with respect to the image sensor 104. The mechanical shutter 105 has a mechanical front curtain and a mechanical rear curtain composed of a plurality of light shielding blades.

  The camera CPU 113 controls driving of the mechanical shutter 105 via the shutter driving circuit 106. Further, a scanning clock (horizontal drive pulse) or a predetermined control pulse is supplied from the pulse generation circuit 107 to the image sensor 104. Of the scanning clock generated by the pulse generation circuit 107, the vertical scanning clock is modulated to a predetermined clock frequency by the vertical drive modulation circuit 108 and input to the image sensor 104. The vertical drive modulation circuit 108 determines a scan pattern for reset scanning as an electronic front curtain. That is, the vertical drive modulation circuit 108 functions as an image sensor control circuit that controls reset scanning of the image sensor 104. The pulse generation circuit 107 also outputs a clock signal to the signal processing circuit 109. The signal processing circuit 109 generates image data by performing predetermined processing (color processing, gamma correction, etc.) on the signal read from the image sensor 104. The generated image data is output to the video display circuit 110 and displayed as a captured image or recorded in the image recording circuit 111. The switch unit 112 includes a switch operated to set shooting conditions and the like, and a switch (release button) operated to start a shooting preparation operation and a shooting operation. Whether or not the switch unit 112 has a function for observing a subject (hereinafter referred to as a live view) by sequentially displaying the image data continuously acquired by the image sensor as a moving image on the video display circuit 110. Includes a switch to switch between. Also included is a switch for selecting whether to perform shooting using the mechanical front curtain when shooting a still image from the state set to live view. The camera CPU 113 performs an operation according to the operation of the switch unit 112.

  Next, the configuration within the interchangeable lens 101 will be described. The taking lens 114 is movable in the optical axis direction. Here, although shown as one lens in FIG. 1, it is actually composed of a plurality of lens units such as a zoom lens. The lens CPU 115 controls driving of the photographing lens 114 via the lens driving circuit 116. The lens CPU 115 also drives the aperture drive mechanism 117a via the aperture drive circuit 117, and controls the aperture according to the subject brightness during the shooting operation. The zoom position is determined by operating the zoom drive mechanism 118 (manual operation in this embodiment). The determined zoom position is detected by the zoom position detection circuit 119 and sent to the lens CPU 115. The lens CPU 115 can communicate with the camera CPU 113 in the camera body 100 via the communication contact 120 on the interchangeable lens 101 side and the communication contact 121 on the camera body 100 side. The lens CPU 115 notifies the camera CPU 113 of the type, focal length, exit pupil distance, zoom position, and the like of the interchangeable lens 101. The scanning pattern holding unit 150 holds a plurality of types of electronic front curtain scanning patterns (reset line operation patterns) to be described later.

  The image pickup apparatus according to the present embodiment employs an electronic shutter (electronic front curtain) instead of the mechanical front curtain when taking a still image from a state where the subject can be observed by the video display circuit 110. However, still image shooting is performed using the electronic front curtain and the mechanical rear curtain.

  FIG. 2 is a diagram illustrating a state in which the image sensor and the mechanical rear curtain are observed along the optical axis direction from the lens side when taking a still image using the electronic front curtain and the mechanical rear curtain. FIG. 2 shows a state in which the electronic front curtain reset scan and the mechanical rear curtain shutter travel are in the middle after shooting is started by pressing the release button. An arrow 1 indicates the scanning direction of the electronic front curtain reset scan (the traveling direction of the electronic front curtain) and the traveling direction of the mechanical rear curtain. Note that when the electronic front curtain reset scan is performed in a photographing operation, the subject image formed on the imaging surface of the imaging element 104 via the photographing lens 114 is inverted upside down. Therefore, when reset scanning is performed from the lower side to the upper side of the imaging surface as shown in FIG. 2, reset scanning and shutter travel are performed from the upper part of the image to the lower part of the image.

  In FIG. 2, reference numeral 2 denotes an imaging surface of the image sensor 104. Reference numeral 3 denotes a mechanical rear curtain of the mechanical shutter 105. FIG. 2 shows a state in which the mechanical rear curtain 3 shields a part of the image pickup surface 2 from light. Reference numeral 4 denotes a line (reset line) on which reset scanning is performed in the image sensor 104. The reset scanning is to make the accumulated charge amount of the pixels on the reset line 4 zero, and the reset line 4 corresponds to the tip of the electronic front curtain.

  A region 6 formed by a slit between the reset line 4 and the front end portion 5 of the mechanical rear curtain 3 is a region (charge accumulation region) where charge accumulation is performed by exposure in the image sensor 104. The charge storage area moves in the direction of arrow 1 as the electronic front curtain and the mechanical rear curtain travel. In the pixel in the image sensor 104, the time from when the reset line 4 passes, that is, from when the reset operation is started until the mechanical rear curtain 3 enters a light shielding state is the charge accumulation time due to exposure of the pixel. Become. Since the reset line 4 travels in the direction of the arrow 1 and charge accumulation of each line is started, the charge accumulation start timing differs for each line of the image sensor 104. That is, the charge accumulation operation is started earliest on the lowest line in the imaging surface 2, and the charge accumulation operation is started latest on the uppermost line.

  The movement of the reset line 4 from the lower part to the upper part of the imaging surface 2 is controlled by the vertical drive modulation circuit 108. The movement of the reset line 4 is controlled as will be described later with reference to FIG. 3, and the movement pattern of the reset line 4 is referred to as a scanning pattern. This scanning pattern can be said to indicate the timing at which reset scanning is performed for each region (line) of the image sensor. The scanning pattern holding unit 150 holds a plurality of such scanning patterns. The camera CPU 113 selects one of these and controls the vertical drive modulation circuit 108 so that the reset line 4 moves according to the selected scanning pattern.

  FIG. 3 is a diagram showing the relationship between the scanning pattern of the electronic front curtain reset scan and the traveling pattern of the mechanical rear curtain in the shutter control. In FIG. 3, the horizontal axis represents time, and the vertical axis represents the distance (position) from bottom to top on the image sensor. In FIG. 3, 12 represents a running curve of the mechanical rear curtain, and represents a state where the speed gradually increases from the start of running. Reference numeral 11 denotes a scanning curve for reset scanning of the electronic front curtain. The distance in the time direction between the scanning curve 11 and the traveling curve 12 represents the exposure time of each line of the image sensor. In FIG. 3, the exposure time is substantially the same from the bottom to the top of the image sensor.

  Next, the operation at the time of still image shooting in the camera having the above configuration will be described using the flowchart of FIG.

  When the camera is set to a mode for taking a still image with an operation member (not shown) of the switch unit 112, the camera CPU 113 starts this flowchart. The flowchart shown in FIG. 4 is mainly instructed and executed by the camera CPU 113.

  First, in step S01, the camera CPU 113 determines whether the switch unit 112 is set to perform live view using the video display circuit 110.

  If the live view is set in step S01, the mirror 102 is raised and retracted from the photographing optical path in step S02.

  In step S03, the mechanical front curtain of the mechanical shutter 105 operates to retract from the aperture of the mechanical shutter, and the image sensor 104 can receive a subject image.

  In step S04, the video display circuit 110 starts a live view function for displaying the image data continuously acquired by the image sensor 104 as a moving image.

  In step S05, AE (automatic exposure control) and AF (automatic focus control) are performed. The signal processing circuit 109 detects the luminance value of the subject and the evaluation value of the focused state using the image data acquired by the image sensor 104 to execute the live view function, and the lens driving circuit 116 and the aperture driving circuit. 117 is driven so that these values reach the target values.

  In step S06, the camera CPU 113 determines whether the release button of the switch unit 112 is half pressed and the switch SW1 is turned on. If the switch SW1 is not turned on, the process returns to step S05 and AF and AE are repeated.

  When the switch SW1 is turned on in step S06, in step S07, a target value at the time of still image shooting is determined on the basis of the luminance value of the subject obtained at that time and the evaluation value of the focused state. Based on this target value, the stop position of the photographing lens 114, the stop position of the aperture driving mechanism 117a, the exposure time of the image sensor 104, the gain in the signal processing circuit, and the like are determined and fixed.

  In step S08, the camera CPU 113 waits until the release button of the switch unit 112 is fully pressed and the switch SW2 is turned on.

  When the switch SW2 is turned on, the camera CPU 113 detects the state of the switch unit 112 in step S09, and the user sets either still image shooting using the electronic front curtain or still image shooting using the mechanical front curtain. Is selected. If still image shooting using the electronic front curtain is selected, the process proceeds to step S10.

  In step S <b> 10, one of the scanning patterns is selected from the scanning pattern holding unit 150 according to the usage history of the camera body and the posture of the camera. This scanning pattern shows the scanning timing of the reset line of the image sensor 104, and the camera CPU 113 controls the vertical drive modulation circuit 108 to execute the reset scanning according to the selected scanning pattern.

  In step S11, the process waits for a predetermined time obtained from the exposure time determined in step S07, and in step S12, the mechanical rear curtain is operated to complete the exposure of the image sensor 104.

  In step S13, image data is read from the light-shielded image sensor 104, and in step S14, the read image data is recorded in the image recording circuit 111.

  In step S15, the mirror 102 is lowered to enter the photographing optical path, the mechanical front curtain and the mechanical rear curtain are charged by a charge lever (not shown), and the process returns to step S01.

  As described above, the reset scanning of the image sensor 104 is performed in step S <b> 10, whereby the timing for starting the accumulation of charges on each line of the image sensor 104 is defined. Then, when the mechanical rear curtain travels in step S12, each line of the image sensor 104 is shielded from light. The scanning pattern stored in the scanning pattern holding unit 150 is set so that the time from the reset scanning to the light shielding by the mechanical rear curtain is equal for all the lines of the image sensor 104. Therefore, according to this method, the charge accumulation amount of the image sensor 104 can be controlled by using the electronic front curtain and the mechanical rear curtain as in the case of using the mechanical front curtain and the mechanical rear curtain. It becomes.

  By using the electronic front curtain, the step of charging the mechanical front curtain and running the mechanical front curtain can be omitted. Therefore, it is possible to immediately shift from the live view state to still image shooting, and the release time lag, which has been a problem in the conventional example, can be greatly reduced.

  Next, processing in the case where still image shooting using the mechanical front curtain has been selected by the switch unit 112 in step S09 will be described.

  If the switch SW2 is turned on in step S08 and the still image shooting using the mechanical front curtain is selected in the switch unit 112 in step S09, the process proceeds to step S21.

  In order to charge the mechanical front curtain, in step S21, the camera CPU 113 once operates the mechanical rear curtain. In step S22, the mechanical front curtain and the mechanical rear curtain are charged by a charge lever (not shown). By charging the mechanical front curtain and the mechanical rear curtain together, the charge lever used in a conventional single-lens reflex camera can be diverted.

  In step S23, the mechanical front curtain of the mechanical shutter operates to retract from the aperture of the mechanical shutter, and the image sensor 104 is ready for exposure.

  In step S24, the process waits for a predetermined time determined from the determined exposure time, and in step S25, the mechanical rear curtain is operated to complete the exposure of the image sensor 104.

  In step S26, image data is read from the light-shielded image sensor 104, and in step S27, the read image data is recorded in the image recording circuit 111.

  In step S28, the mirror 102 is lowered to enter the photographing optical path, the mechanical front curtain and the mechanical rear curtain are charged by a charge lever (not shown), and the process returns to step S01.

  In this way, even if the live view is set, if the user selects the setting for shooting a still image using the mechanical front curtain, the mechanical front curtain and mechanical The exposure time is defined by the travel interval of the trailing curtain.

  Here, the running characteristics of the mechanical shutter 105 deviate from the initial ideal state due to the influence of changes over time, the posture of the camera body, or environmental changes such as temperature and humidity. When the mechanical front curtain and the mechanical rear curtain are compared with each other, the same influence is produced on both, so that it is rare that a large difference occurs in the running characteristics.

  However, when comparing the electronic front curtain and the mechanical rear curtain, the electronic front curtain is not easily affected by changes in the camera body posture or environmental changes such as temperature and humidity. It will shift. For this reason, there is a relative deviation between the scanning characteristics of the electronic front curtain and the running characteristics of the mechanical rear curtain, and the exposure time may vary depending on the scanning line of the image sensor 104.

  In the present embodiment, in order to compensate for this shift, various scanning patterns are stored in the scanning pattern holding unit 150, and a suitable scanning pattern is selected according to the state of the camera. However, the mechanical front curtain can be selected in place of the electronic front curtain in accordance with a user instruction.

  As a result, if it is considered that exposure unevenness is likely to occur due to changes over time or environmental changes, exposure unevenness can be suppressed in advance by selecting to use the mechanical front curtain. .

  Next, processing when the live view function is not selected in step S01 will be described.

  If the live view is not selected in step S01, the process waits until the release button of the switch unit 112 is half-pressed and the switch SW1 is turned on in step S31.

  When the switch SW1 is turned on in step S31, AE and AF are performed using the values obtained by the photometric sensor and the focus detection circuit in step S32.

  In step S33, the luminance value of the subject and the evaluation value of the focused state are detected for the region estimated as the main subject, and the lens driving circuit 116 and the aperture driving circuit 117 are set so that these values reach the target values. Drive.

  In step S34, the camera CPU 113 waits until the release button of the switch unit 112 is fully pressed and the switch SW2 is turned on. When the switch SW2 is turned on, the camera CPU 113 raises the mirror in step S35 and proceeds to step S23.

  After that, the processing from step S23 to S28 described above is performed, and still image shooting is performed.

  As described above, according to the present embodiment, it is possible to immediately shift to the still image shooting from the live view state, and it is possible to provide an imaging apparatus capable of greatly reducing the release time lag.

  Further, when it is considered that there is a high possibility of uneven exposure due to changes over time or environmental changes, it is possible to suppress exposure unevenness by selecting to use the mechanical front curtain.

It is a block diagram which shows the structure of the imaging device concerning embodiment of this invention. It is a front view which shows the relationship between an electronic front curtain and a mechanical rear curtain. It is a figure which shows the relationship between the scanning curve of an electronic front curtain, and the running curve of a mechanical rear curtain. It is a flowchart which shows the imaging | photography operation | movement of the imaging device concerning embodiment of this invention. It is sectional drawing which shows the structure of a single-lens reflex type digital camera.

Explanation of symbols

2 Imaging surface 3 Mechanical rear curtain 4 Reset line 5 Front end of mechanical rear curtain 100 Camera body 101 Interchangeable lens 104 Imaging element 105 Mechanical shutter 106 Shutter drive circuit 107 Pulse generation circuit 108 Vertical drive modulation circuit 109 Signal processing circuit 113 Camera CPU
114 Shooting lens 115 Lens CPU
116 Lens Drive Circuit 117 Aperture Drive Circuit 118 Zoom Drive Mechanism 119 Zoom Position Detection Circuit 150 Scan Pattern Holding Unit

Claims (3)

An image sensor that receives a subject luminous flux , accumulates charges, and outputs an image signal ;
A mechanical shutter with front and rear curtains,
Display means for displaying an image based on the image signal output from the image sensor;
Control means for controlling reset scanning of the image sensor ;
The display means is reset scanning of the imaging device by the control means during still image shooting according to the still image shooting instruction has been made during that sequentially displays an image based on the continuously image signal output from the imaging device And selection means for selecting whether to control the charge accumulation time of the image sensor by traveling of the front curtain of the mechanical shutter,
The display unit selected by the selection unit at the time of still image shooting according to the still image shooting instruction made when the images based on the image signals continuously output from the image sensor are sequentially displayed. by the rear curtain of the mechanical shutter, an imaging apparatus characterized by controlling the charge accumulation time of the image sensor. Whether the selection unit controls the charge accumulation time of the image sensor by reset scanning of the image sensor by the control unit or traveling of the front curtain of the mechanical shutter according to the operation of the operation unit by the user The imaging device according to claim 1, wherein the imaging device is selected. An image sensor that receives a subject luminous flux and accumulates charges and outputs an image signal; a mechanical shutter including a front curtain and a rear curtain; and a display unit that displays an image based on the image signal output from the image sensor; A control means for controlling reset scanning of the image sensor, and a control method for the image pickup apparatus,
Reset scanning of the image sensor by the control unit during still image shooting in response to a still image shooting instruction made when the display unit sequentially displays images based on image signals continuously output from the image sensor. And a selection step of selecting whether to control the charge accumulation time of the image sensor by traveling of the front curtain of the mechanical shutter;
The one selected in the selection step during still image shooting in response to a still image shooting instruction made when the display means sequentially displays images based on image signals output continuously from the image sensor; And a step of controlling a charge accumulation time of the image sensor by means of a rear curtain of a mechanical shutter.

Images