Pentax K-3 Mark III Continuous Autofocus Demystified

When to use the many advanced K-3 III features

By Kobie in Articles and Tips on May 17, 2022

Over the past year of having the K-3 Mark III, I have dived into the many features and options and tried them out back to back. Tested, evaluated, re-tested, re-evaluated. Brain stormed, dreamed about it. Woke up and was back to evaluating it all over again. So, with that said, this article in part is from a post I created in the K-3 Mark III thread.

I've added more to the article such as AF hold and the new options for when AF fails - Drive Lens or Stop Lens. I also explain what they do and when to use them.

As we know, the bells and whistles that are embedded into the K-3 III when it comes to AF can be (are) confusing. "Do I use subject recognition? Zone, Full Auto, SEL-EX (S, M, L?), SEL, Spot, AF.S, AF.C" and the list goes on and on and on.

Through the past year of concentrated shooting to figure out all the ins and outs of this new to Pentax Marvel of AF, I'd like to help others understand what the camera is doing when set to certain settings and when you should use one setting over another.

Keep in mind that my findings are not endorsed, nor has any insider info been provided by Pentax. This is solely my own trial and error over the past year through the many firmware updates that have been released.
Your mileage may vary which I will attempt to also explain why in this post.

Note: I will be focusing on the latest firmware (1.41) as of the writing of this article. From my experiences, previous Firmware's (although improvements end over end) were spotty regarding reliability if you used any sort of tracking AF.C setting.

Okay! Let's begin...

We'll start by looking at the camera itself to show the correlation of AF point vs intended subject over a variety of scenes.

Full Auto with a busy scene

Here are all the settings that were used. Notice the AF red dot that shows where the camera placed focus.
Now let's zoom in and see EXACTLY where it focused in the scene itself.

So what the heck happened here?! Why is it out of focus when it clearly showed an AF point was used?

Well, there's a few things at play here. For one, the AF points on the screen or in the OVF don't actually mean the subject is in focus. They only show which AF point was active during capture (if any).

The 2nd thing is using the Type-1 AF setting (which links both the RGBir metering sensor and the AF system together). I personally leave this setting on, but it's important to know what to expect when using it.

On the surface it sounds incredible! 307,000 pixels to assist the 101 point AF system for improved accuracy and speed in tracking? It's a no-brainer right? Well, not so fast. Yes it does track very well and very fast, however, 307,000 pixels don't divide that well into 101 AF points. There's gaps between the 101 AF points which many times is the reason you'll get images that show no AF points were used at all, or you'll get a sharp image but the AF point is just off the target.

I think what's happening is that the RGBir sensor is telling the AF system where to focus but there's no actual focus point at that location so it picks the next closest actual AF point. In other words, the RGBir sensor is picking AF locations that fall in the "cracks" between the AF sensors 101 points.

Now the 3rd thing is how busy is the actual scene? The subject recognition uses color, shape, and a database of pre-programmed things to recognize. If the scene has many shapes and/or colors (especially if they're similar to the subject itself) it will make it more difficult for the camera to isolate the subject for focusing. This is especially true if using the "Full Auto" setting that uses all 101 AF points which is shown in the above picture (for this scene, Zone would be a better choice (if you wanted the eye detect AF to be more reliable).

Zone AF with a busy scene

Just like before, take a good look at the screen and note the AF point location
Now let's zoom in and see how it looks!

Well that's weird! Why is this one so much more in focus?! By using Zone, you're limiting the area the camera will scan for moving subjects and things to focus on.

This is a great setting to use for complicated scenes with a subject large enough to fill most of or all of the Zone area. Don't forget, you can also move the Zone around with the joystick just like using Sel AF.

Here's an example of using Zone with a subject on the smaller side of things.
And let's zoom in...

Well that totally failed. So, ummm, what happened this time? Color information is too similar between both the subject and the background so it picked an AF point that it believed to still be the correct subject.

For better or worse, I made a video regarding the "PENTAX" folder that's in the SD cards, what some of the data contains and how it correlates to the subject recognition.

Surprise! Clouds is one of the subjects! So if you're experiencing issues with maintaining focus on a subject when using Full Auto or Zone with a cloudy background, it's probably because the camera is recognizing more than one subject at a time and doesn't know exactly which one to stay latched to. Don't forget that both Auto and Zone AF allow for the recognition of eyes in the scene (as long as subject recognition is turned on).

So what settings should be used in AF.C to capture certain subjects since it seems to be really picky about everything? It's not as complicated as it seems to be on the surface. Larger subjects are tracked beautifully with no issues at all (Motorsports, birds in flight that take up at least a full 1/4 of the image area or more).

Shooting speed

But wait! What about the shooting speed? Isn't a faster burst speed better?
Well, I've done a lot of playing around and analyzing this, and these are my findings...
The burst rate to use is actually dependent by the speed of the subject you're trying to capture.

I know... Say what? What does the burst rate have to do with the camera's focusing system?
Well, from all my field testing, it actually does matter, but not in the "traditional" sense. The camera has a new predictive algorithm for focus targeting estimation and that's an important thing to understand.

For example, if you're shooting a car coming towards you at 100 mph (160 Km/h) and it's taking up approx 3/4 of the image area and you're shooting with continuous MED (7 fps), it's very possible for the camera to under/over predict the in focus location for the next shot. So, the full 11 fps would get you more keepers as the camera better matches the subject speed with the "next frame" focus location. However, if the car is traveling at 40 mph (64 Km/h) and you're in full 11 fps burst, the AF location target will be a bit all over the map since the vehicle just isn't traveling fast enough for the cameras settings, so 7 fps would actually be the benefit here. The same holds true for birds in flight. Faster smaller song birds require faster settings. Larger/slower birds require slower settings.

Be deliberate about your settings

At the end of the day, the K-3 III is what I call a "deliberate" camera. You need to think about what you're shooting to apply the correct settings to maximize the keeper rate. Gone are the simple, meh, spot, single shot, I'll get something generalist approach. Now don't get me wrong, I know some of you are doing that and it's working for you, I'm not knocking it. I'm just saying that for more intense split second shooting, you need to apply some thought into the settings and base those settings directly to the subjects that you'll be shooting. It took me quite a while to figure out what was going wrong because everything I did with my K-30 and K-3 just did not work so well with the K-3 III (to the point where I almost sent the camera back to get checked). But I figured there must be something I'm missing here so I just kept testing EVERYTHING to figure it out.

So, in a nutshell:

  • Smaller subjects with erratic movement/faster motion = 11 fps.
  • Larger subjects with more consistent/slower movement = 7 fps.
  • Busy scene taking advantage of subject recognition: Zone AF
  • Isolated subject taking advantage of subject recognition: Full Auto AF (all 101 AF points).
  • Busy scene with tracking ability and no subject recognition: SEL-EX-S
  • Isolated subject with no subject recognition: SEL-EX-M or L depending on how accurately you can track the subject.
  • If the camera is getting confused with where to put the focus point, switch over to AF. This will enable to 5 points in the dead center circle in the viewfinder.
  • If you need ultimate precision, use spot. It is now small enough to allow shooting between branches of trees and Chain-Link fences without you having to be right against them.


I find AF.C SEL-EX-S/M/L does a great job of sticking with the subject under most conditions. It also allows you to start focusing from the center point before the camera will begin tracking.

Conditions where SEL M/L don't work seems to mainly be shooting subjects around water. I strongly think this (again) has to do with color information and the fact that the camera is a deliberate system as I explained before. When I'm shooting swans, ducks, geese out in the water, I switch to AF.S or AF.C AF (the 5 center AF points) so the system won't try "finding" things that are moving.

It seems (to me anyway) that AF.C specifically "scans" for movement which causes AF issues such as jumping from the subject to something else moving. This is especially the case if the intended subject is barely moving but something else in the scene is moving more.

AF.S is how it's always been, so there's nothing new (except for Zone AF, the subject recognition and eye detection) that we aren't already used to.

Example Shots

Here's some more examples with the settings that were used.
Remember, where I've zoomed in is where the AF target is located.

Notice this one shows No AF target but it's still sharp

AutoFocus Hold

There seems to be a fair bit of confusion when it comes to AF Hold status and what it actually does.
I've tested this thoroughly to have a better understanding of it's use case. Contrary to what I've seen posted it does not help with tracking subjects coming towards or moving away from the camera. As a matter of fact, it will actually hinder Z-axis tracking.

What does AF Hold actually do?

Auto Focus Hold does what the name says. It HOLDS the Auto Focus focal distance for a set period of time. Unfortunately, Pentax does not state what that time period is. The only options are Off/Low/Med/High with each one pausing/holding the AF for a longer period of time. Think of it as an Auto Focus Pause feature. It literally pauses the AF system.

Now that you know what it actually does, you can see how it would make tracking Z-Axis (subjects coming towards or moving away) less reliable.

  • OFF
    There is no pausing/holding of the AF at all. It tracks continuously and will jump focus if something gets between the subject and the camera.
  • LOW
    Very short pause/hold of the AF if the subject gets momentarily blocked by another object.
  • MED
    A longer pause/hold if the subject gets momentarily blocked by an object.
  • HIGH
    The longest duration of pausing/holding the AF focal distance in case the subject gets momentarily blocked by an object.

The ONLY use case to use AF Hold for an advantage is when tracking subjects while panning along the X or Y Axis (Horizontal or vertical tracking/panning).

Examples of when to use AF Hold

A specific player in a group sports scenario where another player may come between the subject and the camera briefly, Wildlife that may briefly move behind trees/shrubs etc, motorsports where the subject may get blocked briefly by another vehicle, fencing etc

To test it out, just find 2 subjects close to each other that are at different focal distances. Start with OFF and pan the camera from one subject to the other. Now do the same thing with LOW, MED, HIGH and you'll see how much longer it takes for the AF system to re-initialize. Now, find a subject that takes up a good portion of the viewfinder (1/4 to 1/2 or more). With the shutter button half pressed or back button pressed, move towards the subject with AF hold off, then low/med/high. Or use a subject that is moving towards or away from the camera and pay attention to the length of time it takes for the AF system to drive the lens with each setting.

Pentax's own marketing for AF hold only shows horizontal panning with objects coming between the subject and the camera. Not once is it shown with subjects coming towards or moving away from the camera.

A new option - Drive or Stop Lens

In the menu, go to the Camera icon = Still Image>1 - AF with Viewfinder>7 items down from the top = Action when AF fails>The options are Drive Lens or Stop Lens.
Driving the lens is how it's always been, you focus on something far and you see something close, so you pick up the camera and it will rack the lens back and forth until it gets focus. So what does Stop Lens do? Well, as an example, say you're shooting an erratic subject and as your tracking, it vanishes from the viewfinder.

The distance is still relatively the same, you just lost sight of the subject. If the lens were to try to get focus again, it could be so far out of focus that you wouldn't be able to even make out the subject in the viewfinder again. By using Stop Lens you're telling the system to keep the last known in-focus distance which makes it easier to re-acquire the subject. This is not the same as AF Hold. This is a pseudo focus limiter built into the camera and does come in handy when used in the right situation.

The only issue I've come across when having Stop Lens enabled is sometimes if you've been out shooting and the lens is set for, I dunno, let's go with a close subject but you see something off in the distance so you aim the camera over there but it's a complete blur and now the AF isn't working. Well, you've told the camera to STOP the lens so it won't try to focus since it's already way out of focus. This is where Quick Shift comes into play. You can manually focus the lens to a focal distance close enough to recognize the subject, then the camera will re-activate the AF.

Now get shooting!

I hope this article helps at least one person out when coming to terms with the whizbangetry of the K-3 Mark III with all it's doohickies and whatchamacallits and how it all comes together into one amazing thingamabobber.

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