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

JensR wrote:

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.

Yes, that would be better.

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!

It seem similar to what Nikon users experience. Quickly confirming focus.

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.

The differenc e in PDAF anf CDAF is that with PDAF tHe af system can have one look at rhe AF senor to find out how much to move the focus and in which direction. With CDAF it does not know any of these things. So CDAF need costant polling on AF to first see if focus is getting better or worse. Once it confirmed focus is improving it know it is moving in right direction, but it still do not know ihow much it need to move. So it need to keep pollong AF until the focus get worse again and then it know it has passed best focus.

So with PDAF there is a handful commands and replys between camera and lens before focus is locked, but with CDAF there might behundreds. With PDAF it may always be a fixed number of commands, but with CDAF if will vary depending on how much the focus need to move. The firmware in camera may aslo contain AF algorithm that is fine tuned to each lens, but most likely only for the camera makers own lenses.

Also, some motors designed for PDAF are worce when used for CDAF than others. And longer focal length lenses has heavier lens element to move wich can make it worse with CDAF.

Mirrorless lenses designed for CDAF often focus by moving a small and light lens in the rear of the lens for best CDAF performance, while DSLR lenses designed for PDAF usually move a larger and heavier lens in the front of the lens.

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

Not much hope, but good idea nevertheless!