| 摘要 |
PROBLEM TO BE SOLVED: To make the depth of an entire back projection device as small as possible by allowing a deflection mirror to exist at a position where a minimum angle formed by luminous flux to the surface of a screen while performing deflection is a specified angle which is small. SOLUTION: The deflection mirror 3 is arranged at the angleδwith the projection surface of the screen 2. It is the best to set the upper limit of the angleδto 45 deg.+β-α/4 in order to make the depth of the device minimum. The angle generally defined as the angleβis 0 deg., but it is possible to set the angle smaller than 10 deg. or 5 deg. instead of 20 deg. being the upper limit. Thus, the depth (t) of the device can be made minimum and simultaneously a projection assembly 1 is prevented from projecting from the screen side of the device. Therefore, the optical path of a light beam is bent by the mirror 3, so that the depth of a housing, that is, the depth of the entire back projection device is made small.
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