Depth of Field

Keywords: DOF

Depth of field refers to where the camera is focusing. In short, it determines what part of the image will be sharp and which will be blurry, like the one below.

There are different types of DOF. In the image above it's quite evenly blurred which could be achieved with a gaussian dof. Then there's also bokeh.

An issue many engines have with particles and DOF is that it's based on the depth buffer, which ignores the particles. That means the particles will pick up the blurvalue of whatever is directly behind them. Bad times.