US Patent 7230583 Scanned beam display with focal length adjustment

In a scanning display apparatus an image signal source produces an image signal. A light emitter is coupled to the image signal source and responsive to the image signal to emit light. A lensing system receives light from the light emitter and passes exiting light. A scanner scans the image light. A light sensor detects intensity of background light. A controller adjusts intensity of the image light in response to the detected background light intensity.