| 摘要 |
The elevated projection head of a conventional overhead projector is equipped with a flip panel of opaque material which, in a free-hanging vertical position, blocks light from the projection head and, in a raised position, is clear of the projected light path. The flip panel is attached to the projection head by a free-flexing hinge element to facilitate flipping the panel between its two positions of use. During presentations made with use of the overhead projector, the necessity for turning the projector off and on during brief interruptions of the presentations or while changing transparencies is eliminated. The structure of the projection head need not be altered to accept the flip panel attachment.
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