JP2011146925A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus which can capture an image, in which exposure nonuniformity is reduced, while accelerating a consecutive imaging speed. <P>SOLUTION: The imaging apparatus includes: an imaging element in which pixels are disposed in a two-dimensional shape; a rear-curtain mechanical shutter which opens upper and lower rear curtains 14ru and 14rd disposed with an exposure opening therebetween to be evacuated from the exposure opening to bring the imaging element into an exposure-possible state in a shutter-charged state, and which closes the upper and lower rear curtains 14ru and 14rd in the center of the exposure opening to end exposure of the imaging element; and a front-curtain electronic shutter which has upper and lower front curtain shutters esfu and esfd that respectively correspond to the upper and lower rear curtains 14ru and 14rd, and which is adjusted based on the traveling property of the rear-curtain mechanical shutter in such a way that the time from resetting a pixel at an arbitrary position to shielding light by means of the rear-curtain mechanical shutter becomes equal to a predetermined exposure time. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an imaging apparatus that controls an exposure time using a front curtain electronic shutter and a rear curtain mechanical shutter.

  A single-lens digital camera often takes a still image by a shutter mechanism using a focal plane shutter. A general operation when taking a still image with a digital camera equipped with such a shutter mechanism will be described with reference to FIGS. FIG. 13 is a diagram showing the state of the conventional shutter mechanism when the light shielding state is realized by the front curtain 114f before still image shooting. FIG. 14 shows the front curtain 114f running and then the rear curtain 114r. FIG. 15 is a diagram showing a state of a conventional shutter mechanism when exposure is performed by a slit, FIG. 15 is a diagram showing a state of a conventional shutter mechanism when the trailing curtain 114r is run and the exposure is finished, and FIG. It is a timing chart which shows operation | movement when a still image is image | photographed with a shutter mechanism.

  The exposure opening 41 that defines the light irradiation range to the image sensor is disposed on the optical path in the vicinity of the image sensor and the shutter mechanism.

  A shutter mechanism configured as a focal plane shutter generally includes a front curtain 114f and a rear curtain 114r.

  In such a configuration, when waiting for the start of still image shooting, as shown in FIGS. 13 and 16, the front curtain 114f is in a state of being shutter-charged with the exposure opening 41 closed, and the rear curtain. Reference numeral 114r denotes a state in which the shutter is retracted from the exposure opening 41.

  When the release operation is performed in the state shown in FIG. 13, as shown in FIGS. 14 and 16, the front curtain 114 f is first released and travel is performed, and the exposure start position at which light starts to irradiate the image sensor. Move in front curtain direction. When a predetermined exposure time has elapsed since the release of the front curtain 114f, the rear curtain 114r is released and travels, and the exposure end position at which light irradiation ends moves on the image sensor in the rear curtain travel direction. To do. FIG. 14 shows a state where the shutter speed (exposure time) is faster than the so-called sync speed.

  After that, as shown in FIGS. 15 and 16, after the running of the rear curtain 114r is completed, the exposure opening 41 is closed by the rear curtain 114r, that is, the entire imaging surface of the imaging device is shielded from light. In the state shown in FIG. 15, the image data is read from the image sensor as shown in FIG.

  Further thereafter, as shown in FIG. 16, the front curtain 114f and the rear curtain 114r are charged up.

  When continuous shooting is performed using such a shutter mechanism, the period of continuous shooting (time for obtaining one image in continuous shooting) is TC1 shown in FIG. 16, that is, after the front curtain 114f is released. This is the time until charge up of the front curtain 114f and the rear curtain 114r is completed.

  For example, Japanese Unexamined Patent Application Publication No. 2009-141804 discloses a shutter mechanism in which both the front curtain and the rear curtain are mechanical shutters, and the front curtain is an electronic shutter. FIG. 17 is a timing chart showing an operation when a still image is taken with a conventional shutter mechanism in which the front curtain is an electronic shutter.

  In this configuration, when waiting for the start of still image shooting, the rear curtain 114r is retracted from the exposure opening 41 and is shutter-charged, but a front curtain is provided as a mechanical shutter. For this reason, the imaging element is irradiated with the photographing light flux from the exposure opening 41.

  In this state, since charge is generated in the image sensor, exposure is started by resetting the charge generated by the front curtain electronic shutter esf when the release operation is performed. The running characteristics of the front curtain electronic shutter esf at this time are adjusted in accordance with the running characteristics of the rear curtain 114r which is a rear curtain mechanical shutter (to be basically the same).

  After that, the exposure end and the reading of the imaging data by the running of the rear curtain 114r are the same as in the case of the mechanical focal plane shutter as described above. However, the subsequent charging of the shutter curtain is performed only for the rear curtain 114r.

  When continuous shooting is performed by the shutter mechanism using such a front curtain as an electronic shutter, the continuous shooting cycle is TC2 shown in FIG. 17, that is, the trailing curtain 114r after the front curtain electronic shutter esf starts running. It is time to complete the charge up. This continuous shooting cycle TC2 is substantially the same as the continuous shooting cycle TC1 shown in FIG.

  Incidentally, Japanese Patent Application Laid-Open No. 2008-145478 describes a technique for further shortening the traveling time of the mechanical shutter. The technology described in this publication is such that the rear curtain shutter, which is a mechanical shutter, is closed from both sides of the exposure opening toward the center, and is opened from the center of the exposure opening to both sides. It has become.

  This technology is thought to contribute to improving continuous shooting performance. In other words, in an imaging apparatus such as a camera, it is desired that the continuous shooting performance is as high as possible (that is, the number of continuous shooting per second is large). Here, referring to FIG. 16 and FIG. 17 described above, it can be seen that the time to charge up the shutter curtain of the mechanical shutter occupies a relatively large proportion in one cycle of continuous shooting. This is because the charge-up of the mechanical shutter is a process of compressing a spring for running the shutter curtain using a motor or the like. On the other hand, if the technique described in Japanese Patent Application Laid-Open No. 2008-145478 is used, the movement distance of the shutter curtain accompanying the charge-up can be about half of the length of the exposure opening in the curtain running direction. In addition, it can be seen that the time required for charge-up can be greatly shortened (see also FIG. 5 according to the embodiment of the present invention).

JP 2009-141804 A JP 2008-145478 A

  However, the technique described in the above-mentioned Japanese Patent Application Laid-Open No. 2008-145478 is related to the second operation method related to the front curtain electronic shutter. In order to completely close the aperture, it is necessary to travel from one side of the exposure opening having a square shape to the opposite side parallel to the exposure aperture. "There is a problem of causing a problem", and a similar purpose is described in Paragraph 0025. Therefore, when the release button is pressed in Paragraph 0023, it is accumulated in the solid-state image sensor. It is considered that this is a so-called global shutter in which all the pixels are simultaneously reset at the same time.

  When the front curtain electronic shutter is a global shutter, the exposure time differs between the upper and lower ends and the center of the image sensor, no matter how much the travel time is shortened by closing the rear curtain from both sides ( Since the exposure time is longer in the central part), it is considered that exposure unevenness that cannot be ignored still occurs.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an imaging apparatus capable of obtaining an image with less exposure unevenness while improving the continuous shooting speed.

  In order to achieve the above object, an image pickup apparatus according to an aspect of the present invention is an image pickup apparatus that controls an exposure time by a front curtain electronic shutter and a rear curtain mechanical shutter that is a focal plane shutter. A first rear curtain and a second rear curtain that open in opposite directions from the central portion of the exposure opening, and the first and second rear curtains. By opening the rear curtain and the second rear curtain in a state of being retracted from the exposure opening, the image pickup device can be exposed while being shutter-charged, and the first rear curtain and the second rear curtain are opened. A rear curtain mechanical shutter that terminates exposure of the image sensor by closing at the center of the exposure opening, a first front curtain electronic shutter corresponding to the first rear curtain, and a second curtain corresponding to the second rear curtain. Two-curtain electronic shutter And the running characteristics of the rear curtain mechanical shutter are set so that the time from when the pixel at an arbitrary position of the image sensor is reset to when the pixel is shielded by the rear curtain mechanical shutter is equal to a predetermined exposure time. And a front-curtain electronic shutter that resets the pixel at the arbitrary position.

  According to the imaging apparatus of the present invention, it is possible to obtain an image with less exposure unevenness while improving the continuous shooting speed.

1 is a block diagram showing a circuit configuration and the like of an imaging apparatus according to Embodiment 1 of the present invention. FIG. 3 is a diagram illustrating a state of a shutter mechanism when the rear curtain is in a charged state in the first embodiment. FIG. 3 is a diagram illustrating a state of a shutter mechanism when the rear curtain is in a traveling state in the first embodiment. FIG. 3 is a diagram illustrating a state of a shutter mechanism when the rear curtain is in a travel end state in the first embodiment. 3 is a timing chart showing a shutter operation when shooting a still image in the first embodiment. 5 is a timing chart showing an example of ideal curtain travel in which the upper rear curtain and the lower rear curtain intersect at the same time in the center line of the CMOS sensor in the first embodiment. In the said Embodiment 1, the timing chart which shows the example of curtain driving | running | working when the curtain speed of an upper rear curtain becomes a little slow. 5 is a timing chart showing an example of curtain travel when travel of the upper and lower curtain electronic shutters is delayed in accordance with travel of the upper and rear curtains in the first embodiment. In the first embodiment, an example of curtain traveling when the line where the upper and lower curtain electronic shutters intersect with each other is the same as the line where the upper and lower curtains intersect The timing chart which shows. 3 is a timing chart showing an example of curtain traveling when the lower edge curtain is adjusted to be the same as the front curtain intersection line when the lower rear curtain stops after traveling. The figure which shows an example of how to obtain | require the lower trailing curtain stop line in the said Embodiment 1. FIG. The figure which shows the other example of the method of calculating | requiring the lower trailing curtain stop line in the said Embodiment 1. FIG. The figure which shows a mode when the light-shielding state is implement | achieved by the front curtain before the still image photography in the conventional shutter mechanism. FIG. 10 is a diagram illustrating a state in which exposure is performed by a slit by running a front curtain and then running a rear curtain in a conventional shutter mechanism. The figure which shows a mode when the trailing shutter is made to run and the exposure is complete | finished in the conventional shutter mechanism. 9 is a timing chart showing an operation when a still image is taken with a conventional shutter mechanism. 6 is a timing chart showing an operation when a still image is taken by a conventional shutter mechanism using an electronic shutter as a front curtain.

Embodiments of the present invention will be described below with reference to the drawings.
[Embodiment 1]

  1 to 12 show the first embodiment of the present invention, and FIG. 1 is a block diagram showing a circuit configuration and the like of the image pickup apparatus 11.

  The imaging device 11 is configured as a digital camera, for example, and includes a photographing lens 12 including a focus lens 12a and a diaphragm mechanism 13, a shutter mechanism 14, a CMOS sensor 15, a focus control unit 16, a motor 17, Aperture controller 18, motor 19, shutter controller 20, shutter controller 21, TG circuit 22, signal processing circuit 23, data bus 24, AE processor 25, AF processor 26, Image calculation unit 27, image processing circuit 28, LCD driver 29, LCD 30, nonvolatile memory 31, built-in memory 32, compression / decompression unit 33, removable memory 34, power supply unit 35, and input unit 36 And a main CPU 37.

  The photographing lens 12 is a photographing optical system for forming an optical image of a subject on the CMOS sensor 15.

  The focus lens 12 a is for adjusting the focal position of the photographing lens 12 so that a focused optical image is formed on the CMOS sensor 15.

  The aperture mechanism 13 is for controlling the exposure by regulating the range of the light flux that passes through the photographing lens 12.

  The shutter mechanism 14 is for controlling the exposure by regulating the passage time of the light beam from the photographing lens 12 to the CMOS sensor 15. However, in the present embodiment, the shutter mechanism 14 as a mechanical shutter includes only the rear curtains 14ru and 14rd (see FIG. 2 and the like) for ending the exposure configured as described later. The curtain is performed by an electronic shutter. In the present embodiment, the rear curtains 14ru and 14rd, which are rear curtain mechanical shutters, are configured as focal plane shutters.

  The CMOS sensor 15 is an image pickup element having an image pickup surface in which pixels that accumulate an amount of charge corresponding to the amount of received light are two-dimensionally arranged. The CMOS sensor 15 photoelectrically converts the optical image of the subject formed by the photographing lens 12 via the shutter mechanism 14 to generate and output an electrical image signal.

  The focus control unit 16 controls the focus lens 12 a to be driven and focused through the motor 17 based on the control of the main CPU 37.

  Based on the control of the main CPU 37, the diaphragm control unit 18 drives the diaphragm mechanism 13 via the motor 19 to control the diaphragm aperture diameter according to the exposure value.

  Based on the control of the main CPU 37, the shutter control unit 20 drives the shutter mechanism 14 via the shutter control device 21 and controls the exposure time according to the exposure value.

  The TG circuit 22 outputs a timing signal for driving the CMOS sensor 15 based on the control of the main CPU 37. The electronic shutter in the CMOS sensor 15 (in this embodiment, in particular, the front curtain electronic shutter realized by performing pixel reset) is realized by performing timing control by the TG circuit 22 based on the control of the main CPU 37. Is done.

  The signal processing circuit 23 includes a CDS (Correlated Double Sampling) for performing correlated double sampling, an amplifier circuit for amplifying a signal level, an ADC (Analog to Digital converter) for converting an analog signal into digital data, and the like. It is configured to include. The output side of the signal processing circuit 23 is connected to the data bus 24. Accordingly, the signal processing circuit 23 outputs digital data obtained as a processing result to, for example, the built-in memory 32 and other circuits via the data bus 24.

  The data bus 24 includes a signal processing circuit 23, an AE processing unit 25, an AF processing unit 26, an image calculation unit 27, an image processing circuit 28, an LCD driver 29, a nonvolatile memory 31, and a built-in memory 32. The compression / decompression unit 33, the removable memory 34, and the main CPU 37 are bidirectionally connected to exchange control signals and various data with each other.

  The AE processing unit 25 calculates an AE evaluation value based on the captured image data from the CMOS sensor 15 and outputs the calculation result to the main CPU 37.

  The AF processing unit 26 calculates an AF evaluation value based on the captured image data from the CMOS sensor 15 and outputs the calculation result to the main CPU 37.

  The image processing circuit 28 performs processing such as white balance adjustment and edge processing on the photographed image data stored in the built-in memory 32 and stores the photographed image data as a result of the processing in the built-in memory 32 again. is there.

  The image calculation unit 27 performs addition averaging processing on the captured image data stored in the built-in memory 32 and stores the generated image obtained as a result in the built-in memory 32 again.

  The LCD driver 29 drives the LCD 30 which is a liquid crystal display unit, and displays a through image (image taken in real time by the CMOS sensor 15) output from the signal processing circuit 23.

  The nonvolatile memory 31 is a recording medium that stores various processing programs executed by the main CPU 37, various data necessary for executing the processing programs, user setting data, and the like.

  The built-in memory 32 is, for example, a volatile storage medium that is used for storing captured image data being processed and also used as a memory when the main CPU 37 performs processing.

  The compression / decompression unit 33 compresses the captured image data and stores the compressed image data in the removable memory 34, and expands the image data stored in the removable memory 34.

  The detachable memory 34 is a recording medium for recording processed image data (for example, image data after compression processing) in a non-volatile manner, and is configured to be detachable from the imaging device 11 as, for example, a memory card. Therefore, the removable memory 34 may not have a configuration unique to the imaging device 11.

  The power supply unit 35 includes a battery, a dry cell, and the like, and supplies a current for operating the main CPU 37, a current for driving the motors 17 and 19, a current for driving the LCD 30, and the like with voltages corresponding to each. To do.

  The input unit 36 includes a power switch for turning on / off the power of the imaging apparatus 11, a shooting button for performing a shooting operation, an operation switch for setting a shooting mode, a live view mode, and the like. It is the operation input means comprised by these.

  The main CPU 37 controls the operation of the entire image pickup apparatus 11. For example, the main CPU 37 calculates the subject distance based on the above-described AF evaluation value, controls the focus control unit 16 to drive the motor 17, and controls the aperture value and exposure time (shutter speed) based on the above-described AE evaluation value. ) And the diaphragm control unit 18 and the shutter control unit 20 are controlled to drive the motor 19 and the shutter control device 21. Further, the main CPU 37 controls the electronic shutter by the CMOS sensor 15 via the TG circuit 22. In addition, the imaging apparatus 11 is configured to be capable of live view, and the main CPU 37 performs control so as to start live view in response to an operation from the input unit 36.

  Next, with reference to FIGS. 2 to 5, a shutter operation at the time of photographing will be described. 2 to 4 are diagrams showing an outline of the operation of the shutter mechanism 14. 2 shows a state of the shutter mechanism 14 when the rear curtain is in a charged state, FIG. 3 shows a state of the shutter mechanism 14 when the rear curtain is in a traveling state, and FIG. It is a figure which shows the mode of the shutter mechanism 14 when it exists in a driving | running | working completion state. FIG. 5 is a timing chart showing the shutter operation when shooting a still image.

  The exposure opening 41 that defines the light irradiation range to the CMOS sensor 15 that is the image sensor is disposed on the optical path that is in the vicinity of the CMOS sensor 15 and the shutter mechanism 14.

  As shown in FIGS. 2 to 4, the rear curtain provided in the shutter mechanism 14 which is a mechanical shutter is opposite to the opposite sides of the exposure opening 41 (desirably, in order to shorten the curtain travel time, the exposure curtain The shutter is closed from both sides in the short side direction of the opening 41 (that is, one long side and the other long side) and can be opened from the central part of the exposure opening 41 in opposite directions. An upper rear curtain 14ru and a lower rear curtain 14rd, which are blades, are provided. Here, one of the upper rear curtain 14ru and the lower rear curtain 14rd is the first rear curtain, and the other is the second rear curtain.

  When waiting for the start of still image shooting, as shown in FIG. 2, the upper rear curtain 14ru and the lower rear curtain 14rd are on both sides of the exposure opening 41, that is, the upper rear curtain 14ru is for exposure. The upper trailing edge 14rd of the opening 41 and the lower rear curtain 14rd are retracted in a shutter-charged state below the exposure opening 41 (the other longer side). Accordingly, since the CMOS sensor 15 is in an exposureable state irradiated with a photographing light beam, it is possible to perform a live view when waiting for photographing a still image.

  When the release operation is performed in the state shown in FIG. 2, first, the leading curtain electronic shutter travels as shown in FIG. The front curtain electronic shutter includes an upper front curtain electronic shutter esfu corresponding to the upper rear curtain 14ru and a lower front curtain electronic shutter esfd corresponding to the lower rear curtain 14rd. Of these upper front curtain electronic shutter esfu and lower front curtain electronic shutter esfd, either one corresponding to the first rear curtain is the first front curtain electronic shutter and any one corresponding to the second rear curtain. The other is a second front curtain electronic shutter.

  The front curtain electronic shutter is configured such that the time from when a pixel at an arbitrary position of the CMOS sensor 15 is reset until it is shielded by the rear curtain is equal to a predetermined exposure time set by automatic exposure setting or manual exposure setting. In addition, the pixel at an arbitrary position is reset based on the running characteristics of the rear curtain.

  More specifically, the traveling characteristic of the lower front curtain electronic shutter esfd is such that the traveling characteristic of the upper front curtain electronic shutter esfu matches the traveling characteristic of the upper rear curtain 14ru when the exposure time is zero. Each is adjusted so as to match the running characteristics of the lower trailing curtain 14rd when it is zero. Therefore, the first front curtain electronic shutter resets the pixels based on the travel characteristics of the first rear curtain so that the first rear curtain travels after a predetermined exposure time has elapsed since the first front curtain electronic shutter traveled. The second front curtain electronic shutter resets the pixels based on the travel characteristics of the second rear curtain so that the second rear curtain travels after a predetermined exposure time has elapsed since it traveled.

  Thus, the sequential resetting of the charges accumulated in the pixels in units of horizontal lines (here, the horizontal lines are pixel arrays in the direction orthogonal to the traveling direction of the rear curtains 14ru and 14rd) by the front curtain electronic shutter is as follows. From the upper end side and the lower end side of the imaging surface of the CMOS sensor 15 toward the central portion (here, the “central portion” is a portion in the vicinity of a line (central line) located at the center in the shutter traveling direction). (In this case, there may be some time difference between the start of travel of the upper front curtain electronic shutter esfu and the start of travel of the lower front curtain electronic shutter esfd, instead of being performed completely simultaneously. Will be described later).

  When a predetermined exposure time has elapsed after the upper-curtain electronic shutter esfu has started traveling, the upper rear curtain 14ru is released and traveling is started. Similarly, when the above-described predetermined exposure time has elapsed after the lower front curtain electronic shutter esfd has started to travel, the lower rear curtain 14rd is released to start traveling (see FIG. 3). By performing such processing, an arbitrary line on which the upper front curtain electronic shutter esfu and the upper rear curtain 14ru travel and an arbitrary line on which the lower front curtain electronic shutter esfd and the lower rear curtain 14rd travel are all the same. Therefore, exposure unevenness can be suppressed.

  The exposure is finished when the upper rear curtain 14ru and the lower rear curtain 14rd are closed at the center of the exposure opening 41 and the CMOS sensor 15 is shielded from light, but the upper rear curtain 14ru and the lower rear curtain 14rd travel a little after that. Thus, the traveling is stopped at a position where the leading ends of the curtain traveling are superimposed (see FIG. 4).

  Thereafter, in a state where the CMOS sensor 15 as shown in FIG. 4 is shielded from light, imaging data is read from the CMOS sensor 15 as shown in FIG.

  Thereafter, as shown in FIG. 5, the upper rear curtain 14ru and the lower rear curtain 14rd are charged up. The charge up of the upper rear curtain 14ru and the lower rear curtain 14rd is because the movement distance of the shutter curtain accompanying the charge up is about half of the length of the exposure opening 41 in the curtain running direction (short side direction). The time required for charge-up is significantly shortened compared to the conventional case.

  When continuous shooting is performed using such a shutter mechanism, the cycle of continuous shooting (time for obtaining one image in continuous shooting) is TC0 shown in FIG. 5, that is, the upper front curtain electronic shutter esfu or the lower shutter. It is the time from the start of the front curtain electronic shutter esfd, whichever comes first, to the completion of the charge up of the upper rear curtain 14ru and the lower rear curtain 14rd. This continuous shooting cycle TC0 is effectively shortened compared to the conventional continuous shooting cycle TC1 shown in FIG. 16 and the conventional continuous shooting cycle TC2 shown in FIG. Factors include a reduction in shutter travel time and a reduction in shutter charge-up time. Among these, since the ratio of the shutter charge-up time to the continuous shooting period is relatively large, it can be understood that the reduction of the shutter charge-up time greatly contributes to the reduction of the continuous shooting period.

  Next, the relationship between the exposure amount and the timing at which the upper and lower curtains overlap at the center of the exposure opening 41 will be described with reference to FIGS. 6 to 10, the position of the center line in the vertical direction of the CMOS sensor 15 is indicated by a one-dot chain line, and the vicinity of the center line is enlarged. 6 to 10, the vertical direction of the drawings indicates the vertical direction of the CMOS sensor 15, and the horizontal right direction of the drawings indicates the time direction.

  FIG. 6 is a timing chart showing an example of ideal curtain travel in which the upper rear curtain 14ru and the lower rear curtain 14rd simultaneously intersect at the center line of the CMOS sensor 15.

  Further, the upper front curtain electronic shutter esfu and the lower front curtain electronic shutter esfd are also adjusted so as to intersect at the same time in the center line of the CMOS sensor 15 in accordance with the running characteristics of the upper rear curtain 14ru and the lower rear curtain 14rd.

  FIG. 7 is a timing chart showing an example of curtain traveling when the curtain speed of the upper rear curtain 14ru is somewhat slowed.

  The rear curtain, which is a mechanical shutter, has a structure in which the elastic force of the charged spring is used as a driving source and the elastic force of the spring is released in response to a release signal. It is not always easy to accurately adjust the curtain 14rd so as to intersect the center line (for example, the curtain speed of the upper rear curtain 14ru and the curtain speed of the lower rear curtain 14rd are not exactly the same, or the release signal For example, the time from when the upper rear curtain 14ru is actually released to the time when the lower rear curtain 14rd is actually released after the release signal is output is not exactly the same). Also, the mechanical shutter may change its running characteristics as the number of uses increases (change in the resistance of the trailing curtain speed).

  FIG. 7 shows an example in which the curtain speed of the upper rear curtain 14ru is reduced. The delay of the upper rear curtain 14ru in the vicinity of the center line due to the lowering of the curtain speed is represented by the shift of the traveling characteristic of the upper rear curtain 14ru in the horizontal right direction. It is assumed that the delay time on the center line of the CMOS sensor 15 of the upper and rear curtain 14ru at this time is Δt1. Here, since the curtain speed of the lower rear curtain 14rd is the same as that in FIG. 6, the time from the passage of the lower rear curtain 14rd through the center line to the passage of the upper rear curtain 14ru through the center line is this delay. Time Δt1 is reached.

  On the other hand, since the resistance change does not occur in the running characteristics of the front curtain electronic shutter, the running characteristics of the upper front curtain electronic shutter esfu and the lower front curtain electronic shutter esfd are the same as those in FIG. Therefore, the exposure time above the center line is longer by Δt1 than the exposure time below the center line, resulting in uneven exposure.

  In order to reduce such exposure unevenness, the running characteristic of the upper and lower curtain electronic shutter esfu is adjusted (readjusted if manufactured) in accordance with the running characteristic of the upper and rear curtains 14ru whose curtain speed is slow. It is possible. FIG. 8 is a timing chart showing an example of curtain traveling when the traveling of the upper-first curtain electronic shutter esfu is delayed in accordance with the traveling of the upper rear curtain 14ru.

  Specifically, this adjustment is performed by delaying the time for the upper front curtain electronic shutter esfu to reach the center line by the delay time Δt1 described above from the time for the lower front curtain electronic shutter esfd to reach the center line. Is called.

  However, even if the adjustment shown in FIG. 8 is performed, the line where the upper rear curtain 14ru and the lower rear curtain 14rd intersect is displaced above the center line. In the triangular area ΔEX surrounded by the line indicating the running characteristics of 14 ru, the line indicating the running characteristics of the lower rear curtain 14 rd, and the center line, the exposure start is performed by the upper front curtain electronic shutter esfu, and the exposure end is completed. Since this is performed by the rear curtain 14rd, the exposure amount remains as a shifted portion. This deviation in exposure amount appears as a horizontal dark line near the center line in the captured image, resulting in degradation of image quality due to uneven exposure.

  A first example for solving such uneven exposure will be described with reference to FIG. FIG. 9 shows curtain travel when the line where the upper front curtain electronic shutter esfu and the lower front curtain electronic shutter esfd intersect is adjusted to be the same as the line where the upper rear curtain 14ru and the lower rear curtain 14rd intersect. It is a timing chart which shows the example of.

  In the first solution shown in FIG. 9, in response to the fact that the line where the upper rear curtain 14ru and the lower rear curtain 14rd intersect (referred to as the rear curtain intersection line) is displaced from the center line, The line where the shutter esfu and the lower front curtain electronic shutter esfd intersect (referred to as the front curtain intersection line) is also adjusted so as to be shifted from the center line.

  That is, after the time Δt2 has elapsed since the lower rear curtain 14rd intersected the center line, the upper rear curtain 14ru and the lower rear curtain 14rd intersect at the rear curtain intersection line that is a distance ΔL above the center line. In this case, after the elapse of time Δt2 after the lower front curtain electronic shutter esfd crosses the center line, the upper front curtain electronic shutter esfu and the lower front curtain electronic shutter esfd have the same front curtain as the rear curtain intersection line. It is adjusted to intersect at the intersection line.

  With the configuration shown in FIG. 9, the line whose exposure is started by the upper front curtain electronic shutter esfu is finished by the upper rear curtain 14ru, and the line whose exposure is started by the lower front curtain electronic shutter esfd is Since the exposure is finished by the lower rear curtain 14rd and the exposure time of an arbitrary line becomes the same, the occurrence of exposure unevenness can be suppressed.

  However, the first example for solving the exposure unevenness as described above is, for example, when the running characteristics of the upper rear curtain 14ru and the lower rear curtain 14rd change due to a temperature change or the like, that is, the upper rear curtain 14ru and the lower rear curtain. When the line where the curtain 14rd intersects changes from time to time, it is difficult to control so that the front curtain intersection line and the rear curtain intersection line are always the same.

  Accordingly, a second example for more stably solving the exposure unevenness will be described with reference to FIG. FIG. 10 is a timing chart showing an example of curtain travel when the lower edge curtain 14rd is adjusted to be the same as the front curtain intersection line when the travel direction edge line is stopped after traveling.

  The lower trailing curtain 14rd has a running direction edge positioned on a line (referred to as a lower trailing curtain stop line) that is a distance ΔL2 above the central line when time Δt3 has passed since it intersected the central line. Shall stop. At this time, control is performed so that the upper rear curtain 14ru intersects the lower rear curtain stop line after a predetermined time Δt4 has elapsed since the lower rear curtain 14rd stopped.

  Assuming that the speed of the upper rear curtain 14ru and the speed of the lower rear curtain 14rd are the same and substantially constant when traveling in the vicinity of the center line, the center line is not detected until the upper rear curtain 14ru intersects the lower rear curtain stop line. The time until crossing is Δt3. Therefore, such control is generally performed by releasing the upper rear curtain 14ru after a lapse of time (2 × Δt3 + Δt4) from the release of the lower rear curtain 14rd.

  Here, during the time Δt4, even if the speed of the rear curtain changes due to a temperature change or other factors, the upper rear curtain 14ru crosses the lower rear curtain stop line after the lower rear curtain 14rd has stopped. Is as short as possible. In other words, if the variation width of the crossing time with the lower rear curtain stop line due to temperature change and other factors is Δtu, Δt4 satisfies Δt4> Δtu and Δt4 as much as possible. ≈Δtu (that is, from the time when either one of the first rear curtain and the second rear curtain finishes closing) The time until the edge of the other trailing curtain in the traveling direction passes through the line is set in advance so as to be larger than 0 even if the fluctuation range of the time is taken into account).

  Then, the traveling characteristic of the upper front curtain electronic shutter esfu is adjusted according to the traveling characteristic of the upper rear curtain 14ru, and the traveling characteristic of the lower front curtain electronic shutter esfd is adjusted according to the traveling characteristic of the lower rear curtain 14rd. That is, the lower front curtain electronic shutter esfd is adjusted so as to stop at the lower rear curtain stop line when the time Δt3 has elapsed since crossing the center line. Adjustment is made so that the curtain electronic shutter esfd stops at the lower trailing curtain stop line when the time Δt4 elapses after the curtain electronic shutter esfd stops at the lower trailing curtain stop line.

  10 makes it possible not only to suppress the occurrence of exposure unevenness by making the exposure time of an arbitrary line the same, but also to always keep the rear curtain crossing line constant, that is, the front curtain. Since the intersection line can be kept constant, there is an advantage that stable control can be performed without depending on temperature or the like.

  Next, how to obtain the lower trailing curtain stop line will be described with reference to FIGS. FIG. 11 is a diagram showing an example of how to obtain the lower rear curtain stop line, and FIG. 12 is a diagram showing another example of how to obtain the lower rear curtain stop line. When obtaining the lower trailing curtain stop line, a subject with uniform brightness is taken as an object to be photographed, or a white plate having light transparency is attached to the front surface of the photographing lens 12, for example.

  In the example shown in FIG. 11, in a state where the upper rear curtain 14ru and the lower rear curtain 14rd are retracted from the exposure opening, first, all the pixels of the CMOS sensor 15 are collectively reset (that is, all the pixels are simultaneously reset). To do. After that, when an appropriate exposure time has elapsed, only the lower trailing curtain 14rd is released to run. Subsequently, when a proper time elapses after the travel of the lower rear curtain 14rd is completed, pixel readout in units of lines of the CMOS sensor 15 is performed, for example, at the upper end in the retracted state where the upper rear curtain 14ru is not traveling. The process is sequentially performed from the line to the bottom line. The image 42 read out in this way is divided into a region 42b where the lower rear curtain 14rd has traveled and a region 42a where the lower rear curtain 14rd has not traveled, and these regions 42a and 42b. Since there is a luminance difference at the boundary of the area, the main CPU 37 or the image processing circuit 28 searches for a line where the luminance value is discontinuous, so that the lower trailing curtain stop line can be automatically and easily known. be able to.

  In addition, the example shown in FIG. 12 is sufficient to reset all the pixels of the CMOS sensor 15 at the same time so that the travel of the lower rear curtain 14rd after the lower rear curtain 14rd is released is considered to have ended. This is done after a long time has passed. In the example shown in FIG. 12, since the travel of the lower rear curtain 14rd is completed, that is, the exposure is performed in a state where the lower half of the CMOS sensor 15 is shielded by the lower rear curtain 14rd, the areas 42b and 42a The contrast can be made clearer and the lower trailing curtain stop line can be more easily known.

  10 to 12, the example has been described in which the edge line in the running direction when the lower rear curtain 14rd stops after running becomes the rear curtain crossing line and the front curtain crossing line. Needless to say, the edge line in the traveling direction when the upper rear curtain 14ru stops after traveling may be the rear curtain intersection line and the front curtain intersection line. Therefore, the rear curtain mechanical shutter has a running edge of one of the first rear curtain and the second rear curtain at a time later than when the rear curtain ends the closing operation. What is necessary is just to run so that the running direction edge of the other rear curtain passes through the line. In the above description, a simple configuration is maintained by detecting the rear curtain crossing line and the front curtain crossing line without providing a separate sensor or the like. It is also possible to do. Furthermore, the timing from when the release signal is output until the upper rear curtain 14ru and the lower rear curtain 14rd actually start traveling, characteristics during actual traveling, and the like may be detected by a separate sensor or the like. Absent. This makes it possible to adjust the running characteristics of the front curtain electronic shutter according to the actual running characteristics of the rear curtain.

  In the above description, the CMOS sensor 15 is taken as an example of the image pickup device. However, the image pickup device is not limited to this, and any image pickup device capable of realizing a front curtain electronic shutter by pixel reset in line units may be widely applied. Is possible.

  According to the first embodiment, since the mechanical shutter that opens and closes from both sides of the exposure opening is used as the rear curtain, the continuous shooting speed can be improved.

  And, as the front curtain, an electronic shutter that sequentially resets the pixels from both sides of the image sensor toward the center line in accordance with the running characteristics of the rear curtain that opens and closes from both sides of the opening for exposure is used. Fewer images can be obtained.

  Further, since the same line as the rear curtain intersection line is made the front curtain intersection line, even when the rear curtain intersection line is different from the central line, the exposure time of each line can be made the same.

  In addition, since one of the upper rear curtain 14ru and the lower rear curtain 14rd has finished traveling and the other intersects with the rear curtain intersection line, the electronic shutter is stably controlled. It becomes possible.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Moreover, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, you may delete some components from all the components shown by embodiment. Furthermore, the constituent elements over different embodiments may be appropriately combined. Thus, it goes without saying that various modifications and applications are possible without departing from the spirit of the invention.

DESCRIPTION OF SYMBOLS 11 ... Imaging device 12 ... Shooting lens 12a ... Focus lens 13 ... Aperture mechanism 14 ... Shutter mechanism 14ru ... Upper rear curtain 14rd ... Lower rear curtain 15 ... CMOS sensor (imaging element)
DESCRIPTION OF SYMBOLS 16 ... Focus control part 17 ... Motor 18 ... Aperture control part 19 ... Motor 20 ... Shutter control part 21 ... Shutter control apparatus 22 ... TG circuit 23 ... Signal processing circuit 24 ... Data bus 25 ... AE processing part 26 ... AF processing part 27 ... Image calculation unit 28 ... Image processing circuit 29 ... LCD driver 30 ... LCD
DESCRIPTION OF SYMBOLS 31 ... Nonvolatile memory 32 ... Built-in memory 33 ... Compression / decompression part 34 ... Detachable memory 35 ... Power supply part 36 ... Input part 37 ... Main CPU
41 ... Opening for exposure esfu ... Upper front curtain electronic shutter esfd ... Lower front curtain electronic shutter

Claims (4)

In an imaging apparatus that controls exposure time by a front curtain electronic shutter and a rear curtain mechanical shutter that is a focal plane shutter,
An image sensor in which pixels that accumulate an amount of electric charge corresponding to the amount of received light are arranged two-dimensionally;
A first rear curtain and a second rear curtain that open in opposite directions from the center of the exposure opening, and the first rear curtain and the second rear curtain are retracted from the exposure opening. By opening the shutter, the image sensor can be exposed with the shutter charged, and the first rear curtain and the second rear curtain are closed at the center of the exposure opening to complete the exposure of the image sensor. A trailing shutter mechanical shutter,
A first front curtain electronic shutter corresponding to the first rear curtain, and a second front curtain electronic shutter corresponding to the second rear curtain, and the rear of the pixel at an arbitrary position of the image sensor is reset. A front-curtain electronic shutter that resets the pixel at the arbitrary position based on the running characteristics of the rear-curtain mechanical shutter so that the time until the light is shielded by the curtain mechanical shutter is equal to a predetermined exposure time;
An imaging apparatus comprising: The first front-curtain electronic shutter resets pixels based on the travel characteristics of the first rear curtain so that the first rear curtain travels after the predetermined exposure time has elapsed since it traveled. And
The second front curtain electronic shutter resets pixels based on the travel characteristics of the second rear curtain so that the second rear curtain travels after the predetermined exposure time has elapsed since it traveled. The imaging apparatus according to claim 1, wherein:   The rear curtain mechanical shutter has a running direction edge of one of the first rear curtain and the second rear curtain at a time later than when the rear curtain ends the closing operation. The imaging apparatus according to claim 2, wherein the imaging apparatus is configured to travel so that a traveling direction edge of the other rear curtain passes through the line.   From the time point when the rear curtain of either the first rear curtain or the second rear curtain is closed, the running edge of the one rear curtain is connected to the running edge of the second rear curtain. The imaging apparatus according to claim 3, wherein the time until the point of time passes is set in advance so as to be larger than 0 even if the fluctuation range of the time is taken into account.

Images