JP2001061086A - Image pickup unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image pickup unit that provides a sufficient image diffusion characteristic to correct smear even when employing a light diffusion element configured thin to enhance the response and reduces deterioration in image quality due to the thickness of a cell. SOLUTION: The image pickup unit is provided with an image pickup lens 1 having a movable diaphragm 3 and having a light diffusion element 17 that changes a light diffusion characteristic in response to a control signal, with a CCD image pickup device 5 that applies photoelectric conversion to an output optical image of the image pickup lens and provides the output of the result as an image signal, and with a system controller 12 that controls driving of the CCD image pickup device and the light diffusion element, brings the light diffusion element into a non-diffusion state for a storage period of the image signal and brings the light diffusion element into a diffusion state for a read period of the image signal. The light diffusion element is placed toward the object from the rear lens 1b of the image pickup lens in the vicinity of the movable diaphragm to configure the image pickup unit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image pickup apparatus having a smear reduction function.

[0002]

2. Description of the Related Art In a solid-state imaging device using a CCD imaging device or the like, a smear phenomenon (more precisely, a phenomenon that occurs when intense light is incident) is a phenomenon peculiar to the solid-state imaging device.
Although this phenomenon is caused comprehensively by smearing and blooming, in this specification, image quality degradation due to common use by those skilled in the art (hereinafter simply referred to as smearing) is a problem. In other words, this smear phenomenon is caused by charges that are not trapped in the original charge storage region crossing the potential barrier and leaking into the vertical transfer path, or diffraction components and multiple reflection components of incident light leak into the vertical transfer path under the light shielding film. Is caused by the generation of electric charges
In the case of normal light, this occurs over the vertical transfer period. For example, in the case of spot light, vertical stripes extending up and down the spot light are generated, and image quality is significantly impaired.

There have been proposed several methods of reducing the signal, such as a method of correcting a signal and a method of using an optical shutter. However, the effect of the signal correction is insufficient, and the controllability of a mechanical shutter is poor. The liquid crystal shutter has drawbacks such as insufficient reliability, and the use of polarized light in a liquid crystal shutter, the transmittance of which is theoretically 50% or less (actually even lower).

On the other hand, utility model registration No. 252463
Japanese Patent Application Laid-Open No. 4 (1999) -1992 discloses a method of controlling a liquid crystal element (which has a high transmittance because a polarizing plate is not required) interposed between a photographing optical system and a CCD image pickup device and capable of switching a light diffusion state to generate smear. In the signal reading (CCD transfer) period which causes the above, a technique is disclosed in which spot light is diffused to average the plate surface illuminance to lower the peak value and reduce smear.

[0005]

In the prior art, the effect of reducing smear at the time of diffusion can be obtained.
It has the following problems. As a well-known liquid crystal element for controlling the diffusivity used in the above-mentioned prior art, there is a polymer dispersion type (also referred to as a polymer network type) liquid crystal element. In a transparent cell made of glass or the like in which a transparent resin medium having a predetermined refractive index in which liquid crystal molecules having a variable refractive index are dispersed as a medium is sealed,
When the refractive indices of the medium and the medium are completely the same, the medium enters a transparent (non-diffused) state, and a diffusion state occurs according to the difference in the refractive indices of the medium and the medium.

In such a liquid crystal element, in order to increase the response characteristics of the element, it is essential to reduce the distance between electrodes = the thickness of the active portion (cell thickness) of the element. In addition, since the difference in the refractive index depending on the wavelength of the active portion of the element, that is, the “dispersion” characteristic, is generally larger than that of ordinary optical glass, it is preferable that the cell thickness be smaller in order to reduce the influence (for example, μm to several tens of μm).

However, when the cell thickness is reduced, the degree of diffusion naturally decreases. On the other hand, the average effect (diffusion effect) of plate surface illuminance on an image when liquid crystal elements having the same diffusion degree are used is as follows:
The one far from the CCD image sensor is larger. (This is considered to be the case where the active portion of the CCD image sensor is virtually in contact with the light receiving surface, ie, the image forming surface, of the CCD image sensor. Therefore, the average effect of the illuminance on the plate surface does not occur at all. ")
In the case where a liquid crystal element is arranged between the imaging elements, there is a very high fear that a sufficient diffusion effect on spot light cannot be obtained in practice.

Another problem is that the cell member itself has an adverse effect on the imaging characteristics. That is, the cell as described above is indispensable for configuring an actual element, but since the thickness is required for physical strength, it cannot be configured to be sufficiently thin as the cell thickness described above. Usually, it is about several mm to several mm. Since the effect of refraction is proportional to the thickness of the member, if such a thick liquid crystal element is inserted in the image forming path, a significant aberration will occur according to the refractive index and dispersion of the cell. Since this aberration occurs depending on the angle at which the light beam enters the cell (especially in the case of a telecentric optical system which is configured so that the imaging light beam to the CCD image sensor is substantially parallel (afocal)). In the case where a liquid crystal element is arranged between the taking lens and the CCD image pickup element as described in the above publication, the occurrence of the liquid crystal element is unavoidable.

From the viewpoint of adverse effects on optical characteristics,
There are also problems such as garbage and scratches. That is, since the light transmitting portion of a normal optical member is processed mainly without including steps other than polishing and laminating, if the control in these steps is sufficient (except for the attached dust after the camera is assembled) ), Virtually no garbage or scratch problems. However, in the case of a light diffusing element using a liquid crystal, fine defects due to the incorporation of dust and the generation of scratches may occur separately in the process of forming a transparent electrode and enclosing a resin. When an element having such a defect is arranged as a liquid crystal element between the taking lens and the CCD image pickup element as described in the above-mentioned publication, the image is degraded due to the defect, so that the image quality also deteriorates, In order to avoid this, the criterion for determining the defect must be strict, which leads to an increase in cost due to a decrease in the yield of the light diffusion element.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the conventional image pickup apparatus. The invention according to claim 1 uses a light diffusion element which is thin to increase the response. To provide an image pickup device capable of obtaining image diffusion characteristics sufficient to perform smear correction and reducing image quality deterioration caused by refraction of the cells constituting the light diffusion element and dust and scratches. It is an object of the invention according to claim 2 to substantially prevent image quality degradation in the imaging apparatus according to claim 1.

[0011]

In order to solve the above-mentioned problems, the invention according to claim 1 provides a light diffusion element whose light diffusion characteristic changes according to a control signal, and an imaging optical system having the light diffusion element. System, an imaging element that photoelectrically converts an output optical image of the imaging optical system and outputs it as an image signal, and controls the driving of the imaging element and the light diffusion element to accumulate the image signal to be read out. The light diffusion element in a non-diffusion state, and imaging control means for causing the light diffusion element to be in a diffusion state during the image signal readout period, wherein the light diffusion element is located closer to the last lens of the imaging optical system. Are also arranged on the object side to constitute an imaging device.

As described above, by disposing the light diffusing element on the object side of the last lens of the image pickup optical system, smear correction can be performed even when a thin light diffusing element is used to increase the response. It is possible to obtain image diffusion characteristics sufficient to perform the process, and it is possible to reduce image quality deterioration caused by refraction of the cell and dust and scratches.

According to a second aspect of the present invention, in the imaging apparatus according to the first aspect, the light diffusion element is arranged near a stop position of the imaging optical system. By arranging the light diffusing element in the vicinity of the stop position of the imaging optical system in this way, in addition to the operation of the imaging device according to the first aspect, it is possible to cause almost no deterioration in image quality.

[0014]

Next, an embodiment will be described. FIG. 1 is a block diagram showing a digital camera according to a main embodiment of an imaging apparatus according to the present invention. 1 is an imaging lens composed of a front lens 1a and a rear lens 1b, 2 is a lens driving mechanism composed of a focus actuator 2a and a zoom actuator 2b, 3 is a movable diaphragm, 4 is an optical filter composed of a low-pass filter and an infrared cut filter, 5 is a CCD image sensor, 6 is a CCD driver, 7 is A
A pre-processing circuit 8 including a / D converter is a digital processing circuit which includes a memory as hardware and performs all digital processing. 9 is a memory card interface, 10 is a memory card, 11 is LC
D image display system, 12 is a system controller including a microcomputer as a main configuration, 13 is an operation switch system, 14 is an operation display system including a display LCD, 15 is an aperture actuator, 16
Denotes an actuator driver, 17 denotes a light diffusion element, and 18 denotes a light diffusion element driver.

The digital camera according to the embodiment of the present invention is characterized in that a light diffusing element 17 having a structure in which a polymer dispersed liquid crystal is sealed in a plate cell of an optical glass with a transparent electrode is provided inside the imaging lens 1. It is provided near the movable diaphragm 3 on the subject side with respect to the rear lens 1b.

Next, the light diffusing element 17 will be described in more detail. Two sheets of optical glass are attached to each other to provide a parallel flat glass having a thickness of 0.9 mm as a whole.
It has a flat liquid crystal enclosure of 10 μm. A transparent resin in which liquid crystal is dispersed is sealed in the sealing portion, and an active portion as an element is formed. The connection line drawn from the transparent electrode is connected to the light diffusion element driver 18, and is driven by a known AC drive of a predetermined voltage.

It should be noted that the manner in which the diffusion and non-diffusion (conducting) states are assigned when a voltage is applied and when no voltage is applied (0 voltage is applied in this embodiment to discharge residual charges) is originally arbitrary. However, when combined with a TTL optical viewfinder, the purpose is to obtain the effect of making the viewfinder visible even when the camera power is turned off, or eliminating the need to consume power when no smear-reduced imaging is required. In the present embodiment, non-diffusion is performed particularly when no voltage is applied. After the residual charge is discharged by once applying the zero voltage, the transparent state is maintained even when the power supply to the driver is stopped. It is designed to drip. For this purpose, it is needless to say that the effective refractive indexes of the liquid crystal corresponding to the medium and the resin corresponding to the medium are equal in a state where no voltage is applied.

On the other hand, as described above, the light diffusing element 17 is located in the vicinity of the movable stop 3, more specifically, in the vicinity of the rear, and in the rear ball 1b.
Is provided on the subject side. The imaging lens 1 according to the present embodiment has a so-called two-group zoom configuration as shown in the drawing, and the front lens 1a forms a focusing group, and the rear lens 1b forms a variator group. And the movable diaphragm 3 is of course 2
The light rays are provided between the groups at a position closer to the afocal. The ideal position of the light diffusing element 17 is substantially the same as the position of the movable diaphragm 3. However, if the light diffusing element 17 is provided closer to the subject than the rear lens 1b, the light diffusing element 17 is almost in a practical area in terms of both diffusion effect and image quality deterioration. Therefore, it may be arranged in an appropriate place in consideration of mechanical interference and the like.

Next, the control in the above embodiment will be described. In the digital camera according to the present embodiment, the system controller 12 performs overall control, and controls the movable aperture 3 and the driving (electronic shutter) of the CCD image pickup device 5 by the CCD driver 6 so that exposure is performed. (Charge accumulation) and reading of signals, storing the signals in a digital process circuit 8 through a pre-process circuit 7, and performing all necessary signal processing in the digital process circuit 8, the memory card Ten
It is recorded in. Then, by driving the light diffusion element driver 18 in accordance with the timing of exposure and signal reading, and changing the diffusion characteristics of the light diffusion element 17, smear-reduced imaging can be performed.

That is, while the photoelectric conversion charge of the subject image to be photographed is being accumulated, the light diffusion element 17 is kept in a non-diffused (clear) state, and the transfer pulse TG to the CCD transfer path (vertical shift register) is kept. As soon as appears, the application of a voltage is started to bring the state into a diffusion state. However, it takes a considerable time from the start of driving until the light diffusing element 17 transitions to a practically sufficient diffusion state. This transition time depends on the material of the device, the applied voltage and the driving frequency, but is usually several ms.
~ Several hundred ms. It also depends greatly on the thickness of the element (active part). In the present embodiment, since the thickness is as thin as 10 μm, the transition time is as fast as 10 ms or less, and the reading of the imaging signal (CCD transfer of the signal charge) is started from 10 ms after the TG output. You. Then, after the signal reading is completed, the voltage application to the light diffusion element 17 is promptly and timely changed to the transparent state as zero voltage in order to prepare for the next photographing and to eliminate unnecessary driving power. Thereafter, the power supply to the light diffusion element driver 18 may be stopped.

At this time, if the transition time is a different value, the read start time may be set in accordance with the value. At this time, the reading may be started with a further delay. However, in consideration of the accompanying increase in dark current noise, unnecessary delay is not performed in the present embodiment.

The image signal thus read out is recorded on the memory card 10 or displayed on the LCD image display system 11 through various signal processings as appropriate. At the time of imaging, since the image is diffused at the time of charge transfer, even if spot light exists in the subject, it is averaged without being formed on the photoelectric conversion surface. That is, the recorded or displayed image is a high-quality image in which smear is reduced and, therefore, has no apparent smear. Since the light diffusing element 17 is provided on the object side of the rear lens 1b of the imaging lens 1 and in the vicinity of the movable stop 3, both diffusivity and responsiveness sufficient for smear reduction imaging are achieved. In addition, there is almost no deterioration in image quality due to the refraction of the cell and dust and scratches.

Various embodiments other than the above-described embodiment are conceivable. For example, in the above embodiment, the so-called two-unit zoom is used for the imaging lens.
The present invention can be applied not only to an arbitrary zoom / varifocal lens such as a third-group, fourth-group, or fifth-group zoom, but also to a lens using an arbitrary imaging lens including a short focus lens. That is,
Regarding all these imaging lenses, the problem in the case where the light diffusing element is arranged between the rear lens and the imaging surface is common, and this can be solved by applying the present invention as in the above embodiment. is there.

In the above embodiment, the movable diaphragm 3 is used. However, it is needless to say that the movable diaphragm 3 may be a fixed diaphragm.

Although some embodiments of the present invention have been specifically described above, the present invention is not limited to these embodiments, and can take any form as long as it is described in the claims. Needless to say.

[0026]

According to the first aspect of the present invention, the light diffusing element is disposed closer to the subject than the last lens of the imaging optical system. Even if a thin diffusion element is used to enhance the image quality, it is possible to obtain sufficient image diffusion characteristics to perform smear correction, and at the same time, image quality degradation caused by cell refraction and dust / scratching. Can be obtained. According to the second aspect of the present invention, since the light diffusing element is arranged near the stop position of the imaging optical system, an extraordinary effect that almost no image quality deterioration occurs in addition to the above-mentioned effect can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a digital camera according to an embodiment of an imaging apparatus according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 imaging lens 1a front lens 1b rear lens 2 lens driving mechanism 2a focus actuator 2b zoom actuator 3 movable diaphragm 4 optical filter 5 CCD image sensor 6 CCD driver 7 pre-processing circuit 8 digital processing circuit 9 memory card interface 10 memory card 11 LCD image Display system 12 System controller 13 Operation switch system 14 Operation display system 15 Aperture actuator 16 Actuator driver 17 Light diffusion element 18 Light diffusion element driver

Claims (2)

[Claims] A light diffusion element whose light diffusion characteristic changes according to a control signal; an imaging optical system having the light diffusion element; and an output optical image of the imaging optical system, which is photoelectrically converted and output as an image signal. An image pickup device that controls the driving of the image pickup device and the light diffusing element so that the light diffusing element is in a non-diffused state during the accumulation period of the image signal to be read out, and the light diffusing element during the image signal reading period. An imaging control unit for setting the light diffusion element to a diffusion state, wherein the light diffusion element is disposed closer to a subject than a last lens of the imaging optical system. 2. The image forming apparatus according to claim 1, wherein the light diffusing element is disposed near a stop position of the imaging optical system.
An imaging device according to claim 1.