What is aperture?

What is aperture in photography?

Aperture definition:

The aperture is the the hole in the lens through which the light enters the camera.

Although the lens has a constant diameter, the hole through which the light enters can be varied by the opening or closing of a "shutter" which, like the iris of the eye, makes the hole smaller or larger. In the metaphor where the shutter is the iris, the aperture is the pupil.

Opening the aperture allows more light in, and the more light there is we say you increase the "exposure", and the picture looks brighter or whiter. Opening the aperture also decreases the depth of field (i.e. it decreases the focus range so that only the things at one focal point are sharp and things in other focal points are blurry. For example if the focus is on the foreground, the foreground will be sharp but things in the background appear blurry).

Closing the aperture allows less light in, so this decreases the exposure and makes the picture look darker. Closing the aperture also increases the depth of field (i.e. it increases the focal range so that whether things are close or far away they appear sharp).

How do you change the aperture?

To change the aperture size you need to change the F-number (where F stands for focal length).

What is "focal length"? It is the distance (measured in millimeters) from the center of the camera lens to the focal point of the image (ie, the "image sensor surface").

The F-numbers can range from 1 to 16, although my camera only rangers between F2.4 and F8.0 which I guess means that the maximum distance my camera lens can go from the image sensor surface is 8mm? I need to check this! More sophisticated cameras can have a greater focal length capability.

You can also buy special lenses that have shorter focal lengths of longer focal lengths.
- Short focal length lenses = wide angle lenses
- Long focal length lenses = telephoto lenses

I mentioned above that when you set the camera to have a large aperature there is decreased depth of field. Another way of saying this is that there is an inverse relationship between F-numbers (focal length or depth of field) and aperture size.

To decrease the size of the aperture (i.e. to allow less light in),  you want the F number to be  large. The larger the F number the smaller the aperture. So the larger the F number the darker your picture will appear.

Similarly to increase the size of the aperture (i.e. to allow more light in), you want the F-number to be small. The smaller the F number the larger the aperture and the brighter and more exposed your picture will be.

How do  you change the F-number? 

I suspect you may need to check your camera user manual for how your specific camera works. On my camera (Canon PowerShot Pro 1) you have to set it to manual setting (M) and fiddle around with a dial to change the F-number.