Optics: image projectors – Distortion compensation – For projection axis inclined to screen
Patent
1996-10-21
1998-03-24
Dowling, William
Optics: image projectors
Distortion compensation
For projection axis inclined to screen
353DIG3, 353 69, G03B 2114
Patent
active
057305170
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a projector of the kind defined in the preamble of claim 1. The basic object of the invention is to enable a horizontal transparent image to be reproduced on a vertical screen, and to enable the image to be switched between a position in which it lies to the right or to the left of the projector to a position in which it lies to the left or to the right of said projector while, at the same time, lying either beneath or above the projection head with correct reproduction or imaging on a vertical screen.
According to a first embodiment of the invention, the four-cornered intended for positioning of the image, or picture, is square, meaning that an image can be arranged thereon in different ways, therewith enabling the object of the invention to be achieved by swinging the projection direction through an angle of 90 degrees. According to a second embodiment, the image is rectangular, which is necessary for instance when the image is a TV image. The projection direction must then be rotated through 180 degrees, in order to achieve the general object of the invention.
A known overhead projector (Swedish Patent 8701304-1, Publication No. 457,022) enables an image to be projected on a vertical screen without being twisted or distorted, both above and to one side of the projector. This projector has also the feature of being totally non-glare.
It is a significant disadvantage when an image can be projected only on one side of the projector. It may be desirable to be able to alternate between right-side and left-side projection with one and the same projector, in view of the disposition of the room and the viewers. Lateral projection has important ergonomical advantages, since the operator is able to stand in front of the projector without obstructing the projected light or blocking the picture or image. These drawbacks are apparent with present-day overhead projectors.
When using an overhead projector according to the first embodiment, with the projection head placed so that the orthogonal projection of the head onto the object plate lies in the vicinity of one corner of the object plate facing towards the projection screen, it is possible to alternate or switch between right-side and left-side projection, by rotating the projector through 90 degrees in the horizontal plane so that the projection head will still lie above one corner of the object plate nearest the screen, while at the same time swinging the projection direction through 90 degrees in an opposite direction. This enables the overhead projector to be placed on any side of the wall or projection screen observed by the viewers. When the projection head lies on the right as seen from the auditorium, the image or picture will lie to the right of the projector, whereas when the projection head lies to the left, the image or picture will lie on the left of the projector.
When considering the optical beam path, while ignoring reflection, it will be seen that the image and its reproduction are displaced or offset in relation to the main axis of the lens system, which places high demands on the wide angle properties. Swedish Patent Specification 8803253-7, Publication No. 468335, discloses one example of a usable lens system. According to one embodiment of the invention, the component lens elements have their optical axes parallel but laterally displaced. This reduces the number of lenses required and/or improves image resolution.
The invention can be applied both when the projected image or picture is comprised of a large diapositive, overhead projector, and for projecting electronically generated images by means of an LCD screen. Hitherto, the projection of such images has not been successful in practice, for different reasons. One particular problem in this regard resides in the low thermal resistivity. This problem can be minimized by allowing light that is incident from the illuminating apparatus and which shall not be projected through the objective to spread out in all directions instead of being absorbed. LCD screens th
REFERENCES:
patent: 4133605 (1979-01-01), Wiggin
patent: 5467152 (1995-11-01), Wilson et al.
Patent Abstracts of Japan, vol. 9, No. 54, P-340, abstract of JP, A, 59-192236 (Nippon Denki K.K.) Oct. 31, 1984.
Dowling William
Optica Nova Onab AB
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