Nikon D7100 left focus issue

Started Apr 19, 2013 | Discussions thread
Mako2011
Mako2011 MOD
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In reply to fireplace33, Apr 23, 2013

fireplace33 wrote:

In my D7100 focus results table here, with both copies of the 17-50/F2.8 and the  50/F1.4,  I can see that using the left focus point in live view (CDAF) I get good sharp results for the whole image.

However, if I use the PDAF system by looking through the viewfinder and using the left focus point then the results are very bad for the whole image.

My question is does this point to an error in the lens or an error in the camera?

If it is the lens,  why would it work OK with the CDAF focus system in live view ?

Can anyone help me understand that in this case?

thanks

PDAF needs light coming in in a certain way to function properly (simplified explanation). Focus determination is achieved by dividing the incoming light into pairs of images and comparing them. An optical problem with the lens can make that light path problematic for PDAF on one side or the other. CDAF only cares about the contrast of the image and can correct for it as it works completely different and is unaffected by the light path in the same way PDAF sensors are. CDAF only cares about measuring contrast within a sensor field.

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