JPH0229273B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an exposure amount control device for an imaging apparatus having an imaging means for converting a subject image into an electrical signal.

<Description of Prior Art> Conventionally, so-called auto iris is used in an imaging apparatus for shooting a moving image, which controls the aperture value of an aperture by detecting the level of a video signal obtained by an imaging means. Since the output signal of the imaging means is used in this way, it is possible to control the exposure amount with high precision.

Recently, due to advances in semiconductor technology, CCD,
BACKGROUND ART Solid-state imaging devices such as BBD have been developed, and along with advances in magnetic recording technology, imaging devices that capture still images have also been proposed. When photographing still images, if the exposure amount is not controlled quickly, so-called shutter speed will be missed, so it is desirable to have auto iris operation at all times, but this is not possible in terms of power consumption. Therefore, it is possible to separate the power switch and release switch, but in this case, the time (T1) required for the image sensor and signal processing circuit to stabilize and find the appropriate aperture value after turning on the power switch, When the aperture deviates significantly from the appropriate value, it takes time (T2) to drive the aperture to the appropriate value.

On the other hand, in a conventional camera using a silver halide film, an external photometric element such as an SPC is used as a photometric means, so that exposure control is simple and rapid control is possible. However, when such a method is used, it is inferior to control based on the output of the imaging means in terms of accuracy.

<Objective of the Invention> The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide an exposure amount control device that is capable of rapid and highly accurate exposure control and is suitable for a still image imaging device.

<Description of Embodiments> FIG. 1 is a perspective view of a portion of a still image video camera to which the present invention can be applied.

In the figure, 10 is an aperture ring, 11 is an aperture blade, and 12 is a protruding member fixed to the ring 10 and has a long hole 12a. 13 is an aperture control arm having a pin 13a. Reference numeral 14 denotes an aperture drive motor, and its drive shaft 14a is fixed to the control arm 13. 15 is a half mirror, 16 is a shutter blade, 17 is a shutter drive motor and its drive shaft 10
a is fixed to the shutter blade 16. 18 is a frame transfer type CCD, and 19 is a photometric element.

The driving force of the aperture drive motor 14 is the control arm 1
3. The protruding member 1 is inserted through the pin 13a and the elongated hole 12a.
2 and rotates the aperture ring 10. The rotation of the aperture ring 10 drives the aperture blades 11 and controls the aperture area. A portion of the subject light passing through the aperture is projected onto a photometric element 19 by a half mirror 15, and at the same time is imaged onto the CCD 18 surface. Further, the shutter blade 16 is driven by the motor 17 to rotate at, for example, 60 rpm, and prohibits the irradiation of subject light to the CCD 18 while the CCD 18 is in the transfer operation.
Prevents smearing.

An example of a circuit suitable for controlling such a mechanism is shown in FIG.

In FIG. 2, 20 is a shutter drive circuit;
1 is a phase detection circuit for the motor 17, 22 is a phase control circuit, 23 is a block generator, 24 is a CCD drive circuit, 25 is a signal processing circuit, 26 is an aperture drive circuit that controls the aperture drive motor 14, 28 is an amplifier,
29 is an AND gate, 30 is an inverter, 31,
32 is an analog switch.

The operation of the circuit shown in FIG. 2 will be explained with reference to the time chart shown in FIG.

When the power is turned on by a power switch (not shown), power is supplied to each part shown in FIG. The output clock of the clock generator 23 is supplied to the phase control circuit 2.
2. CCD drive circuit 24 and signal processing circuit 25
supplied to The phase control circuit 22 outputs a phase error signal to the shutter drive circuit 2 using the output signal of the phase detection circuit 21 and the output clock of the clock generator 23.
0 and controls the phase of the motor 17. At the same time, when the phases match, a phase lock signal (FIG. 3e) is output to one input terminal of the AND gate 29.

Further, the CCD drive circuit 24 sends to the CCD 18 a signal instructing the imaging section of the CCD 18 to accumulate, a vertical transfer clock (FIG. 2b), and a horizontal transfer clock (FIG. 2c) for reading out the imaged charge. And time T1~
During T2, unnecessary charges in the imaging section are sent to the storage section by the vertical transfer clock, and then sent to the outside by the horizontal transfer clock. When the unnecessary charges are cleared and the next readout starts by the horizontal transfer clock, the drive circuit 24 is the clear completion signal (Fig. 3 d)
is output to the other input terminal of the AND gate 29. By outputting both the clear completion signal and the phase lock signal, the output signal of the AND gate 29 (FIG. 3f) becomes high level.

Therefore, before that, the analog switch 32 was closed by the output of the inverter 30, and the photometric element 1
A photometric signal obtained by amplifying the output of 9 by an amplifier 28 is transmitted to an aperture drive circuit 26, and the aperture area of the aperture is controlled.

When the output signal of the AND gate 29 becomes high level, the switch 32 is opened.
Close 1. The output of the CCD 18 is then transmitted to the aperture drive circuit 26 via the signal processing circuit 25.
The aperture diameter of the diaphragm is controlled by the output of the imaging means itself.

In this way, the aperture is controlled in advance to a close to accurate value using a photometric means other than the imaging means before the imaging means such as CCD and the shutter etc. operate normally, so the aperture can be controlled by the output of the imaging means. Since the amount can be significantly reduced, control time can be significantly shortened. Moreover, since the aperture is ultimately controlled using the output of the imaging means, extremely high-precision exposure control is possible.

Incidentally, at the output of the signal processing circuit 25, a voltage proportional to a value obtained by weighting and summing the charge levels of each pixel in one screen is generated. Depending on the weighting method, average photometry, center-weighted photometry, partial photometry, etc. are possible, but since these are well known, detailed explanations will be omitted. In this way, various photometry methods can be selected.

FIG. 4 shows a time chart of another control embodiment using the circuit elements shown in FIG. 2.

In FIG. 4, a is a power supply, b is a synchronizing signal applied to the phase control circuit 22, c is a phase lock signal, d is a vertical transfer clock, e is a horizontal transfer clock, and f is an ON signal of the switch 31, respectively. .

After the power is turned on, the shutter drive circuit 20, phase control circuit 22, clock generator 23,
When power is supplied to the aperture drive circuit 26 and amplifier 28 and a phase lock signal is obtained, power is supplied to the CCD drive circuit 24 and signal processing circuit 25.
Then, the vertical transfer clock and horizontal transfer clock, which have a higher frequency than the normal clock frequency, are transferred to the CCD.
18, and unnecessary charges are removed from time T3 to T4.
It is carried out rapidly between. Charges are accumulated in the CCD 18 between times T4 and T5, and the accumulated charges are read out by the horizontal transfer clock from time T6. At this time T6, the control of the aperture drive circuit 26 is changed from control based on the output of the photometric element 19 to the signal processing circuit 2.
This is to switch to control based on the output of No.5. This is because the time required to control the phase of the shutter is much longer than the time required to clear the CCD, and with this configuration, unnecessary power consumption can be avoided.

Although specific wiring for this embodiment is not shown, those skilled in the art can naturally implement it.

In this embodiment, the photometry means is switched using the phase lock signal and the clear completion signal, but the photometry means may be switched using the output of a timer circuit that takes into account the time required for these steps. Furthermore, when controlling the storage time of the CCD, there is no need to use a shutter means, and only a clear completion signal of the CCD, etc., or when an image pickup tube is used, it can be detected that the heater has sufficiently warmed up. The photometry method can be switched simply by doing this.

Further, in this embodiment, photometry is performed using a half mirror, but since the photometry accuracy of an external photometry element may be rough, it may be placed in front of the diaphragm.

Also, frame transfer type is used as an imaging means.
Although a CCD was used, other solid-state image pickup devices or image pickup tubes can also be used.

<Description of Effects> The present invention controls the light amount control member to a certain degree of correct light amount control value using a photometric means other than the imaging means before the imaging means operates normally, and then controls the light amount control member to a certain degree of correct light amount control value by the time the imaging means operates normally. The light amount control member is controlled to an appropriate light amount control value based on the output. This configuration enables highly accurate exposure control in a short time and provides an extremely large degree of freedom in photometry format.

[Brief explanation of drawings]

Fig. 1 is an exploded perspective view of a part of the still image video camera of this embodiment, Fig. 2 is a control circuit diagram, Fig. 3 is an operation timing diagram of each part of Fig. 2, and Fig. 4 is another control example. FIG. 2 is an operation timing diagram. In the figure, 14 is an aperture drive motor, 17 is a shutter drive motor, and 18 is a frame transfer type.
CCD, 19 is a photometric element, 20 is a shutter drive circuit, 22 is a phase control circuit, 23 is a clock generator, 24 is a CCD drive circuit, 25 is a signal processing circuit,
Reference numeral 26 indicates an aperture drive circuit.

Claims (1)

[Scope of Claims] 1. An imaging device that converts a subject image into an electrical signal; A photometric device other than the imaging device that detects the brightness of the subject image; and a light amount limiting member that limits the amount of light irradiated to the imaging device. and a switching means for selectively using the output of the photometry means and the output of the imaging means to drive and control the light quantity limiting member, and the switching means driving and controlling the light quantity limiting member according to the output of the photometry means. control means for sequentially switching and controlling the switching means so as to make fine adjustment of the exposure amount by driving and controlling the light amount limiting member according to the imaging output of the imaging means after roughly adjusting the exposure amount; An exposure amount control device comprising: