[Ayoh]

The story is quite simple: Although I adjusted AF for the Sigma 20/1.4 in front of a D810, the LiveView based contrast detection AF knows better in most cases or equally good and never (!) worse. There are about 3 shots where both kinds of AF came to the same conclusion. I didn't show all the samples. But I've seen enough.

 

It was highly unscientific - without any tripod and probably some blur came for shutter/mirror vibration. I count that as one reason more to abandon mirrors... all shots were done in about ½ hour, just by walking through the streets, take one picture with AF-C, move the AF-point to a suitable place and focus. Then I switched to LV, focused again and released. There's a note in the gallery which tells just what I said. The bicycle was trickier and here I enlarged the AF zone in LV and adjusted manually. The little jewelry tree was also tricky, I didn't see the branch in foreground in the viewfinder, but thought, I was focusing at the face plaquet under the rear branch. That was were I put the AF to in LV, again with manual adjustment. The wall painting with the soldier in a small creek, the light chains on the facia - hopeless to get that with PDAF.

 

In the gallery is only the first picture with PDAF. Plus a comparison of the AF zone at 100% crop. My conclusion: It's close to pointless in terms of getting the full resolution, the most possible information out of a picture if I (you or others may do better) can't rely on PDAF, adjusted as good as it gets with FoCal. Fast lenses = pricey lenses and in my case high resolving sensor, outresolved by the lens in theory. In real life crashed and smashed by a second best AF device. When I was adjusting the lenses, the spread of focus quality is visible in any FoCal protocol although the software triggers AF and shutter. If I go to check various focus points, I even see which one are weak.

 

As you said, dave, LV is a pain in terms of speed and of no use in street photography with a DSLR and I fully agree. Of course, DSLRs are not made for street photography with LV. Checking proper focus afterwards? Yes, why not. Unless I don't compare it with the potential of the LV versions, I was always fine with the results and thought, that's as good as it gets. True, for PDAF it is. But there's more in the lenses and I can't see it in most samples.

If you can accept the lower resolution, I recommend the Sony A7s with dedicated sony lenses for accurate low light AF. The A7s + 55mm 1.8 Zony make a very satisfying combination. Alternatively the A7rii probably has lower AF sensitivity (and less sensitive EVF) due to partial sensor read out in live view but will enable PDAF with DSLR lenses. However the A7s can probably be had for about $1500 used versus $3000+ for the a7rii. Since I got my A7s I am convinced to totally transition away from DSLR cameras as for my style of shooting (portraiture, street, low light) DSLRs are simply obsolete technology ( in the sense that there is a better solution now available).