Is m43 mirrorless system lens back/front focus error free?

Started Jun 28, 2013 | Discussions thread
Spotpuff
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Re: Is m43 mirrorless system lens back/front focus error free?
In reply to Gregm61, Jun 28, 2013

PDAF system front/back focus is caused by mis-alignments in the PDAF sensors relative to the sensor itself.  Light from the lens must go through the DSLR mirror, bounce off another mirror and onto the PDAF sensors, which then measure resolution.  If any of:

  1. the PDAF sensors
  2. the first mirror
  3. the second mirror
  4. the sensor

Are misaligned, you will get front/back focus.

M43 is free from that type of front/back focus, however, keep in mind it has no way of telling distance as the PDAF sensors do.  Thus it has no idea if a subject is in front of a "busy" background or not, so as mentioned earlier in this thread if the camera engine decides to "maximize" contrast, this may mean focusing so that the background contrast is maximized.

While it definitely solves the headache of PDAF system misalignment, as demonstrated above, it doesn't eliminate all the problems.  The camera still has to make a judgement call on how to maximize contrast within a zone; some people make the AF square smaller to avoid errors in this regard but that can make framing difficult.

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