photochronograph

from The Century Dictionary.

• noun An instrument for taking photochronographic pictures. See photochronography.
• noun A picture taken by this method.
• noun An instrument for the observation of star-transits by photography.
• noun A chronograph in which the tracing or record is made by the action of a pencil of light on a sensitized surface.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Physics) An instrument for recording minute intervals of time. The record is made by the power of a magnetic field, due to an electric signaling current, to turn the plane of polarization of light. A flash, coinciding in time and duration with the signal, is thus produced and is photographed on a moving plate.
• noun (Astron.) An instrument for the photographic recording of star transits.