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04-06-2022, 06:06 PM - 33 Likes   #1
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The ins and outs of the K-3 III AF.C system - My own experience and understandings

As we know, the bells and whistles that are imbedded into the K-3 III when it comes to AF can be, well, 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 info been provided by Pentax. This is solely my own trial and error over 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 as of this posting (1.41). From my experiences, previous Firmware's (although improvements end over end) were spotty regarding reliability if you used any sort of tracking AF 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).

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 determined 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 cameras focusing system?
Well, from all my field testing, it actually does, 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 travelling 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 travelling 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.

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 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).

Now, you can also use SEL S/M/L which I found 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 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.

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



I probably missed a couple of things here and there (I'm currently under the Covid weather) but I hope this post 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.


Last edited by Kobie; 04-07-2022 at 02:30 PM.
04-06-2022, 06:41 PM - 2 Likes   #2
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I'm going to have to read this a couple of times! Thanks for the post and all the hard work.
04-06-2022, 07:19 PM - 1 Like   #3
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What Ray said, and I'd bet I'm not the only K3iii owner who will benefit from your observations and how well you presented it. Thank you.
04-06-2022, 08:08 PM - 1 Like   #4
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Thanks, Kobie. Lots to think about. That is always a good thing.

04-06-2022, 10:07 PM - 2 Likes   #5
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Thanks for the research and write up. I just got my K-3 III last Sunday. We have our Spring Test & Tune coming up 4/30 - 5/1. It's going to be interesting to see how this new body stacks up to my K-3. It's been a solid performer the last 8 years for me. I'll report back after that weekend with my results.

This was shot at Wheeling, WV back in 2019. It was taken from the opposite shore with a combo of my K-3, Pentax HD 1.4X AF Tele Converter, & Pentax DA* 60-250mm.
[IMG][/IMG]
04-06-2022, 10:28 PM - 4 Likes   #6
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Please, may I have my Spotty back now?
04-06-2022, 11:53 PM - 3 Likes   #7
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Thanks for your work in figuring this out and putting together such an informative post, Kobie. Man oh man, "Auto"-focus is getting complicated. On the one hand, Ricoh is to be congratulated for such a full-featured AF implementation. On the other, it's unthinkable that something of this complexity should come without detailed, clear documentation to educate the user

04-07-2022, 12:54 AM - 2 Likes   #8
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A very comprehensive resumé … reflecting many of the findings I've made myself
I agree about the a/f system having a problem with subjects on water, especially when shooting from an elevated position. All the flickering ripples really confuse it, but this is an issue with the K-70 and the KP as well, so not a K-3iii specific problem, which actually seems to be more capable … subject recognition possibly playing a part here
Single-spot a/f and a good panning technique definitely helps in these conditions
As with so much equipment, practice (and the subsequent familiarity) will help take advantage of the multitude of configuration options … being able to save a known-good combination in one of the ten User Modes definitely helps here
Having a User Mode put aside specifically for "test purposes" can also be a good thing. Change all the settings you want, secure in the knowledge that, if you "mess things up", just switch off and on again to revert to "normal". Any worthwhile combination of settings can be saved in a different User Mode, as previously suggested
None of this apparent complexity should dissuade any potential purchasers or, indeed, current owners.
The a/f system in the K-3iii is every bit as good (or better) as in the older cameras when used with the default settings.
It's just that the K-3iii has a much greater degree of "fine-tuning" available to help cope with the more traditionally "difficult" subjects … if you're not having a problem, leave well alone
Enjoy

Last edited by kypfer; 04-07-2022 at 01:09 AM. Reason: punctuation
04-07-2022, 01:00 AM - 3 Likes   #9
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Very interesting. Don't have a K-3III but I'm considering it and detailed reports on first-hand experience help a lot. Much appreciated.

There's one conclusion that puzzles me. Not disputing your empirical findings but the motivation for slower burst rate to work better for slower moving subjects is unexpected. Tracking movement at a higher sampling rate , on paper, is expected to deliver better accuracy regardless of the speed of the object being tracked.

The fact that, for slow moving targets, going to 11fps is not required is perfectly sensible, but that it is actually worse leaves me confused. Worst case, it should be equal. Maybe there's another reason, software related ? Could be. But I doubt the explanation lies in "matching" subject speed with the rate at which motion is sampled and predicted. Maybe it is simply the fact that higher burst rate is intrinsically less accurate, and if that rate is not actually required by the scene, the better compromise in terms of keeper rate is obtained with slower burst speed; even if the accuracy in predicting and tracking movement is technically worse but at that rate the rest of the AF and shooting pipeline keeps up better. In an abstract sense, "higher is better" should hold, there should be no need for this "matching".

Last edited by simon_199; 04-07-2022 at 01:10 AM.
04-07-2022, 01:48 AM - 1 Like   #10
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QuoteOriginally posted by simon_199 Quote
Very interesting. Don't have a K-3III but I'm considering it and detailed reports on first-hand experience help a lot. Much appreciated.

There's one conclusion that puzzles me. Not disputing your empirical findings but the motivation for slower burst rate to work better for slower moving subjects is unexpected. Tracking movement at a higher sampling rate , on paper, is expected to deliver better accuracy regardless of the speed of the object being tracked.

The fact that, for slow moving targets, going to 11fps is not required is perfectly sensible, but that it is actually worse leaves me confused. Worst case, it should be equal. Maybe there's another reason, software related ? Could be. But I doubt the explanation lies in "matching" subject speed with the rate at which motion is sampled and predicted. Maybe it is simply the fact that higher burst rate is intrinsically less accurate, and if that rate is not actually required by the scene, the better compromise in terms of keeper rate is obtained with slower burst speed; even if the accuracy in predicting and tracking movement is technically worse but at that rate the rest of the AF and shooting pipeline keeps up better. In an abstract sense, "higher is better" should hold, there should be no need for this "matching".


Interesting observations … probably needing further "testing"
One factor I have found is that using a wider aperture lens, with an inherently narrower depth-of-field, appears to allow the camera to track more successfully, probably simply because there's less "jiggle room", so the camera can confirm which way to focus in less time.
Specifically, my ancient Sigma 70-200mm f/2.8 set to 200mm appears to allow the K-3iii to track more easily than my 150-500mm f/5-6.3 when also set to 200mm.
Inevitably, without "lab conditions" to identically replicate the subject detail, there's always going to be an element of "human error" and, because I usually default to my 150-500mm for overall "reach", I've made very few direct comparisons.
So, if the conditions haven't already been established, one would need to try and replicate each set of comparisons with just the one lens, at a fixed focal length, to try to confirm the results.
All good fun
04-07-2022, 02:01 AM - 1 Like   #11
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Excellent review , and a lot to discuss. i have K3 III and shoot a lot wild life , birds in fly , sports .
You are right in many points . ( I'm not sure about slow moving subject with high burst ) . K3 iii it a complete different Pentax camera . it's very fast and in many cases it's great , but sometimes it's not .
Back to your thoughts . AF.C with zone or in full mode can be very tricky .You mention the surroundings light , color , contrast , and the subject speed . I agree with you . But one of fundamental in wild life it's a focal length and the distance .
the samples of seagulls in sky . bird it's too far . you need to get close or longer focal . When shooting in any moving subject even with AFC auto , zone with or without eye detection , i always keeping eye on green hexagon focus confirmation.
You did a great job . my best to you and your family
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04-07-2022, 06:15 AM - 1 Like   #12
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Wow, great write up and discussion. It has explained some of my failures and confirmed things I've suspected but had not properly tested. Many thanks!
04-07-2022, 01:10 PM - 1 Like   #13
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Good stuff, Kobie, I need to give it a few more reads. Many thanks!!! Now I need to give that D-FA 150-450 a little more purchasing thought!
04-08-2022, 05:23 PM - 1 Like   #14
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Nice write-up! I'll have to read it over a few times and print off a cheat sheet to stick on the back of the camera...

Biggest issue for me is consistency in AF performance. I'll focus on the same thing three different times and get three different results. I was taking some test shots of people walking past my building again today - many in focus, many others weren't. No real rhyme or reason.
04-08-2022, 06:07 PM - 1 Like   #15
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Excellent research and explanations, I too will have to keep this thread for reference, Thank you
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