Comparison and variations of the speed of radiographic film

A study of 50 different batches of film from 20 institutions across Ontario was conducted to measure sensitivities when exposed between intensifying screens and to white light. For films of different types but of the same nominal speed, the x-ray exposures required to produce a net optical density of 1.0 varied by a factor of up to 2.5. For films of the same type from different batches, the required exposure varied by +/- 20%. It was found that sensitivity to white light from the commonly used Wejex sensitometer was not always a good indicator of x-ray sensitivity, and therefore should not be used to compare speeds of different films or films from different batches.