What is focus-by-wire, how do you use it for manual focus, and where is it found?
Asked 8/21/2012
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I’ve read that focus-by-wire is an electronic manual-focusing system rather than a direct mechanical linkage. How does it actually work inside the lens? What is manual focusing like in practice with a focus-by-wire lens, and what are its main limitations or typical use cases? Also, what kinds of cameras or lenses commonly use this system?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
14y ago
2 Answers
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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.
Originally by user10459. Source · Licensed CC BY-SA 4.0
user10459
14y ago
0
Generated from our catalog & community — verify before relying on it.
Focus-by-wire means the focus ring is not mechanically connected to the focusing elements. Instead, turning the ring is detected electronically, and the lens’s motor moves the internal elements accordingly.
In use, manual focus feels broadly the same: you turn the focus ring until the subject looks sharp. The difference is that the ring is sending commands rather than directly moving optics, so some lenses may have a slight response lag.
Common limitations: the lens usually needs power from the camera, so manual focus may not work when the camera is switched off. Accessories such as extension tubes generally need electronic pass-through for the lens to focus this way; with unpowered tubes or reverse adapters, focusing may be limited to changing camera-to-subject distance.
As for where it’s found, focus-by-wire is common in cameras with non-interchangeable lenses, and it is also widely used on autofocus lenses for mirrorless systems. It’s often chosen when a direct mechanical linkage is impractical or there isn’t enough space inside the lens design.
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