BCP Jargon Patrol: 35mm Lens Adapter or Depth-of-Field Adapter

Posted on: Thursday, March 15th, 2007
Comments: 0

What is a 35mm Lens Adapter or Depth-of-Field Adapter?

A depth-of-field adapter (often shortened to DOF adapter) is used to achieve shallow depth of field on a video camera whose sensor size is not adequate to achieve it natively. A DOF adapter could theoretically be used on a multitude of platforms, although it is most useful on prosumer digital camcorders where high resolution is a capability but the sensor size is still small enough to elicit use of the adapter. The term 35mm adapter is common, since most designs use a focusing screen the size of a 35mm film frame (24×36 mm) and interface with lenses designed for 35mm cameras.

How does a 35mm Lens Adapter or Depth-of-Field Adapter work?

A DOF adapter focuses an image onto a translucent screen (similar to how one would look at a focused image through a system camera’s viewfinder) located between an external lens and the camera’s main lens. The camcorder is able to frame this intermediate screen by focusing in macro mode. The principle is similar to pointing a video camera at a movie screen. The lens attached to the adapter now takes the job of the camcorder’s focusing and aperture mechanisms. The camcorder’s only responsibility at this point is to record what is being projected onto the focusing screen (called back focus.)