Originally posted by BarneyL Honestly, I had some hopes that Sigma would actually release something new for the K-mount, seeing how the other DSLR companies are focused on mirrorless now, while most of the Sigma's lineup still consists of lenses designed for the flappy mirror. The demand for those falls, so every bit sold counts a lot more, right?
However, if Pentax comes up with their own 85/1.4 and a F/1.4 UWA prime, there won't be that much to miss really. Their zooms have notorious AF accuracy problems, and primes like 105/1.4, 14/1.8 or 40/1.4 are vanity projects - nice to have such an option, but it's nothing essential.
I have two Sigma zooms and neither one has anything like an AF problem, nor has my Sigma primes.
But, a big but, when I used Sigma zooms on my Pentax K-5 there were a lot of problems, the 150-500 being the worst.
When used with my simpler Nikon cameras the Sigmas I now have are all spot on (no AF adjustment needed), in good light 90% are spot on, at least.
So I don't think the problem was with the lenses, but with the communication between Pentax and Sigma, which for some reason wasn't very good, as I actually don't think Sigma has done some technical miracle, just that they speak the same technical language as Nikon.
Nikon does not always speak with Nikon, that is, some Nikon cameras simply work as bad with certain Nikon lenses as a K-5 with a Sigma lens (you probably know the drill: they hesitate, restart from close-focused, and try again, over and over till they, or you, just give up). But that is extremely rare in the world of Nikon, I hasten to add, and it has never happened with my newer lenses, like the AF-P series.
With my most expensive lens, ever, this weird cycle happened so fast that it sounded like a classic, Great War era, water-cooled machine gun (yep, been around that as well, very live, and very noisy). Asked Nikon to fix it but they could not. All within set limits, they told me.
On FX cameras this lens is still very popular, and it is now much cheaper!
I have no issues with any of my Sigma lenses nowadays, so I am planning to get some more!