This application claims the benefit of Japanese Patent Application No. 2010-256278, filed on Nov. 16, 2010, in the Japanese Patent Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a projection optical system and an image projection device employing the projection optical system, and more particularly, to a projection optical system and an image projection device which allow a large screen to be projected with a short projection distance.
2. Description of the Related Art
Recently, an image projection device (ultra-short focus image projection device) capable of projecting a large screen in spite of a short projection distance has been developed. Since the ultra-short focus image projection device can reduce a distance to a screen, it is easy to install and handle, and it is also useful because there are not frequent occasions when an image cannot be seen due to pass of a person between the screen and the image projection device. In addition, an ultra-short focus image projection device having a zoom function has recently been developed.
However, it is difficult that the ultra-short focus image projection device, due to its ultra-short focal length, designs to simultaneously achieve both high zoom rate and large viewing angle, and experiences a large performance change caused by an assembly error occurring in manufacturing. Consequently, in the ultra-short imaging projection device, a reflecting optical system which does not cause chromatic aberration as well as a refracting optical system is used to solve those problems.
When the reflecting optical system is used, however, a reflection surface is disposed to protrude in the direction of projecting flux and thus may disturb observation of a projection surface. Moreover, in case of shift from a wide-angle end to a telephoto end, the position of a projection screen moves up and down, making it difficult for a user to use the reflecting optical system.
The present invention provides a projection optical system for an ultra-short focus image projection device, in which a reflection optical system does not disturb observation of a projection surface, and an image projection device employing the projection optical system.
According to an aspect of the present invention, there is provided a projection optical system including a first optical system for zooming an image formed by an image display device to form a first intermediate image, a second optical system for enlarging the first intermediate image to form a second intermediate image, and a reflection optical system for reflecting light which forms the second intermediate image, in which an optical axis of the first optical system translates parallel with respect to an optical axis of the second optical system in a direction perpendicular to the optical axis of the first optical system.
The optical axis of the first optical system may coincide with a central normal of the image display device.
The optical axis of the first optical system may pass through an inside or vicinity of the image display device.
According to another aspect of the present invention, there is provided a projection optical system including a first optical system for zooming an image formed by an image display device to form a first intermediate image, a second optical system for enlarging the first intermediate image to form a second intermediate image, and a reflection optical system for reflecting light which forms the second intermediate image, in which an optical axis of the first optical system and an optical axis of the second optical system are approximately on the same straight line.
A central normal of the image display device may translate parallel with respect to an optical axis of the first optical system in a direction perpendicular to the optical axis of the first optical system.
According to another aspect of the present invention, there is provided a projection optical system including a first optical system for zooming an image formed by an image display device to form a first intermediate image, a second optical system for enlarging the first intermediate image to form a second intermediate image, a reflection optical system for reflecting light which forms the second intermediate image, and a plane mirror for reflecting light emitted from the first optical system and causing the reflected light to be incident to the second optical system.
The reflection optical system may include a concave mirror.
An aberration of the first optical system and an aberration of the second optical system and the reflection optical system including the concave mirror may be offset.
The first optical system may be an enlarging/zooming optical system.
An image projection device according to an embodiment of the present invention includes a projection optical system having any one of the foregoing characteristics.
With the projection optical system and the image projection device employing the projection optical system according to an embodiment of the present invention, by using the concave mirror for the reflection optical system, observation of the projection surface can be prevented from being disturbed due to the reflection optical system. Moreover, the lower side or center of the projection screen may not be moved in zooming. Furthermore, by combining the plurality of optical systems, performance change originating from an assembly error occurring in manufacturing can be reduced.
The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:
Hereinafter, a projection optical system and an image projection device employing the projection optical system according to various embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, embodiments of the present invention are not limited to the disclosed embodiments and may be carried out with various modifications thereto.
The first optical system 201 is a refractive optical system which has an optical axis 204 and includes a plurality of refractive lenses having a zooming function. That is, incident light 207 incident into the first optical system 201 penetrates an image display device such as a liquid crystal panel or the like, the plurality of refractive lenses which refract light 208 of an image 206 formed by the image display device are moved in the direction of the optical axis 204, thereby changing a size of a first intermediate image 210 generated by imaging of projection light 209 from the first optical system 201. Herein, the image display device is not limited to a liquid crystal panel and may use various components such as a Digital Micromirror Device (DMD), etc.
The second optical system 202 is a refractive optical system which has an optical axis 205 and includes a plurality of refractive lenses. Once light 211 forming the first intermediate image 210 is incident, the second optical system 202 performs enlargement for projecting an image presented by the first intermediate image 210 onto a screen. Thus, light 212 projected by the second optical system 202 forms a second intermediate image 213.
The reflection optical system 203 enlarges the second intermediate image 213 and projects the enlarged second intermediate image 213 onto the screen. As the reflection optical system 203, a concave mirror may be used as shown in
The reflection optical system 203 may be provided to offset aberration (spherical aberration, coma aberration, astigmatism, field curvature, distortion, etc.) generated in the reflection optical system 203 by aberration generated in the refractive optical system of the second optical system 202. The reflection optical system 203 may have an aspheric shape for aberration correction.
In the current embodiment, the optical axis 204 and the optical axis 205 are approximately parallel with each other, but do not coincide with each other. That is, when the projection optical system is viewed from a side as shown in
In the current embodiment, a normal at a central position of the image display device which forms an image 206 (i.e., a central normal) approximately coincides with the optical axis 204 of the first optical system 201. Consequently, the first intermediate image 210 is zoomed with respect to the optical axis 204 of the first optical system 201. Therefore, it is possible to prevent the center of a projection image from being moved due to zooming on the screen.
Herein, “central position of the image display device which forms the image 206” means a central position of a shape formed by collection of pixels valid for formation of the image 206.
Moreover, in
In the lens structure of the wide-angle end in the upper portion in
In the lens structure in the wide-angle end shown in
Shown in Table 1 and Table 2 are (1) indication of whether each lens surface is aspheric, (2) a radius of curvature of each lens surface, (3) a distance, (4) a d-line refractive index, and (5) an Abbe number. The following values comply with specifications of the projection optical system in which a focal length f is more than 4.3 mm and less than 8.6 mm, an F number is more than 1.5 and less than 3.0, a viewing angle in the wide-angle end is 75.1°, surfaces following a twenty-eighth surface 28 are eccentrically shifted by 15.4 mm (move in perpendicular to the optical axis).
Table 3 shows distance data during zooming. Di indicates a distance of an interval di between a surface having a surface number i and a surface having a surface number (i+1).
In Table 4, aspheric data is shown. When Z is a zag amount of a surface, h is a radius from an optical axis, c is curvature of a radical axis (reciprocal of a radius of curvature), and H is a size in a direction perpendicular to the optical axis, the aspheric equation may be given by:
Z=ch
2/(1+SQRT{1−(1+k)c2h2})+Ah4+Bh6+Ch8+Dh10.
While it is described above that the optical axis 204 of the first optical system 201 and the optical axis 205 of the second optical system 202 are approximately parallel with each other, the embodiment of the present invention is not limited thereto, and a mirror may be disposed in the middle of a light path from the first optical system 201 to the second optical system 202, such that the optical axis 205 of the second optical system 202 may be approximately parallel with an optical axis which has a relationship of a mirror image with the optical axis 204 of the first optical system 201 through the mirror.
As such, in the embodiment of the present invention, a projection optical system having a high zooming rate with a large viewing angle can be obtained. On the screen surface, the center of a projection image does not move due to zooming.
As in the embodiment of the present invention, by dividing the projection optical system into an optical system (first optical system) for zooming an image and an optical system (second optical system and reflection optical system) for enlarging an intermediate image obtained from the first optical system onto the screen based on functions, designing of an ultra-short focus image projection device can be facilitated.
For example, by using the first optical system as an enlarging/zooming optical system, the F number of the second optical system may be designed to be large.
According to another embodiment of the present invention, the normal (central normal) in the central position of the image display device and the optical axis 204 of the first optical system 201 are approximately on the same straight line, such that the center of an image projected onto the screen does not move due to zooming. That is, a position in which the optical axis 204 of the first optical system 201 passes through an image formed by the image display device may not move even due to zooming.
Accordingly, by setting a position of the image display device such that the optical axis 204 of the first optical system 201 passes through the inside or vicinity of the image formed by the image display device, movement of the projected image can be easily expected when zooming is performed by adjusting the first optical system 201.
For example, as shown in
While a term such as ‘lower’, ‘lower side’, or the like has been used in the foregoing description, it merely indicates a relative direction. For example, when
When the first optical system 201 and the second optical system 202 have the common optical axis 204 as described above, the central normal of the image display device needs to be moved in perpendicular to the common optical axis 204 to form the projection image in an inclined upward direction. In the telephoto end, the projection image moves downward with respect to the embodiment of
Moreover, in the current embodiment, the projection image interferes with the refractive lens of the second optical system 202 at the screen side in the telephoto end, such that the other area than a valid light area of the refractive lens of the second optical system 202 is cut.
In the lens structure of the wide-angle end in the upper portion in
In the lens structure in the wide-angle end shown in
Shown in Table 5 and Table 6 are (1) indication of whether each lens surface is aspheric, (2) a radius of curvature of each lens surface, (3) a distance, (4) a d-line refractive index, and (5) an Abbe number, when a surface number is added to a lens surface in the order of light incidence/emission, regarding the image display device as the first surface. The following values comply with specifications of the projection optical system in which a focal length f is more than 4.3 mm and less than 8.6 mm, an F number is more than 1.5 and less than 2.4, and a viewing angle in the wide-angle end is 74.02°.
Shown in Table 7 is distance data in zooming. Di indicates a distance of an interval di between a surface having a surface number i and a surface having a surface number (i+1).
Shown in Table 8 is aspheric data. The aspheric equation is the same as in the foregoing embodiment.
In Table 9, aspheric data of surface numbers 57, 58, and 59 is shown. In this case, the aspheric equation is given by
Z=ch
2/(1+SQRT{1−(1+k)c2H2})+C3h3+C4h4+C5h5+C6h6+C8h8+C9h9+C10h10.
In the current embodiment, the optical axis of the first optical system and the optical axis of the second optical system approximately coincide with each other, thereby reducing an error in assembly, caused by mismatch of the optical axes.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.
Number | Date | Country | Kind |
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2010-256278 | Nov 2010 | JP | national |