To enable the Depth of Field post-process shader, open the Shading panel by using either the Managers > Shading command.
Once the Shading panel is opened, select the Rendering tab: the first column on the left displays the Rendering chain which lists, among others, the Depth of Field option. Check the radio button on to enable it and be allowed to modify parameters that are displayed in the column beside.
This post processing shader lets you simulate camera depth of field effects.
Default value are:
"focal length" 50.0
"aperture" 5.6
"focus plane" 9.0
"units" 1.0
"near focus" 0.0
"far focus" 0.0
"far blur" 1.0
"near blur" 1.0
The depth of field effect is controlled either by parameters describing the camera model (lens focal length, aperture stop) or directly (distance to near and far boundary of field in focus, level of blurring in near and far field).
The effect, if desired, can be controlled separately in near field and far field without regard to physical correctness - this gives the ability to create impossible but desirable effects.
The shader also queries the front and back clipping planes. The back clipping plane is used to establish the distance to background. All objects further away than the back clipping plane are set to the distance of the far clipping plane.
The front clipping plane is used to clip nearer objects. If the front clipping plane is nearer to the observer than the focal length, then it is adjusted to focal length with 10 (e.g., if near plane is set on 0.1 mm. while the focal length is 50 mm., then actual near plane will be set on 55 mm). It is so because an image of points closer to the camera than focal distance does not exist.