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01-24-2015, 01:39 PM   #1
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diffrence between focussing in lv and phase detect

When using focus adjust for a front focussing tamron lens, I stumbled acros the the fact that although I can perfectly correct the lens using focus adjust,
it only needs to be done when focussing via the view finder. ie when the camera is using phase detect .
If I use live view the camera and lens focus perfect .
Could anyone explain? I am aware that the 2 focusing systems differ but I was under the impression that front or back focussing was a lens/body maladjustment that should
exist no mater the focus system used?


Thx in advance.

01-24-2015, 01:42 PM   #2
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Front and back focus only applies to viewfinder AF. Here's an explanation why:
Fixing Front and Back Focus - Causes of Front- and Back-Focus - In-Depth Articles

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01-24-2015, 01:44 PM   #3
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QuoteOriginally posted by Adam Quote
Front and back focus only applies to viewfinder AF. Here's an explanation why:
Fixing Front and Back Focus - Causes of Front- and Back-Focus - In-Depth Articles
Wow that is quick. Thank you!
01-24-2015, 03:31 PM   #4
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As far as I know, Live view focusing use contrast detect AF system (CDAF) which is different from PDAF using viewfinder. So, it is conceivable that you may have FF or BF issue using PDAF.

01-24-2015, 03:41 PM   #5
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The viewfinder prism might need to be shimmed. If you're using a split prism, I'd put money on it. There are plenty of threads you can look up describing the issue and fix if this happens to be the case.
01-24-2015, 06:09 PM   #6
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CDAF uses the imaging sensor to focus. There's no front- or back-focus issues because of that.

Phase detect (or manual focusing in the viewfinder) follows a different optical path and calibration can be off.
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