Originally posted by reh321 AF is a specialty of/to itself. Large producer Nikon has several lines of camera, only one of which features fast AF, and/but most of those cameras don't have particularly high Image Quality. Pentax doesn't have the resources to provide multiple lines, so they must me more focused on what they provide; from their words and actions, they have made clear that they are seeking high Image Quality. They are also making marginal AF strides, but they simply cannot focus on everything at once.
D500, D850, D5 are in another league in terms of af. D810 was not bad either, just not at the level of their newer flagships. I'd say K-1 is similar to d800 in terms of af, at least from what I remember shooting with d800 few years back.
I'd vote for a significant af improvement for the next update, which I'm sure Pentax will implement.
---------- Post added 05-20-18 at 11:48 AM ----------
Originally posted by rawr Pentax has it's strengths and weaknesses in AF, just like many other brands.
It seems common to assume AF only has to be is 'fast' to be good. But often other dimensions of AF performance are missing from this common measure of 'good'.
A few things that spring to mind are the accuracy of camera AF performance (with related issues of how
consistently accurate the AF is), and the working range of the AF, in particular it's light sensitivity. If the AF can't work in low-light, a whole range of shooting scenarios are off-limits, and the calculus of what 'good' AF performance means needs to reflect that.
On the 'accuracy' variable, Pentax has usually tracked well here from various testing sites (if memory serves, demonstrated by tests from France 'Chasseur d'Images' & 'DigitalFotoNetz' in Germany) where the measure is reliably producing sharp images. But there is a big caveat, of course, to any claims of superior
shot-to-shot AF accuracy in any PDAF system, where accuracy depends on, amongst other things, normal camera/lens variation.
On the matter of low-light AF, it's notable that Pentax has consistently led other DSLR brands with the low-light sensitivity of it's camera AF: the K-5II came with -3EV AF sensitivity in 2012, whilst the first Nikon to meet that specification (the FF D750) came out in 2014, and the first Nikon APS-C to match -3EV (the D7200) only came out in 2015. Similarly with Canon - the FF 6D did -3 EV in 2012, but no other Canon until the APS-C 7D2 in 2014 was provided with the same sensitivity. And despite the 645Z/K-3/K-3II/K-S2/K-70 etc coming along, no Sony got anywhere near -3EV EV AF sensitivity until the A7S was released in 2014.
TL; DR - AF is a huge can of worms. Pentax does OK, depending how you look at it.
I had massive issues with af indoora with an expensive "pro" dfa 15-30, slightly better with dfa 28-105. Screw drive lenses - 50/50, which isn't a great result. I don't think speed is a huge issue, accuracy is, at least to me