PROJECTION SCREEN OF GREAT LIGHT GAIN

Screen of light gain, used for low luminosity sources, such as video projectors, for instance, are usually slightly reflective; their concave shape allows them to guide the light so that the luminosity can be more or less uniform to the spectators at every point of its surface.

However, a screen cannot be mirrored, because, as anyone with a slight knowledge of optics knows, what would be seen, besides the room and the projector, would be the circle of the lens at the point corresponding to the lens of the projector existing in the virtual room on the other side of the surface of the mirror.

So the image can be seen, the surface of the screen must diffuse the light in all directions, so that the light can reach the spectators from each and every point of the screen, even if they change position. As the surface becomes more opaque, it starts to absorb light and the solution found to date now, is the use of slightly reflective dim pellicles (as if it were a dirty mirror, in which we can see hardly anything, but which still maintains some metallic brightness) being half way between mirrored and opaque. Nevertheless, in a bright environment, especially with low luminosity sources, the result is still unsatisfactory, because when the screen becomes semi-obscure, it only reflects part of the light, absorbing the rest, which is better in respect of a white wall, but is still far from being ideal. This has led to the designing of brighter projectors, with more powerful and expensive lamps, and a greater need for refrigeration, at prices which are inaccessible to the average person.

The solution now presented, though the pratical results are considered magnificent by professionals, is nevertheless very simple to accomplish: conjugation of materials in order to obtain the characteristics of the obscure screen as a light diffuser in a wider reflected beam, but without the consequent absorption of light, seeking to keep characteristics close to those of the mirror, i.e. with the maximum reflection capacity possible.

Therefore, besides the screen's structural support (1), two pellicles with very different actions were used: one (2), which is slightly translucent, produces almost without light absorption the scattering of the light that passes through it, due to the micrometrical irregularity of its surface. The second one (3), which completely mirrored, recedes the light in the oposite direction and, by crossing the first pellicle, scatters the light a bit more. Since the pellicles are thin, they can be adhesive, and the first one can also have other characteristics, such as a surface with a configuration of multiple tiny lenses side by side or having a fluted or wavy surface, vertically or crossed vertically and horizontally causing a sufficient scattering of the light by diffraction so that transparent material can be used in order to make even more use of the light.

In aii extreme experimental situation, at around midday in the sun, using side by side one of the best screens currently used and the sereen now presented, for a demonstration shooting, the latter screen was the only one to sustain an image with both a shape and colour reading.