JPS63316573A - Image pickup device - Google Patents

Abstract

PURPOSE:To prevent a photographing chance from being missed by arranging a liquid crystal filter in front of an image pickup device and control ling light transmissivity so that the filter acts as an optimum light reducing filter. CONSTITUTION:The liquid crystal filter 4 is arranged between a lens and an image pickup tube 2. The filter 4 consists of polarizing plates 4A, 4E, transparent electrodes 4B, 4D and TN-type liquid crystal plate 4C. The output voltage 2a of the tube 2 is impressed between the electrodes 4B, 4D through a filter driving circuit 3. When the polarizing plates 4A, 4E are arranged in parallel and the voltage is impressed between the electrodes 4B, 4D to make the TN-type liquid crystal transparent, an output equivalent to a case removing the filter 4 is obtained from the tube 2. When an input signal 2a is less than a determined threshold, the driving circuit 3 outputs a fixed voltage for making the liquid crystal transparent. When the input signal 2a exceeds the threshold, the output voltage is dropped from the fixed value and the light transmissivity of the filter 4 is reduced so that the tube 2 can be prevented from being saturated. Consequently, the optimum light reduction can be instantaneously obtained and a photographing chance is not missed.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to improvements in imaging devices.

[Conventional technology]

In an imaging device such as a television camera, the amount of incident light during shooting is determined by the aperture mechanism of the optical lens.

Optimal adjustment is made by changing the amplification degree of the image pickup tube. However, this adjustment range has a limit, and when the amount of incident light exceeds this range, a neutral density filter is installed before, after, or in the middle of the optical lens to prevent the image pickup tube output from becoming saturated.

[Problem that the invention seeks to solve]

As mentioned above, with conventional imaging devices, it is necessary to attach and remove a neutral density filter according to the amount of light7, and it is not possible to obtain the necessary amount of light attenuation under shooting conditions that require instantaneous shooting. There was a drawback.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks and provide an imaging device that can instantaneously obtain the required amount of light attenuation without the need to attach or remove a dark filter.

[Means for solving problems]

The imaging device of the present invention includes a liquid crystal filter on the front surface thereof,
When the output voltage of the imaging device exceeds a certain threshold,
The light transmittance of the liquid crystal filter is controlled by the output voltage, so that the liquid crystal filter can operate as a dark filter having an optimal amount of light attenuation. In this case, the liquid crystal filter refers to a filter that controls the light transmittance of a liquid crystal plate by applying a voltage.

Say something.

〔Example〕

An embodiment of the present invention will be described below. FIG. 1 is a schematic configuration diagram of an embodiment, in which a liquid crystal filter 4 is disposed between an optical lens section 1 and an image pickup tube 2. In FIG. LCD filter 4
consists of 4A and 4E polarizing plates, 4B and 4D transparent electrodes, and 4C TN type liquid crystal plate. The output voltage 2a of the image pickup tube 2 is input to the filter drive circuit 3, and the transparent electrode 4 of the liquid crystal filter 4
The voltage applied between B and 4D is supplied from the filter drive circuit 3.

Polarizing plates 4A, 4E=i arranged in parallel, transparent electrodes 4B, 4
When a sufficient voltage is applied across D to make the TN type liquid crystal transparent, the image pickup tube 2 can obtain almost the same output as when no liquid crystal filter 4 is provided. If the human input signal 2a is below a predetermined threshold, the filter drive circuit 3 outputs a constant voltage sufficient to make the TN type liquid crystal transparent. The human input signal 2a is the output voltage of the image pickup tube 2, and when the amount of incident light is large and the output is in the saturation region or close to it, the filter drive circuit 3
Exceeds the threshold set in . Then, the output voltage of the filter drive circuit 3 decreases to a certain level, the light transmittance of the liquid crystal filter 4 decreases, and saturation of the image pickup tube 2 can be prevented.

FIG. 2 shows a transparent electrode 4B obtained by the above control.

This figure shows how the voltage between 4D changes depending on the amount of incident light. The output of the image pickup tube 2 corresponding to the amount of light indicated by P at which the amount of incident light moves to the saturation region of the image pickup tube 2 becomes the threshold value for the human input signal 2a of the filter drive circuit 3. Therefore, when the amount of incident light exceeds this amount,
The voltage across the transparent electrodes 4B and 4D of the liquid crystal filter 4 decreases proportionally, and the light transmittance decreases accordingly. That is, the liquid crystal filter 4 automatically adjusts the amount of light attenuation in accordance with the amount of incident light. When the amount of incident light is below P, it does not operate as a neutral density filter, and the amount of incident light enters the image pickup tube 2 almost unchanged.

In the above embodiments, the TN type liquid crystal filter with parallel polarizing plates is placed between the optical lens section and the image pickup tube, but it can be placed in front of or inside the optical lens section. Furthermore, although a TN type liquid crystal plate parallel to the polarizing plate was used as the liquid crystal filter, other types of liquid crystal plates may also be used. It goes without saying that the imaging device is not limited to an imaging tube, but can also be applied to other photoelectric conversion devices such as a COD.

〔Effect of the invention〕

As explained above, even when the amount of incident light is large and enters the saturation region, the imaging device of the present invention does not require the trouble of attaching a special light reduction lens and removing it when the amount of incident light decreases. , the liquid crystal filter automatically becomes a neutral density filter with the optimum amount of light attenuation. Most of the incident light is transmitted when the amount of incident light is below the saturation region. Therefore, it is possible to instantly determine the optimum amount of light reduction, which often results in missed photo opportunities.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a diagram showing control characteristics of the voltage applied to the transparent electrode of a liquid crystal filter with respect to the amount of incident light. 1... Optical lens section, 2... Image pickup tube, 3...
Filter drive circuit, 4... Liquid crystal filter, 4A, 4E... Polarizing plate, 4
B, 4D...Transparent electrode, 4C...TN type liquid crystal plate.

Claims (1)

[Claims] A liquid crystal filter is provided in front of the imaging device, and when the output voltage of the imaging device exceeds a certain threshold, the light transmittance of the liquid crystal filter is controlled by the output voltage to achieve an optimal amount of light attenuation. An imaging device characterized by operating as a neutral density filter.