[beholder3]

Autofocus in 2022 is a complex automated process in photo cameras. Since there also are vastly different use cases out there the makers reacted by offering tons of settings the photographer can adjust to make the camera work exactly as the user wants it.

First learning point:
One static set of setting in your camera will definitely not cover all different shooting scenarios. It is bound to be great in scenario A, so-so in scenario B and poor in scenario C. If you want the best results you *have to* adjust things per scenario. This is true for all cameras on the market.

Then there is the thing about words/language used when explaining things.

First keep in mind "autofocus" just means that the camera somehow measures the distance to your subject and uses a motor (in the camera or lens) to adjust the lens so that the actual plane of focus (the distance where the image will be the sharpest) to exactly your subject.
So in its basic feature autofocus just moves the focus plane along the z-axis (from near you to far away).

In"AF-C" this distance measurement is taking place multiple times a second (the newer the camera, the more powerful its processors are the higher the frequency of measurements). So if a dog comes running towards you, the camera measures continuously and will get different distances each time.
In an extremely oversimplified example the distance in meters could be measured as over a time period of 1-2 seconds:
10 10 9 9 88 8 7 7 6 6 5 4 3 3 2

The AF distance measuring takes place in the viewfinder frame at a location we call"AF point". DSLRs have lots of them to choose from. many people select just the one in the middle, but you can use any one.

Please note that until now there has been no mentioning of the term "tracking".Tracking does not in any way describe the core autofocus process directly, but it does describe a separate user supporting automatism. Tracking is all about automated choosing of the optimal AF point somewhere in the frame and to be more exact: automated choosing of the active AF point if the photographer is unable or unwilling to keep the main subject under the previously chosen AF point.

Tracking(automation) effectively means that the camera tries to guess what part of the currently framed image is your intended main subject so the camera then can automatically choose and activate AF points over this subject in case the subject moves around in the frame.

So for example if you would shoot a train coming absolutely straight at you (you standing on the rails; do not do this! ) and you pointed the central AF on the front of the train then you do need zero tracking as the subject will stay in the middle of the frame. You just need AF-C to make the lens adjust the focus plane as the train approaches.

On the other side you might want to shoot a football player and since he is moving around fast you might have some stress keeping him framed exactly how you want it. maybe he first is in the middle but then quickly runs to the right frame edge and you are a little too slow swinging the camera and for half a second he is on the right hand side of the frame. In this case your previously selected center AF point stares at the distant grass now. Without any tracking the camera will now want to focus on the distant grass. With tracking automatism the camera might understand that the intended subject has moved to the right side of the frame and activate an AF point there instead of the center one.

Please note that tracking is a "smarter" software algorithm than just pure"automated AF point selection" which has been around a long time (for example in "green mode"). The latter did also work in a limited way,but had a primitive logic: It simply assumed that the one item on the frame(and covered by available AF points) that is closest to the camera must be the desired subject and so it did activate the AF point on it. This can be correct, but in many scenarios it is not. Tracking still is just automated point selection but with a more intelligent subject identification.
Most modern cameras such as the K3-III actually use some image pattern recognition techniques to guess what part of the image is the desired key subject and where it moves in the frame - to always activate the AF points over the assumed key subject.
A specialized form of tracking is the "Eye AF " that especially searches for things which look like eyes.

Now back to core autofocus and where AF-hold plays a role.

Scenarios:

Let me first describe a few scenarios of the camera measuring the distance of the focus plane (super simplified):

1. A) dog running slowly towards you
   9 9 9 8 7 65 4 3 2 1
2. B) dog running from left to right but you are not able to keep the chosen AF point onit during two measurements (the center points at the far grass)
   5 4 4 4 4 44 9 9 4 3
3. C) dog very fast running towards you and back again
   9 6 3 1 1 36 9 12 15

What does"AF hold" do?
It sets the"distance-stickyness" of the AF system to a certain distance.

It sets how long it intentionally ignores unpredicted and bigger (!) jumps in distance measurements.
Nothing else.
It is good for ignoring brief interruptions/outliers.


Now lets us look at two variants of each of the three scenarios above.
Variant 1:AF-hold = off
Variant 2:AF-hold = long

Scenario A)9 9 9 8 7 6 5 4 3 2 1


Since the measurements are very continuous without sudden jumps and the changes are notall extremely big there is zero difference effect between the settings variants. The reason is that AF hold on "long" will not really interfere with nicely predictable changes of AF distance as it happens here. It does not "hold back AF" operations overall.



Scenario B)5 4 4 4 4 4 4 9 9 4 3

Here it starts to get interesting.

Variant 1:AF-hold = off à Focuswill jump to the far away background under the chosen center AF-point immediatelyand loose focus on the dog (at the “9” in the numbers). It should also comeback relatively quickly to the “4” later on, but we know that in reality itdoes take time due to the major racking of the lens in between.

Variant 2:AF-hold = long à whilefocus on the subject may be off somewhat the focus plane will likely be around “4”and stay there briefly with a good chance to pick it up quickly afterwardswithout major racking of the lens. Here this variant is the betterchoice.
The AF holdignores the big jump from “4” to “9” for a brief period and sticks to thedistance level.


Scenario C)9 6 3 1 1 3 6 9 12 15
Variant 1:AF-hold = off à TheAF will focus correctly on the dog (given the AF motor drive is fast enough andyou are able to keep the AF point perfectly on the subject. This is the betterchoice here.
Variant 2:AF-hold = long à Itis likely that the stickiness of the AF distance here will initially ignore thenon-predicted and big jump from “3” to “6” and then to “9” but instead waithalf a second at the “3” distance. Maybe it will recover later on but that willtake some time.

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Last edited by beholder3; 05-20-2022 at 06:13 AM.

[que es tu]

This setting has always baffled me. So, does AF hold only have usefulness with AFC? What affect does it have with AFS??

[clackers]

This setting has always baffled me. So, does AF hold only have usefulness with AFC? What affect does it have with AFS??

None.

[clackers]

you might want to shoot a football player and since he is moving around fast you might have some stress keeping him framed exactly how you want it. maybe he first is in the middle but then quickly runs to the right frame edge and you are a little too slow swinging the camera and for half a second he is on the right hand side of the frame. In this case your previously selected center AF point stares at the distant grass now. Without any tracking the camera will now want to focus on the distant grass. With tracking automatism the camera might understand that the intended subject has moved to the right side of the frame and activate an AF point there instead of the center one.

Absolutely, B3.

I've seen some people suggest to leave AF Hold off if the subject is in clear view. But if it's moving, and someone's tracking and panning photography skills are not up to the motion, the camera correctly detects that the AF point is now on the background, and is never be able to catch up when the owner finally moves it back to the subject, so the whole sequence is ruined. And then they will post on the internet that their camera can't do sports.

I would say, scenario dependent, it's actually the safest for a beginner, it's more forgiving of errors. It's *permanently* on for me, for example, in case I forget in the excitement of setting up for a quick shot of some action.

Does an owner need L, M or H? Well, that's on the owner's accuracy, and the timing of any obstacles between the lens and the subject, that's exactly why the setting is variable, and why high end Canikony models have it too.

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Last edited by clackers; 05-18-2022 at 07:04 PM.

[wadge22]

I've got no dog in this fight; I rarely use AF for moving subjects (I don't have a K3ii, and have never turned AFc on on the cameras I do have).

Just dropping in to say that this frontpage article by @Kobie about K3iii AFc is another good point of reference on the subject, for those who found this writeup helpful and are looking for more. Great job @beholder3 .

[que es tu]

None.

Okay I think I just got the idea down of how this works. Correct me if I’m wrong: I am in AFC with AF Hold on high. I am tracking the elusive Boojum in the view finder and it is moving parallel to me. Suddenly, he passes behind some bushes and is briefly obscured. Since I have AF Hold on, the camera does not refocus on the bushes, but “holds” the autofocus. Then, when Boojum appears again, he is still in focus! Unfortunately I realize too late that the SD card is not in my camera!

[gatorguy]

Okay I think I just got the idea down of how this works. Correct me if I’m wrong: I am in AFC with AF Hold on high. I am tracking the elusive Boojum in the view finder and it is moving parallel to me. Suddenly, he passes behind some bushes and is briefly obscured. Since I have AF Hold on, the camera does not refocus on the bushes, but “holds” the autofocus. Then, when Boojum appears again, he is still in focus! Unfortunately I realize too late that the SD card is not in my camera!

LOL. First point definitely got it! Second point more common than any of us admit to.

[que es tu]

LOL. First point definitely got it! Second point more common than any of us admit to.

Yes especially when you spot Sasquatch, Boojum, or even the Wild Man of Cataloochee!!

[clackers]

Okay I think I just got the idea down of how this works. Correct me if I’m wrong: I am in AFC with AF Hold on high. I am tracking the elusive Boojum in the view finder and it is moving parallel to me. Suddenly, he passes behind some bushes and is briefly obscured. Since I have AF Hold on, the camera does not refocus on the bushes, but “holds” the autofocus. Then, when Boojum appears again, he is still in focus! Unfortunately I realize too late that the SD card is not in my camera!

Exactly. You tell the camera beforehand what time delay is intentional and what isn't, and you get your shot!

[beholder3]

AF hold is good for:

1. Subjects temporarily being obscured/covered by trees, grass, branches, other potential subjects (teamplayers, cyclists, horses etc)
2. Subjects which stay in a similar distance to the photographer but erratically change direction in the frame, so it is likely the photographer is unable to keep the selected focus point continuously over the subject (e.g. birds in flight not very close and not coming straight at the photographer; straightly running dogs filling the frame so the subject bounces up and down faster than the photographer can follow to tilt the lens)

AF hold is bad for:

1. Subjects accelerating and decelerating (towards the photographer along the z-axis) a lot and erratically (dogs toying; small birds close up)
2. Scenarios where the photographer intentionally does not want to stick with one initial target but wants to switch them in split seconds and the subjects are in different distances (sports with many participants where the photographer has no fixed intention on who she/he wants to follow)

I think one can explain the "AF hold" algorithm also as "temporary focus limiter", where temporary is 1/4 of a second or so and where the focus limiter does NOT limit already predicted changes of subject distance (e.g. a train coming at you).