ISO
There are three parts to controlling exposure, and three elements which affect exposure. The first is the ISO value. In traditional photography, this referred to the film "speed", or its sensitivity to light. In digital photography it refers to the sensitivity of the sensor. A higher ISO will be more sensitive to light, good for fast shutter speeds, or shooting in low light. The downside to high ISO's is the increased likelihood of noise in the photograph. Noise is the digital equivalent of graininess in film. There are times when you may need a high ISO. In low light, with the help of a tripod, high ISO's will allow you to capture good exposures with the little light available. The lower ISO speeds offer less sensitivity to light, but produce the highest quality images. ISO is just one aspect of exposure. Combining ISO with a selected shutter speed, aperture, or both is the way to take real control over the exposure.
Aperture
The aperture is the second component of exposure. The aperture is the part of the lens that opens or closes to let in light. The f-stop refers to the size of the aperture currently set in the lens. A low f-stop like f2.8 or lower will gather a lot of light. A large f-stop like f16 or f22 will be a much smaller opening in the lens, letting in far less light. Controlling the amount of light entering the lens is critical to the exposure, and when combined with an appropriate shutter speed and ISO will give you a good exposure. This isn't all there is to aperture control though. Just as important, and possibly more so, is the aperture's effect on depth of field. Depth of field refers to the area in front of, and behind your subject. This can be very important to the photograph. For example, in a portrait you would probably want just your subject in focus, with the background a pleasant blur. To accomplish this you would need a low f-stop, meaning the aperture is open wider. In a landscape though you would want everything from the trees in the foreground, to the mountains in the distance to have detail in the photo, and would want to use a small aperture, like f22. Depth of field can have just as much of an effect on a photo as accurate exposure. This is a great way to get creative with photos as well, and take more control. The other way to gain control over exposure and get creative is by controlling shutter speed.
Shutter Speed
Shutter speed is the amount of time the camera exposes the photograph. The longer the shutter stays open, the more light is let in. This is the third element of exposure. In combination with the aperture and the ISO setting, shutter speed makes for correct exposure. But just like the f-stop, the shutter speed does a lot more than just aid in exposure. It can help you take control of photographs in a way that the automatic settings on your camera just can't do. By using high shutter speeds you can take much better action shots. High shutter speeds will let you freeze objects in motion, even in mid-air, for those dramatic sports shots. Slowing down the shutter can help to make creative effects, like the controlled blur of moving objects like people, cars, or water. By controlling blur with slow shutter speeds you can get very creative effects, or just help with exposure in low light. Just remember the tripod.
These are just some of the things that you can do by taking control over exposure. The best way to learn about and improve your skills with both aperture and shutter controls is to experiment. You'll see how ISO plays a role as well. Just take a few pictures that are exactly the same, but keep changing the aperture, or the ISO. You'll see how much of a difference it can make. Shutter control is often the only way to get what you want out of an action shot. Learn to control exposure, and you'll open up a whole new level of photography, and really learn to get creative.
If you want to take your photography to the next level, check out the classes section of penncamera.com to see the many classes we offer to help you take the next step and get the most out of every photograph!
