Pentax K70

Interesting comment from JAK..
I never had any AF problems with the K-50. I could certainly focus on a bird among branches without the camera deciding otherwise.

IMGP2033 by Steve Ledger, on Flickr

IMGP2348 by Steve Ledger, on Flickr

IMGP3085 by Steve Ledger, on Flickr

Looking back I've had similar shots over the years with the K-30 and K-S1 also.

Personally my biggest issue with AF has been around tracking. ie having a child running towards you, or locking on and tracking a bird against a plain background, and I suspect that's more what the reviews are referencing.

Well from those images it would suggest there isn't much wrong the the AF on recent Pentax cameras. To be honest I didn't believe there is. Perhaps the reviewer of the review referenced to above had the camera on fully auto where mis-focussing is more likely as the camera has no idea of the intended subject and give it a whole frame to choose from its odds in it will make a mistake sometimes, as any other camera would. It isn't capable of mind reading! Provided the person using the camera knows what they are doing Pentax focussing is a non issue and re-pedalling a myth which for a Pentax forum is doing the brand no favours (or should that be favors given it's from an American forum? ) There are thousands of photos posted on our (and their) forum which dispel the Pentax AF myth.
Beginners may pick up a SLR/DSLR (any brand) for the first time and try and nail a shot of a moving target and it doesn't come out right for a multitude of reasons. It's easy to blame the tool when it's lack of experience and knowledge that is to blame.

There's probably an element of truth in all sides of the AF argument.

I've used a lot of different camera lately and there are some that track flying birds better than Pentax, but equally well some that struggle with subjects that would not have been a problem with Pentax. There is a marque I wouldn't buy because of its focusing performance, for the type of images I shoot. It has plenty of other good qualities for other photographers' needs though, so it's just "swings and roundabouts" in the end.

Great that tracking birds is a shared obsession amongst Pentax users. It may be a whole topic of itself, but certain lighting conditions can make it doubly difficult. Here's one. Anyone venture a diagnosis?

The water drops where the birds were do seem to be in focus so its down to the shutter lag between pressing the button and the shutter firing. It had been in focus a moment earlier! This has always been the Achilles heel with all SLRs. Lifting the mirror and firing the shutter isn't instantaneous.
To quote Ken Rockwell, "By the time the SLR mirror gets out of the way, your decisive moment is gone."
http://www.kenrockwell.com/tech/rangefinder-vs-slr.htm

Just to add, the trailing bird is more in focus than the one in front and from your original image it might sharpen up quite well.

The technique is to release the shutter before the bird is in the place you want so that the shutter lag is taken into account. This might be in the region of 10-20ms. It's enough for something to move, so the AF version would need to have predictive capabilities built in.