[FozzFoster]

Back button and shutter button behaved differently for some reason.

I am unable to replicate your results with my K-3 III.
Autofocus area, mounted on a tripod, with a static subject
With multiple tests, pressing the backbutton AF yield different initial AF points for the same scene.
With multiple tests, pressing the shutter AF yield different initial AF points for the same scene.

Both options do not yield the exact same selected AF point every time.

In addition, for your test (using AF-C for a static subject), there were other points that could have been selected that were JUST as contrasty as the centre point in your shutter AF test... why didn't it choose any of those other contrasty points?

And I really agree with what biz-engineer stated:

I doubt back button AF and shutter button would drive different auto-focus algorithm.

[Larrymc]

I call the mode Kobie was in when he discovered the "problem" the CBS (clear blue sky) mode which is probably only good for tracking objects with a clear sky type background. The Mk III in that mode will select lock onto and track BIF easily but with other contrasty object mixed in with the BIFs in the scene it is a toss up as to what it will lock onto and track. I rarely use the CBS mode but instead I opt for one of the expanded area select modes with AFC tracking.

[Kobie]

I am unable to replicate your results with my K-3 III.
Autofocus area, mounted on a tripod, with a static subject
With multiple tests, pressing the backbutton AF yield different initial AF points for the same scene.
With multiple tests, pressing the shutter AF yield different initial AF points for the same scene.

Both options do not yield the exact same selected AF point every time.

In addition, for your test (using AF-C for a static subject), there were other points that could have been selected that were JUST as contrasty as the centre point in your shutter AF test... why didn't it choose any of those other contrasty points?

And I really agree with what biz-engineer stated:

Which Firmware are you on out of curiosity?

[FozzFoster]

Which Firmware are you on out of curiosity?

The latest one released not long ago (1.10):

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[mctaveck]

If that's the case, then why did that NOT happen when using the shutter button? I was out there for a while and tested this on many different subjects with consistent results. I didn't shoot each one as I was only testing the AF system to see where it would focus. Flowers, plants, bees, birds. Back button and shutter button behaved differently for some reason.

I did another thest with the camera steady on a table and a focus chart, used the 55-300 plm. I did not notice any real changes in focusing behaviour. The red dot that is showing the focus point after the shoot is not always there (no red dot at all) but the black square in the viewfinder was the same and the image comparison is almost the same. I did not updated the firmware with the last one (the one that allow electronic shutter)
I'll try tomorrow with another lens.
What i saw is that, for whatever reason it seem the focusing algorithm prefers side points not the central ones. Maybe there is a logic (rule of third?) maybe not. Other than this I am not sure I can do such test with birds but... let see.
Danilo
Thanks

[Joe Schmoo]

Hm. Kobie seems to have encountered unexpected behaviour of his K-3 III in AF.C Auto via back-button AF, where it would erratically jump to various suboptimal focus points instead of focusing on the most contrasty subject. This was different from what it did when the AF was activated with the shutter button, in which case it would invariably pick the contrasty sign in the centre of the frame as its AF target. Whatever caused this, it would seem that back-button and shutter operation yield different results in AF point selection, which clearly shouldn't happen.

#shorts I think I just cracked the Pentax K-3 Mark III AF.C issues. Check this out - YouTube

Can any K-3 III user confirm that this is a replicable issue? If that should be the case, let's hope that people at Ricoh put this on their to-do list for the next firmware update.

Maybe, just use a single center point, aim it at what you want, with AFC BBF and press the shutter when you want. It's not rocket surgery .

[Madaboutpix]

If there was already AF lock on a point, a new attempt to focus will select the next nearest point. Typical behavior of auto-AF point selection on my K1. It's quite smart. We need to understand how our gear works before claiming it's faulty.

Actually, the last time I used AF.A mode was 6 or 7 years ago on my K-7, before I became more confident in selecting and moving AF points myself and configured the camera for back-button AF.C. Grown to appreciate that extra bit of control over what the camera does, I've never used Auto-select mode on my K-3, so I welcome your information about how your K-1 and likely other models behave. BTW, I didn't claim that any gear definitely was faulty, I was just curious if what Kobie observed amounted to a real issue that should be brought to Ricoh's attention. After all, I'm looking to replace my K-3 with the new model at some point and so follow reports of possible issues closely, regardless of how much I already like the camera. And I figured it wouldn't hurt to run this by people on a tech-centered forum, which is arguably one the main points of such a forum. I tend to be a truth-seeker, not a fault-finder, ya know.

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Last edited by Madaboutpix; 07-29-2021 at 02:33 AM. Reason: Nuance.

[Rondec]

Probably the take home message is not to use AF-C for static scenes -- either with back button AF or shutter release AF. Better to use AF-S and choose your auto focus point.

[biz-engineer]

BTW, I didn't claim that any gear definitely was faulty, I was just curious if what Kobie observed amounted to a real issue that should be brought to Ricoh's attention. After all, I'm looking to replace my K-3 with the new model at some point and so follow reports of possible issues closely, regardless of how much I already like the camera.

Would be interesting to know if the AF point selection is repeatable or not, after resetting lens focus to the same position (e.g prefocused at infinity) between each auto-focus trial. It's because the initial condition of the lens focus is likely to impact how repeatable is AF lock on which target. With my K1 or K3, in live view mode face detection on a group of people, if I refocus after a first focus attempt, the camera won't refocus on the same face, it will alternate from face to face each time I refocus. I watch the vid. of Kobie, he doesn't reset lens focus before pressing the back button AF after the camera already locked focus on target using the shutter button half-press.

[c.a.m]

The red dot that is showing the focus point after the shoot is not always there (no red dot at all)

If the AF Button is enabled and the shutter half-press disabled (i.e., back-button focusing), I believe that the AF button must be kept pushed in at the time of shutter release, for the red focus points to be registered.

When using AF.S and the AF Button, I usually release the AF button prior to pushing the shutter button, so the red dots are not registered.

- Craig

[Mikesul]

Thanks C.A.M, that seems to be the explanation. I haven't cared a lot but I have wondered about the, occasionally useful, record of the focus points. We are gradually understanding our excellent new camera.

[house]

Probably the take home message is not to use AF-C for static scenes -- either with back button AF or shutter release AF. Better to use AF-S and choose your auto focus point.

Does anyone know if any auto focus algo these days are reliable enough to pick the right subject in full auto? DSLR or mirrorless. I just can't imagine it working how could the camera know what to focus on unless you stick to obvious styles such as portraits etc.

[Larrymc]

Does anyone know if any auto focus algo these days are reliable enough to pick the right subject in full auto? DSLR or mirrorless. I just can't imagine it working how could the camera know what to focus on unless you stick to obvious styles such as portraits etc.

The only way any will pick the right subject is if the "right Subject" is the only subject visible to the camera when focusing, for instance a bird flying in the clear blue sky.

[mctaveck]

If the AF Button is enabled and the shutter half-press disabled (i.e., back-button focusing), I believe that the AF button must be kept pushed in at the time of shutter release, for the red focus points to be registered.

When using AF.S and the AF Button, I usually release the AF button prior to pushing the shutter button, so the red dots are not registered.

- Craig

Run a test now. It is correct what you say. Clever !! I'll save it in the "undocumented feature 3d"

Thanks
Danilo

[mctaveck]

I can confirm no differences in AF point selection in my case, also using the Pentax 16-86. Back button or shutter button detect the same Spot, almost identical. Firmware issue?