By Aaron Raisey
Last time we talked about the basic simplicity of the camera and the two things that come together to create the all-important exposure ― aperture and shutter speed. This week, we’ll examine the aperture in a bit more detail. We need to get into Av (Aperture value) mode on that DSLR dial to isolate the aperture and experiment with the different values. But first, what exactly is the aperture?
The aperture acts like the iris in your eye: opening to let in more light, and closing to restrict the light. But unlike your eye which is automatic, in Av mode on the camera you have control over the size of the aperture. Bigger for more light; smaller equals less light. Sounds simple, right? Well, yes and no. Buckle up folks, there’s a lot of very important and useful information in a very small space coming up.
First, the way the aperture is described seems to be counter-intuitive. This is very important and can be confusing for those new to the concept ― a large aperture (more light) is described by a small number, and a small aperture (less light) is indicated by a larger number. Aperture values are called ‘f-stops’ and typically values range from f/2.8, f/3.2, f/4 and on up to f/22. Some lenses can have a maximum aperture of f/1.2, some have a minimum of f/32. What these numbers actually mean is rather complex so for the sake of simplicity let’s stay with small numbers indicating larger apertures and larger equaling smaller.
The selected size of your aperture has a very dramatic effect on your image. When we take a picture, we usually have a subject in mind ― something we focus on. Perpendicular to our (or the camera’s) line of sight at the subject is what’s called the “plane of focus.” How much of the final image in front of and behind the subject (the plane) that is actually in focus is determined by the size of the aperture. This area forward and back of the plane of focus is called the “depth of field” (DoF).
Let’s dispense with the theory and get to the practical applications of all this. If we select a small aperture, say f/16, what impact does this have? By way of example, smaller apertures are typically used in landscape photography. It’s important to get as much of the image in focus as possible, so the DoF needs to be as deep as possible to achieve this.
Conversely, in portrait photography, a larger aperture is often employed. To blur out the background and bring attention to the subject we need a shallow DoF. Selecting a larger aperture such as f/2.8 or f/4 gives us this effect. The creative possibilities at larger apertures are exciting.
That’s the basics, but there are several other important considerations. Enlarging the aperture means the shutter speed has to increase to compensate for more light entering the camera and correspondingly, closing the aperture necessitates a slower shutter speed to maintain optimal exposure. Also, the further you are from the focal plane, the deeper the apparent DoF for the same f-stop. Another variable to take into account is the focal length of your lens. Shorter focal lengths increase the DoF. For example, a 22mm lens at f/4 has a deeper DoF than a 105mm lens at f/4.
Now you have the basics of aperture it’s time to get out there and experiment. Switch into Av mode and explore the creative possibilities. Experiment a lot, then shoot even more, and head on over to the Seoul Photo Club to see examples of great expat photography and get some tips and advice from the best expat photographers in Korea.
Aaron Raisey is the leader of the Seoul Photo Club on Flickr (www.flickr.com/groups/seoulphotoclub), Korea’s premier expat photography society. If you have any questions or inquiries you can contact him at aaron.raisey@gmail.com.