[davidmanze]

  There's something strange for it to be so unreliable as that, many threads about  Sigma's art range on Nikons. PentaxForums tested a Sigma with hopeless AF results, they spoke to Sigma ,  tried two  more lenses tested by Sigma etc. All adjustments tried with the docking station, they could only get it to focus reliably at one distance. Others talk about problems because of their reverse AF engineering........

 

Anyway, it sounds like you've had it up  to your ears and are leaning towards a mirror-less of some sort, a Sony A7RII would be my choice, but looking at the model upgrade speed maybe waiting another year or two will bring about the perfect Sony mirror-less!

 

 

PentaxForums link:

                            http://www.pentaxforums.com/reviews/sigm...focus.html

 

and here:

                 http://www.pentaxforums.com/reviews/sigm...usion.html

 

quotes from the latter;

               

Pros:

Perfectly accurate autofocus, regardless of aperture, when using Contrast Detect AF (Live View)


Cons:

 

Dreadful autofocus accuracy when using PDAF (looking through viewfinder)


Read more at: http://www.pentaxforums.com/reviews/sigm...z3vHNjI4bC