Pentax K-3 Review

Autofocus

Based on its specifications, the Pentax K-3 promises to deliver a plethora of autofocus improvements over older models.  On this page, we'll do our best to investigate just how much more beefy this camera's AF has become!

Screwdrive Motor

During our initial hands-on testing of the K-3, it felt like the K-3's screwdrive AF motor might be a bit more powerful than before.  To confirm, we took a slow screwdrive lens (the D-FA 100mm macro), turned it all the way to the closest focus setting, and let the camera focus on a distant subject using PDAF.  We repeated this test 7 times with both the K-3 and the K-5 II; the table below cites the median time to focus rounded to the nearest tenth of a second.

Camera
Time to Focus
K-3 1.4s
K-5 IIs 2.1s
Screwdrive AF motor speed test

These results suggest that the K-3 will focus up to 50% faster with screwdrive lenses.  The practical benefit of this improvement will be the most significant on lenses with a long focus throw, such as telephoto or macro lenses.  The increase in speed should be observable both in live view and when focusing through the viewfinder. 

Even though screwdrive is slowly starting to be a thing of the past, the majority of Pentax's current lens lineup doesn't yet have in-lens motors, so we feel that the improvement that Pentax has made in this area is important and will be enjoyed by many.

Contrast Detect (Live View) AF

The live view autofocus system in the K-3 feels very decisive- better than in any Pentax camera that came before it.  When used with a lens that has an average or short focus throw, we found the system to be so reliable that it could easily be used in place of the phase detect autofocus for everyday shooting, for those who enjoy using live view.  Compared to the K-5 II, the K-3 focuses much more quickly, and it rarely has trouble locking focus.  Compared to the mid-range K-50, which was already a marked improvement over the K-5 II, the K-3 is also slightly faster.  Unless there is absolutely no contrast in the selected AF area, the K-3 will almost always lock focus in CDAF mode.  Hunting has become a thing of the past!

Feature-wise, the K-3's live view autofocus system isn't just a copy of that found in the K-50; it has seen a few new modes as well as changes to the way that it behaves.


CDAF Mode Selection from the K-3's Info Screen

Let's start with the CDAF modes:

  • Face detection: In this mode, the camera focuses looks for faces within a 9x5-point grid spanning nearly the entire viewfinder.  If no faces are detected, the camera focuses within a 3x5-point grid just like it would in multi-point mode.
  • Tracking: In this mode, the camera tries to keep the focus locked on a moving subject.  Like in earlier models, this feature doesn't work reliably.
  • Auto-area AF: You choose an AF area and the camera automatically focuses within that area.  Supported area sizes include 1x1, 3x3, 5x3, and 7x3.  You cannot select a 2x1 area as you could on the K-50.  The areas do not have to be centered and they can be moved to anywhere within the camera's 9x5 master grid.
  • Select: You can move a 1x1 square to just about anywhere on the screen.  In this mode, you place the AF point in-between the auto-point AF gridlines.
  • Spot: A 1x1 square in the middle is used for focusing

Auto-area AF is illustrated below:

AF area and position selection in Auto-area AF

Auto-area AF showing 10/15  points as being in focus

In single-point select mode, a square with solid lines can be placed just about anywhere on the screen:


Single point selection screen

Single point moved to the left

Refer to this video for a quick demonstration of the K-3's live view autofocus (lens used: DA 21mm Limited):

Our only gripe about the K-3's CDAF implementation is that the camera needs to spend time re-focusing even if the scene was already in focus to begin with.  This behavior is shared with all earlier Pentax models.  Perhaps in the future, PDAF sensors will be added to the imaging sensor to help alleviate this issue and further improve CDAF performance!

CDAF Speed

To ensure that all our AF speed testing would not be affected by the K-3's faster screwdrive motor, we chose to use the Pentax 18-135mm DC lens, which has a built-in focusing motor.  So, does the K-3 lock focus faster than earlier cameras?  To find out, we put the K-3, K-5 IIs, and K-50 in spot focus mode repeatedly focused on two separate subjects.

Camera
Subject 1 (5EV)
Subject 2 (7EV)
K-3 1.0s 0.7s
K-50 1.3s 0.8s
K-5 IIs N/A 1.2s
CDAF Speed tests

When focusing on Subject 1, the K-5 IIs could not reliably lock focus.  When it did, which happened about 1 in 10 times, it spent over 4 seconds "hunting" for the target.  When combined with the results from Subject 2, our findings suggest that the K-3 is significantly faster than its predecessor and also slightly faster than the K-50.

Our test setup was performed in indoor light with a small and rather taxing subject to focus on.  In real life, where you'll most likely be using multi-area AF, you can expect the K-3 to consistently lock focus in under a second in live view mode.  Subjectively, we find this performance to be superior to what the Nikon D7100 (the K-3's closest competitor) and D610 can deliver.  We are very happy with the K-3 CDAF speed and believe that this is one of the most important improvements that Pentax has made to the camera.  In many situations the CDAF feels almost as fast as the PDAF.  We performed the tests above using PDAF as well and got an average AF lock time of 0.9s for Subject 1 and 0.7s for Subject 2 (with both the the K-3 and K-5 IIs).

Overall, the K-3's live view focusing speed is a big improvement over earlier cameras, and the CDAF system is the best that we've seen in any Pentax camera to date in terms of usability.  So, if you're a frequent user of live view, you'll love the K-3's new focusing system!

Focus Peaking

In live view, the K-3 supports a feature called focus peaking that works as an aid to manual focusing.  Objects that are in focus will have their edges outlined in white when focus peaking is enabled.


Focus Peaking Off


Focus Peaking On

Below is a close-up view of a focus peaking on with 4x zoom:

Combining this feature with live view magnification makes it very easy to focus manually.  However, there are still no options to control the appearance or color of the outlines.  It would have been nice if Pentax had incorporated the vast array of focus peaking modes from the Ricoh GR.

Phase Detect (Viewfinder) AF

The SAFOX 11 viewfinder autofocus system in the Pentax K-3 combines the class-leading low-light capabilities of the K-5 II (the previous Pentax flagship) with a new 27-focus-point layout.  The K-3 is the first Pentax DSLR ever to feature more than 11 AF points.

Like the K-5 II, the K-3 can focus in as little as -3 EV of light (closer to -2 EV in practice), and it does so with exceptional accuracy.  That's virtually pitch-black, and it certainly works as advertised based on our tests.  All 25 cross-type points in the center matrix are equally sensitive in low light, and this is surely one of the most impressive aspects of the K-3's autofocus.  For detailed information on the low-light capabilities, see the autofocus section of our K-5 II review (we won't be repeating ourselves on this page).  This aspect of the K-3's viewfinder AF system is not to be underestimated.

Tracking

The K-3 features the following AF servo modes:

  • AF.S: locks focus only once
  • AF.C: continuously adjusts the focus to stay locked on your subject
  • AF.A: tries to automatically re-adjust the focus setting if your subject moves

AF Mode Selection from the K-3's Info Screen

These servo modes have been present in all Pentax DSLRs since 2010 (exception: the K-5 and K-5 II/IIs lacked AF.A), so nothing's really new there.  Due to the unpredictability of AF.A, advanced users will normally prefer to stick to AF.S unless shooting moving subjects.

The K-3 does introduce some some new AF area modes, however:

  • Spot: focuses using the central AF point only
  • Auto-9: uses the central AF point as well as the 9 points surrounding it
  • Auto-27: uses all AF points based and automatically tries to identify your subject
  • SEL-1: lets you specify a single AF point to use
  • SEL-2/SEL-S: you specify a single starting AF point, but the AF system can utilize any of the Auto-9 AF points if your subject moves.  The expanded area shift if you select a focus point close to any edge of the matrix.
  • SEL-3/SEL-M: you specify a single starting AF point, but the AF system can utilize any of the 25 cross-type points if your subject moves
  • SEL-4/SEL-L: you specify a single starting AF point, but the AF system can utilize any other AF point if your subject moves (all 27 points are in use)

AF Area Selection from the K-3's Info Screen

The new SEL-2, SEL-3, and SEL-4 modes can be used for subject tracking.  On earlier Pentax cameras (the K-30, K-50, K-5 II, and K-5 IIs), this feature was known as "AF Point expansion" and had to be enabled separately in the menu.  Those cameras supported either 5-point or 11-point AF expansion modes.  With the K-3, you get to choose between 9, 25, or 27 points.

In addition to a focus priority and a release priority mode, the K-3 has also gotten a new custom setting (C16) which lets you enable focus priority for the first frame of a continuous burst, and then release priority for all subsequent frames.  An additional custom function (C18) allows you to add a delay between focus re-acquisition, but we recommend that you keep this setting disabled unless your subject predictably moves out of the frame.  Even though release priority mode will allow you to get a higher sustained framerate, blurry photos are no good, so we generally recommend sticking to focus priority mode over FPS priority or auto priority mode.  The better mode will depend on the nature of the motion of your subject, though.

K-3 AF System K-5 II AF
K-3 II AF Point Layout K-5 II AF Point Layout

The increase in the number of AF points suggests that the K-3's AF system can do a better job of tracking subjects than its predecessor.  We find that there are still two fundamental issues that might get in the way of this, however.  First, as you can see in the diagram above, the K-3's AF system covers the same exact area as the K-5 II (and all earlier flagships), and the gap between the cross sensors and the lone line sensors on either side is still fairly large (this is one area that could easily be improved).  That means that the K-3 doesn't give you the liberty of using more of the viewfinder for tracking.  Second, the fundamental AF point layout remains the same; the K-3 simply has a higher point density.  Therefore, as long as your subject is big enough, the tracking should behave in the same manner on the K-3 as it did on the K-5 II.  With fast lenses, you may experience slightly better performance in Auto-9 or Select-2 mode due to the presence of two additional F2.8 luminance flux sensors, but this doesn't contribute much to full-area tracking.

Our experiences in the field confirmed that K-3 AF system implementation feels very similar to that of the K-5 II in terms of the rate at which it re-acquires focus and the way that it operates, though the higher point denstiy does make it slightly more decisive.  Only one point will light up at a time, though, and it seems that the focus motor pauses for a split second while the camera is making its next measurement.  The SEL-4 AF area expansion mode actually feels very similar to the Auto-27 mode, which means that the K-3's predictive tracking capabilities continue to be somewhat basic.  We also feel obliged to mention that fast-focusing telephoto lenses, which are still scarce in the Pentax lineup, are just as important to successful tracking as is the camera body. 

To put the K-3's high-speed focusing capabilities in perspective, we compared the it to the K-5 II (w/ Pentax 60-250mm F4) and the Nikon D610 (w/ Nikon 70-200mm 2.8) in the field, shooting a moving subject in focus priority mode to see how many sharp frames we could get.  We made sure that the moving subject, a bicyclist, followed the same route when testing each of the three cameras.  The subject's distance ranged from 10 to 100 feet.  The K-3 was set to SEL-27 with focus priority, the K-5 was in 11-point mode with focus priority, and the D610 was in 3D Tracking mode (39 points total). 

Before moving on, we would like to note that this test is not a technical comparison of the three camera bodies, but rather a mere subjective test to see how the three cameras operate in practice.

Camera
Photos in Focus
Total Photos
"Keeper Rate"
Pentax K-5 II s
36 68 53%
Pentax K-3
57 85 67%
Nikon D610 80 82 97%
Continuous AF Field Test

This test, which is summarized above, shows that while the K-3 is an improvement over the K-5 II, it still lags behind the competition in this particular area.  The expanded area AF mode (27-point SEL 4) often "expands" to an entirely different subject, which requires the photographer to let go of the shutter button and re-focus once he or she realizes the error, which may not be easy when your subject is far away. 

Note that our results are in no way representative of the actual "keeper rate" you might get from an action shoot with any of the three cameras.  Many variables, including the lens used, the available light, the speed and distance of the subject, and the photographer's technique will affect the practical outcome of a high-speed burst.  The results simply show the relative performance of the three cameras under our test conditions.

PDAF Speed

With our discussion of tracking and AF.C out of the way, let's take a look at another important aspect of the K-3: the autofocus speed in spot AF mode.  Our studio tests found that in low light and daylight, the AF speed of the K-3 is about the same as that of the K-5 II, when used with SDM/DC lenses.  Based on the K-5 II's track record, this means that the AF is more than good enough to satisfy the needs of just about any stills shooter!

When using screwdrive lenses, the K-3 actually has an edge over its predecessor, as it incorporates a more powerful focusing motor as we've already mentioned.

AF Adjustments

If you encounter front-focus or back-focus issues with one or more lenses, it will not always be necessary to send your gear in for calibration thanks to the K-3's handy in-camera AF adjustments.  Separate adjustments can be made for up to 20 different lenses.  There is also a global setting that can be used for lenses that the camera doesn't recognize (i.e. manual lenses).  The AF Fine Adjustment option is found in the custom function menu.

Pentax K-3 AF Adjustments

For the majority of users, the amount of AF correction that this setting offers will be sufficient to correct any inaccuracies in autofocus.  Only rarely will professional adjustments beyond the supported +10 to -10 range be necessary.

PDAF Verdict

So, who will benefit the most from the K-3's new 27-point AF system? We believe that the users who will truly enjoy SAFOX 11 are those who can appreciate the high-density AF point layout.  When shooting in Auto-9 mode, for instance, the K-3 can focus much closer to the center of the frame than the K-5 II could in Auto-5.  This will make it much easier to focus on subjects that might move slightly while remaining roughly in the middle of the viewfinder.  Based on subjective tests, it is our impression that the K-3's autofocus points are smaller than those of its 11-point predecessors, with the exception of the central AF point.  If you don't already have a K-5 II (i.e. you have a K-5 or earlier), the K-3's PDAF improvements will be more noticeable in practice.  One change that you might notice when upgrading from any earlier Pentax is that when using all 27 focus points in Auto-27 mode, the K-3 does a better job of guessing where your subject is compared to the old Auto-11 mode.

The Bottom Line

When we reviewed the Pentax K-5 II last fall, we said that as a next step, Pentax should implement a more powerful screwdrive motor, and that it should add more AF points.  Well, it seems our wishes came true, as Pentax engineers have done exactly that!  Even though we were expecting an AF point increase to coincide with a larger AF area, we really have nothing to complain about with respect to the K-3's autofocus. Model by model, Pentax has been improving its AF technology.  Even though Pentax might still lag behind the competition when it comes to action photography, we are confident that any enthusiast photographer that picks up the K-3 (with a silent-focusing lens) will not be disappointed.

The improvements made to the K-3's live view autofocus are monumental, and this makes us think very highly of the everyday user experience that it can deliver with respect to AF.  50% faster screwdrive speed is just icing on the cake for users already invested in the Pentax lens system. 

Our in-depth autofocus tests have confirmed our original findings from the first impressions review with respect to PDAF. We feel that the practical improvements to the viewfinder autofocus are nowhere near as significant as improvements to the CDAF system and the screwdrive AF motor, which can be easily be observed after just minutes of use. In other words, if you currently own a Pentax K-5 II, you won't notice a very big improvement to the viewfinder autofocus.  However, if you're currently using a Pentax K-5 or older, then the K-3's SAFOX 11 will certainly feel like an upgrade.

We'd like to note that the autofocus performance you experience with the K-3 will greatly depend on the lens that you're using.  A modern DC/SDM (silent drive) lens, such as the 18-135mm, focuses very quickly.  On the other hand, screwdrive lenses with long throws, such as the DA 55-300mm, still feel like equipment from the last decade, even when paired with the K-3.  Primes with shorter focus throws such as the DA limiteds will focus quickly, but adjustments to the AF are nowhere near as smooth or accurate as with DC/SDM lenses.

What's next?  Pentax needs to redesign SAFOX so that it can work faster and provide better feedback about which points are in focus.  An increase in active AF area would also be very welcome.  Pentax's viewfinder display should be able to highlight all the points that are in focus, much like the competition already does.  The LED lights used to display AF points could further be upgraded to an LCD-based overlay, as this would make it easier to view AF points against bright backgrounds.  Lastly, if Pentax ever wants to be a big player in terms of PDAF, it will also need to redesign its lens lineup to improve the speed of SDM and refrain from using screwdrive AF in anything but ultra-compact primes.  Fortunately, based on the lens announcements that we've seen over the course of the past two years, it would seem that screwdrive autofocus is already being phased out slowly.


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