A Tedious Explanation of the f/stop
by Matthew Cole Photographers set their exposure using a combination of shutter speeds and f/stops to get the correct amount of light on the sensor (or film). The shutter speed regulates how long the sensor is exposed to light coming through the lens. The f/stop regulates how much light is allowed through the lens by varying the size of the hole the light comes through. For any given film speed (ISO) and lighting combination there is one correct amount of light to properly expose the image. This amount of light can be achieved with many different combinations of f/stops and shutter speeds. Back in the days of film, that was pretty much it for exposure because your ISO (and white balance too) was set by your film choice and you couldn't vary it within the roll. Despite being one of the exposure controls in photography, the f/stop (or aperture, the terms are interchangeable) remains a source of confusion and mystery to many photographers, even to some who use it all the time. F/Stops Yes.