ISO and exposure go hand-in-hand, but contrary to popular belief they are not the same thing. ISO stands for International Standards Organization. It measures how sensitive film is to light exposure, whereas the exposure itself is how much light is received through the shutter of the camera. The ISO number on the film helps guide photographers to know how much light exposure is needed to produce a proper image. Film with higher ISO numbers need less exposure to make a clear image than film with lower ISO numbers. Since higher ISO numbered film is more sensitive to light exposure, the resulting images may appear grainier than images shot on film with a lower ISO.
