The exposure triangle is composed of three sides: Aperture, shutter speed, and ISO. In this post I’ll discuss the first: Aperture.
Aperture is controlled by the lens diaphragm, opening and closing inside a camera lens. It is a space that controls the amount of light entering the camera. The more it is open, the more light enters; the more it is closed, the less light enters.
Aperture can be fixed or variable, depending on the type of lens you use. Its size is referred to in f-stops as (f/22, f/16, f/11… f/2.0, f/1.8). Each stop you open the aperture, twice as much light will enter. This means that, for example, f/16 will allow twice as much light to enter the camera as f/22, and so on.
The image below is a visual representation of several apertures.
So you see, you must have enough light enter the camera to have a clear, well exposed picture. This, of course, combined with Shutter speed and ISO, which I will talk about in future posts.
Depth of Field and Aperture
The other main use of aperture is to control depth of field (DOF). It is the “distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image” (Wikipedia). This definition seems accurate to me.
Imagine a landscape, as the one you see below. Every object is sharp, from the foreground to the background. This means the image has a large depth of field. To achieve this effect, you must have as small an aperture as possible (f/11 in this case, but smaller is even better). Small aperture = large DOF.
On the other hand, on the dolls picture, the first one is sharp, but the other ones progressively become blurred. This image has a low (or shallow) depth of field. To get this effect, you must have a large aperture (f/2.8 for example). Large aperture = Shallow DOF.
This allows you great creative freedom when planning your photos. Depth of Field is one of the most used creative effects photographers use to convey different moods and ambiances. Play with it, and see what feels right to you.
In a future post I’ll be talking about Shutter speed, the second side of the exposure triangle.
How do you use aperture creatively? Share your experience in the comments.