3. Design and functions
Barco - OverView D series - Doc-3353-2 - user's manual - Revision 04 - April 2005
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3-4
3.2
Screen
The image is generated in the screen.
Fresnel lens
The screen consists of a Fresnel lens and a Front Element Screen. The Fresnel lens deflects the light coming from
the projection lens system such that it falls perpendicularly onto the front element screen.
Front element
The front element screen guarantees that the light is distributed horizontally and vertically, while maintaining a
high contrast.
Texture of surface
The surface of the screen has a special non-glare texture. This texture minimizes the direct reflection of the light
of the surrounding and contributes also to the high contrast of the screen.
3.3
Principle of DMD projection technology
For a one-chip projection system, the DMD is sequentially illuminated with the three primary colors, red, green,
and blue (RGB)
Figure 3-2
principle of a single-chip DLP projection system
A condenser lens collects the light, which is imaged onto the surface of a transmissive color wheel. A second lens
collects the light that passes through the color wheel and evenly illuminates the surface of the DMD. Depending
on the rotational state of the mirror (+12 or -12 degrees), the light is directed either into the pupil of the projec-
tion lens (on) or away from the pupil of the projection lens (off). The projection lens has two functions: (1) to
collect the light from each on-state mirror, and (2) to project an enlarged image of the mirror surface to a pro-
jection screen.
The example shows a color wheel with three segments red, green, and blue. It is also possible that the segments
for the primaries exist twice (RGBRGB), or that a white segment is added (RGBW).
