What does Power Focus do on certain Canon telephoto lenses?
Asked 5/14/2013
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Some recent Canon telephoto lenses include a Power Focus (PF) setting, such as the EF 300mm f/2.8L IS USM II, EF 400mm f/2.8L IS USM II, and EF 200-400mm f/4L IS 1.4x USM. What is this mode for, and does it offer any benefit for still photography, or is it mainly intended for video use?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
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Power Focus is described on Canon's Infobank page as "a mode that allows you to drive the autofocus motor electronically instead of having to use the focus ring." As you indicate in your question, it's meant for changing focus from one point to another very smoothly, for use while shooting video.
As one doesn't normally change focus in the middle of taking a photograph, it's hard to see how Power Focus would be useful for still photography. The same page goes on to say: "It is aimed at users shooting HD EOS Movies with their DSLR cameras..."
Originally by user4262. Source · Licensed CC BY-SA 4.0
user4262
13y ago
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Generated from our catalog & community — verify before relying on it.
Power Focus is a video-oriented feature. In PF mode, the lens’s autofocus motor is driven electronically so focus can be changed smoothly, rather than by manually turning the focus ring in the usual way.
Its main purpose is to make controlled focus pulls while recording movies, giving a smoother transition from one focus distance to another. Canon specifically aimed it at EOS movie shooting.
For still photography, it generally offers little or no real advantage, because you normally set focus before taking the shot rather than changing focus during the exposure.
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