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Ultra short focal projection screens are specifically designed for projection in a bright environment with an ultra short focal projector. They have a technical canvas which returns in the axis of the screen, towards the spectators, the projected image and limits the reflection of the light coming from the video projector. This technical canvas also acts on the ambient light which it reflects outside the projection screen. The result: a more contrasted image and saturated colors, even in broad daylight.
Ultra short focal projection screen: controlling the light
Manufacturers of ultra short throw projectors often put forward as a decisive argument the possibility of projecting the image directly on a white wall. You just need to place the projector directly above the wall to immediately enjoy a big, beautiful picture. The reality is a little more nuanced ...
The surface of a wall, as clean and smooth as it is, does not make it possible to obtain an image as beautiful as a suitable screen. This is especially true during the day or in a lighted room, and more generally when you want to enjoy a beautiful, bright and contrasting image. The often clear walls are all surfaces that reflect light and in particular that emitted by the video projector itself, with an even more noticeable effect in the dark. Light pollution is the main enemy of contrast.
To meet the specific constraints of projection "at the foot of the wall" in a domestic environment that is lit or plunged into darkness but generates light pollution, several manufacturers offer projection screens with a specially adapted canvas. We generally speak of fabrics using an ALR technology (Ambient Light Rejecting).
Ultra short focal projection screen: technical canvas
These projection screens dedicated to ultra short throw video projectors are fitted with a technical canvas designed to control the scattering of light. It is most often a micro structured canvas, the surface of which has micro reliefs. This specific structure, which adopts very regular patterns, performs a dual function.
First, it directs the reflection of the light beam emitted by the video projector almost exclusively in the axis of the projection screen, towards the spectators. In doing so, it very significantly attenuates the reflection of light from the video projector on the walls and ceiling of the room. This greatly reduces a primary source of light pollution of the image, and helps maintain the darkness of the room for nighttime screenings.
In addition, these micro-reliefs on the surface of the projection screen divert light pollution from the walls and the ceiling outside the axis of the projection screen. The projection surface is almost no longer illuminated by ambient light reflections. Contrast is preserved.
Ultra short focal projection screen: flat surface
Ultra short throw projectors are placed very close to the screen and project with a closed angle to conventional projectors that are facing the screen.
Since they project almost in “grazing light” compared to the projection screen, they are extremely sensitive to the curling of the canvas. The slightest bump or ripple on the projection surface generates a deformation and can even result in the projection of a shadow on the part of the image behind this bump.
This is why it is highly recommended to opt for a fixed projection screen or for a tensioned electric projection screen when you want to use an ultra-short throw video projector, in order to avoid any problem of image geometry. .
Ultra short focal projection screen: what format?
Ultra short throw video projectors all adopt a 1080p HD or even UHD 4K matrix, in native 16/9 format. The manufacturers of dedicated projection screens therefore offer fixed projection screens in this format.
Ultra short focal projection screen: the concept of gain
The gain of a canvas indicates its property to absorb (negative gain, less than 1) or reflect light (positive gain, greater than 1). The higher the gain (value greater than 1), the more the canvas is able to reflect a significant amount of the light projected by the video projector. A gain measured at 1 is considered neutral.
A projection screen with a canvas with a high gain is therefore recommended with video projectors whose brightness is low, and for projection in broad daylight and in a bright environment. It is also recommended for installations where the distance between the video projector and the projection screen is large, for projecting a very large image, for example. In fact, the further you move the video projector away from the projection screen, the more you enlarge the image and the more its brightness decreases. A projection screen with a significant gain makes it possible to compensate for this phenomenon.
Conversely, with an ultra short focal length projector generally very bright and positioned very close to the screen, it is safe to use a projection screen whose gain is neutral (gain value = 1) or low (gain of 0.5). Screens with a gain greater than 1 may indeed cause a bright halo in the center of the image, if the projector is very bright or if it is installed a short distance from the projection screen.