Remotely operable electronic apparatus are applied to distance measurement and picture/sound recording wherein, for example, a remote unit may be equipped with a microphone and an active range finder coupled to an auto-focussing capability. In one embodiment a camera is adapted to transmit a signal to the remote unit which returns a signal enabling the camera to accurately calculate distance and adjust focus in accordance with time-of-flight. The transponder preferably forms part of a wireless microphone, with the signal transmitted by the camera being preferably acoustical in nature. The acoustical signal transmitted by the camera is preferably modulated onto a return RF signal, enabling at least a portion of the audio circuitry associated with voice modulation to be used for the purpose of modulating the ranging signal, thereby realizing a very efficient and economical approach to remote sound detection and active ranging finding.