GB2229014A

GB2229014A - Overhead projector optical system

Info

Publication number: GB2229014A
Application number: GB8905152A
Authority: GB
Inventors: Michiro Tsuchida
Original assignee: NIPPON AIDEX CO Ltd
Current assignee: NIPPON AIDEX CO Ltd
Priority date: 1989-03-07
Filing date: 1989-03-07
Publication date: 1990-09-12
Also published as: DE3908871A1; FR2644253A1; GB8905152D0

Description

- - - - 1 n OVERHEAD PROJECTOR The present invention relates to an

overhead projector.

Fig. 3 shows the basic composition of a conventional overhead projector.

Referring to Fig. 3, numerals represent various components as follows; 1 for a light source, e.g. halogen bulb, 2 for a reflection type focusing lens immediately underneath a stage arranged across an optical axis k of the light source 1 for collecting the light of the light source 1, 3 for a first projection lens arranged across the optical axis k of the light reflected from the focusing lens 2 in cooperative positional relationship with said light source 1, 4 for a reflection mirror which bends the optical axis k passing through the projection lens 3 in the direction of a screen 5 while projecting light onto said screen 5 and 5 for said screen arranged vertical to the optional axis k after being bent rectangularly. Said reflection mirror 4 is mixed at the first projection lens 3 with an inclination angle of 450 to the screen 5.

The light source 1 and the first projection lens 3 can move in the direction vertical to the screen 5 while maintaining said cooperative positional relationship.

Because of such a configuration as described above, when an object of projection is placed on the stage, the image of the object is magnified by the first projection lens 3 and projected on the screen 5 by means of the reflection mirror 4.

However, a conventionl projector known in the prior art is constructed in such a structure that only an object of projection is projected. Therefore, if entering of new information (letter, figure, etc.) on the object of projection is required, the user must write information on said object of projection using a writing tool.

Such additional writing is operable as long as the volume of additional information is not so much. However, once the volume is excessive and multilateral-, it often occurs that information written on the object of projection is so duplicated and complicated as projected image cannot be understood easily. For instance, when a detail of the description on the object of projection is to be classified or masked according to a preferred pattern, it is not possible to classify or mask any portion which was once classified or masked before. In order to avoid duplication of written information for easy understanding, it is preferred to erase information once written. However, such erasing is so laborious as presentation or lecture, etc. cannot be operated smoothly

41 while adversely affecting the efficiency.

The present invention has been accomplished in order for solving such conventional problems. An object of the present invention is to provide such an overhead projector as a second projection image is easily added to a first projection image without requiring to use a writing tool while an added second projection image being removable easily out of a first projection image and vise versa.

An overhead projector according to the present invention comprises a light source, a reflection type focusing lens arranged across an optical axis thereof for focusing light emitted from said light source, a first projection lens arranged across an optical axis of light reflected by said focusing lens and a reflection mirror which reflects an optical axis of light, emitted from said light source and passing through said first projection lens, in a direction towards a screen and projects an image on said screen; wherein a transparent type focusing lens and a second projection lens are arranged. sequentially from the light source side.

A first object of projection, placed on said reflection type focusing lens, is projected on a screen as a first projection image by means of a first projection lens and a reflection mirror, in the same way as before.

is On the other hand, a projector is composed by means of a light source, a transparent type focusing lens, a second projection lens and a reflection type focusing lens, with said reflection type focusing lens acting as a screen. Therefore, a second object of projection, placed on a stage positioned between said transparent type focusing lens and the second projection lens, is projected on said reflection type focusing lens acting as a screen. The projected image is also projected on the screen as a second projection image by means of the first projection lens and the reflection mirror.

Therefore, said first and second projection images can be projected in superposition on the screen by making the images the same in size. In addition, any one of the first and second projection images as projected in superposition is removable by removing the relevant object of projection of the first or second projection objects.

Fig. 1 shows the basic composition view of an overhead projector according to an embodiment of the present invention. Fig. 2 is the expanded view of an important portion of Fig. 1. Fig. 3 shows the basic composition view of an overhead projector known in the prior art. 1 - Light source 2 Reflection type focusing lens i -1 3 - First projection lens 41 9 Reflection mirrors 5 - Screen 6 - Transparent type focusing lens 7 Second projection lens k - Optical axis Fig. 2 shows the basic composition of an overhead projector according to an embodiment of the present invention.

Referring to Fig. 2, numerals 1 - 5 shows the same portions as those with Fig. 3; 6 for transport type focusing lens, 7 for a second projection lens, 8 for a stage and 9 for a reflection mirror for reflecting the optical axis k of a light source 1, towards a reflection type focusing lens 2.

Said light source 1, transparent type focusing lens 6, second projection lens 7 and said reflection type focusing lens 2 construct a projector with said reflection type focusing lens 2 acting as a screen (hereinafter referred to as subprojector).

A single focus type lens is used as said reflection type focusing lens 2. Therefore, the variation of a projections iris occurs, associated with the change of view angle because the lens angle is made larger. Thus, light quantity becomes insufficient in the outer periphery of 1 the lens for projection. In order to compensate such insufficient light quantity, the reflection surface of said reflection type focusing lens 2 is made non-spherical. More explicitly referring to Fig. 2, the reflection surface 2a of the reflection type focusing lens 2 is made nonspherical so that a light beam kl, emitted from the reflection type focusing lens 2 and corresponding to each view angle, certainly enters the injection iris of the first projection lens 3.

Next, detailed operation will be described in the following.

Now, a first object of projection, e.g. a map describing only geographical shape of Japan is placed on the stage of the reflection type focusing lens 2. Then, said geographical shape is projected on the screen 5 by means of the first projection lens 3 and the reflection mirror 4, as a first projection image.

On the other hand, with this geographical shape still projected, a Japanese road map, for instance, is placed as a second object of projection on the stage 8. Then, this is projected on the reflection type focusing lens 2 which functions as a screen. The projection image is projected on the screen 5 as a second projection image. At that time, both first and second projection images are magnified so that their sizes become the same on the screen 5.

1 Thus, a road network is projected on the screen 5 in superposition with the geographical shape of Japan.

In place of said road map, a railroad map of Japan can be set on the stage 8. Then, the railway network of Japan is projected in superposition with the geographical shape of Japan. When the geographical shape is removed out of the stage on the contrary, only the railway network is projected.

When the subprojector is not used, the device is operable also as a projector provided with the same functions as conventional devices known in the prior art.

As described above, the first projection image coming from the first object of projection and the second projection image coming from the second object of projection can be projected in superposition whenever required, on the screen. Therefore, the second projection image is easily added to the first projection image while also the added second projection image being removable easily out of the first projection image, and vise versa.

Accordingly, the user can create a projection image easily discriminable avoding the duplication of anothe-r projection image to be added thereto, thereby proceeding more efficiently with lecture, presentation, etc.

Claims

1. In an overhead projector comprising a light source, a reflecting type focusing lens arranged across an optical axis thereof f or focusing light emitted from said light source, a first projedtion lens arranged across an optical axis of light reflected by said focusing lens and a reflection mirror which reflects an optical axis of light, emitted from said light source and passing through said first projection lens, in a direction towards a screen and projects an image on said screen; the overhead projector wherein a transparent type focusing lens and a second projection lens are arranged sequentially from the light source side.

2. An overhead projector comprising a light source, a reflection focusing lens for focusing light emitted from said light source, a first projection lens disposed in the path of light reflected by said focusing lens and a reflection mirror for reflecting light emitted by said light source through said first projection lens so as to project an image on a screen, a transparent focusing lens and a second projection lens being sequentially in the path of light emitted by the light source.

3. An overhead projector substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

Published 1990 at The Patent Office. StateHouse.6671 High Holborn. londonWCIR4TF-FILL-ther copies maybe obtained froin The Patent 0-11,, Wes Branch, St Mary Cray. Orpington. Kent BR5 3RD. Printed by Multiplex techniques ltd. St Mary Cray. Ken', Con 1!87