K-1, 14 months, 20000 photos (gets a bit nitpicky)

My responses was to your suggestion that 2s delay bracking should always be one-touch.

Oh I see. oops. I think (hope!) I wrote that should be the default, but ultimately it doesn't matter.

But we agree on this one? One-touch+2s should keep the mirror up after the preflip.

Interesting. This means that CDAF is not really a fully closed control loop, but has some open-loop or feed-forward characteristics.

It can be looped, but Sigma lenses may not respond correctly, or not at all. As Sigma reverse engineer firmware it may be thing they get incorrecly inplemented. But it may only show up later when cameras are released with new functionallity that Sigma has not been able to test.

->

If you have links regarding this, I'd be interested in them

If you google for "sigma liveview AF" or something simlilar you should get plenty of links showing the problem, mostly nikon though. If only interested in Pentax specific problems just add "pentax" to the search.

The links I found were all about either not working at all or trying and failing. My experience was quick and decisively focusing wrongly - with focus confirmation!

I will admit I don't understand what firmware does for screw drive PDAF. Turn the shaft one way, lens goes one way, turn the shaft the other way, lens goes the other way. Turn the shaft fast, lens focuses fast,...
I am not saying it doesn't have an influence, and we know from PDAF that is has impact there, but on an AF system that can/could/should be closed-loop, I don't understand.

Check with Sigma if they have updates fo the lenses you gave pronlem with.

Not much hope, but good idea nevertheless!