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I find that viewfinder never beeps to confirm focus. It also is much quicker (~0.5s) but sometimes jumps around constantly and never settles to a focus point. LiveView probably gets less light for focussing with but can take several seconds and then beeps to confirm a lock.

Why is this?

Anything else to be aware of?

marked as duplicate by mattdm, MikeW, Paul Cezanne, AJ Henderson, John Cavan Nov 1 '13 at 9:54

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  • Much of the answer to your question is dependent upon the camera model and the settings that you have selected for it. To get a complete answer you should let us know what camera you are using as well as any applicable settings that differ from the default set for that camera model. – Michael C Oct 23 '13 at 21:34
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The beeping is probably just a setting.

Generally, the VF is faster, but not as accurate as live view.

The view finder uses phase-detection auto-focus (I'm not going to try to describe it any better than can be found on wikipedia) which uses a dedicated sensor whereas live view uses the same sensor that captures the image and is called contrast-detect auto-focus.

If your AF (through the viewfinder) is hunting back and forth then there isn't enough light or there isn't enough detail (contrast) for the AF to lock onto.

  • Solved the problem! Was on AI Servo AF rather than single shot! – mel Oct 25 '13 at 14:54
  • On my cameras (Canon), the AF point blinks red when it achieves focus while on servo and continues to search after that. – tenmiles Oct 27 '13 at 18:39
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The beeping is normally just a focus lock notification setting in the camera. Typically there is also a color change of either the focus point in the view finder or a color change of the focus square on the LCD.

Viewfinder uses Phase Detect Auto Focus on a dedicated sensor which can detect when focus is achieved more quickly, but generally requires more light. It should generally avoid focus hunting (where it goes in and out.)

Live view on the other hand is putting light on the image sensor rather than the AF sensor(since the mirror is up), so it has to focus by adjusting the focus and seeing if contrast gets better or worse (looking for sharp edges). since it is a trial and error approach, it can end up hunting back and forth, it also makes it slower, though it can generally work in lower light. It is also generally slightly more accurate, but PDAF is generally preferred for speed.

  • But why is it impossible to get a beep confirmation with the viewfinder? And why does it never seem to "lock"? – mel Oct 23 '13 at 21:04
  • @mel- best bets are either too dark, too close or a problem with the lens or AF sensor. It should be able to get a lock when in the viewfinder without much issue in a well lit scene that is beyond the minimum focus distance. – AJ Henderson Oct 24 '13 at 1:53

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