Traditionally most cg rendering systems use an idealized lens to simplify the math. Matrix projection transformations simulate a pinhole lens. This does mean t

Traditionally most cg rendering systems use an idealized lens to simplify the math. Matrix projection transformations simulate a pinhole lens. This does mean that all images are perfectly sharp however, so for depth-of-field, bokeh, and other realistic lens blurring effects the position of the idealized lens (i.e. virtual pinhole) is varied over samples creating a sort of fuzzy pinhole.