Photography is about “painting with light,” and as such, the control of the light entering the camera is the very essence of photography. This process of controlling the light that is being recorded is called “exposure,” as it is the process of exposing the camera to the light. One may control this light in one of three ways: setting the length of the exposure (shutter speed), the sensitivity to the light (ISO), and the amount of light that enters the lens (aperture).
“Aperture” refers to the opening inside the lens through which light passes on its way to the camera’s sensor or film. This opening can be controlled to be larger or smaller to let in more or less light pass through the lens. Sometimes this setting is called “f-stops,” after the f/numbers that represent the size of the opening. The smaller the aperture, the larger the f/stop and the less light is let through. For example, f/2.8 lets more light through than f/8, which is smaller. Photographers would say that f/2.8 is “faster,” as it lets more light through and allows the photographer to use a faster shutter speed. These f-stops are usually displayed in “whole stops.” Each stop is either twice as large or half the size, depending on whether you are going left or right on the chart. The range of whole stops is listed below:
(more light, faster) f/1.4 … f/2 … f/2.8 … f/4 … f/5.6 … f/8 … f/11 … f/16 … f/22 … f/32 (less light, slower)
Lenses each have a range of aperture settings that can be used, the largest of which is usually advertised in the lens name. A lens that is called “AF 85mm f/1.4” has a maximum aperture of f/1.4, which is quite large. Remember, smaller f/numbers mean larger openings and more light. A lens that reads “AF 18-70mm f/3.5-4.5” means that at 18mm the maximum aperture is f/3.5, while at 70mm the maximum setting is a smaller f/4.5. These are called variable-aperture lenses, and are more common in the consumer range of less expensive lenses. Typically, f/2.8 or better is considered “professional,” although many professionals use slower (meaning darker) lenses too. Each lens has a sweet-spot for its aperture where it is sharpest (generally around f/5.6 or f/8).
Setting the right aperture on your lens is crucial for capturing a quality image. It determines the depth-of-field in your image (how much of your subject is in focus) along with how fast of a shutter speed you are able to use. There are some guidelines that will help you get the right aperture and that will provide a baseline from which to experiment on your own. See the quick reference guide below:
- Landscapes: f/16-18 (to get everything in focus)
- Portraits: f/2.8-5.6 (to get sharpness, but still blur the background)
- Outdoors: f/8 (good all-around setting for direct sunlight)
- Flowers: f/2.8-4 (to blur the background)
- Macro: f/18-22 (to get everything in focus)