Definition of Aperture

An opening that lets light in.

The simple definition of aperture is the amount of light that is allowed to enter your camera. It is different from shutter speed which also controls the amount of light.

Aperture vs. Shutterspeed

Lets compare aperture and shutter speed to a window. Aperture is the size of the window. A big window means lots of light comes in really fast and a small window means a little light comes in at a time. Your shutter is like the blinds on your window. The the longer you open the blinds the more amount of light comes in.

Aperture is how much light at a time and shutterspeed how long you let the light in. Both will have different effects on your photo. Because aperture is the size of the opening, it effects the depth of field.

F-number (or f-stop)

Before we get into how depth of field and aperture are related lets look at how the f-number (or f-stops) work.

If stop is the number that describes the size of the opening in relationship to focal length of the lens. In simple terms this means a smaller f-number is equal to a larger opening and a larger f-number is equal to a smaller opening. The diagram on the right shows an example of how the opening gets smaller as the f-number gets larger.

At each f-stop the light decreases by one half. Below is a chart that starts at f/1.0 and shows the f-stops up to f/22 for each time the amount of light is halfed. The reason you should know these numbers will be discussed later.

Aperture and Depth Of Field

Now how does aperture effect depth of field? The smaller the f-number you sent your camera to, the smaller your depth of field will be and the larger the f-number you use then the larger your depth of field will be. If you have your aperture set to f/1.4 then your aperture will be small and less of your photo will be in focus. If you have the aperture set to f/16 more of your photo will be in focus.

Many times photos of as landscapes, for example, are taken with a high f-stop number (small aperture)  so that the majority of the scene is taken in focus. On the other hand portraits of people are taken with a small f-stop (large aperture) so that the person is in focus but the background distractions are blurry.

Importance of Knowing Your F-Stops

If you are shooting a photo at f/4.0 and your shutter speed is set to 1/100th sec. but you want to make the background behind your subject more blurry then you need to adjust your aperture. Lets say you want to change your aperture to f/2.8 this means the light is doubled so you will have adjust your shutter speed to compensate for the amount of light coming in. If you were shooting with f/4.0 and 1/100 sec and you want to shoot at f/2.8 you will need to have a shutter speed of 1/200th sec.

Conclusion

That is how aperture works. Aperture effects your depth of field and the amount of light that reaches your photo.