JPS63204237A - Automatic iris circuit for image pickup device - Google Patents

Abstract

PURPOSE:To prevent hunting from occurring in a high-brightness state by providing a stop detecting means which detects a stop-down quantity and making the response of an iris control loop lower as the stop-down quantity is larger according to the detection result of the stop detecting means. CONSTITUTION:When a stop is rather closed to a stop-down quantity larger than a preset value, the output voltage of the stop detecting element 13 rises above a reference voltage and a comparing circuit 14 outputs a signal which turns on a switch 16. The parallel circuit of damping resistances R1 and R2 is therefore formed and the value of the resistance R(=R1XR2/R1+R2) of this parallel circuit becomes smaller than when only the R1 is provided, so that damping effect increases. Consequently, when the stop is rather closed in a high-brightness state, the response speed of the stop 3 is slowed down and hunting becomes hard to occur.

Description

[Detailed description of the invention] The present invention will be described in the following order.

A. Field of application in business B1 Overview of the invention C9 Prior art [Fig. 3] D1 Problem to be solved by the invention E0 Means for solving the problem F0 Effect G. Examples [Fig. 1, Figure 26 H0 Effects of the Invention (A, Industrial Application Field) The present invention relates to an auto-iris circuit for an imaging device, and particularly to an auto-iris circuit for an imaging device that prevents hunting from occurring when the aperture is close to closing.

(B. Summary of the Invention) The present invention prevents aperture hunting that occurs when attempting to photograph a high-brightness subject while improving responsiveness under normal photographing conditions in an auto-iris circuit of an imaging device. Therefore, an aperture detection means is provided so that the response becomes low when the amount of aperture is large.

(c, prior art) [Figure 3] The brightness of a subject on a video camera varies depending on the subject.
Since the brightness varies over a wide range from 100,000 to 100,000 lux, video cameras are provided with an iris to ensure that the brightness on the surface of the image sensor becomes an appropriate brightness.

Such video cameras are generally equipped with an auto-iris function that automatically controls the iris in order to always provide a constant brightness to the image sensor regardless of changes in the brightness of the subject. The auto iris function is a function that increases the amount of aperture when the subject is bright, and conversely decreases the amount of aperture when it is dark, so that the brightness on the image sensor surface is always constant. Therefore, it can be said that the iris plays a role as a variable attenuator of 80 dB (100,000 to 100,000 lux).

FIG. 3 shows an example of a conventional auto iris circuit, in which 1 is an image sensor made of, for example, a CCD, 2 is an image sensor, 3 is an aperture, 4 is an amplifier that amplifies the output signal of the image sensor 1, and 5 is a gate circuit. , 6 is a level detection circuit, 7 is a comparison circuit, and 8 is an aperture driving means, which includes a drive coil 9 and a damping coil 10. 11 is an adder, 12 is a reference voltage source, and R1 is a damping resistor.

Next, the operation of this circuit will be explained. A video signal from the image sensor 1 is amplified by the amplifier 4 and sent to a video processor (not shown).

Further, this video signal is transmitted to a level detection circuit 6 via a gate circuit 5. The output signal of the level detection circuit 6 is added to the voltage generated by the damping coil 10 by an adder 11. A comparison circuit 7 compares the output signal of the adder 11 with a reference voltage, and controls the aperture 3 by driving the drive coil 9. damping coil 1
0 is wound together with the drive coil 9 (that is, magnetically coupled to each other), and has the function of suppressing changes in the current flowing through the drive coil 9. Therefore, it plays the role of slowing down the change in the aperture amount. R1 is a damping resistor, and the larger the resistor R1, the smaller the current flowing through the damping coil 10, and therefore the smaller the turn pink effect.

In this auto-iris circuit, when the subject is bright and the brightness on the imaging surface of the image sensor 1 becomes too bright, the level of the output signal of the amplifier 4 becomes too high. the result,
The comparator circuit 7 outputs a signal that drives the aperture 3 in the direction of closing, the aperture amount increases, and the brightness on the imaging surface of the image sensor 1 is brought to normal brightness. In this way, the auto iris circuit forms a closed iris control loop.

(D. Problem to be Solved by the Invention) By the way, in the auto iris circuit, the transmission gain increases as the aperture amount increases due to the structure of the aperture 3. This is because when the diaphragm 3 is in a slightly closed state, even if the diameter of the aperture changes slightly, the brightness on the imaging plane will change greatly, and the rate of change in brightness will take on a large value. Therefore, the responsiveness of the auto iris control loop changes depending on the brightness of the subject, and when photographing a high-brightness subject, the aperture tends to close, so the transmission gain increases. As a result, there is a problem in that hunting is more likely to occur.

Of course, hunting can be prevented by lowering the responsiveness of the iris control loop by, for example, reducing the damping resistor R1, but if you do this, it will be difficult to prevent hunting when shooting a subject with normal or low brightness. When the response becomes too low, the aperture amount cannot respond quickly to changes in brightness.

The present invention has been made to solve these problems, and is capable of photographing high-brightness objects without reducing responsiveness when photographing objects with normal brightness or lower brightness than normal brightness. The purpose of this is to prevent hunting from occurring when

(E. Means for Solving Problems) In order to solve the above problems, the auto iris circuit of the imaging device of the present invention is provided with an aperture detection means for detecting the amount of aperture, and based on the aperture detection result, when the amount of aperture is large, The responsiveness is changed so that the responsiveness becomes lower.

(F. Effect) According to the auto iris circuit of the imaging device of the present invention, the aperture detection means detects whether or not the aperture with a high transmission gain is close to closing, and when the aperture is in that state, the responsiveness of the aperture increases. be lowered.

Therefore, hunting can be prevented without reducing responsiveness when photographing a subject with normal brightness or low brightness.

(G. Embodiment) [FIGS. 1 and 2] The auto-iris circuit of the imaging apparatus of the present invention will be described in detail below according to the illustrated embodiment.

FIG. 1 shows one embodiment of an auto-iris circuit of an imaging apparatus of the present invention, and FIG. 2 shows an outline of an aperture drive mechanism.

In the drawings, 1 is an imaging element, 2 is an imaging lens, 3 is an aperture, 4 is an amplifier, 5 is a gate circuit, 6 is a level detection circuit,
7 is a comparison circuit, 8 is an aperture drive means, and a drive coil 9
and a damping coil 10. 11 is an adder, 12 is a reference voltage source, and R1 is a damping resistor, which is the same as the configuration of the conventional auto-iris circuit shown in FIG. 3.

Reference numeral 13 denotes an aperture detection element, which is made of, for example, a Hall element, and is provided close to the movable magnet 17 of the aperture drive mechanism that drives the aperture 3 shown in FIG. It detects the aperture amount, converts it into an electrical signal, and outputs it. A drive coil 9 and a damping coil 10 are integrally wound around the movable magnet 17, and these two coils 9
．． 10 is fixed. When the movable magnet 17 rotates in response to the electromagnetic force generated by the current flowing through the drive coil 9, the diaphragm 3 is driven via the transmission member 18, and the degree of closing of the opening 0 is controlled.

A comparison circuit 14 receives the output signal of the aperture detection element 13 at its non-inverting input terminal, receives the reference voltage from the reference voltage source 15 at its inverting input terminal, and compares the two. R2 is a second dubbing resistor, which is connected in series with the switch 16, and this series circuit is connected in parallel with the damping resistor R1. The comparison circuit 14 then controls the opening and closing of the switch 16. Specifically, when the aperture amount is close to being larger than a preset value, the output voltage of the aperture detection element 13 becomes higher than the reference voltage. Then, the comparison circuit 14 outputs a signal that turns on the switch 16. Then, a parallel circuit of damping resistors R1 and R2 is formed, and the resistance R of this parallel circuit (=R1xR2/
The value of R1+R2) is smaller than that of R1 alone.

As a result, the damping effect becomes larger.

This is because resistor R1 or R is tamping coil 1
0 in series to reduce the current flowing through the coil 10. Therefore, when the current flowing through the drive coil 9 changes drastically and the amount of throttling is about to change greatly, the damping coil 10 works to slow down the change in the current flowing through the drive coil 9. The smaller the resistance value, the stronger it becomes. Therefore, when the switch 16 is turned on, the damping effect increases.

Therefore, when the diaphragm 3 is almost closed at high brightness, the response speed of the diaphragm 3 becomes slow and hunting is less likely to occur.

On the other hand, when the aperture amount is smaller than a preset value, that is, when the brightness is normal or low, the output voltage of the aperture detection element 13 becomes lower than the reference voltage, and the comparison circuit 1
4 does not generate an output voltage that turns on the switch 16. Therefore, the switch 16 is turned off and the damping resistor is composed only of R1, so that the resistance value of the damping resistor becomes larger than the resistance value of the parallel combined resistor of R1 and R2, and the damping effect becomes weaker. As a result, responsiveness becomes higher.

As is clear from the above, hunting can be prevented from occurring at high brightness without reducing the responsiveness of the iris control loop at normal brightness or low brightness.

In this embodiment, the damping resistor is switched depending on whether the circuit is close to closed or not, but the same effect can be obtained by switching the gain and frequency characteristics of the entire circuit according to the detection result.

(H, Effect of the Invention) As described above, the auto iris circuit of the imaging device of the present invention includes an aperture detection means for detecting the amount of aperture, and the response of the iris control loose is determined based on the detection result of the aperture detection means. This is characterized in that the response is controlled to be low when the aperture amount is large.

Therefore, according to the auto iris circuit of the imaging device of the present invention, the response of the aperture is lowered when the aperture amount is large to photograph a high-brightness subject, so the response of the aperture is lowered when the aperture is used to photograph a high-brightness subject. It is possible to prevent hunting from occurring at the bottom.

[Brief explanation of the drawing]

1 and 2 are for explaining one embodiment of the auto iris circuit of the imaging device of the present invention, FIG. 1 is a block diagram of the auto iris circuit, FIG. 2 is a schematic diagram of the aperture drive mechanism, FIG. 3 is a block diagram of a conventional example. Explanation of symbols 1...Image sensor, 3...Aperture, 9...Drive coil, 10...Rimbling coil, 13...Aperture detection means, 14...Comparison circuit, 16... switch, R1, R2
...damping resistance. Figure 3

Claims (1)

[Claims] (1) An aperture detection means for detecting the amount of aperture is provided, and based on the detection result of the aperture detection means, the responsiveness of the iris control loop is controlled such that when the amount of aperture is large, the responsiveness becomes low. An auto iris circuit for an imaging device characterized by