'Focus-By-Wire' is a term for a newer focusing technology found in many camera lenses these days, this technology allows for smooth and silent autofocus which is great for videography. This also allows for less expensive and lighter weight lenses.

 

Focus by wire is a lot like 'drive by wire' where the gas pedal is not mechanically coupled to the engine but instead is an electronic switch that tells a computer how much gas to toss into the engine. In focus by wire, the focus ring is not mechanically coupled to the glass. It's just an input device like an old Atari paddle that tells a computer to go ahead and move the glass elements. When you turn the focus ring on a FBW lens, you’re actually sending a signal back to the camera motor telling it how to move the elements of the lens itself.

 

Focus by wire means a system where your turning of the focus ring actuates an electric motor that moves the glass elements of the lens to the proper position to achieve sharp focus. The alternative is a mechanical system where your turning of the focus ring moves the elements directly. Perhaps people say it stinks because it is not as fast or precise as mechanical focusing. That may be true for some Focus by Wire systems but the more advanced ones have 2 or 3 user-selectable speeds and can work very well.

 

Unlike mechanical AF lenses, using the motor requires power, so when a FBW lens is not connected to a camera, the camera is switched off or power is not enabled to the lens (such as when using a lens mount adapter) changing the focus is impossible.


Focus-By-Wire Lens Codes:


Nearly all MILC lenses:


For more information, check these pages out: