How is the OMD so fast

Started Jan 7, 2013 | Discussions thread
sgoldswo Veteran Member • Posts: 5,717
Re: Good tracking requires PDAF.

Paul De Bra wrote:

Your expectation that CDAF will somehow be able to track in the future is somewhat unrealistic. The fundamental difference in property is that with CDAF when a subject goes out of focus the image does not have any information whether the subject is coming closer or moving further away. This could be done with clever motion analysis but from a single image captured by the sensor you cannot know this. With PDAF when a subject goes out of focus the sensor can detect whether it is out of focus because the subject is too close or because it is too far away. It works like with the "two halves" in older MF dslrs: the two halves of the focus point move away in one way when you focus closer and the other way when you focus further away, and with PDAF this info is used. So PDAF knows in which direction focus needs to be adjusted and CDAF does not know and has to try one way and if the image becomes more blurred then try the other way... The info for selecting the right direction just isn't there in the image. An image sequence is needed and clever processing to detect the direction of motion. We need a serious gain in on-board processing power to achieve that.

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Slowly learning to use the Olympus OM-D E-M5.
Public pictures at

And yet the GH3 (CDAF only) CAF, though not perfect, is an incremental improvement on the E-M5 in this regard. It seems about as good as an entry level DSLR (which admittedly won't have the best PDAF in the world).

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