terminology - How does a fly-by-wire focusing lens work?

I have learnt that fly-by-wire focusing is an electrical manual focusing system. But how does this focusing method work?

• How do you manually focus with fly-by-wire?


• What is the scope of this focusing method?


• Which cameras have this feature?

Answer

Function: Normally the focus ring is mechanically connected to the inside of the lens so that when you turn the focus ring some of the lenses inside the lens move directly. With focus-by-wire the movement of the focus ring is measured electronically, and then a motor moves the lenses inside.

Drawbacks: As focussing is now only possible when the lens has power, it is impossible to focus, when the camera is switched off. And for macro work special extension tubes are needed, which have electrical coupling to allow for power and communication between the lens and camera. Also with macro reverse adaptors (and unpowered extension tubes) the only way to focus is by changing the distance between camera and subject.

Lenses which support focus-by-wire:

• Most AF lenses for mirrorless cameras support focus-by-wire.



• Nearly all Panasonic and and Olympus FourThirds and Micro-FourThirds AF lenses feature only focus-by-wire (with the exception of the M.Zuiko 12mm/2.0, which features additionally a true direct coupling between the focus ring and the lenses inside).


• All Canon EOS-M lenses.


• All Nikon 1 lenses.


• All Sony E mount lenses.


• All Fuji X mount lenses.


• Most Samsung NX mount lenses.