Understanding Exposure and F-Stops

In capturing the perfect picture, you have to have the right exposure. In order to do this, you have to understand how the different exposure settings in your SLR camera work. There's the ISO setting, the shutter speed, and the aperture or F-Stop. A combination of these different exposure elements and the right mix is crucial in coming up with that perfectly-lit photograph.

The Relationship between ISO, Shutter Speed and F-Stop

The ISO determines your film speed, or the amount of light the film is capable of absorbing. The lower the ISO setting, the less light it takes in. Higher ISO settings are perfect for low-lit conditions. Digital SLR cameras also have ISO settings. Though they forego the use of traditional 35mm films, the ISO settings also work the same way. Shutter speeds refer to the amount of time it takes for the shutter to snap and capture the image. Usually in increments of seconds, the higher the fraction of a second, the faster the shutter snaps and the less light is absorbed by the image. So for night shots, a longer shutter speed and exposure is often used.

The third exposure element is the aperture or F-Stop. This refers to the opening in the lens, thus controlling the amount of light that's let in as well as the depth of field. As a basic rule of thumb, the lower the F-Stop number, the bigger the opening and the lower the depth of field. Most standard lenses have the following basic F-Stop numbers: f/2.8, f/4, f/5.6, f/8, f/11 and f/16 Here are some basic rules regarding F-Stop and Aperture that will help you understand this exposure element better.

F-Stop and Opening

The lower you go in your F-Stop number, the bigger your aperture is and the more light comes in. In principle, you should go with a low F-Stop, such as f/2.8 or f/4, accompanied by a fast shutter speed. Depending on lighting conditions also, a lower F-Stop is not recommended during very sunny weather, because you run the risk of overexposing your shot. If you're in low-lit situations, a lower F-Stop will be suitable to allow more light in, and to get the perfect shot.

Depth of Field

More than light control, the Aperture is used widely for controlling the depth of field. The lower the F-Stop number, the less depth of field you get. With minimal depth of field, your subject becomes sharply focused while the background and foreground are blurred. This is perfect for dramatic macro shots and outdoor portraits. Use a low F-Stop if you want to isolate your subject and create drama. If you're taking a wide landscape, and you want to maximize the depth of field, a stop of f/11 or f/16, or even higher, is most recommended. Keep in mind that this is a small aperture, and you will have to make sure that you have ample light, or compensate with a slower shutter speed.

Knowing how to use the F-Stop and control the aperture is key not only to a good exposure, but to a good photo composition as well.