Exposure time testing apparatus for focal-plane cameras

摘要

Herein is disclosed an apparatus and system for testing exposure times of focal-plane cameras of the shutter-curtain variety. After removal of the camera lens assembly and selection of the exposure time desired to be tested, there is fitted onto the camera body in front of its focal plane a removable testing unit comprising a light-tight cannister housing containing at least one vertical subminiature, high-intensity light source, at least one photosensitive photodiode, and electronic clock-timing circuitry. Also forming part of this system is a dummy roll of film, disposed within the focal plane, which is completely blackened except for a thin, vertical, light-reflecting strip. Said band is visually aligned with said light source parallel to the central axis of the camera aperture. To time exposure time, the light source is energized and the shutter curtains are released from spring loaded positions. A light beam from said source impinges upon the shutter curtains moving across the beam path until the normal exposure aperture between said curtains permits said beam to pass through said aperture and impinge upon said reflective band and be reflected back through said curtain aperture to impinge on said photodiode. Said diode then creates an electrical potential which enables said electronic clock-timing circuitry to output a signal susceptible to modulation for digital readout of exposure elapsed time on an external display device. When said curtains have traveled to the point where said aperture no longer passes the reflected light, the photodiode disables said circuitry, thereby stopping said clock and preserving the elapsed time readout.