Lens

Focal length (in millimeters): Defines the Field of View (FOV) of the render, along with the Camera Sensor size.
Shorter focal lengths, often called wide-angle lenses, will increase the Field of View, i.e. render more of the scene.
Longer focal lengths, called telephoto lenses, will narrow the Field of View and magnify distant objects.

Fisheye (Cycles only): Adds spherical distortion.
Wide-angle focal lengths (like 8mm) will show the full 180-degrees spherical field of view, but longer focal lengths will only display a small amount of distortion in the corners of the frame.

Dolly Zoom: Focal length adjustment, compensated by a Camera translation in depth.
Click on the surface of the object that will be the reference point in the 3D View, then drag the mouse left or right. Hold-Shift for more precision, Right Click / Esc to cancel.

Can be easily animated using Set Dolly Zoom Key.
Set Dolly Zoom Key: Set key on Focal Length, Focus Distance and Camera location.

Depth of Field Characteristics:
Anamorphic Ratio: Anamorphic squeeze value that will scale bokeh horizontally.
Blades: Simulates Iris blades from the Lens diaphragm. 0 will render a round bokeh, minimum value is 3 (triangle shape).
Rotation: Rotates the Iris blades.