Archive 2022 · Is the A7IV AF-C Eye tracking affected by raw file type?

aCuria
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p.1 #1 · p.1 #1 · Is the A7IV AF-C Eye tracking affected by raw file type?

I have noticed that when using AF-C for portraits of a fidgety kid that my hit rate seems to be affected by the choice of raw file type (firmware 1.01)

Specifically, when doing 6fps bursts with compressed lossless raw + jpeg, the distance of the focus point indicated (green box shown in camera) seems to be consistently further from the actual eye position than when using 10fps bursts with compressed lossy raw.

Has anyone else noticed something like this?

AF-C priority - balanced emphasis
AF Tracking Sensitivity - 3 (Standard)
Aperture Drive - Focus Priority

Jun 08, 2022 at 03:23 PM

Daran
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p.1 #2 · p.1 #2 · Is the A7IV AF-C Eye tracking affected by raw file type?

aCuria wrote:
I have noticed that when using AF-C for portraits of a fidgety kid that my hit rate seems to be affected by the choice of raw file type (firmware 1.01)

Specifically, when doing 6fps bursts with compressed lossless raw + jpeg, the distance of the focus point indicated (green box shown in camera) seems to be consistently further from the actual eye position than when using 10fps bursts with compressed lossy raw.

Has anyone else noticed something like this?

AF-C priority - balanced emphasis
AF Tracking Sensitivity - 3 (Standard)
Aperture Drive - Focus Priority

I only have the A1, but I can tell you that the "green box shown in camera" position is always lagging after where focus actually happens. Apparently the position of that indicator is smoothed over time, maybe to be more easily observable. Rubbish implementation, if you ask me. Anyway, you can e.g. circle your camera around a tracked target and never have that indicator get close to the target and focus on the tracked target still works fine. The effect likely is worse when the camera updates the view less frequently, as would be the case with lossless RAW. So just ignore the exact location of the green box.

Ignoring the box, changing RAW modes may or may not matter on the A7IV. Since the shutter spends less time being operated, there is more time to focus, but also much more CPU activity for compression.

Side node: in general focus works better when tracking without shooting. So e.g. on the A7R4 I would wait till peak action before actually shooting, to increase chances I'm in focus when it counts.
Side node 2: tracking also works much better if the tracking rectangle stays reasonably constant within the frame; that also reduces softness due to movement.

Jun 08, 2022 at 06:34 PM

aCuria
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p.1 #3 · p.1 #3 · Is the A7IV AF-C Eye tracking affected by raw file type?

Daran wrote:
I only have the A1, but I can tell you that the "green box shown in camera" position is always lagging after where focus actually happens. Apparently the position of that indicator is smoothed over time, maybe to be more easily observable. Rubbish implementation, if you ask me. Anyway, you can e.g. circle your camera around a tracked target and never have that indicator get close to the target and focus on the tracked target still works fine. The effect likely is worse when the camera updates the view less frequently, as would be the case with lossless RAW. So...Show more →

Ok, at least I am not hallucinating about the green box… I have to investigate if the green box is indeed not showing the actual focus point on the A7iv, I have not noticed the green box location not reflecting the real focus point

Maybe uncompressed raw is the right way to go if the idea is to reduce the load on the CPU

Theoretically there should be less (!) shutter blackout when the burst rate is lower, but the drift gets worse here. Wondering if electronic shutter makes a difference

Jun 08, 2022 at 10:51 PM

osv2
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p.1 #4 · p.1 #4 · Is the A7IV AF-C Eye tracking affected by raw file type?

aCuria wrote:
AF-C priority - balanced emphasis
AF Tracking Sensitivity - 3 (Standard)
Aperture Drive - Focus Priority

if you think that your camera cpu is somehow overloaded, set it to release instead of balanced, because then the camera won't have to use cpu cycles to determine if the shot is in focus before releasing the shutter:

"Try Balanced Emphasis, which provides a good balance between the existing AF and Release settings. Useful to combine maintaining accurate focus with catching a crucial moment when shooting a moving object. The shutter cannot be released before the subject is in focus." https://support.d-imaging.sony.co.jp/support/ilc/autofocus/ilce9/en/tips.html#:~:text=the%20original%20subject.-,Priority%20Set%20in%20AF%2DC,when%20shooting%20a%20moving%20object.&text=The%20shutter%20cannot%20be%20released%20before%20the%20subject%20is%20in%20focus.

i'd also try setting the tracking to lock-on.

Jun 09, 2022 at 04:33 PM

aCuria
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p.1 #5 · p.1 #5 · Is the A7IV AF-C Eye tracking affected by raw file type?

osv2 wrote:
if you think that your camera cpu is somehow overloaded, set it to release instead of balanced, because then the camera won't have to use cpu cycles to determine if the shot is in focus before releasing the shutter:

"Try Balanced Emphasis, which provides a good balance between the existing AF and Release settings. Useful to combine maintaining accurate focus with catching a crucial moment when shooting a moving object. The shutter cannot be released before the subject is in focus." https://support.d-imaging.sony.co.jp/support/ilc/autofocus/ilce9/en/tips.html#:~:text=the%20original%20subject.-,Priority%20Set%20in%20AF%2DC,when%20shooting%20a%20moving%20object.&text=The%20shutter%20cannot%20be%20released%20before%20the%20subject%20is%20in%20focus.

i'd also try setting the tracking to lock-on.

Actually this "determine if the shot is in focus" thing is pretty damn difficult (maybe currently impossible) by analyzing a specific image frame using traditional computer vision. I tried my hand at it before.

In contrast detect af the camera racks focus until the resultant image starts getting "less sharp", this is not difficult to implement

Its much more likely that in "AF" priority the camera just doesnt trigger unless the AF motor has stopped moving. (aka it reached the spot the Phase detect sensor told it to go to). This shouldnt really consume cpu cycles i think

Jun 26, 2022 at 09:56 PM

osv2
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p.1 #6 · p.1 #6 · Is the A7IV AF-C Eye tracking affected by raw file type?

af-c on these cameras does not use the cdaf cycle, i guess that it could be implemented but not at 20-30fps because there just isn't enough time.

the a9 can get bogged down when it's using that af priority setting, which is why i think that it's doing more than just waiting on the af motor or something similar.

there are other things that can also affect the af, like the aperture setting and available light.

Jun 27, 2022 at 07:00 AM


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