| 摘要 |
A device to attach to an optical projector having a beam opening for passage of a beam of light rays to project a primary image on a main surface, a lens system to simultaneously produce a duplicate image of the primary image on a second surface beamed in a direction different from that of the primary image and which includes a hollow tubular member mounted to the projector and including a first and a second spaced plane mirror oriented with respect to one another to project a secondary beam through the member and wherein the first plane mirror is oriented in the peripheral zone of the path of the main beam of light from the projector.
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