In early days of photography, available shutter speeds were not standardized, though a typical sequence might have been 1/10 s, 1/25 s, 1/50 s, 1/100 s, 1/200 s and 1/500 s. Following the adoption of a standardized way of representing aperture so that each major step exactly doubled or halved the amount of light entering the camera (2.8, 4, 5.6, 8, 11, 16, etc.
Hitrost zapiranja zaklopa pri 1/50 sekunde z lečo fokusa f/4.0, ima enako vrednost osvetljenosti kot 1/100 sekunde zaklopa z f/2.8 zaslonko in enako vrednost osvetljenosti kot 1/200 sekunde zaklopa z zaslonko f/2.0 .