What is Aperture?

Aperture helps your picture to obtain a proper exposure. This can be achieved by regulating the amount of light that enters into the camera. It depends on the lens that you use, and also the maximum aperture supported. All of the lenses have aperture blades that act as an iris. Iris controls the amount of light to fall on the sensor.

More light enters when iris is wide open. This results in a lower F-number moreover gives shallow depth of field. Narrow Iris allows lesser light on to the sensor that results in higher F-number. This number is represented as: f/1.4, f/1.8, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22 etc.

The eye should learn to listen before it looks. Robert Frank

An out of focus background is the bi-product of a large aperture. A focused background is the bi-product of a small aperture. An interesting thing to note here is that while most lenses create a sharper image at about f4.0-8.0, it is not the same with all of them.

You have to try several apertures to know the sweet spot of your lens.