JPH0670229A - Exposure controller - Google Patents

Abstract

PURPOSE:To improve the deterioration of performance of an exposure controller that is caused by the low luminous intensity of a object by setting the output of the image pickup signal received from a CCD image pickup element at a fixed level to the luminous intensity of the object regardless of the viewing angle of the object. CONSTITUTION:An exposure controller consists of an aperture correction/control circuit 21 which controls the exposure value of an iris 2 included in an optical system 20, an AGC control circuit 22 which controls the gain against the output level of the image pickup signal received from a CCD image pickup element 3, a detecting circuit 14 which detects the zoom position of a lens system 1 included in the system 20, and a ROM 15 which stores the changed variable of the output level of the image pickup signal of the element 3 that is caused by the change of the F value set to the zoom position of the system 1. Then the ROM 15 outputs the changed variable of the output level of the image pickup signal to the circuit 22 in response to the zoom position information given from the circuit 14. Then the circuit 22 changes the output level of the image pickup signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is arranged, for example, in an image pickup device such as a video camera equipped with an optical system such as a zoom lens, and automatically adjusts the aperture amount of an iris constituting the optical system. The present invention relates to an exposure control device having an auto iris function for adjusting the amount and an auto gain control function for automatically adjusting the output level of an image pickup signal by a charge coupled device.

[0002]

2. Description of the Related Art Conventionally, image pickup devices such as video cameras have been
For example, as shown in FIG. 6, light from the imaging target (hereinafter,
This is called imaging light. ) Is imaged on the image pickup screen of a charge-coupled device, a so-called CCD image pickup device 103, via the optical system 101, and when an image pickup signal from this CCD image pickup device 103 is supplied to the signal processing circuit 116, the optical system 1
Aperture correction control circuit 10 which is an iris opening degree adjusting means for automatically adjusting the light amount of the imaging light passing through 01 to an appropriate amount.
4 and an automatic gain adjustment (hereinafter referred to as AGC) control circuit 105 which is an automatic gain adjustment means for automatically adjusting the output level of the image pickup signal from the CCD image pickup device 103. It is equipped.

In the aperture correction control circuit 104, as shown in FIG. 6, first, an output signal from the CCD image pickup device 103 is supplied to a detection circuit 112, for example, an average detection output is taken out. Then, the detection output from the detection circuit 112 is supplied to the inverting input terminal of the comparison circuit 113. At this time, the reference voltage for diaphragm control by the reference power supply 114, that is, a so-called reference voltage is supplied to the non-inverting input terminal of the comparison circuit 113. As a result, the comparison circuit 113 causes the detection circuit 1 to the inverting input terminal.
The detection output by 12 and the reference voltage by the reference power supply 114 to the non-inverting input terminal are compared. Then, the comparison result by the comparison circuit 113 is the iris 2
03 is supplied to the iris drive circuit 115.
Then, the iris drive circuit 115 changes the comparison circuit 11
The aperture amount of the iris 203 is adjusted on the basis of the output of No. 3.

Further, in the AGC control circuit 105,
As shown in FIG. 6, first, the output signal from the CCD image pickup device 103 is sent to the detection circuit 1 via the AGC circuit 106.
07, and the detection output from the detection circuit 107 is supplied to the inverting input terminal of the comparison circuit 108. At this time, the reference voltage for AGC adjustment by the reference power supply 109, a so-called reference voltage, is supplied to the inverting input terminal of the comparison circuit 108. Then, the comparison circuit 108 compares the detection output from the detection circuit 107, which is the supply voltage to the inverting input terminal, with the reference voltage from the reference power supply 109, which is the supply voltage to the non-inverting input terminal. The comparison result is supplied to the limiter 110. The limiter 110 is supplied with a voltage for setting the AGC maximum gain by the maximum gain setting power supply 111, a so-called maximum gain setting voltage. Then, the limiter 110 limits the output voltage from the comparison circuit 108, for example, using the maximum gain setting voltage from the maximum gain setting power supply 111 as an upper limit setting value. The result is the AGC circuit 1.
06. Then, the AGC circuit 106 is responsive to the output from the limiter 110 for the CCD image pickup device 10
3 controls the output level of the image pickup signal. For example, in the AGC circuit 106, the illuminance of the object to be imaged (hereinafter referred to as “subject illuminance”) is the maximum gain setting power supply 111.
If the illuminance is equal to or higher than the maximum gain setting voltage
The signal processing circuit 116 has a constant output level (100IRE)
The gain is controlled so that the above image pickup signal is not supplied, and if the illuminance of the subject is equal to or less than the illuminance corresponding to the maximum gain setting voltage by the maximum gain setting power supply 111, the maximum gain is obtained with respect to the output level of the image pickup signal. Have control.

[0005]

By the way, a so-called zoom lens having a variable focal length is applied to the optical system 101 mounted on the above-described image pickup apparatus or the like. As shown in FIGS. 7 to 9, for example, the optical system 101 includes a first lens group 201 that constitutes a front lens portion that captures the imaging light and a second lens that configures a variator for enlarging / reducing the imaging light. A group 202, an iris 203 that adjusts the light amount of the imaging light to an appropriate amount, a third lens group 204 that corrects the direction of the imaging light, and a fourth lens group 205 that forms a focus for imaging the imaging light. ,
The prism 206 is configured to color-separate the imaging light. Therefore, the second lens group 202 is the first lens group 2
01 and the iris 203 move in the movable range along the optical axis direction to change the focal length (optical system 1
When 01 is composed of a plurality of refracting surfaces or the like, it is referred to as a combined focal length. ) Can be continuously variable.

Here, when the combined focal length of the optical system 101 is changed to change the angle of view of the object to be imaged, if so-called zooming is performed, the incident light beam diameter d of the imaged light increases as the combined focal length increases. Is gradually widened. That is, as shown in FIG. 7, the second lens group 202 extends from the position closest to the first lens group 201 along the optical axis direction to the first lens group 20 as shown in FIG.
When it is operated to a substantially intermediate position of the movable range regulated by 1 and the iris 203, the incident light beam diameter d of the imaging light is gradually widened by the diaphragm amount of the iris 203. Note that, in the state shown in FIG. 7 in which the second lens group 202 is closest to the first lens group 201, the combined focal length of the optical system 101 is set to the shortest distance. Then, when further zooming is performed, the incident light flux diameter d of the imaging light is made wider, and the first lens group 201 is reached before the second lens group 202 reaches the position closest to the iris 203 shown in FIG. The diameter of the light flux of the imaging light passing through is equal to the diameter of the lens on the rear side of the first lens group 201. When the second lens group 202 comes closest to the iris 203, the combined focal length of the optical system 101 is set to the longest distance.

Therefore, the incident light beam diameter d of the imaging light is the first
After the diameter of the lens on the rear side of the lens group 201 becomes equal to that of the first lens group 20
When passing through 1, vignetting occurs in the vicinity of the outer periphery of the lens on the rear side of the first lens group 201. In other words, the incident light beam diameter d of the imaging light is not the aperture amount of the iris 203 but the first lens group 201. Since it is determined by the diameter of the lens on the rear side, the incident light flux diameter d of the imaging light is constant. At this time, there is a non-interference part, a so-called dead zone, between the luminous flux diameter of the imaging light passing through the iris 203 and the aperture amount of the iris 203, that is, the aperture diameter of the iris 203, and the width of the dead zone is increased according to the zooming. Since the width is wide, the F value of the optical system 101 is lower than the theoretical F value determined by the combined focal length of the optical system 101 and the incident light flux diameter d of the imaging light (this is called the F drop phenomenon. I call it.). Due to this F drop phenomenon, the output level of the image pickup signal supplied from the CCD image pickup element 103 to the signal processing circuit 116 is, as shown in FIG. 10, a combined focal length of the optical system 101 even if the illuminance of the subject is the same. Will change.

For example, when the object to be imaged is imaged with the synthetic focal length of the optical system 101 as the shortest distance, when the illuminance of the subject is equal to or more than the illuminance corresponding to the maximum gain setting voltage by the maximum gain setting power source 111 shown by L ₁₁ in FIG. If so, the AGC control circuit 105 controls the gain of the image pickup signal from the CCD image pickup device 103, and the output level of the image pickup signal supplied to the signal processing circuit 116 is 1 as shown by the solid line in FIG.
00IRE is fixed. Then, when the illuminance of the subject falls below the illuminance L ₁₁ corresponding to the maximum gain setting voltage by the maximum gain setting power supply 111, the imaging supplied to the signal processing circuit 116 regardless of the maximum gain of the AGC control circuit 105. The output level of the signal gradually decreases as the subject illuminance decreases, as indicated by the solid line in FIG. Note that the illuminance L ₁₁ corresponding to the maximum gain setting voltage by the maximum gain setting power supply 111 is referred to as the subject illuminance at which the gain of the AGC control circuit 105 becomes maximum at the shortest combined focal length. In addition, the subject illuminance L _{12 at} which the output level of the image pickup signal supplied to the signal processing circuit 116 is 50 IRE,
This is called the minimum subject illuminance at the shortest combined focal length.

When the object to be imaged is picked up with the combined focal length of the optical system 101 as the longest distance, the F drop phenomenon occurs in the optical system 101 as described above, the illuminance of the object is lowered, and at the shortest combined focal length. The gain of the AGC control circuit 105 becomes maximum before the subject illuminance L _{11 at} which the gain of the AGC control circuit 105 becomes maximum. Here, the illuminance L that maximizes the gain of the AGC control circuit 105.
₂₁ is the AGC control circuit 105 at the longest combined focal length
Is called the illuminance of the subject that maximizes the gain. Then, the AGC control circuit 10 when the illuminance of the subject is the longest combined focal length
If the subject illuminance L _{21 at} which the gain of 5 becomes maximum becomes lower,
Even though the gain of the AGC control circuit 105 is maximized, the output level of the image pickup signal supplied to the signal processing circuit 116 is, as indicated by the broken line in FIG. , Gradually decreases. here,
The subject illuminance L _{22 at} which the output level of the image pickup signal supplied to the signal processing circuit 116 is 50 IRE is referred to as the minimum subject illuminance at the longest combined focal length. Therefore, as a result of the F drop phenomenon occurring in the optical system 101, as shown in FIG. 10, the output level of the image pickup signal supplied to the signal processing circuit 116 is approximately 10 dB even if the illuminance of the subject is the same.
Will fall. As a result, the performance of the imaging device when the illuminance of the subject is low is significantly degraded.

To solve this, the luminous flux diameter of the imaging light passing through the iris 203 is set so that the luminous flux diameter of the imaging light passing through the iris 203 constituting the optical system 101 becomes larger than the aperture width of the iris 203. Therefore, it is necessary to increase the diameter of the first lens group 201. However, when the diameter of the first lens group 201 is increased, the weight is inevitably increased, which is not preferable for an image pickup apparatus in which size reduction and weight reduction are desired. Further, if the size of the first lens group 201 is increased, the cost also increases.

Therefore, the present invention has been made in view of the above circumstances, and when an object to be imaged is imaged with the combined focal length of the optical system set as the longest distance, even if an F drop phenomenon occurs in the optical system. The output level of the image pickup signal supplied from the charge-coupled device to the signal processing circuit is, for example, up to the illuminance at which the gain of the automatic gain adjusting means becomes maximum when the image pickup target is imaged with the synthetic focal length of the optical system as the shortest distance. It is an object of the present invention to provide an exposure control device that can be kept constant.

[0012]

SUMMARY OF THE INVENTION An exposure control apparatus according to the present invention has a lens system that makes it possible to change the focal length of light (imaging light) from an object to be imaged and an appropriate amount of light from the object to be imaged. An image is formed on the image pickup screen of the charge coupled device via an optical system having an iris for narrowing down the amount, and the aperture amount of the iris is adjusted based on the output level of the image pickup signal from the charge coupled device. An exposure control device comprising an iris aperture adjusting means and an automatic gain adjusting means for adjusting an output level of the image pickup signal, wherein the detecting means detects a zoom position of the lens system, and the zoom of the lens system. A storage unit that stores the amount of change in the output level of the imaging signal from the charge-coupled device due to the change in the F value with respect to the position
The storage unit outputs to the automatic gain adjustment unit a change amount of the output level of the image pickup signal from the charge coupled device corresponding to the zoom position information from the detection unit, and the automatic gain adjustment unit outputs from the charge image pickup device. The above problem is solved by changing the output level of the image pickup signal.

[0013]

In the exposure control apparatus according to the present invention, when the image pickup light is imaged on the image pickup screen of the charge coupled device via the optical system, the detecting means detects the zoom position of the lens system constituting the optical system. Then, the storage unit outputs the amount of change in the output level of the image pickup signal from the charge coupled device corresponding to the zoom position information from the detection unit to the automatic gain adjustment unit, and the automatic gain adjustment unit outputs the charge image pickup device. The output level of the image pickup signal from the charge-coupled device does not depend on the angle of view of the image pickup target because the output level of the image pickup signal from
It is constant with respect to the illuminance of the subject.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an exposure control apparatus according to the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the exposure control apparatus according to the present embodiment has a lens system 1 which makes the focal length of light from an object to be imaged variable and an appropriate amount of light from the object to be imaged. An image is formed on an image pickup screen of a charge-coupled device, a so-called CCD image pickup device 3, through an optical system 20 having an iris 2 for narrowing down. Based on an output level of an image pickup signal from the CCD image pickup device 3, The system includes an aperture correction control circuit 21 which is an iris opening degree adjusting means for adjusting the aperture amount of the iris 2 arranged in the system 20, and an AGC control circuit 22 which is an automatic gain adjusting means for adjusting the output level of the image pickup signal. Which is an exposure control device, and is a detection circuit 1 which is a detection means for detecting the zoom position of the lens system 1 arranged in the optical system 20.
4 and a ROM (Read Only Mem) which is a storage means for storing the amount of change in the output level of the image pickup signal from the CCD image pickup device 3 due to the change of the F value with respect to the zoom position of the lens system 1.
ory) 15 and the ROM 15 has the detection circuit 14
CCD image sensor 3 corresponding to the zoom position information from
The change amount of the output level of the image pickup signal from the AGC control circuit 22 is output to the AGC control circuit 22.
The output level of the image pickup signal from the D image pickup device 3 is changed.

The optical system 20 is a so-called zoom lens having a variable focal length.
A first lens group that configures a front lens unit that captures light from an imaging target (that is, imaging light), a second lens group that configures a variator that magnifies / reduces the imaging light, and a luminous flux diameter of the imaging light (or The iris 2 for adjusting the light amount), the third lens group for correcting the direction of the imaging light, the fourth lens group for forming a focus for imaging the imaging light on the imaging screen of the CCD image sensor 3, and the imaging light. It is composed of prisms for color separation. The second lens group corresponds to the lens system 1 described above, and is movable along the optical axis in a movable range restricted by the first lens group and the iris 2, for example. The combined focal length of the optical system 20 can be made variable without changing the position of the CCD image pickup device 3. In FIG. 1, only the lens system 1 and the iris 2 are shown.

Further, the aperture correction control circuit 21 includes a detection circuit 10 to which an image pickup signal from the CCD image pickup device 3 is supplied,
It is composed of a comparison circuit 11 to which an output from the detection circuit 10 and a reference voltage for diaphragm correction control from a reference power supply 12, that is, a so-called reference voltage are supplied, and an iris drive circuit 13 to which a comparison result by the comparison circuit 11 is supplied. Has been done. A drive motor or the like is applied to the iris drive circuit 13, for example. Further, the AGC control circuit 22 includes an AGC circuit 4 to which an image pickup signal from the CCD image pickup device 3 is supplied, a detection circuit 6 to which an output from the AGC circuit 4 is supplied, an output from the detection circuit 6 and a reference power supply 8. A comparison circuit 7 to which a reference voltage for AGC adjustment, a so-called reference voltage is supplied, and a CCD image pickup device 3 corresponding to the comparison result by the comparison circuit 7 and zoom position information from the detection circuit 14 output from the ROM 15 The limiter 9 is supplied with the amount of change in the output level of the image pickup signal.

Here, a case will be described in which an image pickup target is imaged by an image pickup apparatus to which the exposure control apparatus of the present embodiment is applied. First, the light from the imaged object (that is,
The imaging light) is imaged on the imaging screen of the CCD imaging device 3 via the optical system 20. At this time, since the combined focal length can be changed by operating the lens system 1 that constitutes the optical system 20 along the optical axis direction, the angle of view is continuously changed and the object to be imaged is changed. It can be imaged.
That is, when the lens system 1 is operated along the optical axis in the movable range toward the object to be imaged, the object to be imaged can be imaged in a wide angle with the combined focal length of the optical system 20 as the shortest distance. 1 is CC in the movable range along the optical axis direction.
When operated on the D imaging element 3 side, imaging can be performed with the combined focal length of the optical system 20 as the maximum distance. The position of the lens system 1 where the combined focal length of the optical system 20 is the shortest distance (hereinafter, this is referred to as the zoom position) is referred to as the zoom position having the shortest combined focal length, and the combined focal point of the optical system 20 is also referred to. The zoom position of the lens system 1 having the longest distance is referred to as the zoom position having the longest combined focal length.

Then, the image pickup signal from the CCD image pickup device 3 is supplied to the aperture correction control circuit 21, and the aperture correction control is performed. That is, in the aperture correction control circuit 21, C
When the output signal from the CD image pickup device 3 is supplied to the detection circuit 10, for example, average detection is performed. The detection output from the detection circuit 10 is supplied to the inverting input terminal of the comparison circuit 11. At this time, the reference voltage from the reference power supply 12 is supplied to the non-inverting input terminal of the comparison circuit 11. As a result, the comparison circuit 11
The detection output from the detection circuit 10 to the inverting input terminal is compared with the reference voltage from the reference power supply 12 to the non-inverting input terminal. Then, the comparison result by the comparison circuit 11 is supplied to the iris drive circuit 13. The iris 3 is driven and controlled by the output from the iris driving circuit 13.

Further, the image pickup signal from the CCD image pickup device 3 is supplied to the AGC control circuit 22 to perform AGC control. At this time, the above-described zoom position of the lens system 1 is detected by the detection circuit 14. This detection circuit 14
2 is a variable resistor 16 for detecting the zoom position of the lens system 1, and an analog / digital (A / D) converter 1 to which the output from the variable resistor 16 is supplied.
7 and 7. Then, both ends of the variable resistor 16 are fixed biased, and the arm tip installed in the lens barrel of the lens system 1 slides on the variable contact portion of the variable resistor 16 as the lens system 1 moves. Is configured. Therefore, the zoom position of the lens system 1 is detected as a variable voltage by the variable resistor 16. When the output from the variable resistor 16 is supplied to the A / D converter 17, the A / D converter 17 subjects the zoom position information of the lens system 1 from the variable resistor 16 to A / D conversion, The digitized zoom position information of the lens system 1 is stored in the ROM 15
Is supplied to.

The ROM 15 stores, for example, the amount of change in the output level of the image pickup signal corresponding to the zoom position of the lens system 1 shown in FIG. From the CCD image pickup device 3 to the signal processing circuit 1
The output level of the image pickup signal supplied to 6 becomes lower than the theoretical F value in which the F value of the optical system 20 corresponds to the zoom position of the lens system 1 and is determined by the combined focal length and the incident light beam diameter d of the image pickup light. It decreases with the decrease. That is, as shown in FIG. 3, the lens system 1 moves within the movable range by 0 mm in FIG.
3 from the zoom position which is the shortest combined focal length shown in FIG.
When operated toward the zoom position having the longest combined focal length indicated by medium 20 mm (therefore, in this embodiment, the movable range of the lens system 1 is 20 mm), the zoom position of the lens system 1 is from 0 to 18 mm. The output level of the image pickup signal gradually decreases to 4.5 dB during the operation, and the F drop phenomenon occurs in the optical system 20 while the zoom position of the lens system 1 is operated up to 18 to 20 mm. The output level of 1 drops sharply to 10 dB. The output signal from the detection circuit 14 is the ROM.
When supplied to the limiter 15, the ROM 15 supplies the change amount information of the output level of the image pickup signal corresponding to the zoom position of the lens system 1 to the limiter 9 constituting the AGC control circuit 22. Therefore, the output signal from the A / D converter 17 constituting the detection circuit 14 is used as the address signal of the ROM 15.

Then, in the AGC control circuit 22,
The output signal from the CCD image pickup device 3 is first supplied to the detection circuit 6 via the AGC circuit 4, and the detection output by the detection circuit 6 is supplied to the inverting input terminal of the comparison circuit 7. At this time, the non-inverting input terminal of the comparison circuit 7 is supplied with the reference voltage for AGC adjustment from the reference power supply 8, that is, a so-called reference voltage. Then, the comparison circuit 7 compares the detection output from the detection circuit 6 to the inverting input terminal with the reference voltage from the reference power supply 8 to the non-inverting input terminal, and the comparison result is supplied to the limiter 9. As described above, the limiter 9 is supplied with the change amount information of the output level of the image pickup signal corresponding to the zoom position of the lens system 1 by the ROM 15. As a result, the limiter 9 performs the amplitude limiting process on the output from the comparison circuit 7 with the output from the ROM 15 as the upper limit set value. Then, this result is supplied to the AGC circuit 4. Then, this AGC circuit 4 has a limiter 9
The output level of the image pickup signal from the CCD image pickup device 3 is controlled based on the output of In this way, by controlling the gain of the AGC control circuit 22, the signal processing circuit 5
The output level of the image pickup signal supplied to is constant with respect to the illuminance of the subject regardless of the angle of view of the image pickup target, that is, the combined focal length of the optical system 20.

Here, when the image pickup signal from the CCD image pickup device 3 is supplied to the aperture correction control circuit 21 and the AGC control circuit 22 which constitute the exposure control apparatus of this embodiment, the gains of the respective circuits 21 and 22 are changed. The change will be described with reference to FIG. The upper part of FIG. 4 shows a gain curve showing the change of the gain of the iris 3 with respect to the illuminance of the subject, and the lower part of FIG. 4 shows the gain curve showing the change of the gain of the AGC circuit 4 with respect to the illuminance of the subject. ing. Further, among the gain curves shown in FIG. 4, each of the gain curves shown by a solid line shows a change in gain when the combined focal length of the optical system 20 is set to the shortest distance so that the object to be imaged is imaged at a wide angle. Further, each gain curve indicated by a broken line shows a change in gain when the combined focal length of the optical system 20 is the longest distance.

For example, when the object to be imaged is imaged with the synthetic focal length of the optical system 20 as the shortest distance, the aperture width of the iris 2 becomes maximum due to the decrease in the illuminance of the object.
The gain of the aperture correction control circuit 21 gradually increases. That is, the aperture width of the iris 2 gradually increases as the subject illuminance decreases. At this time, the AGC control circuit 22
The gain of is supposed to be constant. Then, after the aperture width of the iris 2 becomes maximum, the aperture correction control circuit 21
While the gain of the AGC control circuit 22 is constant, the gain of the AGC control circuit 22 is decreased until the subject illuminance reaches the subject illuminance L _{11 at} which the gain of the AGC control circuit 22 becomes maximum at the shortest combined focal length. It gets bigger and bigger.
Then, the AGC at the shortest combined focal length when the subject illuminance is
After the illuminance L _{11 of the} subject at which the gain of the control circuit 22 is maximized, the gain of the AGC control circuit 22 is kept constant. When the combined focal length of the optical system 20 is the shortest distance, the gain of the aperture correction control circuit 21 is maximized, and A
The illuminance L _{31 at} which the gain of the GC control circuit 22 starts to increase is determined by the aperture correction control circuit 21 and the AGC at the shortest combined focal length.
This is called the subject illuminance at which the gain of the control circuit 22 is switched.

Further, the synthetic focal length of the optical system 20 is set to the shortest distance.
When imaging an object to be imaged as a separation, the illuminance of the subject is still
Coupled with the decrease in
Then, the gain of the aperture correction control circuit 21 gradually increases.
However, in this case, at the above-mentioned shortest combined focal length
The gains of the aperture correction control circuit 21 and the AGC control circuit 22 are turned off.
Subject illumination to be changed L₃₁Optical system 2 with brighter subject illuminance
Since the F drop phenomenon occurs at 0, the aperture correction control
The gain of the path 21 is determined by the beam diameter of the imaging light passing through the iris 2.
It will be the maximum. Here, the effective maximum of the aperture correction control circuit 21
Subject illuminance L_{twenty one}At the maximum combined focal length
The gains of the noise correction control circuit 21 and the AGC control circuit 22 are switched.
This is called the subject illuminance. And pass through iris 2
The luminous flux diameter of the image pickup light of the rear lens of the first lens group 201
Since it is determined by the diameter, it should be placed at the longest combined focal length.
The gain of the aperture correction control circuit 21 and the AGC control circuit 22
Subject illuminance L to switch_{twenty one}Even if the subject illuminance decreases,
The effective gain of the correction controller 21 is constant. So
Then, the effective gain of the aperture correction control circuit 21 is maximized.
After that, the gain of the AGC control circuit 22 is
Of the image pickup signal corresponding to the zoom position of these lens systems 1
Based on the level change information, the illuminance of the subject is the shortest synthetic focus.
The gain of the AGC control circuit 22 becomes maximum at the point distance
Subject illuminance L ₁₁Until the subject illuminance decreases
It gets bigger and bigger. Then, the gain of the AGC control circuit 22
Is the AGC control when the subject illuminance is the shortest combined focal length
Subject illuminance L that maximizes the gain of the circuit 22₁₁Since
Descending, constant.

Therefore, when the object to be imaged is imaged, the output level of the image pickup signal supplied to the signal processing circuit does not depend on the angle of view of the object to be imaged, that is, the combined focal length of the optical system. Is made constant.

Although one embodiment of the exposure control apparatus according to the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the concept of the present invention. For example, as shown in FIG. 5, in the subsequent stage of the AGC control circuit 22, the output level of the image pickup signal supplied to the signal processing circuit is made constant from the ROM 15 to the illuminance of the subject regardless of the combined focal length of the optical system. The AGC control circuit 22 based on the change amount information of the output level of the image pickup signal
A gain control amplifier circuit 18 for increasing the output of the above may be provided. At this time, the AGC control circuit 22 and the AGC circuit 4 to which the image pickup signal from the CCD image pickup device 3 is supplied,
The detection circuit 6 to which the output from the AGC circuit 4 is supplied, the output from the detection circuit 6 and the A from the reference power supply 8.
It may be composed of a comparison circuit 7 to which a reference voltage for GC adjustment is supplied. As a result, the same effect as that described above can be obtained. Since the other configurations are similar to those of the above-described embodiment, detailed description will be omitted.

[0028]

As is apparent from the above description, according to the exposure control apparatus of the present invention, the detecting means for detecting the zoom position of the lens system and the change of the F value with respect to the zoom position of the lens system are detected. And a storage unit for storing the amount of change in the output level of the image pickup signal from the charge coupled device, the storage unit outputting the image pickup signal from the charge coupled device corresponding to the zoom position information from the detection unit. The amount of change in level is output to the automatic gain adjusting means, and the automatic gain adjusting means changes the output level of the image pickup signal from the charge image pickup device. It is constant with respect to the illuminance of the subject regardless of the angle of view of the object. Therefore, it is possible to improve the performance deterioration in the conventional imaging device when the illuminance of the subject is low.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of an exposure control apparatus according to the present invention.

FIG. 2 is a block diagram showing a schematic configuration of a detection circuit constituting an exposure control device according to the present invention.

FIG. 3 is a characteristic diagram showing a change in output level of an image pickup signal based on an F drop phenomenon with respect to a position of a lens system that constitutes an optical system.

FIG. 4 is a characteristic diagram showing changes in the gain of the AGC control circuit and changes in the gain of the iris of the optical system with respect to the illuminance of the subject.

FIG. 5 is a block diagram showing a schematic configuration of another embodiment of the exposure control apparatus according to the present invention.

FIG. 6 is a block diagram showing a schematic configuration of a conventional exposure control apparatus.

FIG. 7 is a side view showing a state where the combined focal length of the zoom lens is set to the shortest distance.

FIG. 8 is a side view showing a state where a combined focal length of the zoom lens is set to an intermediate distance.

FIG. 9 is a side view showing a state where the combined focal length of the zoom lens is set to the longest distance.

FIG. 10 is a characteristic diagram showing a change in output level of an image pickup signal with respect to illuminance of a subject.

[Explanation of Codes] 1 ・ ・ ・ ・ ・ Lens system 2 ・ ・ ・ Iris 3 ・ ・ ・ CCD image sensor 14 ・ ・ ・ Detection circuit 15 ・ ・ ・ ・ ・ ROM 20 ・ ・ ・ ・ ・Optical system 21 ・ ・ ・ Aperture correction control circuit 22 ・ ・ ・ ・ ・ AGC control circuit

Claims (1)

[Claims] 1. Charge coupling through an optical system including a lens system that allows light from an image-capturing object to have a variable focal length and an iris that restricts the amount of light from the image-capturing object to an appropriate amount. Iris aperture adjusting means for adjusting the aperture amount of the iris based on the output level of the image pickup signal from the charge-coupled device and an automatic gain for adjusting the output level of the image pickup signal. An exposure control apparatus comprising: an adjusting unit; a detecting unit that detects a zoom position of the lens system; and an image pickup signal from the charge-coupled device according to a change in F value with respect to the zoom position of the lens system. A storage unit for storing a change amount of the output level, wherein the storage unit obtains the change amount of the output level of the image pickup signal from the charge coupled device corresponding to the zoom position information from the detection unit by the automatic acquisition The exposure control device is characterized in that the automatic gain adjustment means changes the output level of the image pickup signal from the charge image pickup device.