JPH04124980A - Focus adjusting device for front projector - Google Patents

Abstract

PURPOSE:To easily and rapidly execute the adjusting of focus by adjusting the focus by adjusting the focus of a projecting lens and making the positions of two spots projected on a screen by a projecting device coincident. CONSTITUTION:Two groups of light flux 7 and 7' emitted from two optical fibers 6 and 6' are projected on a position except the picture of the lower edge center part neighborhood of a screen 3 as two spots 8 and 8' and the two spots 8 and 8' changes their size by adjusting the focus of a projecting lens 2 and moves differentially right and left simultaneously. Then, focusing can be executed by making the positions of the right and left spots coincident on the screen 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a focus adjustment device for a front projector.

[Summary of the Invention] The present invention takes out two groups of light beams in the left-right direction from near the center of the upper side of the liquid crystal panel of a color liquid crystal projector, for example, and adjusts the focus of the projection lens to adjust the light beams of the two groups in the left-right direction. The optimum focus is obtained by aligning the positions of the two spots on the screen.

[Prior Art and its Problems] A lens-type front projector does not require RGB registration adjustment and can freely change the projection distance, but requires focus adjustment. Conventionally, adjustments were made while looking at the image on the screen, which resulted in differences in the way the adjustments were made and the problem that adjustments could not be made quickly.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention extracts two groups of light beams in the horizontal direction from near the center of the upper side of the display surface of the source display device constituting the front projector. By adjusting the focus of the projection lens, a configuration is adopted in which the positions of two spots of the two groups of light beams on the screen in the left-right direction are made to match, thereby obtaining the optimum focus.

(Embodiment J Two embodiments in which the present invention is applied to a single-panel color liquid crystal projector will be described below.As a color liquid crystal projector, a liquid crystal whose display mode is twisted nematic mode,
A device employing an active matrix driving method using a thin film transistor (TPT) is known. Therefore, an embodiment will be described in which the present invention is applied to the color liquid crystal projector described above, one having a structure with a coarse pixel pitch and the other having a structure with a fine pixel pitch.

(First Embodiment) The one shown in Fig. 1 is an embodiment applied to a structure with a fine pixel pitch.
3 is a projection lens, 3 is a screen, 4 is a light source such as a metal halide lamp, 5 is a cold reflector (visible light reflecting paraboloid! These are two optical fibers fixed to the liquid crystal plate surface and arranged so as to intersect with the liquid crystal plate surface in order to extract a group of light beams.The two optical fibers 6
．． 6°, it is possible to produce a light beam of 7.7° with a small divergence angle toward the left and right peripheral portions of the projection lens 2.

To explain the focus adjustment in this embodiment, two groups of light beams 7.
7° is projected as two spots 8.8° at a position outside the image near the center of the lower side of the screen 3 as shown in FIG. By adjusting, the size changes and at the same time it moves differentially to the left and right (.Then, by aligning the positions of the left and right spots on the screen 3, focusing can be performed.

(Second Embodiment) The embodiment shown in Fig. 2 is applied to a structure with a coarse pixel pitch.The difference from the first embodiment is that two optical fibers of 6.6゜ are connected from the surface of the source display device. The difference is that they are staggered and arranged in an intersecting manner, but the rest is the same as the first embodiment.

To explain the second embodiment in detail, a light beam 7 with a small divergence angle toward the left and right peripheral parts of the projection lens 2 is directed to the left and right peripheral parts of the projection lens 2 by two optical fibers 6.6' disposed intersectingly and offset from the liquid crystal plate surface near the center of the upper side of the liquid crystal plate l. .7° is produced.

To explain the focus adjustment in this embodiment, two groups of light beams 7.7
As shown in Fig. 3, the angle is projected as two spots 8.8° at a position outside the image near the center of the lower side of the screen 3, but these two spots 8.8° are focused on the projection lens 2. As the size of the adjustment changes, it moves left and right at the same time, and focusing can be performed by matching the positions of the left and right spots on the screen 3.

Here, to explain the reason why the two optical fibers are arranged so as to be offset from the liquid crystal plate surface, by shifting the intersection point 9 of the two optical fibers to the front of the position of the liquid crystal plate 1, the light emitted from the pixels is slightly diffused. This is because by setting the position to be the position of the object point, it is possible to make image roughness and horizontal lines between horizontal lines less noticeable even if the pixel pitch of the liquid crystal plate is coarse and the aperture ratio is low.

In the case of a liquid crystal display employing the active matrix driving method, as shown in FIG. 4, the cell structure includes a portion 10 that becomes a pixel and a portion 11 that becomes a shadow against light where thin film transistors and wiring are located. If the pixel pitch is coarse, the portion 11 having the above shape becomes a horizontal line between horizontal lines and stands out. Therefore, the optimum position 12 of the object point is projected onto the screen so that the light transmitted through the portion 10 that becomes the pixel is diffused and the pixel becomes inconspicuous. Therefore, in the case of the second embodiment, it is clear that it is appropriate to adjust the focus by setting the intersection point 9 of the two optical fibers at the optimum position 12 of the object point as described above.

In both of the above embodiments, as shown in FIG. 3, the projection positions of the two light beam spots at 8.8 degrees are slightly shifted up and down to prevent them from overlapping, in order to make it easier to see the spot positions when adjusting the focus. It's for a reason.

Although the embodiments of the present invention have been described above using a single-panel color liquid crystal projector, the present invention is not limited to this, and can also be applied to focus adjustment of a three-panel color liquid crystal projector or a projector that employs an index tube. Further, instead of the two optical fibers, two semiconductor lasers may be fixedly attached near the center of the upper side of the source display device to serve as a spot light source.

[Effects of the Invention] As is clear from the above detailed description, the present invention allows focus adjustment to be performed easily and quickly regardless of whether the pixels of the source display device are coarse or fine. This has the effect of making it possible.

[Brief explanation of the drawing]

1 and 2 are explanatory diagrams of an embodiment of the present invention, FIG. 3 is a diagram showing the position of a spot on a screen, and FIG. 4 is an explanatory diagram of a second embodiment. 1. Source display device 2. Projection lens 3. Screen 4. Light source 5. Cold reflector 6
,6°...Optical fiber 7.7°...Light flux 8.
8゛...Spot 9...Optical fiber crossover, ton

Claims (1)

[Claims] a projection device that extracts two groups of light beams from near the center of the upper side of the display surface of the source display device in the left-right direction and projects them onto the screen, and adjusts the focus of the projection lens and projects them onto the screen by the projection device; A focus adjustment device for a front projector, characterized in that the focus is adjusted by matching the positions of two spots.