Novel methods for measuring the shutter speed of film cameras using image processing

Abstract

In photography, there are three exposure parameters: the shutter speed, the aperture, and the film sensitivity (ISO). In modern cameras, the camera body is responsible for setting the shutter speed (i.e., exposure time) and the ISO, while film cameras set only the shutter speed, therefore it is their main performance parameter. The shutter mechanism in most film cameras is mechanical, involving the use of springs. The springs wear in time, leading to losing the calibration of the shutter speed, thus the exposure time becomes longer than the designed value. The accurate measurement of the shutter speed is thus a very important performance evaluation process that allows a proper estimation of the camera's market value. This paper presents two innovative methods that allows the precise measurement of a camera's shutter speed using image processing. They involve the recording of the mechanical shutter during the exposure process using a high-speed camera, then applying the corresponding image processing algorithm on each of the recorded frames to automatically determine the exposure time. The paper presents the experimental setup, the image processing algorithms and the results obtained during testing.