| 摘要 |
A device may include a magnifying lens having a focal length that defines a focal plane, a light source providing visible light directed toward the focal plane, and a controller. The controller may be programmed to receive a signal indicative of the distance from the device to an object, cause the light source to emit light at a first brightness if the distance is at least substantially equal to the focal length of the lens, and cause the light source to emit light at a second brightness, dimmer than the first brightness, if the distance is not at least substantially equal to the focal length of the lens.
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