The Depth of Field for a rendering scene is, in short, where the focus of the camera is and how much more far away a scene can be rendered before it starts losing focus.
It’s very easy to adjust the depth of field but it has to be enabled in two places:
- in the rendering options for the scene
- in the camera configuration
Once you got it, enabling the camera to show its limits will show the depth of field too, which makes it very visual to adjust.