Is CDAF really derived from in-cam JPG adjustments?

Started May 27, 2012 | Discussions thread
Timur Born
Senior MemberPosts: 3,665
Re: What limits AF settling time
In reply to Detail Man, Jun 1, 2012

It's a bit hard to put into good words. What happens in normal mode is that when you move the camera over a dark shadow area the screen gets laggy (jumpy pan movement on screen) and (still) focusing on such an area takes longer (including in AF-S, may even happen with AF assist light). On such areas you may see the focus hunt back and forth whereas it will lock faster and with less hunting when negative exposure compensation is used.

Using "High" Frame Rate is kind of like using negative exposure compensation for this specific quirk. With high frame rate you never get the laggy/jumpy areas and positive exposure compensation preview gets limited by the camera. For shadow areas it can happen that you will not see any more changes on screen for anything higher than +1 EC, while in bright areas the screen will happily preview all the way up to +3 EV.

The latter leaves me to believe that there is some "neutral" EC value that cannot be pushed when high frame rate is used. And the combination of auto screen exposure + exposure compensation preview will lead to lag once this neutral point is overstepped in combination with "Normal" Frame Rate.

Live View Boost turns of the exposure compensation preview, but it does not turn off auto screen exposure. So it will help against the exposure lag in those situations where positive exposure compensation dialing would push over the lag limit, but does not help against situations where automatic screen exposure does so.

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