Camera Aperture

So what is camera aperture?

The camera aperture is the opening in the camera lense that allows light through to the sensor behind. The aperture can be likened to the pupil in the human eye. Together with the ISO value and shutter speed it controls the the light exposure used to create your photograph.

The smaller the f number the larger the aperture.

aperture fstop diagram
Aperture values are measured in f/stops and each f/stop will allow either double or half the light through the lens depending on whether you make the aperture larger or smaller than the previous f-stop.
 
For example, look at f/2.8 in the above diagram the white center area is your camera aperture.  
 
If you change your aperture setting on your camera from f/2.8 to f/4 the aperture is smaller than it was at the f/2.8 setting.  Only half as much light passes through to your camera's sensor. 
 
If however you change your aperture setting from f/2.8 to f/2 the aperture is now larger than at the f/2.8 setting and twice as much light passes through to your camera's sensor.
 
Changing your aperture f/stop value has two different effects on the end result of the photo you take. It determines both how bright or dark your photo will come out and also the depth of field. 

Photograph brightness

The larger the f/stop number the smaller the aperture size. Less light is allowed through and your photo will be darker. The smaller the f/stop number the larger the aperture size. More light is let through therefor your photograph will be brighter.

Depth of field

Depth of field refers to how much of an image is in focus. When you look through your camera and focus on a subject, there will be some amount of material both in 
front of and behind the subject that is also sharp and in focus. After that, focus will drop off, and anything that is further away from your focal point will appear soft or out of focus.

Shallow depth of field.

Wide depth of field.

shallow depth of field
Wide depth of field
A larger aperture (smaller f/stop number) will produce a shallower depth of field. This photo was taken on the f/sop 2.8 setting and the trees in the background are out of focus.
A smaller aperture (larger f/stop number) will produce a deeper depth of field. This photo was taken on the f/stop 8 setting and the trees in the background are in focus.
1/3 of the range of material in focus falls in front of the point at which you focus your camera. 2/3 of the range of material in focus falls behind the point at which you focus your camera.
 
Assuming that the closest point in your photo is at the bottom of the view finder and the furthest point is at the top. To achieve the greatest amount area in focus, you should focus at a point in the view finder 1/3 of the way up.