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10-16-2012, 05:02 PM   #1
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AF accuracy

Hi all,

Which is more accurate, the AF through the viewfinder or the liveview focus?
I know the difference in speed for sure>>

Are typical screw-driven lenses more accurate or are SDM systems better?

thanks

10-16-2012, 05:20 PM   #2
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Contrast detect is always going to be more accurate than phase detect, especially considering that it isn't subject to front/back focus. I don't think mount type has much, if any, influence on AF accuracy, as it's all about how the AF module tells the camera to adjust the focusing ring.

Sony's new A99 has a three-stage AF system where first traditional PDAF is used for speed, then PDAF segments on the actual imaging sensor are used, and finally, CDAF is applied to fine-tuning the focus. On conventional DSLRs, PDAF alone is usually good enough, though if sharpness if of the essence and you have a lot of time on your hands, you may as well use live view.

You might want to give this article a read for more details on how PDAF and CDAF systems are implemented:
Fixing Front and Back Focus - Causes of Front- and Back-Focus - PentaxForums.com

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