Learn photography episode 05 - ISO

In the very early days of photography, shutter speeds were usually always very long, usually minutes. 30 seconds was considered a short exposure.

One reason that shutter speeds were so long then, is that the films of the day were not very light sensitive. It took a long time for them to gather enough light to create an image. As film technology and lens technology improved, and the light gathering speeds of film increased, shutter speeds could get shorter. We measure the light gathering speed of a film using a scale called ISO.