JP4453196B2 - Electronic still camera - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electronic still camera that captures a subject image using an image sensor.
[0002]
[Prior art]
In order to obtain an appropriate exposure amount with the camera, an apex calculation is performed in which an exposure calculation is performed by the following equation (1) using the aperture value AV of the photographing lens, the TV at shutter speed, the subject brightness BV, and the exposure sensitivity SV. ing.
[Expression 1]
EV = AV + TV = BV + SV (1)
However, EV is an exposure amount. In the case of a film camera, the SV is determined by the sensitivity of the film to be used, so the aperture value AV and shutter time TV are calculated according to the subject brightness BV.
[0003]
[Problems to be solved by the invention]
The aperture value AV is an important factor that determines the depth of the subject by the photographing lens, and the shutter time TV is an important factor that suppresses blurring of a moving subject or creates a lively feeling. Therefore, it is convenient that the aperture value AV and the shutter time TV can be set with priority. However, if the exposure sensitivity SV is determined first as in a film camera, it is necessary to adjust the aperture value AV and shutter time TV according to the subject brightness BV, and the aperture value and shutter time are given priority. It is difficult to set and obtain an appropriate exposure amount.
[0004]
SUMMARY OF THE INVENTION An object of the present invention is to provide an electronic still camera in which an aperture value and a shutter time are preferentially set and exposure is adjusted by changing exposure sensitivity in an imaging means.
[0005]
[Means for Solving the Problems]
  An electronic still camera according to a first aspect of the present invention is set in an imaging unit that captures a subject image through a photographing lens, a luminance detection unit that detects subject luminance, an exposure time set in the imaging unit, and a photographing lens. A calculation means for calculating the exposure sensitivity according to the aperture value and the subject brightness detected by the brightness detection means, an exposure sensitivity adjustment means for adjusting the exposure sensitivity by the imaging means, and the exposure sensitivity calculated by the calculation means And a control means for controlling the exposure sensitivity adjustment means. The exposure sensitivity adjustment means is a floating at the time of charge voltage conversion of an image signal output from the imaging means when the calculated exposure sensitivity is equal to or less than a predetermined value. When the exposure sensitivity is adjusted by the first sensitivity adjustment process for changing the capacity and the calculated exposure sensitivity is greater than a predetermined value, the first sensitivity adjustment process and , And adjusting the exposure sensitivity by the second sensitivity adjustment processing for changing the amplification degree of the image signal output in the imaging unit.
According to a fifth aspect of the present invention, there is provided an electronic still camera according to the present invention. A ratio of performing charge accumulation time and charge non-accumulation time alternately within a set exposure time, and a calculation means for calculating exposure sensitivity according to the aperture value and the subject brightness detected by the brightness detection means The exposure sensitivity adjusting means for adjusting the exposure sensitivity by the image pickup means by changing the above and the control means for controlling the exposure sensitivity adjusting means so as to obtain the exposure sensitivity calculated by the calculating means.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing an outline of an electronic still camera according to an embodiment of the present invention. In FIG. 1, the electronic still camera includes a lens diaphragm 11, a mirror 12, a luminance detection circuit 13, a CCD 14, a CDS circuit 15, a variable gain amplification circuit 16, an A / D conversion circuit 17, and signal processing. A circuit 18, an image buffer memory 19, an MPU 20, an LCD monitor circuit 21, an LCD monitor 22, a memory card 23, an operation member 24, an aperture value setting member 25, a shutter speed setting member 26, A control sensitivity range setting member 27 is provided.
[0008]
The subject light passes through the diaphragm 11, is reflected by the mirror 12, and is input to the luminance detection circuit 13. The luminance detection circuit 13 detects the subject luminance and sends a detection result to the MPU 20. The MPU 20 receives an operation signal from the operation member 24, each set value by the aperture value setting member 25, the shutter time setting member 26 and the controlled sensitivity range setting member 27. When the release half-press operation signal from the operation member 24 is input to the MPU 20, the MPU 20 outputs a control signal for the CCD 14. The CCD 14 that is an imaging device controls the operation timing for charge accumulation and accumulated charge readout by a control signal. The MPU 20 performs a predetermined exposure calculation based on the set value input from each setting member and the subject brightness input from the brightness detection circuit 13.
[0009]
When a release full-press operation signal is input to the MPU 20 following the release half-press operation signal, the MPU 20 drives a mirror drive mechanism (not shown) to raise the mirror 12. As a result, a subject image is formed on the CCD 14. The CCD 14 accumulates signal charges according to the brightness of incident subject light. The signal charge accumulated in the CCD 14 is discharged by a timing signal sent from the MPU 20 and input to the CDS circuit 15. The CDS circuit 15 removes low frequency noise such as reset noise and amplifier noise of the CCD 14 included in the imaging signal output from the CCD 14.
[0010]
The variable gain amplifier circuit 16 performs signal amplification on the analog image signal with the amplification gain set by the MPU 20. The A / D conversion circuit 17 converts the analog image signal after signal amplification into a digital signal. The digitally converted image signal is guided to the signal processing circuit 18 where image preprocessing such as contour compensation, gamma correction, color temperature adjustment, and color space conversion processing is performed. The image data after the image preprocessing is temporarily stored in the buffer memory 19.
[0011]
The image data after image preprocessing stored in the buffer memory 19 is processed into image data for display by the MPU 20 and is displayed on the LCD monitor 22 as a photographing result by a video signal generated by the LCD monitor circuit 21. The MPU 20 further performs format processing (image post-processing) for JPEG compression on the image data that has been subjected to the image pre-processing described above. The MPU 20 compresses the image data after image post-processing to a predetermined ratio using the JPEG method. Image data that has been subjected to data compression in the JPEG format is recorded on a memory card 23, which is a detachable nonvolatile recording medium (PC card, CF card, etc.) given a predetermined data name by the MPU 20.
[0012]
The controlled sensitivity range setting member 27 is an operation member that sets a predetermined value used to determine whether or not to display a warning for an effective sensitivity value calculated by an exposure calculation described later. When the photographer operates the controlled sensitivity range setting member 27, a predetermined value used for the determination is set.
[0013]
FIG. 2 is a diagram for explaining the signal output unit of the CCD 14. In FIG. 2, FET 142 and FET 148 constitute a source follower circuit. The sum of the capacitances Cf and Cf1 of the floating capacitors 143 and 144 becomes a floating capacitance (charge-voltage conversion capacitance). The FET 145 is an FET that changes the floating capacitance, and is on / off controlled by the MPU 20. The inverter 146 is a buffer that transmits a control signal output from the MPU 20 to the gate terminal of the FET 145. The resistor 147 is used as a load resistance.
[0014]
When the reset pulse signal φRs is input to the gate of the FET 142 provided at the output of the CCD register 141, the FET 142 is turned on and the source of the FET 142 is charged to the power supply voltage Vdd. When the reset pulse signal φRs is not input, the FET 142 is turned off, and the source of the FET 142 becomes the feedthrough level. When a signal charge is output from the CCD register 141 in this state, the signal level of the source of the FET 142 changes to a voltage corresponding to the signal charge output from the CCD register 141. This voltage ΔV is expressed by the following equation (2).
[Expression 2]
ΔV = ΔQ / (Cf + Cf1) (2)
However, ΔQ is a signal charge output from the CCD register 141, and (Cf + Cf1) is a floating capacitor. The voltage ΔV is amplified by the FET 148, and the amplified voltage signal is sent to the CDS circuit 15. From the above equation (2), the smaller the floating capacitance, the larger the voltage ΔV, and the greater the change in the signal level of the source of the FET 142. That is, the smaller the floating capacitance, the higher the signal charge detection sensitivity.
[0015]
When the MPU 20 increases the signal charge detection sensitivity in the signal output section of the CCD 14, the FET 145 is turned off to set the floating capacitance to Cf. On the other hand, when the detection sensitivity of the signal output unit of the CCD 14 is lowered, the FET 145 is turned on to set the floating capacitance to (Cf + Cf1).
[0016]
FIG. 3 is a diagram illustrating the variable gain amplifier circuit 16. In FIG. 3, the variable gain amplifier 161 amplifies the analog image signal output from the CDS circuit 15. Here, the amplification gain of the variable gain amplifier 161 is set by the MPU 20. When the MPU 20 outputs the amplification gain control signal as a digital value, the D / A conversion circuit 162 converts it into an analog voltage signal corresponding to the digital value and outputs it to the variable gain amplifier 161. The variable gain amplifier 161 sets the amplification gain according to the input analog voltage.
[0017]
FIG. 4 is a diagram illustrating the CCD 14. The CCD 14 controls the exposure amount by fixing the control time by so-called electronic shutter control to 1/125 seconds, for example, and changing the duty to alternately repeat charge accumulation and charge discharge within 1/125 seconds. Is done. In FIG. 4, the photoelectric conversion photodiode 41 constitutes a pixel of the CCD 14. A charge discharging drain region 42 is provided above the photoelectric conversion photodiode 41. A charge discharge gate 45 is provided between the photoelectric conversion photodiode 41 and the charge discharge drain region 42. A charge storage unit 43 is provided on the left side of the photoelectric conversion photodiode 41. An accumulation shift gate 46 is provided between the photoelectric conversion photodiode 41 and the charge accumulation unit 43. A charge transfer CCD register 44 is provided on the left side of the charge storage unit 43. A read gate 47 is provided between the charge storage unit 43 and the charge transfer CCD register 44.
[0018]
FIG. 5 is a diagram showing the timing of control signals for the CCD 14 when the exposure time of the CCD 14 is controlled with a duty of 50%. The electronic shutter signal Sig14 is a charge accumulation signal for the CCD 14, and the H level section in FIG. 5 corresponds to 1/125 seconds. The control signal Sig45 is a control signal for the charge discharging gate 45, and the control signal Sig46 is a control signal for the accumulation shift gate 46. The control signal Sig47 is a control signal for the read gate 47. Each of the control signals Sig45 to 47 opens each gate at the H level and closes each gate at the L level.
[0019]
Before the exposure is started by the CCD 14 (Sig14 is at L level), the charge discharge gate 45, the accumulation shift gate 46, and the read gate 47 are opened, and the charge generated by the photoelectric conversion photodiode 41 and the charge accumulation unit 43 are opened. The charge accumulated in the charge discharge drain region 42 and the charge transfer CCD register 44 are discarded. When exposure is started in the CCD 14 (Sig14 is at H level), the readout gate 47 is closed, and pulse signals having opposite phases are applied to the charge discharge gate 45 and the accumulation shift gate 46, respectively.
[0020]
When exposure is completed in the CCD 14 (Sig14 is at L level), the readout gate 47 is once opened, and the charge accumulated in the charge accumulation unit 43 is transferred to the charge transfer CCD register 44. The readout gate 47 once opened is then kept closed until the readout of the transfer charge from the charge transfer CCD register 44 is completed. When the readout of the transfer charge from the CCD 44 is completed, the readout gate 47 is opened and waits until the next exposure starts. On the other hand, the charge discharge gate 45 and the accumulation shift gate 46 are opened when the exposure by the CCD 14 is completed, and wait until the next exposure starts.
[0021]
In FIG. 5, when the storage shift gate 46 is opened, that is, when Sig 46 is at the H level, charges are stored in the charge storage unit 43. When the accumulation shift gate 46 is closed, that is, when the Sig 46 is at the L level, no charge is accumulated in the charge accumulation unit 43. The charge generated in the photoelectric conversion photodiode 41 during a period in which no charge is accumulated in the charge accumulation unit 43 is discharged from the charge discharge drain region 42. As a result, even when the H level period of the electronic shutter signal Sig14, that is, when the shutter time for the CCD 14 is controlled to 1/125 seconds, no charge is accumulated in the 1/2 period, so the actual exposure time by the CCD 14 is It is controlled to be equivalent to 1/250 seconds. In the electronic still camera of this embodiment, the mechanical shutter mechanism for controlling the opening time is omitted, and the shutter time is controlled by so-called electronic shutter control.
[0022]
When the exposure time of the CCD 14 is controlled with a duty of 75%, a pulse signal for setting the ratio of the H level to the L level of the control signal Sig46 to 75% is applied to the accumulation shift gate 46 while the electronic shutter signal Sig14 is at the H level. . A pulse control signal Sig45 having a phase opposite to that of the control signal Sig46 is applied to the charge discharging gate 45. As a result, even when the H level period of the electronic shutter signal Sig14, that is, when the shutter time for the CCD 14 is controlled to 1/125 seconds, no charge is accumulated in the 1/4 period, so the actual exposure time by the CCD 14 is It is controlled to be equivalent to 1/167 seconds.
[0023]
When the exposure time of the CCD 14 is controlled with a duty of 25%, a pulse signal for setting the ratio of the H level to the L level of the control signal Sig46 to 25% is supplied to the accumulation shift gate 46 while the electronic shutter signal Sig14 is at the H level. Apply. A control signal Sig45 having a phase opposite to that of the control signal Sig46 is applied to the charge discharging gate 45. As a result, even when the H level period of the electronic shutter signal Sig14, that is, when the shutter time for the CCD 14 is controlled to 1/125 seconds, the charge is not accumulated in the 3/4 period, so the actual exposure time by the CCD 14 is It is controlled to be equivalent to 1/500 second.
[0024]
FIG. 6 is a diagram illustrating each pulse waveform example of the control signal Sig46 when the duty is controlled at 50%, 25%, and 75%. If the control signal Sig46 is set to the H level, that is, duty 100% in the entire section in which the electronic shutter signal Sig14 is set to the H level, the exposure time by the CCD 14 is 1/125 seconds, which is the same as the H level period of the electronic shutter signal Sig14. Be controlled.
[0025]
The exposure calculation performed by the electronic still camera described above will be described. The electronic still camera has the following exposure modes (1) to (4). (1) Sensitivity control AE that controls effective sensitivity by giving priority to both the set lens aperture value and shutter speed, and (2) Aperture that controls the shutter time by giving priority to the set lens aperture value. Priority AE, {circle around (3)} Shutter priority AE for controlling the lens aperture value by giving priority to the set shutter time, {circle around (4)} Control the lens aperture value and shutter time according to pre-programmed shooting conditions Program AE. These exposure modes are switched by a mode setting dial (not shown) provided on the operation member 24. Here, the effective sensitivity is controlled by changing any of the above-described signal charge detection sensitivity of the output unit of the CCD 14, the amplification gain of the variable gain amplifier circuit 16, and the exposure amount due to the duty change of the operation timing of the CCD 14. It means quantity. The electronic still camera of the present embodiment is characterized by sensitivity control AE that performs exposure adjustment by actively controlling only the effective sensitivity of (1), and therefore the sensitivity control AE will be mainly described.
[0026]
FIG. 7 is a flowchart for explaining the flow of exposure calculation processing performed by the MPU 20. When the release half-press operation signal is input from the operation member 24, the MPU 20 starts the exposure calculation process of FIG. In step S71, the MPU 20 determines whether or not the exposure mode set by the photographer operating the operation member 24 is the sensitivity control AE of (1) described above. An affirmative determination is made in S71 and the process proceeds to step S72. On the other hand, if it is set to any one of (2) Aperture priority AE, (3) Shutter priority AE, and (4) Program AE, a negative determination is made in step S71 and the process proceeds to step S78.
[0027]
In step S72, the MPU 20 sets the lens aperture value AV that is set when the photographer operates the aperture value setting member 25, and the shutter speed that is set when the photographer operates the shutter time setting member 26. Time TV is read and the process proceeds to step S73. Here, each set value is stored in a register in the MPU 20 when the operation members 25 and 26 are operated.
[0028]
In step S73, the MPU 20 reads the subject luminance value BV output from the luminance detection circuit 13, and proceeds to step S74. In step S74, the MPU 20 calculates an effective sensitivity value SV by the following equation (3) using the shutter time TV, the lens aperture value AV, and the subject luminance value BV, and then proceeds to step S75.
[Equation 3]
SV = TV + AV-BV (3)
FIG. 8 is an example of a program diagram used when the shutter time TV is set to 1/125 seconds by the photographer. The MPU 20 calculates the effective sensitivity SV according to the aperture value AV. In FIG. 8, for example, when the aperture value AV is set to 5.6 by the photographer and the exposure amount EV is 12, the effective sensitivity SV = 5 is obtained. The exposure amount EV is given by SV + BV.
[0029]
In step S75, based on the calculated effective sensitivity value SV, the MPU 20 calculates the exposure amount due to the duty change of the signal charge detection sensitivity of the output unit of the CCD 14, the amplification gain of the variable gain amplification circuit 16, and the operation timing of the CCD 14. Change. FIG. 9 is a table showing the relationship between the effective sensitivity value SV, amplification gain, floating capacitance (charge-voltage conversion capacitance), and duty. In FIG. 9, the MPU 20 sets the amount of change in the gain of the variable gain amplifier circuit 16 to 0 dB when the effective sensitivity value SV is in the range of 0-6. Further, the MPU 20 changes the amplification gain so that the effective sensitivity value SV is in the range of 6 to 11 and one stage of SV corresponds to the gain change amount 6 dB of the variable gain amplifier circuit 16.
[0030]
Further, the MPU 20 turns on the FET 145 of the CCD 14 when the effective sensitivity value SV is in the range of 0-5. At this time, if the capacitances Cf and Cf1 of the floating capacitors 143 and 144 are both 1 pF, the floating capacitance is 2 pF. The MPU 20 turns off the FET 145 of the CCD 14 when the effective sensitivity value SV is in the range of 5-11. As a result, the floating capacitance becomes 1 pF.
[0031]
Further, the MPU 20 changes the duty of the control signals Sig46 and Sig45 of the CCD 14 so that the effective sensitivity value SV is in the range of 0 to 5 and one step of the SV value corresponds to twice the exposure amount of the CCD 14. Further, the MPU 20 has the effective sensitivity value SV in the range of 5 to 11, and the duty of the control signals Sig46 and Sig45 is set to 100%, that is, the control signal Sig46 is set to the H level in all the sections where the electronic shutter signal Sig14 is set to the H level. Control to be.
[0032]
When the MPU 20 finishes setting each unit based on the effective sensitivity value SV as described above, the process proceeds to step S76. In step S76, the MPU 20 compares the effective sensitivity value SV calculated by comparing the predetermined value set by the photographer operating the controlled sensitivity range setting member 27 with the effective sensitivity value SV calculated in step S74. <Determining whether or not the value is a predetermined value. If the effective sensitivity value SV <predetermined value, an affirmative determination is made in step S76, the process of FIG. 7 is terminated, and a shooting process following the release full-press signal is performed. If the effective sensitivity value SV ≧ the predetermined value, a negative determination is made in step S76, and the process proceeds to step S77. In step S77, the MPU 20 displays a warning on the LCD monitor 22. In the warning display, for example, when the SV is 10 or more, as a result of increasing the gain of the variable gain amplifier circuit 16 and increasing the signal level while the accumulated charge of the CCD 14 is small, the S / N ratio may be deteriorated. This is to notify the photographer of this fact.
[0033]
In step S78, which is determined to be negative in step S71 described above and proceeds, the MPU 20 performs a predetermined exposure calculation in another set exposure mode, and ends the process of FIG.
[0034]
In FIG. 9 described above, the effective sensitivity is lower at the upper side of the table, and the effective sensitivity is higher at the lower side of the table. In the case where the effective sensitivity is lowered by changing the duty of the operation timing of the CCD 14, the longer the interval in which the electronic shutter signal Sig14 is set to the H level, that is, the shutter time set by the photographer, is more effective. On the contrary, when a short shutter time TV is set by the photographer, the frequency of the control signals Sig46 and Sig45 for changing the duty is set higher and the effective sensitivity value SV is set lower.
[0035]
According to the embodiment described above, the following operational effects can be obtained.
(1) The shutter time TV set by the photographer operating the shutter speed setting member 26 and the lens aperture value AV set by the photographer operating the aperture value setting member 25 are changed. The exposure time during which charges are actually accumulated in the CCD 14 is controlled to be shorter than the shutter time TV by changing the duty for alternately repeating charge accumulation and charge discharge. For example, it is assumed that the photographer sets the lens aperture value AV to an arbitrary value in order to obtain a predetermined depth of field, and sets the shutter time TV to 1/125 seconds. At this time, when the MPU 20 calculates the shutter time TV corresponding to 1/500 second for proper exposure, the MPU 20 sets the duty of the control signal Sig46 to 25%. Since the exposure amount of the CCD 14 is changed to 1/4, the exposure time is equivalent to an exposure amount of 1/500 seconds in the shutter time, but the image blur to be picked up is equivalent to 1/125 seconds in the shutter time. Become. As a result, it is possible to obtain an image having a desired depth of field while expressing a fluid feeling such as a water flow.
(2) By reducing the floating capacitance in the signal output section of the CCD 14, the signal charge detection sensitivity is increased, and the output value of the image signal output from the CCD 14 is apparently increased. When the photographer sets the lens aperture value AV and the shutter time TV to arbitrary values, if the exposure amount EV calculated by the exposure calculation of the MPU 20 is under, the MPU 20 reduces the floating capacitance at the time of charge-voltage conversion. Increase the signal level. As a result, when photographing a moving subject, the photographer can set a shorter shutter time TV, so that blurring of the subject can be suppressed. Furthermore, since it is not necessary to open the lens aperture value AV, a desired depth of field can be realized.
(3) The output value of the image signal output from the CCD 14 is apparently increased by changing the signal amplification gain of the image signal by the CCD 14. Therefore, similarly to the above (2), it is possible to suppress blurring of a moving subject and to realize a desired depth of field.
(4) The effective sensitivity value SV calculated in step S74 is compared with a predetermined value set by the photographer. For example, the effective sensitivity value SV is like the SV value marked with a star in FIG. In the case of ≧ predetermined value, a warning is displayed on the LCD monitor 22. As a result, the photographer is notified that the S / N ratio of the photographed image may be deteriorated by increasing the gain of the variable gain amplifier circuit 16 and increasing the signal level in a state where the charge stored in the CCD 14 is small. Can do.
[0036]
In the above description, the setting values by the aperture value setting member 25 and the shutter time setting member 26 are input to the MPU 20. However, the setting values are respectively input to the lens aperture value setting member 25 and the shutter time setting member 26. May be provided, and detection signals from the respective detection sensors may be input to the MPU 20 respectively.
[0037]
Further, in the above description, the warning display is performed on the LCD monitor 22 in step S77. However, the warning display is performed, and after the processing of FIG. You may make it prohibit.
[0038]
Further, although it has been described that one predetermined value is set by the photographer from the controlled sensitivity range setting member 27, two predetermined values indicating the lower limit and the upper limit of the controlled range of the effective sensitivity value SV are set. May be. For example, taking the program diagram of FIG. 8 as an example, the lower limit value of the effective sensitivity value SV controlled linearly is 1, and the upper limit value of the effective sensitivity value SV is 8. Therefore, the photographer sets the first predetermined value to 8 and the second predetermined value to 1 from the controlled sensitivity range setting member 27, and the MPU 20 has the calculated effective sensitivity value SV in the range of 1-8. Display a warning when you are outside.
[0039]
The combination of the amplification gain of the variable gain amplifier circuit 16 set based on the effective sensitivity value SV, the floating capacitance (charge voltage conversion capacitance) of the CCD 14, and the duty of the control signal of the CCD 14 is not as shown in the table shown in FIG. May be. Instead of changing any one of the amplification gain, floating capacitance, and duty, a plurality of control amounts may be changed simultaneously.
[0040]
The above-described electronic still camera has been described by taking an example of a camera that can change the setting of the lens aperture value and the shutter time. However, the electronic still camera is also applicable to a camera in which the lens aperture value is fixed or the shutter time is fixed. The present invention can be applied.
[0041]
In the above description, the electronic still camera has been described. However, the present invention can also be applied to an electronic camera and a movie camera that output moving images.
[0042]
The correspondence between each constituent element in the claims and each constituent element in the embodiment of the invention will be described. The CCD 14 is the imaging means, the subject luminance detection circuit 13 is the luminance detection means, and the shutter time TV is the exposure time. In addition, the lens aperture value AV is the aperture value, the brightness value BV is the subject brightness, the effective sensitivity value SV is the exposure sensitivity, the MPU 20 is the calculation means, the exposure sensitivity adjustment means, and the control means, and the MPU 20 and the LCD monitor 22 are warned. It corresponds to each means.
[0043]
【The invention's effect】
  According to the present invention, the sensitivity can be appropriately adjusted to the exposure sensitivity according to the exposure time, the aperture value, and the subject brightness.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an outline of an electronic still camera according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a signal output unit of a CCD.
FIG. 3 is a diagram illustrating a variable gain amplifier circuit.
FIG. 4 is a diagram illustrating a CCD.
FIG. 5 is a diagram showing the timing of control signals when the exposure time of the CCD is controlled with a duty of 50%.
FIG. 6 is a diagram illustrating an example of a control signal pulse waveform when the duty is controlled at 50%, 25%, and 75%.
FIG. 7 is a flowchart illustrating the flow of exposure calculation processing.
FIG. 8 is a program diagram for determining an exposure amount when the shutter speed is set to 1/125 seconds.
FIG. 9 is a diagram illustrating a relationship between an effective sensitivity value, amplification gain, floating capacitance (charge-voltage conversion capacitance), and duty.
[Explanation of symbols]
11 ... Aperture, 13 ... Subject luminance detection circuit,
14 ... CCD, 16 ... variable gain amplifier circuit,
20 ... MPU, 22 ... LCD monitor,
25: Aperture value setting member, 26: Shutter time setting member,
27 ... Controlled sensitivity range setting member, 41 ... Photoelectric conversion photodiode,
42 ... drain region for discharging electric charge, 43 ... charge accumulating part,
44 ... Charge transfer CCD register, 45 ... Charge discharge gate,
46 ... Accumulation shift gate, 47 ... Read gate,
141: CCD register, 142, 145, 148 ... FET,
143, 144 ... floating capacity,
161: Variable gain amplifier

Claims (5)

An imaging means for imaging a subject image through a taking lens;
Luminance detection means for detecting subject luminance;
A calculation means for calculating an exposure sensitivity according to an exposure time set in the imaging means, an aperture value set in the photographing lens, and a subject brightness detected by the brightness detection means;
Exposure sensitivity adjusting means for adjusting exposure sensitivity by the imaging means;
Control means for controlling the exposure sensitivity adjusting means so as to be the exposure sensitivity calculated by the calculating means ,
When the calculated exposure sensitivity is less than or equal to a predetermined value, the exposure sensitivity adjustment means adjusts the exposure sensitivity by a first sensitivity adjustment process that changes a floating capacitance at the time of charge-voltage conversion of an image signal output from the imaging means. If the calculated exposure sensitivity is greater than a predetermined value, the exposure sensitivity is adjusted by the first sensitivity adjustment process and the second sensitivity adjustment process for changing the amplification degree of the image signal output from the imaging means. An electronic still camera characterized by The electronic still camera according to claim 1.
  When the calculated exposure sensitivity is equal to or lower than a second predetermined value lower than the predetermined value, the exposure sensitivity adjusting means alternately changes a charge accumulation time and a charge non-accumulation time in the set exposure time. When the exposure sensitivity is adjusted by a third sensitivity adjustment process for changing a ratio to be performed and the exposure sensitivity is greater than the second predetermined value and less than or equal to the predetermined value, the first sensitivity adjustment process and the third sensitivity adjustment process are performed. The exposure sensitivity is adjusted, and when the calculated exposure sensitivity is equal to or greater than the predetermined value, the exposure sensitivity is adjusted by the first sensitivity adjustment process, the second sensitivity adjustment process, and the third sensitivity adjustment process. An electronic still camera. The electronic still camera according to claim 1 or 2 ,
An electronic still camera, further comprising a warning unit that warns when the exposure sensitivity calculated by the calculation unit is equal to or higher than a third predetermined value or less than a fourth predetermined value that is smaller than the third predetermined value. . In the electronic still camera according to any one of claims 1 to 3 ,
An electronic still camera, further comprising setting means for presetting a range of exposure sensitivity controlled by the control means. An imaging means for imaging a subject image through a taking lens;
Luminance detection means for detecting subject luminance;
A calculation means for calculating an exposure sensitivity according to an exposure time set in the imaging means, an aperture value set in the photographing lens, and a subject brightness detected by the brightness detection means;
Exposure sensitivity adjusting means for adjusting exposure sensitivity by the imaging means by changing a ratio of alternately performing charge accumulation time and charge non-accumulation time in the set exposure time;
An electronic still camera comprising: control means for controlling the exposure sensitivity adjusting means so that the exposure sensitivity calculated by the calculating means is obtained.

Images