Take photos in minimal light by changing the ISO
ISO is an acronym for the International Standards Organization. ISO numbers tell you how sensitive your camera is to light.
You can achieve two things by setting your camera to a high ISO: you can get a good exposure if there is not enough light, and you can create a grainy look for your photos even when there is plenty of light.
ISO Numbers and Sensitivity to Light
ISO numbers are typically used for film. When you go to the drugstore to purchase a roll of Kodak 200, 200 is the ISO number. You may have also seen 100 and 400 films. These three numbers are the most common.
With film, the ISO number indicates how sensitive the film is to light. With digital cameras, the ISO setting is somewhat artificial, but it basically tells you how sensitive the camera will be to light (since there is no film in it).
This is a sequence of some of the most common ISO numbers available with digital cameras today:
100 200 400 800 1600
A low ISO number is not very sensitive to light, which means that you have to adjust your aperture and shutter speed to let more light onto the camera's image sensor. Low ISO numbers result in images with less noticeable grain.
A high ISO number is more sensitive to light, which means that you can adjust your aperture and shutter speed to reduce the amount of light. High ISO numbers produce photographs with noticeable grain.
Changing the ISO in the Real World
The only reason that you should ever have to manually change the ISO number on your camera is if you are in a dark location and you don't have a tripod. If you remember from the section on shutter speed, you can only handhold your camera without blurring the photo down to a shutter speed of about 1/60.
But what if your camera is telling you that you need to use a shutter speed of 1/15 to get a correct exposure? Change your ISO setting to its highest number (1600) so that the camera is more sensitive to light. Then you should be able to take the photo at a shutter speed of 1/60 and still get a correct exposure.
This is only if you don't have a tripod with you. If you do, leave the camera set to a lower ISO and stabilize it with the tripod. This will ensure that your photo does not have a lot of grain in it.