Which film speed requires greater exposure to obtain the same image density?

• A. Slow speed film
• B. Fast speed film
• C. Medium speed film
• D. High-speed film

Answer: (A)

Film speed is about how sensitive the film emulsion is to X-ray exposure. The slower the film, the less sensitive its emulsion is, so you need more X-ray photons to create enough latent image centers to reach the same visible density after development. In contrast, faster films are more sensitive and reach the same density with fewer photons. So the slowest film requires greater exposure to obtain the same image density. This is why slower films give finer detail but require higher patient exposure, while faster films reduce dose but may have coarser grain.