The Fog section blends the fog color into every surface according to its distance from the camera. Up close nothing changes; far away the color takes over. It is the cheapest way to give a shot depth and to separate what is in front from what is behind.

Controls

Enable fog: Turns the fog on.
Color: The color everything moves toward with distance. A gray blue reads as air on a clear day; a warm tone reads as dust or late afternoon.
Start: The distance, in meters, where the fog starts to show. Before that the image is untouched.
End: The distance where the surface has fully taken the fog color.

How to use it

Put the start right behind the main object and the end a little past the farthest point, so the whole range fits inside the shot. If the fog does not show up, it is almost always because what is open spans only a few meters and the start was set too far.

Fog acts on geometry, not on the background. For the image to hold together, pick a fog color close to the background in use on the environment page.