Put quite simply your camera aperture is the opening in your camera’s lens that allows differential amounts of light through the lens to the cameras light sensitive sensor behind it. Together with the ISO value and shutter speed of your camera it controls the light exposure used to create your photograph.
The size of your camera aperture is controlled by settings called f/stops. An f/stop can also be likened to the human eye as the iris which controls the size of the eye’s pupil. Similarly the smaller the f/stop value (iris) the larger the camera aperture (pupil) and the more light that passes through the lens to the cameras sensor. The larger the f/stop value the smaller the aperture and the less light passes through..
Digital cameras will allow you to choose from an f/stop range dependent on your camera lens capabilities. For example purposes let’s say from f/stop 1.4 to f/stop 8. Imagine that you are sitting in a dark room, the pupil in your eye (camera aperture) will be fully open to allow enough light through to your eye’s retina to enable you to see more clearly. This would be f/stop 1.4 on our example scale. If you then walk out of the dark room into bright sunlight the pupil in your eye would close considerably to prevent you from becoming blinded by the sun. In our example scale this would mean the aperture would close to f/stop 8.
This example uses extremes at both ends of the f/stop scale but of course there are steps in between. If you change your aperture setting on your camera from f/1.4 to f/2 the camera aperture is smaller than it was at the f/1.4 setting and It lets half as much light pass through the lens to the cameras sensor than it did at the f/1.4 setting. This remains true each time you move to the next highest f/stop value.
If however you change your aperture in the other direction from f/2.8 to f/2 then the reverse is true and the aperture is now larger than it was at the f/2.8 setting and twice as much light passes through to your camera’s sensor. This is again remains true each time you move to the next lowest f/stop value.
Changing your aperture f/stop value has two different effects on the end result of the photo you take. It determines both how much of the photo will be in focus (the depth of field) and working in conjunction with your ISO and shutter speed values determines how bright or dark your photo will come out.
The term depth of field refers to how much of an image is actually 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. As a general rule approximately 1/3 of the range of material in focus falls in front of the focal point and 2/3 of the range of material in focus falls behind the focal point.
Photo brightness is affected not only by camera aperture settings but also by ISO values and shutter speeds. This though is how your camera aperture affects the brightness of your photo. The larger the f/stop number the smaller the aperture size. Therefore less light is allowed through your lens and your photo will be darker. The smaller the f/stop number the larger the aperture size. More light is let through the lens therefore your photograph will be brighter.