JP2007017788A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a display device capable of preventing a decrease in display brightness due to temperature influence.
An in-finder display element 9 is a diffractive type element formed by alternately stacking a refractive index isotropic region layer made of a refractive index isotropic material and a refractive index anisotropic region layer containing liquid crystal. It has a display part. Illumination light emitted from the light source 10 enters from the side surface of the in-finder display element 9 and is diffracted by the display unit toward the pentaprism 7, and a display image by the diffracted light is observed through the eyepiece 8. The light source driving unit 16 adjusts the brightness of the light source 10 based on the ambient temperature of the in-finder display element 9 detected by the temperature sensor 14 or the temperature of the in-finder display element 9 itself so that the brightness of the display image is constant. Control.
[Selection] Figure 1

Description

  The present invention relates to a display device that performs display by diffracting illumination light with a diffractive optical element using liquid crystal.

  Conventionally, a display device that performs display using a hologram is known (see, for example, Patent Document 1). In the display device described in Patent Document 1, light from an information display source composed of a fluorescent display tube is diffracted toward an observer by a combiner and displayed as a virtual image. In the combiner, a hologram using a photosensitive material as a hologram material is formed on a base material made of a glass substrate or a transparent resin substrate.

  In this display device, a fluorescent display tube is used as an information display source, the incident angle of light with respect to the hologram is approximately equal to the diffraction angle from the hologram, and the distance between the virtual image and the hologram is determined between the information display source and the hologram. It is characterized by being less than three times the distance between. With such a configuration, even if the hologram reproduction wavelength fluctuates due to manufacturing variations or temperature fluctuations, a great reduction in luminance does not occur.

JP-A-10-197824

  However, when a holographic liquid crystal element, which is a refractive index type diffraction grating using liquid crystal, is used as a hologram, not only the above-described fluctuation of the hologram reproduction wavelength but also the temperature dependence of the liquid crystal material causes a decrease in the luminance of the display image. I found that there was a cause. Therefore, even if the above-described conventional technique is applied, there is a problem in that a decrease in display luminance due to the temperature dependence of the liquid crystal cannot be suppressed.

  The present invention provides a diffractive optical element having a diffractive display section formed by alternately stacking a refractive index isotropic region layer composed of a refractive index isotropic material and a refractive index anisotropic region layer containing liquid crystal, A light source that makes illumination light incident on the diffractive display portion of the diffractive optical element in the stacking direction, and is applied to a display device that diffracts and displays the illumination light on the diffractive display portion. Detecting means for detecting the ambient temperature of the diffractive optical element; and light quantity control means for controlling the quantity of diffracted light emitted from the diffractive display unit so that the display luminance is constant according to the temperature detected by the detecting means. It is provided with.

  According to the present invention, the amount of diffracted light from the diffractive display unit is controlled so that the display luminance is constant according to the temperature of the diffractive optical element detected by the detecting means or the ambient temperature of the diffractive optical element. Therefore, it is possible to prevent a decrease in display luminance due to a temperature rise.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an embodiment of the present invention, and is a diagram showing a schematic configuration when a display device according to the present invention is used for display in a finder of a single-lens reflex camera. A lens barrel 3 including a photographic lens 2 is mounted on the camera body 1 in a replaceable manner. In FIG. 1, a single-lens reflex camera using a silver salt film 4 for image recording is shown as an example, but in the case of a single-lens reflex digital camera, an image sensor such as a CCD or CMOS is used as a recording medium.

  A quick return mirror 5 that reflects subject light toward the pentaprism 7 is disposed between the photographic lens 2 and the film 4. Although not shown, a shutter is provided between the film 4 and the quick return mirror 5. A finder screen 6 is disposed at a position optically equivalent to the photosensitive material surface of the film 4, and subject light from the subject 11 is reflected by the quick return mirror 5 and forms an image on the finder screen 6. The subject image formed on the finder screen 6 can be observed through the pentaprism 7 and the eyepiece 8. At the time of shooting, the mirror 5 is moved from the optical path of the subject light to the outside of the optical path, and a subject image is formed on the film 4.

In the camera body 1, an in-finder display element 9 is disposed adjacent to the finder screen 6. A light source 10 for illuminating the in-finder display element 9 is disposed on the side of the in-finder display element 9. An LED or the like is used for the light source 10, and its input power is controlled by the light source driving unit 16. A polarizing plate 12 is provided between the light source 10 and the display element 9 in the viewfinder, and the light emitted from the light source 10 is converted by the polarizing plate 12 into linearly polarized light (P-polarized light) whose vertical direction is illustrated. Then, it enters the element from the side surface of the in-finder display element 9.

  As will be described later, the in-finder display element 9 is a diffractive optical element having a display unit using a refractive index type diffraction grating, and diffracts light incident on the in-finder display element 9 toward the pentaprism 7 by the display unit. The viewfinder display is performed. Turning on / off the display by the in-finder display element 9 is controlled by the drive circuit 13.

  The diffracted light emitted from the in-viewfinder display element 9 is reflected by the pentaprism 7, and a display image formed by the diffracted light is observed by the photographer via the eyepiece 8. As a result, the display image is superimposed on the above-described subject image and displayed in the viewfinder field, and the photographer can observe the subject image and the display image at the same time. For example, the focus detection area display is displayed so as to overlap the subject image in the viewfinder field.

  Reference numeral 14 denotes a temperature sensor which is disposed in the vicinity of the in-finder display element 9 or in contact with the in-finder display element 9. The temperature sensor 14 is provided to detect the environmental temperature in the vicinity of the in-finder display element 9 or the temperature of the in-finder display element 9 itself, and the temperature is detected by a temperature detection circuit 15 connected to the temperature sensor 14. The obtained temperature data is input to the light source driving unit 16 of the light source 10.

[Description of Display Element 9 in the Finder]
Next, the in-finder display element 9 will be described in detail. FIG. 2 is a diagram for explaining the display portion 24B and the non-display portion 24A of the in-finder display element 9, and schematically shows a cross section of the in-finder display element 9. As shown in FIG. The in-finder display element 9 includes a pair of glass substrates 20 and 2.
1 and transparent electrodes 22 and 23 are formed on the opposing surfaces of the glass substrates 20 and 21, respectively. The transparent electrodes 22 and 23 are formed in the same shape, and have a shape corresponding to the display form (characters and figures) of the display unit 24B. The transparent electrodes 22 and 23 are connected to the drive circuit 13 described above, and the drive circuit 13 controls on / off of the voltage applied to the transparent electrodes 22 and 23.

  A liquid crystal member 24 is provided between the glass substrates 20 and 21 provided with the transparent electrodes 22 and 23, and is sealed by a sealing material 26 disposed on the periphery of the glass substrates 20 and 21. The liquid crystal member 24 includes a non-display portion 24 </ b> A where the transparent electrodes 22 and 23 are not provided and a display portion 24 </ b> B sandwiched between the transparent electrodes 22 and 23. In the non-display portion 24A, the polymer material having the refractive index isotropic property and the material having the refractive index anisotropy (liquid crystal) are mixed in an uncured state.

On the other hand, the display portion 24B is a portion that is a liquid crystal hologram that can be electrically turned on and off, and is in the direction along the surface of the in-finder display element 9, that is, in the traveling direction of illumination light, the refractive index isotropic region layer 241. And a refractive index anisotropic region layer 242 have a striped multilayer structure in which the layers are alternately repeated. The refractive index isotropic region layer 241 is a region in which the above-described polymer material is cured to become a polymer, and the refractive index anisotropic region layer 242 is made of a refractive index anisotropic material in the cured polymer polymer. It contains many liquid crystal droplets.

  The refractive index isotropic region layer 241 made of a polymer has an isotropic refractive index regardless of whether or not a voltage is applied to the transparent electrodes 22 and 23. On the other hand, in the refractive index anisotropic region layer 242, the orientation of the liquid crystal changes depending on whether a voltage is applied to the transparent electrodes 22 and 23, and the refractive index changes accordingly.

In a state where no voltage is applied to the transparent electrodes 22 and 23, the refractive index of the liquid crystal and the refractive index of the polymer are obtained for light incident in the stacking direction of the display unit 24B, such as illumination light of the light source 10. Have different refractive index values that satisfy the Bragg diffraction condition. That is, in a state where no voltage is applied, a refractive index type diffraction grating in which layers having a high refractive index and layers having a low refractive index are alternately arranged is formed in the display unit 24B. The diffraction conditions at this time are set so that the illumination light is diffracted in the direction of the pentaprism 7 (see FIG. 1).

  On the other hand, in a state where a voltage is applied, the orientation of the liquid crystal in the refractive index anisotropic region layer 242 changes and the refractive index also changes, and the refractive index of the liquid crystal and the refractive index of the polymer for illumination light traveling in the stacking direction. And become equal. As a result, the incident illumination light passes through the display unit 24B without being diffracted.

FIG. 3 is a diagram showing the relationship between on / off of the voltage to the transparent electrode of the in-finder display element 9 and display on / off. FIG. 3A shows a state where the applied voltage is off, and FIG. 3B shows a state where the applied voltage is on. In FIG. 3, the display unit 9 in the finder is provided with three display units 30A, 30B, and 30C, and each of the display units 30A to 30C has a refractive index isotropic region layer similar to the display unit 24B described above. And a refractive index anisotropic region layer are formed.

  When the applied voltage of the transparent electrodes sandwiching the display units 30A to 30C is turned off, the layer structure portion functions as a refractive index type diffraction grating as described above, and the illumination light is illustrated upward (penta prism 7 as shown in FIG. 3A). Direction) and emitted from the in-finder display element 9. As a result, the photographer observes the display image (for example, AF area display) of the display units 30A to 30C superimposed on the subject image. On the other hand, when the voltage applied to the transparent electrode is turned off, the illumination light is transmitted without being diffracted by the layer structure portions of the display units 30A to 30C as shown in FIG. Only the subject image is observed by the photographer without being guided.

As described above, in this embodiment, in the state where no voltage is applied, a refractive index difference is generated between the refractive index of the liquid crystal and the refractive index of the polymer, and light is diffracted. Thus, the refractive index of the liquid crystal is equal to the refractive index of the polymer. However, the orientation of the liquid crystal is not limited to this, and the refractive index of the liquid crystal and the refractive index of the polymer are equal when no voltage is applied. A configuration in which a difference in refractive index occurs between them to diffract light may be adopted.

  In the above-described embodiment, the transparent electrode having the same shape is formed on each of the pair of glass substrates 20 and 21, but the transparent electrode is formed on one of the glass substrates 20 and 21, and the other You may make it form a transparent electrode uniformly in the whole substrate surface in a glass substrate. Even in the in-finder display element having such a configuration, the display image by the diffracted light can be displayed in the viewfinder field as in the above-described in-finder display element 9.

Since only the P-polarized light is diffracted by the in-finder display element 9 of the present embodiment, the other polarized components are scattered by making the illumination light enter the in-finder display element 9 after being converted to P-polarized light by the polarizing plate 12. It is possible to prevent a decrease in display contrast due to.

<About display brightness control according to temperature>
By the way, it has been found that when the temperature of the display element 9 in the finder rises, the refractive index of the liquid crystal changes, the diffraction direction by the display unit 24B changes, and the quantity of emitted diffracted light decreases. For this reason, the brightness of the display decreases as the temperature of the in-finder display element 9 increases. According to the study by the present inventor, there is almost no decrease in luminance in the temperature range of −10 ° C. to 30 ° C., but the luminance gradually decreases when the temperature exceeds 30 ° C., and the luminance decrease is about −0 at 40 ° C. when converted to an EV value. It was found to be about 3 EV, about −0.6 EV at 50 ° C. and about −1.0 EV at 60 ° C. It has also been confirmed that there is almost no variation in the relationship between the temperature and the luminance reduction as long as the element is manufactured under a certain condition.

Therefore, in the present embodiment, the brightness (that is, input power) of the light source 10 is set according to the temperature detected by the temperature sensor 14 so that the luminance of the display image observed through the eyepiece 8 is constant. I adjusted it. For example, at 40 ° C., the brightness decrease converted to the EV value is about −0.3 EV, so that the brightness of the light source 10 is increased by increasing the current value by ΔI (40 ° C.) so as to compensate for the display brightness decrease. Increase brightness by +0.3 EV. That is, if the current value of the light source 10 set for −10 ° C. to 30 ° C. is I ₀ , the current value is I ₀ + ΔI (40 ° C.) when the temperature is 40 ° C.

  Similarly, the display brightness at −10 ° C. to 30 ° C. is set to a current value that gives a display brightness of +0.6 EV at 50 ° C., and the current value that gives a display brightness of +1.0 EV at 60 ° C. The current of the light source 10 is set. By increasing the current value in this way, it is possible to avoid a decrease in display brightness when the temperature rises. The correlation between the temperature and the current setting value of the light source 10 is stored in advance in the storage unit of the light source driving unit 16, and the light source driving unit 16 is based on the temperature obtained by the temperature detection circuit 15. To control the current value.

[Modification]
In the embodiment described above, by controlling the current value of the light source 10, the display brightness is prevented from being lowered due to a temperature rise. However, the display brightness can also be changed by controlling the applied voltage during display. In other words, the display luminance can be controlled by turning on and off the applied voltage at very short time intervals during display and changing the ratio between the off state (lighted) and the on state (light off). In this case, when the off ratio is increased, the display brightness is increased, and when the off ratio is decreased, the display brightness is decreased.

  FIG. 4 is a diagram showing an example of the on / off pattern of the applied voltage. The pattern A is an on / off pattern when the temperature is −10 ° C. to 30 ° C., and the pattern B is the on / off pattern when the temperature is 40 ° C. In the case of pattern A, the pulse width t1 corresponds to the ON time, and the pulse is generated with a period t4. Therefore, the ratio between the off (lighting) time and the on (light extinguishing) time is expressed as (t4-t1) / t1.

  On the other hand, in the case of the pattern B, since the pulse width is t1 and the period is t3 (> t4), the ratio of the off time to the on time (t3−t1) / t1 is larger than that of the pattern A, and the display luminance is increased. Will increase. Since the decrease in display brightness at 40 ° C. is about −0.3 EV as described above, the ratio of the on / off time of pattern B may be set so that the display brightness is increased by +0.3 EV as compared with pattern A. Note that the periods t3 and t4 are preferably set to about 20 Hz to 200 Hz in consideration of display flicker and influence on the liquid crystal.

  As described above, in the present embodiment, even if the display luminance changes due to a change in the diffraction state (diffraction direction or amount of diffracted light) by the in-finder display element 9 which is a diffractive optical element using liquid crystal, By controlling the brightness of the light source 10 and the on / off (lights on / off) pattern of the in-finder display element 9 according to the temperature, it is possible to prevent a decrease in luminance of the observed display. In the above-described example, the case where the brightness of the light source 10 is changed and the case where the on / off (lights on / off) pattern of the display element 9 in the viewfinder is controlled are applied separately. Of course, the two methods are applied together. You may do it.

  Note that the present invention is not limited to the above embodiment as long as the characteristics of the present invention are not impaired, and can be applied not only to the display in the camera finder but also to various display devices.

It is a figure which shows one embodiment of this invention, and is a figure which shows schematic structure at the time of using the display apparatus by this invention for the display in a finder of a single-lens reflex camera. It is a schematic diagram which shows the structure of the display element 9 in a finder. It is a figure which shows the relationship between the voltage to the transparent electrode of the display element 9 in a finder, and a display, (a) shows the state of an applied voltage OFF, (b) shows the state of an applied voltage ON, respectively. It is a figure which shows an example of the on-off pattern of an applied voltage.

Explanation of symbols

9: Display element in viewfinder 10: Light source 13: Drive circuit 14: Temperature sensor 15: Temperature detection circuit 16: Light source drive unit

Claims (2)

A diffractive optical element having a diffractive display section formed by alternately stacking a refractive index isotropic region layer made of a refractive index isotropic material and a refractive index anisotropic region layer containing liquid crystal, and the diffractive optical element A display device that diffracts the illumination light by the diffraction display unit and displays the illumination light.
Detecting means for detecting the temperature of the diffractive optical element or the ambient temperature of the diffractive optical element;
A display device comprising: a light amount control unit configured to control a light amount of diffracted light emitted from the diffractive display unit so that display luminance is constant according to the temperature detected by the detection unit. The display device according to claim 1,
The display device according to claim 1, wherein the light amount control means controls the light amount of the diffracted light by controlling the input power of the light source to adjust the brightness of the light source.

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