The camera is fixed at the origin, looking down the negative Z axis, with up being the positive Y axis. To view a scene from a given position and orientation, the scene must be transformed such that the camera is at this standard location.
By default, the camera is a pin-hole perspective camera for which the focal length, aperture and aspect ratio may be specified in either the camera construct of the input file or on the command line of mental ray. Optionally, lens effects such as depth of field can be achieved by specifying one or more lens shaders.