Capturing tests that clearly illustrate changes in autofocus performance on flawless video is very difficult, as cameras can't be expected to behave identically during every test attempt. Nevertheless, through tests below, as well as other tests, we were able to conclude several things about how exactly the K-5's autofocus has been improved.
This first video is just one of our many tests of the live view system. All the tests comfortably showed that in live view mode, the K-5's autofocus is much faster and more accurate that the K-7's. It seems that while the K-7 turns the AF ring slowly in an attempt to "feel its way" to the focal point, the K-5 knows where its going, and moves the AF ring quickly with a little fine-tuning at the end. The difference isn't as landmark in this video (just over 4 seconds for the K-7, just under 3 for the K-5), but if we were to put the cameras in more extreme conditions, the K-7 wouldn't stand a chance.
This test shows that the AF assist light is effective in low-light scenarios. It also shows that the K-5's screwdrive focusing motor is not faster than that of the K-7 (it's likely the same unit). In tests prior to this one, we noted much greater consistency from the K-5's sensor, as well as less hunting. However, since neither AF sensor in this test seemed to have trouble finding the focal point, we were able to isolate the performance of the AF motor itself.
This test gave us some very positively-surprising results, and we think it's the most exciting one of them all (although we unfortunately aren't able to do a video for it). Our setup involved a hand-held K-5 trying to focus on a moving bicycle at varying distance. We tried using both focus priority and FPS priority, as well as spot AF, 5-point green AF, and 11-point green AF.
What we found, simply put, is that the K-5 excels at continuous autofocus for action shots. We didn't expect this going into the test, but during the test, we didn't miss a single shot that we wanted to take, and the K-5 didn't do any hunting at all. It was right on the money, accurate, and fast. Even in spot focus mode, it never hunted to get in focus. However, the best overall results were obtained in 11-point green AF mode, as only in this mode can the camera utilize its full AF potential to keep the subject in focus. FPS priority mode was a bit of a disappointment, unfortunately, as sometimes the camera simply gives up focusing in favor of shooting at maximum FPS, but we're assuming that that's the purpose of this mode. Thus, we recommend that you stay in focus priority mode for action photography, as it seems to consistently deliver very accurate results at a fairly good framerate (3-4 FPS). Pentax should be proud of the K-5 in this area, as it's certainly a big step up over the older bodies for action photography!
The K-5 proved to be consistently faster in everyday focusing than the K-7. It released the shutter first in 9 back-to-back tests at an EV of 10 (the rim of a very dim lamp), as shown below:
Our SDM tests with the DA* 50-135mm show that the K-5's AF system is more accurate, but that the speed at which the SDM operates is unchanged. We might have to wait for a new series of SDM lenses to witness an improvement in SDM speed (perhaps the upcoming DA 18-135mm lens will surprise us). While the AF accuracy itself is an improvement, a faster screwdrive motor would have certainly also been nice to see.
In conclusion to all these tests, we can see that the K-5's AF is only faster than the K-7's because it is more accurate and rarely hunts. You will notice faster performance for everday photography because of this, but where the K-5's new AF system truly shines is during continuous focusing with moving subjects. The K-5's AF accuracy blew us away. While the overall AF performance may still be worse than that of high-end competing bodies costing several thousand dollars more, the K-5's image quality leaves many competitors in the dust. We think that it's great to see such big improvements by Pentax and are confident that this will set a precedent that will begin to give Pentax the edge it needs for continued future success.