Photocopying – Projection printing and copying cameras – With focusing or projection screen
Reexamination Certificate
2001-02-09
2003-07-15
Gray, David M. (Department: 2851)
Photocopying
Projection printing and copying cameras
With focusing or projection screen
C355S032000, C355S043000, C355S045000, C355S046000, C353S030000, C353S031000, C353S034000, C353S038000, C353S040000, C353S122000, C349S005000, C349S007000, C349S067000, C349S108000
Reexamination Certificate
active
06593996
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an illuminating device having an optical integrator, especially for a system for projecting or displaying images. It also relates to such a system.
BACKGROUND OF THE INVENTION
In the projection (or display) of images, especially of television type, it is known practice to use a liquid-crystal optical valve, the transparency of each image-forming element of which is controlled as a function of the luminance of each point of the image to be formed.
The luminous energy for the projection is delivered by an illuminating device behind the valve and an optical system in front of the valve projects the image onto a screen. It is also possible to display the valve either directly or by way of an optical magnifying system.
In order for the projected or displayed image to correctly restore the image formed in the valve, it is necessary for the illuminating of the valve to be uniform. This problem is not easily solved, in particular, because the illumination originates from a source of limited extent.
One solution consists in using an optical integrator. An example of a known projector having an integrator is depicted in FIG.
1
.
In this example, the source
10
is associated with a reflector
12
and the pencils of light reflected by this reflector are collected by a first array
14
of small lenses
14
1
,
14
2
. . . .
The shape (contour) and the proportions of each lens
14
i
correspond, preferably, to the shape and to the proportions of the optical valve
16
. For example, if the valve is rectangular with proportions of 4:3 or 16:9, the lenses will exhibit the same proportions. With each of these lenses
14
i
there is associated another small lens
18
i
of a second array
18
. This lens
18
i
is arranged in such a way that it forms the image of the lens
14
i
over the whole extent of the valve
16
. Thus, even if the various pencils of light originating from the reflector
12
have different energies, this heterogeneity does not result in a heterogeneity of illumination on the valve
16
, since the energy of each pencil is distributed over the whole surface of the valve. Furthermore, if the shape and the proportions of each lens
14
i
correspond to the shape and to the proportions of the valve
16
, losses of light are minimized.
The reflector
12
is, for example, elliptical and the source
10
is arranged at the first focus and the pencils received by the lenses
14
i
are slightly convergent.
A projection objective
20
is provided downstream of the valve
16
.
This projection system is of fairly high cost, especially since its various optical components are of large dimensions.
SUMMARY OF THE INVENTION
The invention makes it possible to reduce the dimensions of the optical components.
It starts from the finding that the aperture of the projection objective depends on the angle a at which the centre 0 of the valve sees the second array
18
of lenses and that it is therefore beneficial to decrease this angle and, as a consequence, to decrease the extent of the integrator.
Starting from this finding, the inventors have observed that the surface of the array
18
is not used in an optimal manner. This observation appears in
FIG. 1
a
where it may be seen that the array
18
, of circular general shape, is illuminated at localized sites
22
1
,
22
2
, etc., that is to say sites which are separated from one another, the sum of the areas of the illuminated zones being substantially less than the area of the disk formed by the array
18
.
The illuminating device according to the invention is characterized in that it comprises a means for focusing the light pencils from the reflector onto the integrator.
Thus, each lens of the first array is illuminated at a considerable angle; as a result of this the associated lens of the second array, which lens is intended to image the first lens on the valve, also receives a light beam of considerable angle, this making it possible to increase, preferably maximize, the area of the illuminated part of the second array of lenses. Furthermore, it is possible to minimize the dimensions of the optical integrator, thereby minimizing its cost. Decreasing dimensions of the arrays of the integrator leads to the desired decrease in the angle at which the valve sees the integrator and hence a decrease in the aperture of the projection objective.
Decreasing the aperture of the projection objective makes it possible to increase the contrast since it is known that the use of light rays which are steeply inclined with respect to the normal to the plane of a liquid-crystal valve leads to a decrease in the contrast.
To focus the beam from the reflector onto the integrator, there is provided either a focusing lens or an appropriately shaped reflector, for example an elliptically shaped reflector in which the source is arranged at the first focus and the integrator at the second focus.
The position of the integrator at a point of convergence of the beam makes it possible to use this integrator in a device for projecting or displaying colour images employing a single valve in which each image point is formed from several (in general three) image elements, each of these elements being assigned to a specified colour (red, green and blue, for example), the optical illuminating system being such that a light beam of a specified colour reaches only the image element assigned to this colour. The coloured beams are created from a source of white light and from means of angular separation according to colour. The position of the integrator is such that it does not modify the relative orientation of the rays and thus makes it possible to retain the angular separation of the colours.
In one embodiment, each beam of a specified colour illuminates a part of the surface of the integrator which is assigned thereto. Stated otherwise, the surface of the integrator is divided into several distinct parts and each part is used for a single colour. As a variant, provision is made for juxtaposed integrators, the number of integrators being equal to the number of colours.
In embodiments in which maximum illumination on the valve is desired, a collecting lens is employed between the integrator and the valve so as to superimpose the various beams reaching the screen.
If no collecting lens is used, it is possible to maximize the uniformity of illumination and hence the contrast of the projected or displayed image.
REFERENCES:
patent: 4770525 (1988-09-01), Umeda et al.
patent: 5098184 (1992-03-01), van den Brandt et al.
patent: 5150138 (1992-09-01), Nakanishi et al.
patent: 5418583 (1995-05-01), Masumoto
patent: 5467206 (1995-11-01), Loiseaux et al.
patent: 5701169 (1997-12-01), Yoshioka
patent: 5755503 (1998-05-01), Chen et al.
patent: 5758940 (1998-06-01), Ogino et al.
patent: 5786939 (1998-07-01), Watanabe
patent: 5865521 (1999-02-01), Hashizume et al.
Battarel Denis
Drazic Valter
Brown Khaled
Fried Harvey D.
Gray David M.
Kolodka Joseph J.
Thomson Licensing SA
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