Simply put, Depth of Field refers to the area in front of your camera that is in focus.
If your camera is set to focus one metre from the lens, Depth of Field refers to the area in front of, and behind one metre from the camera where subjects are still sharp enough to be considered in focus.
Along with Exposure and Composition, Depth of Field is one of the most important aspects of photography.
How do you control it?
Less is more
The main way to affect the Depth of Field is by adjusting the value of the Aperture
The bigger you set the aperture size (smaller number), the smaller your depth of field will be. The smaller you set the aperture size (bigger number), the bigger the depth of field will be. I know that sounds confusing but hopefully this diagram will help to explain it.
The yellow area shows the area in front of and behind the focal plane (the point when the camera is focused) that is in focus. It’s just a guide with no actual scale.
The Depth of Field is actually also affected by the focal length of the lens, and also the distance of the subject from the camera (which is why there is more in-focus area behind the subject than in front of it), however for the benefit of just getting you started, in this post I’ll only talk about the aperture value.