Film Speed

Film is made up of grains of light sensitive silver suspended in a gelatine emulsion. The grains of silver react when exposed to light, and clump together when put in the chemical developer. Different "speed" films have different size grains, which allows for a faster or slower absorbtion of light. "Slow" films, such as 50, have small grains, which absorb light slowly. Faster films, such as 400 or 800, have larger grains, which absorb light more quickly. When enlarged, "grainy" films such as 400 or 800 show visible grain, while slow films, such as 50 or 100, will show very little grain. The downside of a slow film is that because it absorbs light more slowly the shutter door must be open longer, and with a longer shutter speed there is a greater chance of blurriness. This is great if your camera is on a tripod and you're shooting a waterfall, but not so great if you're shooting a soccer game.

Think of film grain like a sponge... a sponge with big holes ::::::::: will absorb water quickly, while a brick (with small holes) ::::::::::::::: will absorb water much more slowly. The holes in the brick are less visible than the holes in the sponge, particularly when enlarged.

Here are two shots of your classmate, one shot at 400 speed and one at 3200. Notice how much "grainier" the 3200 shot appears.