JP4961933B2 - Electronic camera - Google Patents

Description

  The present invention relates to an electronic camera.

  There is known an electronic camera in which the shutter is fully opened to start the charge accumulation of the image sensor, and the shutter is closed after a preset charge accumulation time has elapsed (see, for example, Patent Document 1).

Prior art documents related to the invention of this application include the following.
Japanese Patent Laying-Open No. 2005-156841

  However, in the above-described conventional electronic camera, extra light is incident on the image sensor from the end of charge accumulation of the image sensor to the time when the shutter curtain starts to close the image capture screen, so that blooming occurs and image quality deteriorates. Sometimes.

The electronic camera according to claim 1 has an imaging element that receives subject light and accumulates electric charge, a front curtain and a rear curtain, and an open state in which the photographing screen is fully opened and a closed state in which the photographing screen is shielded. And a charge accumulation time from the start of charge accumulation by the imaging device to the termination of charge accumulation by the imaging device when it is detected that the light shielding member is in the open state. Accumulation control means, setting means for setting an allowance time in consideration of an operation variation accompanying the initial operation of the rear curtain and an operation variation that changes with time and environment, and a conditional expression
(Time from when the trailing curtain is released until the trailing curtain blocks at least a part of the shooting screen) ≧ (the charge accumulation time + the margin time)
When the determination unit determines that the conditional expression is satisfied, the holding of the trailing curtain is released when the light shielding member is detected to be in the open state. When the determination means determines that the conditional expression is not satisfied, {(the charge accumulation time) + (the margin time) − (the rear curtain) from the time when the light shielding member is detected to be in the open state. Drive control means for releasing the holding of the rear curtain after a lapse of time from the release of the holding until the rear curtain shields at least a part of the shooting screen)}.

<< First embodiment of the invention >>
FIG. 1 is a diagram showing the configuration of the electronic camera of the first embodiment. Note that illustration and description of camera devices and circuits not directly related to the present embodiment are omitted. Light from the subject that has passed through the photographing lens 1 enters the image sensor 3 via the shutter 2. The shutter 2 includes a front curtain and a rear curtain (not shown). At the time of shooting, the front curtain travels to cancel the blocking of the subject light, and the shooting screen (aperture) of the image sensor 3 is fully opened. Next, the rear curtain travels to block the subject light, and the photographing screen of the image sensor 3 is closed. The drive circuit 4 drives the front curtain and rear curtain of the shutter 2 to travel.

  The switch 5 is turned on when the front curtain of the shutter 2 travels to cancel the shielding of the subject light and the front curtain further moves slightly in the opening direction after the shooting screen of the image sensor 3 is fully opened. In general, this is a switch called “X contact” indicating completion of full opening of the photographing screen. The switch 6 is a switch that is turned on when a shutter button (not shown) is pressed. The image sensor 3 receives subject light, accumulates charges, and outputs an image signal. It should be noted that when the imaging screen of the image sensor 3 is in an open state and subject light is incident on the image sensor 3, the time for accumulating charges in the image sensor 3 (charge accumulation time) is the shutter time of a conventional camera. Correspondingly, the image sensor 3 has a so-called “electronic shutter function”. The shutter 2 cancels the shielding of the subject light before the charge accumulation of the image sensor 3 is started, opens the shooting screen, and closes the shooting screen by shielding the subject light after the charge accumulation is completed.

  The A / D converter 7 converts the analog image signal output from the image sensor 3 into a digital signal. The ASIC 8 performs various image processing such as white balance processing and compression / decompression processing of the image signal on the digital image signal. The recording medium 9 records the image data after compression processing. The timing circuit 10 generates timing signals necessary for the operation of the image sensor 3 and the A / D converter 7. The control circuit 11 includes a CPU 11a and an EEPROM 11b, and performs various controls of the electronic camera such as opening / closing control of the shutter 2 and charge accumulation control of the image sensor 3, arithmetic processing, sequence processing, and the like.

  FIG. 2 is a timing chart showing the movement of the shutter 2 at the shutter release of the front curtain FC and the rear curtain RC. Here, a typical focal plane shutter having a front curtain FC and a rear curtain RC will be described as an example. Further, in the first embodiment, the variation in operation of each part in the same type of shutter of the same type of camera is handled by dividing it into “initial part” and “age and environmental change part”. The former initial variation is an initial operation variation caused by a manufacturing error, an assembly error, an adjustment error, and the like, and is an operation variation that does not change due to aging and environment. On the other hand, the latter operation variation that varies with age and environment is variation that varies with age due to mechanical fatigue and wear, and variation that varies with operation environment such as temperature and humidity.

  In FIG. 2, it is assumed that the holding of the leading curtain FC is released at time t0 and the traveling of the leading curtain FC is started. With reference to FIG. 2, the error factor of the movement of the leading curtain FC and the trailing curtain RC will be considered. If the holding of the front curtain FC is released at time t0 and the front curtain FC starts to open the shooting screen A at time t1, the face-out time T2 of the front curtain FC from time t0 to t1 is, for example, a standard value of 2.8 ms. In contrast, there is an initial operation variation of ± 0.9 ms. The “front curtain speed” from when the front curtain FC starts to open the shooting screen A at time t1 to when the shooting screen A is completely opened at time t2 is, for example, ± 0. It has an initial variation of 7 ms.

  Next, the X delay time from when the photographing screen A is opened at time t2 to when the X contact (the switch 5) indicating completion of the full opening of the photographing screen is turned on at time t3 is 0 to +0.6 ms. . Further, if the holding of the rear curtain RC is released at time t4 and the rear curtain RC starts to close the shooting screen A at time t6, the appearance time T4 of the rear curtain RC from time t4 to t6 is, for example, 2.8 ms. There is an initial operation variation of ± 0.9 ms with respect to the standard value. The total of the initial operation variations of the respective shutter parts is 3.1 ms at the maximum.

  In the first embodiment, the initial operation variation of the shutter 2 (the above-mentioned “initial amount”) is measured and stored as “correction time”, and the holding release timing of the rear curtain RC is corrected during correction. Is compensated for by the amount of, and the initial operation variation is eliminated. On the other hand, since it is not possible to measure and correct in advance an operation variation that changes with time and environment, in order to avoid the trailing curtain RC from starting to close the photographing screen A during the charge accumulation period of the image sensor 3. In addition, a “full opening margin time” for compensating for an operation variation that changes with time and the environment is set in advance, and the holding release timing of the trailing curtain RC is compensated by the amount of the fully opening margin time during shooting. The fully open margin time is set in advance so that the trailing curtain RC starts to close the photographing screen A after the charge accumulation time of the image sensor 3 has elapsed even if there is a secular change or a change in the operating environment.

  With reference to FIG. 2, a method for determining the correction time for compensating the initial operation variation of the shutter 2 will be described. Normally, this correction time is determined and adjusted and stored in the EEPROM 11b of the control circuit 11, for example, during shipping adjustment in the camera manufacturing process. When the X contact is turned on at time t3, the image sensor 3 starts charge accumulation, and ends charge accumulation at time t5 after the shutter time T5 has elapsed. During the time T6 from the end of charge accumulation at time t5 to time t6 when the trailing curtain RC starts to close the photographing screen A, the shutter 2 is in an open state, and subject light is unnecessarily incident on the image sensor 3. to continue. If the time T6 can be reduced to 0, unnecessary object light can be prevented from entering the image sensor 3, and the occurrence of blooming or the like can be prevented.

Therefore, in this embodiment, the time T8 from when the X contact is turned on at time t3 until the trailing curtain RC starts to close the photographing screen A at time t6 is measured, and the correction time C is determined by the following equation.
C = T8-T5 (1)
In the equation (1), T8 is a measurement time from the X contact point ON to the start of light shielding by the rear curtain RC, and T5 is a shutter time. Here, the shutter time is normally obtained by exposure calculation based on subject brightness, aperture value, and ISO sensitivity. When determining the correction time C at the time of shipping adjustment, at least during the charge accumulation of the image sensor 3. A shutter time is set so that light shielding by the rear curtain RC does not start. In this example, since the maximum of the total initial operation variation of each part of the shutter is 3.1 ms (= 1/322 s), in order to determine the correction time C at a time longer than 1/322 s, for example, 1/250 s. The shutter time of The determined correction time C is stored in the EEPROM 11b of the control circuit 11.

  Further, “full opening allowance time” for compensating for variation in operation that varies with time and environment is preset for each camera type and shutter type, and is stored in the EEPROM 11 b of the control circuit 11 as the full opening allowance time M. Further, the control circuit 11 sets the standard value T3 (here, 5.0 ms) of the leading curtain speed until the shooting screen A is completely opened at the time t2 after the leading curtain FC starts to open the shooting screen A at the time t1. Stored in the EEPROM 11b.

Next, the hold release timing of the rear curtain RC during actual shooting will be described with reference to FIG. In FIG. 3, the same reference numerals are assigned to the same time and time as shown in FIG. 2, and the differences will be mainly described. Time T10 is the shutter time at the time of shooting. In the first embodiment, a time T1 from time t0 when the holding of the front curtain FC is released to time t4 when the holding of the rear curtain RC is released is determined by the following equation.
T1 = T10 + T3-C + M (2)
In Formula (2), T3 is a standard front curtain speed (here, for example, 5 ms) from when the front curtain FC starts to open the shooting screen A at time t1 to when the shooting screen A is completely opened at time t2. ), C is the above-described correction time, and M is the above-described fully open margin time.

  The control circuit 11 reads the correction time C, the fully open margin time M, and the standard front curtain speed T3 stored in the EEPROM 11b at the time of shooting, and determines the shutter determined by the exposure calculation based on these values, subject brightness, aperture value, and ISO sensitivity. Based on the second time T10, the holding release time T1 of the rear curtain RC is determined by the equation (2), the driving circuit 4 is controlled, and the holding of the front curtain FC is released at time t0. Release RC holding.

As described above, according to the first embodiment, when determining the holding release timing of the rear curtain RC, the initial shutter shutter series 2 of the front curtain appearance, the front curtain speed, the X contact delay, and the rear curtain appearance is displayed. Is corrected, and the time from the end of charge accumulation in the image sensor 3 until the trailing curtain RC starts closing the shooting screen A is shortened by the correction time C. The extra amount of incident light can be reduced, and blooming can be prevented and image quality can be improved.
In addition, in order to compensate for the variation in operation of the shutter 2 due to the aging and environment, the holding release timing of the rear curtain RC is delayed by a preset full opening margin time M. It is possible to prevent the shooting screen A from being closed by the curtain RC and so-called “shooting of the shooting screen”.
In other words, according to the first embodiment, the amount of extra light incident on the image pickup device 3 is suppressed to a minimum while preventing the vignetting of the shooting screen A by the rear curtain RC, and the occurrence of blooming is prevented. Can be improved.

<< Modification of First Embodiment >>
In the first embodiment described above, an example in which the hold release timing of the trailing curtain RC is determined in consideration of the fully open margin time M for compensating for the operation variation of the shutter 2 that changes with time and the environment. However, when the adjustment time C is frequently updated after the factory shipment as shown in FIG. 2, the fully open margin time M is omitted, and the {(shutter seconds (Time T10) + (Lead Curtain Standard Traveling Time T3) − (Correction Time C)} The retention of the rear curtain RC may be released after elapse of time. Even in this case, it is possible to minimize the extra light amount incident on the image sensor 3 while preventing the vignetting of the shooting screen A by the rear curtain RC, and to prevent blooming and improve the image quality.

<< Second Embodiment of the Invention >>
In the first embodiment described above, the initial operation variation of the shutter 2 is measured and stored as the correction time C, and the holding release timing of the rear curtain RC is compensated by the correction time C at the time of shooting to initially Although an example in which the operation variation is eliminated is described, a second embodiment in which the measurement of the correction time C is omitted will be described. The configuration of the second embodiment is the same as the configuration shown in FIG.

  FIG. 4 is a timing chart showing the movement of the shutter 2 of the shutter 2 of the second embodiment during shutter release of the rear curtain RC. In addition, the same code | symbol is attached | subjected and demonstrated to the time similar to the time shown to FIG. 2 and FIG. In the first embodiment, the holding release timing of the rear curtain RC is determined based on the time t0 when the holding of the front curtain FC is released. In this second embodiment, the X contact (switch 5) The hold release timing of the trailing curtain RC is determined from the time t3 when the turn-on turns on. The traveling of the front curtain FC of the second embodiment is the same as the traveling of the first embodiment shown in FIGS.

  In the second embodiment, since the holding release timing of the trailing curtain RC is determined starting from the time t3 when the X contact is turned on, it is not necessary to consider the initial operation variation regarding the leading curtain FC. Only the initial operation variation of the RC appearance time T4 needs to be considered. If the holding of the rear curtain RC is released at time t4 and the rear curtain RC starts to close the shooting screen A at time t6, the appearance time T4 of the rear curtain RC from time t4 to t6 is, for example, a standard value of 2.8 ms. In contrast, there is an initial operation variation of ± 0.9 ms.

  On the other hand, since it is not possible to measure and correct in advance an operation variation that changes with time and environment, it is necessary to compensate for an operation variation that changes with time and environment. In the second embodiment, the “full opening margin time M ′” is set in advance in consideration of the above-described initial operation variation of the rear curtain RC and the operation variation that changes with time and the environment. The holding release timing of the curtain RC is delayed by the fully open margin time M ′. As the fully open margin time M ′, a time is set in advance so that the trailing curtain RC starts to close the photographing screen A after the charge accumulation time of the image sensor 3 elapses even if there is a secular change or an operating environment change.

Then, based on the determination result by the following determination formula based on the rear curtain RC appearance time T4 (standard value), the shutter time T10, and the fully open margin time M ′, the release cancellation of the rear curtain RC is controlled in two ways. To do.
T4 ≧ (T10 + M ′) (3)
When the determination formula (3) is satisfied, that is, when the shutter time T10 is relatively short, the holding of the trailing curtain RC is released at time t3 when the X contact is turned on. On the other hand, when the judgment formula (3) is not satisfied, that is, when the shutter time T10 is relatively long, the holding of the trailing curtain RC is released after the time (T10 + M′−T4) has elapsed from the time t3 when the X contact is turned on. .

  According to the second embodiment, the charge accumulation is completed by the time t6 when the trailing curtain RC starts to close the photographing screen A, the vignetting of the photographing screen A by the trailing curtain RC does not occur, and after the charge accumulation is completed. The extra light quantity incident on the image sensor 3 can be reduced.

The figure which shows the structure of one embodiment Timing chart for explaining a method for determining a correction time for compensating for an initial operation variation of the shutter according to the first embodiment Timing chart for explaining the operation for releasing the rear curtain holding at the time of shooting according to the first embodiment Timing chart for explaining the operation for releasing the holding of the trailing curtain during shooting according to the second embodiment

Explanation of symbols

2 Shutter FC front curtain RC rear curtain 3 imaging element 4 drive circuit 5 switch 10 timing circuit 11 control circuit

Claims (1)

An image sensor that receives subject light and accumulates charges;
A light-shielding member that has a front curtain and a rear curtain, and that displaces an open state that fully opens the photographing screen and a closed state that shields the photographing screen;
Accumulation control means for controlling a charge accumulation time from the start of charge accumulation by the image sensor when the light shielding member is detected to be in the open state to the end of charge accumulation by the image sensor;
A setting means for setting an allowance time in consideration of an operation variation associated with an initial operation of the rear curtain and an operation variation that changes with time and environment;
Conditional expression
(Time from when the trailing curtain is released until the trailing curtain blocks at least a part of the shooting screen) ≧ (the charge accumulation time + the margin time)
Determining means for determining whether or not
When it is determined by the determining means that the conditional expression is satisfied, the holding of the rear curtain is released when the light shielding member is detected to be in the open state, and it is determined by the determining means that the conditional expression is not satisfied. At the time of detecting that the light shielding member is in the open state {(the charge accumulation time) + (the margin time) − (at least one of the shooting screens after the holding of the trailing curtain is released). Drive control means for releasing the holding of the rear curtain after elapse of time)}
An electronic camera characterized by

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