JPH0272324A - Liquid crystal focal plate - Google Patents

Abstract

PURPOSE:To provide the focal plate which is well visible even in a diffusion state and transmission state, allows easy focusing in the diffusion state and has a high grade by specifying the volume of the domains of the liquid crystal in the liquid crystal element formed by dispersing a nematic liquid crystal into a high-polymer film. CONSTITUTION:The film 13 formed by dispersing the nematic liquid crystal having positive dielectric anisotropy into the high polymer which exhibits the refractive index nearly equal to the refractive index of the liquid crystal to ordinary light and has no dielectric anisotropy is crimped by transparent substrates 11 having a pair of transparent electrodes 12 facing each other. The total of the volume of the domains 4 of the liquid crystal formed in the high-polymer film 13 is so controlled as to attain the value between 20 to 50% of the volume of the high-polymer film 13. The transmission of the component of the light to hinder the diffusion state or transmission state is obviated in this way and the focal plate having the high grade is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a focus plate using liquid crystal, and particularly to a focus plate for a single-lens reflex camera whose diffusion characteristics can be controlled.

(Prior Art) Conventionally, as a focus plate for a single-lens reflex camera whose diffusion characteristics can be controlled, liquid crystal focusing plates have been used, for example, as disclosed in Japanese Patent Laid-Open Nos. 48-37379 and 59-195633. There is a method of switching the reticle between a transmitting state and a diffusing state depending on the presence or absence of an applied voltage by utilizing the property of the dynamic scattering mode to diffuse light, and changing the applied voltage as disclosed in Japanese Patent Application Laid-Open No. 115525/1983. There is a known method for switching the diffusion characteristics.

Also, JP-A-60-250337 and JP-A-60-22
Japanese Patent No. 1729 discloses a focus plate that utilizes the birefringence of liquid crystal. According to these, one substrate surface is made into a scattering surface, a transparent electrode is formed thereon, and the scattering characteristics thereof are controlled. FIG. 3 shows this conventional example, where 33 is a liquid crystal layer, 31 and 32 are transparent electrodes, and 3
Reference numeral 5 denotes a substrate, and 35' has unevenness formed thereon. Further, 36 indicates a power source for driving the element. Using a member whose refractive index is almost the same as that of the liquid crystal and the substrate, and
If initial alignment is performed so that the long axis of the liquid crystal is parallel to the substrate surface, when a voltage is applied, the liquid crystal molecules rise according to the electric field and form a transparent state. On the other hand, when no voltage is applied, diffusion occurs based on the difference in refractive index between ne of the liquid crystal and the unevenness of the substrate, and it acts as a focusing plate.

(The problem that the invention is trying to solve) However,
In the conventional example described above, the element that utilizes dynamic scattering of liquid crystal has the following drawbacks.

In this dynamic scattering state, a light scattering effect is obtained by the liquid crystal molecules forming a turbulent state within the liquid crystal layer. However, the size of this liquid crystal molecular group is usually several tens to several hundred μm,
If the focus plate is placed in a viewfinder that has several times the magnification, such as a camera viewfinder, this turbulence will be visible, resulting in a poor-quality focus plate.

Furthermore, even in devices that utilize the birefringence of liquid crystals, the scattering state is formed based on the difference in refractive index between ne of the liquid crystal and the substrate; Since there is no difference between the refractive index of the substrate and the refractive index of the substrate, light with a vibration surface acting in this direction is transmitted. In other words, half of the light is transmitted without being diffused. The transmitted light during this scattering makes it difficult to see the blurred image on the reticle, reducing the ease of focusing.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a liquid crystal focusing plate that solves the problems of the prior art described above.

(Tanu's means of solving problems) The above objects are achieved by the present invention as described below.

That is, the present invention comprises a pair of opposing films in which a nematic liquid crystal with positive dielectric anisotropy is dispersed in a polymer having no dielectric anisotropy and having a refractive index approximately equal to the refractive index of the liquid crystal with respect to ordinary light. In a liquid crystal focusing plate that has a structure in which transparent substrates are sandwiched between transparent electrodes, the total volume of liquid crystal molecules formed in a polymer film is 20% of the volume of the polymer film.
50%.

(Function) According to the present invention, a nematic liquid crystal with positive dielectric anisotropy,
A film dispersed in a polymer with a refractive index almost equal to that of the liquid crystal is sandwiched between a pair of transparent conductive films, and a voltage applied to the conductive films controls the diffusion and transmission states to create a high-quality focal point. A board is provided.

A liquid crystal element in which nematic liquid crystal is dispersed in a polymer film has already been disclosed in JP-A-58-501631. However, since this element was designed primarily for display purposes, it could not function as a high-quality variable focus plate for cameras.

Therefore, the inventors of the present invention have made extensive studies to provide a high-quality varifocal plate for cameras, and have found that the total volume of the liquid crystal domains formed in the polymer film is 20% of the volume of the polymer film. % to 50%, it has been found that this device can function as a high-quality varifocal plate. It has also been found that an even better varifocal plate can be formed when the thickness of the polymer film is between 2 μm and 50 μm. The reason why this liquid crystal element can work well as a varifocal plate in this range can be considered as follows.

Liquid crystal domains in a polymer film usually exist with a size distribution. Volume ratio of liquid crystal to polymer is 50%
Beyond 30μ, the coupling between domains becomes significant
There will also be domains larger than m. At this time, when the image is enlarged using a camera finder or the like, some large domains become visible, leading to a decrease in quality. Further, in an element having a volume ratio of less than 20%, the angle at which the diffused light spreads becomes small, resulting in a small blur. As a result, the reticle becomes difficult to focus.

Furthermore, if the film thickness is less than about 2 μm, a sufficient amount of diffusion as a focusing plate cannot be obtained. Furthermore, if the film thickness exceeds 50 μm, the focusing range on the reticle becomes large, making it difficult to perform focusing. or,
As the film thickness increases, the amount of diffusion in the transmission state tends to increase, so if the thickness exceeds about 50 μm, a good transmission state cannot be formed.

In this liquid crystal element, when no voltage is applied, the liquid crystal is aligned in a certain direction for each domain. Further, at this time, the orientation of the liquid crystal indicated by each domain exists randomly in the polymer film. As a result, when no voltage is applied, this element forms a diffused state based on the difference between the refractive index of the liquid crystal ne and the polymer.

When a voltage is applied to this liquid crystal element, a force acts in each domain in the polymer film to direct the liquid crystal molecules in the direction of the electric field. At this time, the liquid crystal molecules reach a certain equilibrium state due to this force due to the strength of the electric field, the alignment regulating force received from the polymer film, and the elastic energy of the liquid crystal. When the liquid crystal molecules approximately follow the direction of the electric field, the device forms a good transmission state. Further, at an intermediate voltage, the diffusion state becomes intermediate.

In this liquid crystal element, the liquid crystal domains formed in the polymer film are sufficiently small that they cannot be recognized even when viewed under magnification through a camera finder or the like. Also, unlike the dynamic scattering state, no reduction in visibility due to turbulence is observed.

Furthermore, since the orientation of each liquid crystal domain in the polymer film is random, the polarization characteristics of each domain are averaged over the entire device. Therefore, the characteristics of the entire element for each polarized light are uniform. As a result, in the diffused state or the transmitted state, light components that interfere with the state (transmitted light in the diffused state, diffused light in the transmitted state) do not pass through, making it possible to form a high-quality reticle. It became.

(Examples) Hereinafter, the present invention will be described in more detail using Examples, but the present invention is not limited thereto.

Embodiment 1 FIGS. 1 and 2 show a first embodiment of the present invention. 1st
The figure is a cross-sectional view of a liquid crystal element, where 11 is a transparent substrate, 12 is a transparent conductive film, 13 is a polymer film, and 14 is a liquid crystal domain contained in the polymer film. FIG. 2 shows a cross-sectional view of a camera when this liquid crystal element is used as a focusing plate of a camera, where 21 is a photographing lens, 22 is a pentaprism, 23 is an eyepiece lens, 24 is a Fresnel lens, 25 is a liquid crystal focusing plate, 26 is a film, 27 is a camera body, and 28 is a mirror.

A method for manufacturing this element and a method for driving the element as a focusing plate will be described below.

Polyvinyl alcohol (PVA) I with a degree of polymerization of about 500
g, 4 g of Merck's ZLI2061 liquid crystal (registered trademark) and 10 g of water were mixed and stirred to form a milky liquid. Approximately 1 at room temperature
After standing for a while, it is dropped onto a glass substrate with ITO and stretched into a film. After drying the film for about 2 hours at about 30° C., an ITO-covered glass substrate was bonded to the film to produce the device shown in FIG. The thickness of the polymer film can be changed depending on the conditions for stretching it into a film, and in this example, it was stretched to a thickness of about 10 μm using a rod with a sharp surface.

The final film thickness after drying was about 8 μm, and the total volume of the liquid crystal domains was about 30% of the volume of the polymer film.

When this element is used as a focus plate for a single-lens reflex camera, it will look like the one shown in Figure 2. When no voltage was applied, a diffused state was formed in which good focusing was possible. Also, 50V
When a rectangular wave was applied, a high-quality transparent state was formed, and instantaneous switching between the transparent state and the diffused state was possible by turning the voltage application on and off. Furthermore, by controlling the diffusion state of the element by applying a voltage in between, it has become possible to confirm the depth of field.

Example 2 A device having a structure similar to that of Example 1 was manufactured in the following manner.

Polyvinyl alcohol (PVA) with a polymerization degree of about 5005
g, Rotsch's TN-2108 liquid crystal (registered trademark) 4g
and 15 g of water are mixed and stirred to form an emulsion.

After leaving it at room temperature for about 1 hour, it is formed into a film on an ITO-coated glass substrate using a spinner. Furthermore, dry the membrane for about 5 hours at room temperature? A device was fabricated by bonding glass substrates with U I TO. The thickness of the polymer film can be changed by changing the rotational speed of the spinner when forming the polymer film, and in this example, the film was formed at a rotational speed of about 3.0OOr, p, m. The final film thickness after drying was about 18 μm, and the total volume of the liquid crystal domains was about 40% of the polymer film.

Similar effects were obtained when the film was used as a focusing plate for a camera in the same manner as in Example 1.

(Effect of the invention) As explained above, in a liquid crystal element in which nematic liquid crystal is dispersed in a polymer film, the total volume of the liquid crystal domains is between 20% and 50% of the total volume of the polymer film. As a result, it has become possible to form a high-quality variable liquid crystal focusing plate that has good visibility in the diffused state and the transmitted state and is easy to focus in the diffused state. Furthermore, this effect is enhanced when the thickness of the polymer membrane is approximately 2 μm to 50 μm.

Also, since this liquid crystal focusing plate does not use dynamic scattering mode,
Even in the diffused state, no turbulent flow of the liquid crystal is visible. Further, it has the effect of exhibiting similar diffusivity and transmission characteristics for each polarized light.

Furthermore, at intermediate voltages, the diffusion state is also intermediate, so by correlating the appearance of each state with the depth of field of the camera, it is possible to provide a focus plate that allows depth confirmation without aperture. There is.

[Brief explanation of the drawing]

1 and 2 are detailed explanatory diagrams of the present invention, and the first
The figure is a cross-sectional view of a liquid crystal element, and FIG. 2 is a cross-sectional view of a camera equipped with a liquid crystal focusing plate. FIG. 3 is an explanatory diagram of a conventional example,
FIG. 2 is a cross-sectional view of a liquid crystal element. 11.35: Transparent substrate 12.31.32: Transparent conductive film 13: Polymer film 14: Liquid crystal domain 21: Taking lens 22: Pentaprism 23: Eyepiece lens 24: Fresnel lens 25: Liquid crystal focusing plate 26: Film 27: Camera body 28: Mirror 33: Liquid crystal layer 36: Drive circuit Figure 1 Figure 2

Claims (2)

[Claims] (1) A pair of opposing transparent electrodes is made of a film in which a nematic liquid crystal with positive dielectric anisotropy is dispersed in a polymer without dielectric anisotropy that has a refractive index almost equal to the refractive index of the liquid crystal with respect to ordinary light. In a liquid crystal focusing plate having a structure sandwiched between transparent substrates, the total volume of liquid crystal molecules formed in a polymer film is between 20% and 50% of the volume of the polymer film. Features a liquid crystal focusing plate. (2) The liquid crystal focus plate according to claim 1, wherein the thickness of the polymer film is between 2 μm and 50 μm.