The present invention relates to an image display device having optical elements that are a left eye member and a right eye member, and optical elements that are a left eye member and a right eye member.
For example, a head mounted display (HMD) is known as an image display device that displays an image displayed on an image display element, through left and right optical elements. An HMD is an image display device that is mounted on the head of an observer and that can provide a desired image to the observer.
It is desirable that image display devices such as HMDs be wearable by a wide variety of persons and the displayed image can be appropriately seen. In addition, in order to reduce the burden of an observer wearing an HMD, the whole device is desired to be reduced in size and weight.
In general, when trying to provide an image having a wide angle of view to an observer, the whole optical system including optical elements tends to increase in size and weight. Since an HMD is mounted on the head of an observer, the increase in size of the whole optical system is undesirable in view of the burden of the observer. Ways to suppress the increase in size of the whole optical system include reducing the exit pupil diameter of the optical system. However, in that case, the distance between the observer and the exit pupil needs to be reduced, and the left and right optical elements may touch the nose of the observer.
In order to solve the above problem, PTL 1 discloses removing parts that may touch the nose of an observer from optical elements that are a left eye member and a right eye member.
PTL 1: Japanese Patent Laid-Open No. 2009-036835
In an image display device of PTL 1, parts that may touch the nose of an observer are removed from optical elements that are a left eye member and a right eye member, and therefore an image having a wide angle of view can be provided while preventing the increases in size of the whole optical system. However, some of rays that should form an image are lost owing to the partial removal of the optical elements, and the luminance of part of the displayed image decreases.
PTL 1 also discloses electrically compensating the decreased luminance, but does not mention any optical approach for suppressing the decrease in luminance of the displayed image, and suppression of the decrease in luminance of the displayed image is insufficient.
The present invention provides an image display device having optical elements that are a left eye member and a right eye member in which the decrease in luminance of the displayed image is suppressed while preventing the optical elements from touching the nose of an observer.
In an aspect of the present invention, an image display device includes optical elements that are a left eye member and a right eye member. The image display device has an image display element that displays an image to an observer through the optical elements. The optical elements each have at least one part shape formed so as to avoid the contact with the nose of the observer. The surface of the at least one part shape is substantially parallel to the direction of a principal ray from the image display element.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Embodiments of the present invention will now be described with reference to the drawings.
The principal ray 18 is emitted from the lower right corner of the display surface of the image display element 10. The principal ray 18 enters through the C surface 16. The principal ray at this time is denoted by 18a. After that, the principal ray 18a travels to the A surface 14. Because the principal ray 18a is at a shallow angle to the A surface 14, the principal ray 18a is totally reflected by the A surface 14. After the reflection, the principal ray 18a becomes a principal ray 18b, and reaches the B surface 15. Because an aluminum vapor-deposited film is formed on the B surface 15, the principal ray 18b is reflected by the B surface 15. Then, the principal ray 18b becomes a principal ray 18c, exits through the A surface 14, and is guided to the eye of the observer.
The principal ray 19 is emitted from the lower left corner of the display surface of the image display element 10. Since the prism body 11 has a bilaterally symmetrical shape, the principal ray 19 is guided to the eye of the observer through an optical path symmetrical to the optical path of the principal ray 18. The surface 21 is a surface that forms part of the nose side part 12, and is a nose side removal surface. The principal ray 19c is parallel to the nose side removal surface 21, and the principal ray 19c is located on the nose side removal surface 21. The nose side removal surface 21 is painted black to prevent ghost images due to internal reflection of unwanted rays and to block light from entering from the outside of the effective optical path.
Since the prism body 11 has a bilaterally symmetrical shape, part of the effective bundle of rays including the principal ray 19 is vignetted by the nose side removal surface 21 also in the nose side part 12 on the left side of the prism body 11. The rate of vignetting is a half of the effective light beam consisting the principal ray 19c, and the amount of vignetting of the effective bundle of rays forming the principal ray 19c is the same at any cross-section. In the above display optical system, prism bodies 11 are disposed at positions corresponding to both left and right eyes.
As described above, parts of the prism bodies 11 that are near the nose are removed at the nose side removal surfaces 20 and 21 such that the principal rays 18c and 19c nearest to the nose side removal surfaces 20 and 21 are parallel to the nose side removal surface 20 and 21. Thereby, a display optical system can be achieved in which prism bodies 11 are unlikely to interfere with the nose of an observer, and the decrease in the amount of light of the observed display image is minimized.
Although, in this embodiment, the principal rays 18c and 19c are parallel to the nose side removal surfaces 20 and 21, respectively, the present invention is not limited to complete parallelism. A case in which the angle between the principal ray 18c and the nose side removal surface 20 is 5 degrees is within the range of “substantially parallel” in this embodiment. Suppose, for example, a case in which the angle between the principal ray 18c and the nose side removal surface 20 is 5 degrees, and the maximum thickness of the prism body 11 near the left and right nose side removal surfaces 20 and 21 is 5 mm. In that case, the amount of vignetting of the effective bundle of rays is larger than when the principal ray 18c is parallel to the nose side removal surface 20 by 5*tan (5 deg)=0.437 [mm]. However, a margin of an optical effective bundle of rays of 0.5 mm is generally allowed, and 0.437 mm is within this range. Therefore, the influence of the decrease in the amount of light of the observed image is small.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2015-146837, filed Jul. 24, 2015, which is hereby incorporated by reference herein in its entirety.
Number | Date | Country | Kind |
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2015-146837 | Jul 2015 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2016/003354 | 7/15/2016 | WO | 00 |