Pentax K-50 Review

Autofocus

The Pentax K-50 inherits the 11-point SAFOX IXi+ phase detect autofocus system of the K-30; this is Pentax's second most recent AF system, which is a generation older than the SAFOX X implementation found in the K-5 II and K-5 IIs.  In addition to this primary AF system, which works when shooting through the viewfinder, the K-50 has an improved contast detect autofocus system in live view, which is noticeably better than the one found in the Pentax K-5 II family of cameras (i.e. the current flagship).

As we have already carefully analyzed the performance of SAFOX IXi+ and compared it to the SAFOX IX+ system in the original Pentax K-5, for this review we will only be comparing the AF speed of the K-50 to the K-5 II/IIs.

Phase Detect Autofocus

The K-50's viewfinder-based autofocus system has 11 autofocus points, with 9 cross-type points in a 3x3 grid and two standard points on either side of it, as shown below:

The autofocus points can be illuminated in the viewfinder so that you always know which points are being used for focus.

The K-50 supports in-camera, per-lens autofocus adjustments, a feature that's unusual for its class.  This means that if you experience front-focus or back-focus issues with one or more of your lenses, you can often make the necessary adjustments in the comfort of your home, rather than having to get your camera serviced.

While the number of AF points or the performance of the system in continuous mode are certainly not industry-leading, we feel that most users will have no problems whatsoever with the K-50's autofocus.  We will, however, recommend that you look at competing bodies if your sole interest is action photography.

Three AF modes are available when shooting through the viewfinder: AF.S (single), AF.C (continuous), and AF.A (automatic selection of focus or release priority in AF.S).  You can set the camera to use any single point, the 5 central points, or all 11 points.  The K-50 also supports "expanded area AF", a rudimentary tracking feature which attempts to keep your subject in focus even if it leaves the selected AF point.  It is our opinion that the K-50 does not have enough AF points to support robust subject tracking.

Live View Autofocus

When focusing in live view, the K-50 does not magnify the image by default like its predecessors did.  Instead, magnification occurs about half a second after focus is locked, but only if you continue half-pressing the shutter release button (or the AF button).  This not only allows you to confirm the focus setting more easily, but allows the camera to dedicate additional CPU power to the autofocusing task.

In order to speed up their contrast detect AF, it looks like Pentax made another small change: during focusing, the live view picture resolution is reduced dramatically until focusing is locked.  This seeminly-clever optimization can be a bit annoying at times, as it prevents you from clearly being able to see the live view image.  The view below demonstrates this quirk:

Fortunately, based on our subjective testing and everyday shooting in the field, it seems that the K-50's live view autofocus performance is slightly better than that of the K-30, and still miles ahead of that of the K-5 family of cameras.  In live view, the K-50 holds its ground very well against competing cameras.

In live view, you can either just use the center of the frame to focus, or select the area size and location manually:

The K-50 also supports face detection and tracking.  The live view tracking feature should be avoided, as it simply does not work.  The face detection works reasonably well, but it is not as responsive as we'd like, and it likes to mis-identify objects as faces:

AF Tests

We compared the autofocus performance of the K-50 to that of the Pentax K-5 IIs two real-world scenarios: an outdoor scene (approximately 13EV) and an indoor scene (approximately 5.5EV).  In both tests, the cameras were pointed at a subject approximately 15 feet (5 meters) away from the camera.  The same Pentax 18-135mm lens was used on both cameras.

The table below shows the measured time between when the shutter button was depressed and when the photo was taken.  In order to ensure accurate results, we performed each test five times and calculated the median result as our final figure.

Our results were extremely consistent and offer no surprises: the K-5 IIs was always faster to focus through the viewfinder, while the K-50 was always faster to focus in live view (by a larger margin).  Both cameras were very decisive and exhibited no hunting in these tests.

AF Noise

Because most Pentax lenses still have an older-style screwdrive autofocus mechanism, some lenses, including the 18-55mm kit lens, can be quite loud when focusing.  The 18-135mm, on the other hand, is virtually inaudible.  The video below compares the two AF types:

AF Verdict

We were positively surprised with the live view autofocus of the Pentax K-50, and we're very happy to see that minor improvements have been made to this system.  The viewfinder autofocus remains unchanged compared to that of the Pentax K-30, which sets the Pentax somewhat behind the competition.

All things considered, though, the K-50's autofocus is good and very reliable for everyday use.  Nothing about this camera's autofocus performance would deter us from buying it unless we were looking for a camera purely for sports photography.  We are convinced that if you buy the K-50 as your first DSLR, you will be satisfied by its AF performance, especially if you enjoy using live view mode.  The AF system feels very decisive overall and in most situations, the focus will lock in well under a second.

Our only other gripe is about the lack of silent autofocus in the 18-55 and 50-200mm kit lenses, though you can always opt for the 18-135mm (or modern Sigma lenses) if silent AF is a priority.