JP2001092007A - Overhead projector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an overhead projector which projects a picture free from trapezoidal distortion on a projection screen by resolving the problem of a conventional overhead projector that an unsightly trapezoidal distortion is caused because a picture is magnified and projected in order to show the projected picture to many spectators. SOLUTION: The overhead projector is used to project and show materials like transparent films where pictures including characters, line drawings, photographs, etc., are recorded. A projection reflection mirror 2 is inclined at 45 deg. from a chart surface 3 and an optical axis 11 of a projection lens 1, and the projection reflection mirror 2 is practically integrated with the projection lens into a head unit A, and the chart surface 3 is so arranged that it may be always placed in the tangential direction of a circle which has a rotation center 111 of the head unit A as the center and has the distance to the chart surface 3 as a radius R when the head unit A is inclined in accordance with a projection position with the optical center of the projection lens 1 as the rotation center 111 of the head unit A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overhead projector for projecting an image having a small trapezoidal distortion on a projection screen.

[0002]

2. Description of the Related Art Overhead projectors are used to project images including characters, line drawings, photographs, and the like recorded on a transparent film or the like.

In order to show a projected image to a large audience using an overhead projector in a large venue,
It is necessary to project an image with a large magnification upward.

Further, in order to project a large image at an appropriate upper position which is easy for the audience to see using a conventional overhead projector, as shown in FIG. I had to tilt my back more than 45 °.

[0005]

As shown in FIG. 3, when the angle of elevation of the reflecting mirror 2 is further tilted from 45 ° to θ °, the angle of elevation of the projected image with respect to the projection plane becomes 2 °.
θ °.

In this case, the square image 31 placed on the chart surface 3 is displayed on the projection screen surface 4 as an image 4 having a large trapezoidal distortion.
2, a large trapezoidal distortion occurs when projecting a large image to a large audience, and the trapezoidal distortion remains even if the projection screen is tilted forward so as to correct the elevation angle of the reflection mirror 2. It was unsightly and improvement was desired.

As shown in FIG. 4, the conventional overhead projector can project an image free of trapezoidal distortion because the inclination angle of the reflection mirror 2 is set to the chart surface 3.
Alternatively, the angle is set to 45 ° with respect to the optical axis of the projection lens 1, and the square image 31 placed on the horizontal chart surface 3
Forms an image 41 without trapezoidal distortion on the vertical screen surface 4.

However, in this usage, since the overhead projector must be set at a position substantially at the center of the projection screen surface 4, at least half of the projected image is formed below the height of the reflection mirror 2, and a small projected image is formed. Although suitable for showing to a small number of people, there is a problem that it is not practical to show to a large number of people in a large venue because the overhead projector hinders the audience's field of view.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems. That is, the overhead projector of the present invention is substantially integrated with the projection lens by inclining the reflection mirror by 45 ° with respect to the chart surface and the optical axis of the projection lens as in the example shown in FIGS. Regardless of height, the overhead projector is characterized in that the chart surface is always arranged in the tangential direction of a circle whose radius is the distance between the optical center of the projection lens and the chart surface. is there.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in more detail with reference to FIGS. FIG. 1 is a schematic diagram of an optical path for explaining a head unit according to an embodiment of the present invention. The projection mirror 1 is inclined by 45 ° with respect to a chart surface 3 and an optical axis 11 of the projection lens 1. The head unit A is integrated.

The head unit A is connected to a chart base B by an arm C such that the chart surface 3 is perpendicular to the optical axis 11 of the projection lens 1, and the optical axis 111 of the projection lens 1 is used as a central axis. It has a rotatable structure. Since the head unit A can be rotated in accordance with the projection position, the optical path exiting from the head unit A can be set on the back. Further, with this structure, the chart surface 3 is always arranged in the tangential direction of the circle drawn by the arm C about the optical center 111 of the projection lens 1.

In this embodiment of the present invention, the reflection mirror 2 is always mechanically held at 45 ° with respect to the chart surface 3 and the optical axis 11 of the projection lens 1 regardless of the projection position. No trapezoidal distortion of the projected image occurs.

FIG. 2 is a schematic diagram showing an optical path in the case of projecting on the back using the overhead projector according to the embodiment of the present invention described with reference to FIG.

In order to show a greatly enlarged projected image to a large audience, the head unit A is rotated on the back, and the optical path from the head unit A is moved on the back to adjust the projection position.

As described above, even when the position of the projected image is turned upward, the chart surface 3 is always arranged in the tangential direction of a circle whose radius is the distance R from the optical center 111 of the projection lens 1 as described above. So, as shown in FIG.
No trapezoidal distortion of the projected image occurs when the projection position is adjusted with only the reflection mirror 2 turned on the back using a conventional overhead projector.

When the overhead projector of the present invention projects on a vertical projection surface such as a wall surface, a trapezoidal distortion occurs because the optical path passing through the optical axis of the projection lens 1 on the reflection mirror 2 side and the projection surface do not become perpendicular. As shown in FIG. 2, when the head unit A is turned upright by β ° as shown in FIG. 2, the projection screen surface is inclined forward by β °, and the projection surface 4 is turned to the optical axis on the reflection mirror 2 side of the projection lens 1. , The trapezoidal distortion of the projected image can be eliminated.

As an embodiment of the present invention, a mechanism for mechanically directly connecting the head unit A and the chart surface 3 has been described, but the present invention is not limited to this.

That is, the present invention can be practiced with a mechanism for individually controlling the head unit A and the chart surface 3 without mechanically directly connecting them. That is, the reflection mirror 2 is fixed at an angle of 45 ° with respect to the chart surface 3 and the optical axis 11 of the projection lens 1 and is integrated with the projection lens 1 so that the optical center 111 of the projection lens 1 and the chart surface 3 A structure that allows the chart surface 3 to be movably arranged in the tangential direction of a circle having a distance R as a radius R, and a mechanism for arranging the chart surface 3 at a position perpendicular to the optical axis 11 of the projection lens 1 when projecting. It may be an overhead projector that has.

The present invention can be applied not only to a transmission overhead projector but also to a reflection overhead projector.

[0020]

According to the present invention, the reflection mirror 2 is always at 45 ° with respect to the chart surface 3 and the optical axis 11 of the projection lens 1.
Since the projected image has no trapezoidal distortion, it is possible to form an image without trapezoidal distortion even when projecting a large image for a large number of people in a large conference hall. Suitable as an overhead projector.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a head unit A in which a reflecting mirror 2 is inclined by 45 ° with respect to a chart surface 3 and an optical axis 11 of a projection lens 1 and a lens, and an optical path to be projected by the lens, in an embodiment of the present invention. FIG.

FIG. 2 is a schematic diagram showing an optical path in a case where an overhead projector according to an embodiment of the present invention is used to project upward from the back.

FIG. 3 is a schematic diagram showing an optical path of a transmission type overhead projector of the related art.

FIG. 4 is a schematic diagram illustrating an optical path when an image without trapezoidal distortion is projected by a conventional overhead projector.

[Explanation of symbols]

Reference Signs List A Head unit B Chart table C Arm connecting head and chart surface R Distance between optical center of lens and chart surface 1 Projection lens 2 Reflection mirror 3 Chart surface 4 Projection screen surface 5 Light source lamp 11 Optical axis of projection lens 31 Chart Figure 41 of a square placed on the surface 41 Image without trapezoidal distortion 31 projected on the projection screen surface 42 Image with 31 trapezoidal distortions projected on the projection screen surface 111 Optical center of projection lens / head unit A Rotation center

Claims (1)

[Claims] 1. A reflection mirror which is inclined at 45 ° with respect to the chart surface and the optical axis of the projection lens to be substantially integrated with the projection lens, so that the chart surface is always optically irrespective of the height of the projection position. An overhead projector characterized by being arranged in a tangential direction of a circle having a radius of a distance between a target center and a chart surface.