A6400 AF-C during burst with back button autofocus

jablesblack · Jun 4, 2024

I am having an issue with my A6400. During a burst in the continuous drive mode, the camera does not refocus after each shot in the burst when I use back button autofocus. I've set up BBAF by: setting "AF with shutter: OFF", and setting the AF/ML button to "AF-ON". Also, AF-C is used. I've been using BBAF for years, and it is working as expected.

However, when I

Hold back button down
Hold shutter down to take a burst

The focus does not update throughout the burst. I've tested this in two scenarios:

first holding the back button to get focus, then taking a burst while panning the camera to something else I'd like to focus on.
having the camera out of focus, starting a burst, then once the burst has started, holding the back button.

In either of the above situations, I would expect the AF-C to update the focus during the burst. In both situations, the focus does not change during the burst. Clearly, this is desired for action/motion photography such as birds in flight. If I stop taking the burst while back button is pressed, the AF-C kicks back in and focus is updated.

When I have "AF with shutter: ON" (not back button autofocus, default half press shutter focus), then the focus updates during the burst as expected. So, I have narrowed this down to something to do with BBAF.

Tldr: focus is locked during burst when using BBAF, but not with default half press focus.

Henry Richardson · Jun 4, 2024

I am sorry that I cannot help you with your Back Button Focus issue, but I hope someone here can help you. I am also having an issue with Back Button Focus.

https://www.dpreview.com/forums/post/67732523

On my A6700 for some types of photos I prefer to use Back Button Focus and for other types I prefer the default Shutter Button Focus.

Unfortunately, I cannot find how to save the menu selection AF w/Shutter in one of the 3 camera memory locations on the mode dial. When I save settings to one of the camera memory locations it remembers other settings, but it does not remember the setting for AF w/Shutter. Probably there is a setting buried in the menu I have not yet found to make it save that. Anyone know how to do it? Thank you.

ARSPR · Jun 4, 2024

jablesblack said:
I am having an issue with my A6400. During a burst in the continuous drive mode, the camera does not refocus after each shot in the burst when I use back button autofocus. I've set up BBAF by: setting "AF with shutter: OFF", and setting the AF/ML button to "AF-ON". Also, AF-C is used. I've been using BBAF for years, and it is working as expected.

However, when I

Hold back button down

Hold shutter down to take a burst

So you are releasing that BBAF button, aren't you?

jablesblack said:
The focus does not update throughout the burst. I've tested this in two scenarios:

first holding the back button to get focus, then taking a burst while panning the camera to something else I'd like to focus on.

having the camera out of focus, starting a burst, then once the burst has started, holding the back button.

In either of the above situations, I would expect the AF-C to update the focus during the burst. In both situations, the focus does not change during the burst. Clearly, this is desired for action/motion photography such as birds in flight. If I stop taking the burst while back button is pressed, the AF-C kicks back in and focus is updated.

When I have "AF with shutter: ON" (not back button autofocus, default half press shutter focus), then the focus updates during the burst as expected. So, I have narrowed this down to something to do with BBAF.

Tldr: focus is locked during burst when using BBAF, but not with default half press focus.

If I have understood you, BBAF is working as expected. Shutter button has nothing to do with AF anymore, therefore if you release the BBAF button the camera stops changing the focus distance. It doesn't matter if AF-C or AF-S, by releasing the BBAF you are telling the camera: "do not focus anymore"

Htbaa · Jun 5, 2024

Plus another thing to keep in mind with burst mode Hi+ focus is locked once the burst is initiated. Not sure about Hi, but with Medium and Low the focus doesn’t stay locked (e.g. continually focuses).

jablesblack · Jun 10, 2024

Thanks for your reply. I am not releasing the back button during the burst, and therefore I expect the focus to update during the burst. However, even though I have the back button pressed, the focus does not update. When I am using shutter button autofocus, the focus does update during a Hi+ burst.

The focus lock limitation you're talking about is based on f-stop, if I recall correctly (and I am clearly not running into this limitation, since it updates when I use shutter button autofocus).

Htbaa · Jun 10, 2024

jablesblack said:
Thanks for your reply. I am not releasing the back button during the burst, and therefore I expect the focus to update during the burst. However, even though I have the back button pressed, the focus does not update. When I am using shutter button autofocus, the focus does update during a Hi+ burst.

The focus lock limitation you're talking about is based on f-stop, if I recall correctly (and I am clearly not running into this limitation, since it updates when I use shutter button autofocus).

I checked the manual and it seems my info was a bit off. Don't know where I got the impression that with Hi+ the camera would only focus once in AF-C. It seems that only happens when shooting at f/11 or greater when in Hi+, Hi or Mid. I'm sure that has to do with the camera switching to CDAF as it's unable to use PDAF with those apertures.

jablesblack said:
When the F-value is greater than F11 in [Continuous Shooting: Hi+], [Continuous Shooting: Hi] or [Continuous Shooting: Mid] mode, the focus is locked to the setting in the first shot.

https://helpguide.sony.net/ilc/1810/v1/en/contents/TP0002264680.html

If you're shooting below f/11 and only run into this issue with back button focus my guess would be that the camera simply doesn't allow this kind of operation. Or maybe some other setting is getting in the way.

Dave981 · Jun 10, 2024

I just tried this with my a6400 and it appears to work (AF-C, AF w/shutter off, Hi+, bbf, jpg). I did notice that when panning to a smaller, closer object, AF didn't pick up the new object when in wide mode (but it did in center/spot/zone). Going the other way was fine.

(Not sure that this actually helps the OP.)

At least in my case, it appeared that the AF in wide mode was happy being locked onto the background and not interested in the closer object. Whether hi+ taxes AF or this is in part an artifact of EVF lag, though, I'm not sure.

But this little test did highlight a few areas that my a6700 is better than my a6400 - less evf lag in burst mode, less rolling shutter, and much faster buffer clearing.

ARSPR · Jun 11, 2024

jablesblack said:
Thanks for your reply. I am not releasing the back button during the burst, and therefore I expect the focus to update during the burst. However, even though I have the back button pressed, the focus does not update. When I am using shutter button autofocus, the focus does update during a Hi+ burst.

My fault I didn't understand you.

I don't know what it can be. But in my a6700 I've noticed you have two possible settings "AF ON" and "Tracking ON + AF ON". The last one is the default one for the back "AF-ON" button and it actually overrides AF-S with tracking. Do you have a similar option in 6400?

jablesblack said:
The focus lock limitation you're talking about is based on f-stop, if I recall correctly (and I am clearly not running into this limitation, since it updates when I use shutter button autofocus).

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A6400 AF-C during burst with back button autofocus

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