A9 focus fails

Ziggy99

TalkEmount Veteran
Joined
Jan 25, 2019
Messages
330
Location
Australia
When you can cite the factory on how they dovetail their AF modes come back and talk again. The rest is speculation.
My A9 shoots at 20fps in low light so according to the factory it can do it with CDAF alone.
 

Dan Euritt

TalkEmount Veteran
Joined
Jan 11, 2014
Messages
220
I already cited the factory menu that expressly disables hybrid af capability on the a9, but you refuse to acknowledge it.

I also referenced multiple authoritative links that backed up what I said, so it's clearly not speculation.

You are posting claims about things like DFD, that have nothing to do with the a9, it does not use DFD.

Yes, Sony hybrid af can revert to CDAF alone in extreme low-light conditions, with native lenses, but you are not shooting birds in extreme low-light conditions, so I don't know why you keep bringing it up.

Since you mentioned the a7rii and CDAF, tho, lets look at what happens with it in low-light conditions, see this quote from Rishi, the DPR tech editor, in the comment section:
"B/c no PDAF means poor continuous AF and hunting, something pros can't put up with. Same goes for the a7S. It can focus in much lower light than any DSLR, but only by hunting/wobbling.
The point of this article is that the a7R II can actually focus in these dim conditions using phase-detection - that's the noteworthy achievement ."
https://www.dpreview.com/articles/6884391759/sony-alpha-7r-ii-can-match-or-beat-dslr-low-light-af-performance
 
Last edited:

Ziggy99

TalkEmount Veteran
Joined
Jan 25, 2019
Messages
330
Location
Australia
Peltier doesn't reference DfD so his opinion of CDAF's max speed is worthless.

Your Pana doc shows the GH5 can focus in 0.05s. The Pana G9 would be less that half that as it does CAF at 20 fps. Tell me why that's not fast enough for a Sony that does 20 fps.

I reference CDAF because with DfD or as PD hybrid it's fast enough for Sony to use in its A9 (that's what hybrid means), its A7ii, and at least one of its 6nnn. And it's fast enough to run on its own in low light at 20 fps - because I believe the A9 factory specs.

But my typical focus fails will most likely be using hybrid AF - that's at least the dominant view of pro photographers and most likely the inheritance from Sony's generations of AF development. If that's the case, why does it flatly fail in the circumstances I've shown? If it's PDAF, much vaunted, why does it fail? Actually IME CDAF is most likely to account for a fail like this.
 

bdbits

TalkEmount Hall of Famer
Joined
Sep 10, 2015
Messages
2,242
Real Name
Bob
Since my last comment in this thread, I looked up some information on Sony PDAF, CDAF, and AF in general. The reality is nobody really knows for sure how Sony is implementing AF because Sony seldom talks about it in any technical detail. I would guess they consider it a trade secret. People who work at or frequent DPR do discuss it now and then, but unless Sony told them some secrets (unlikely without an NDA which would make it pointless), it is speculation however knowledgeable it may be. And as fast as Sony has evolved their technology in recent years, I'm going to venture to say it is not necessarily the same between models even in the same generation or with similar sensors. On top of that, the advanced AF modes in current bodies incorporate AI particularly for tracking, so who knows how that might be affecting algorithms.
 

Ziggy99

TalkEmount Veteran
Joined
Jan 25, 2019
Messages
330
Location
Australia
Yes. Tracking involves deciding what the shooter (apparently) wants, isolating some characteristics and following them around the frame.

I would say low-light CDAF can be banked on - it's written in the specs - and some combo otherwise of CD and PD. While Sony will have done some development since the A7R II I'd say it's very unlikely they've thrown all that out. The obvious strengths of each can be deployed in sequence: first PD for speed, then CD for fine-tuning. That's when speed is critical. Some folk say CD is fine for SAF and may be used for that on Sony's since speed isn't at a premium but accuracy is.

You're sposed to be able detect CD working by hunting in the lens but I wonder whether that's it. Sampling is 60 fps on a Sony and apparently 480 fps on a Panasonic! With a quick lens it'd be all over before you noticed.
 

Dan Euritt

TalkEmount Veteran
Joined
Jan 11, 2014
Messages
220
Peltier doesn't reference DfD so his opinion of CDAF's max speed is worthless.
You specifically brought up CDAF, repeatedly, and what he posted is 100% true, CDAF is slow compared to PDAF. Even Nikon will tell you that CDAF is slower on the Z7:

"This option uses contrast based autofocus and is only available when shooting stills and Single AF is selected for Focus mode. Focusing may be slower than with Single-Point AF. This AF Area Mode prioritizes focus precision over speed." https://cdn-7.nikon-cdn.com/Images/Learn-Explore/Camera-Technology/Mirrorless-Cameras/2019/Z-series-Understanding-AF/Media/Z_7_Autofocus_Guide.pdf

"Disadvantages of contrast assessment
The major drawback to contrast assessment autofocus is that it is slow. The pattern of move – assess – move – assess takes time and the camera may well start by moving focus in the wrong direction and then have to reverse itself. Because it is slow and offers no predictive possibilities, contrast detection is inappropriate for action or sports shooting. The slowness can be aggravating even for stills and portraits. Contrast assessment also requires a bit better light than phase-detection autofocus, and obviously it requires an area of good contrast in the image." https://www.lensrentals.com/blog/2010/07/how-autofocus-often-works/

"Although contrast-detect AF has some advantages, it is substantially slower than phase detect AF" https://www.the-digital-picture.com/Photography-Tips/canon-eos-dslr-autofocus-explained.aspx

I reference CDAF because with DfD
DFD is proprietary, CDAF is not, and Sony does not use DFD, it's not relevant to this a9 discussion, why do you keep bringing it up? It's totally inferior for shooting sports.

But my typical focus fails will most likely be using hybrid AF - that's at least the dominant view of pro photographers
You can't prove that anything you have shot actually used hybrid af, that is just speculation on your part.

You can however prove that your pics use PDAF with this program, which shows the active focus points in certain focus modes: http://www.soens.de/downloads/
 

Ziggy99

TalkEmount Veteran
Joined
Jan 25, 2019
Messages
330
Location
Australia
This is a thread about focus fails.
Nothing you've contributed sheds any light on it or how to deal with it.
If you want to discuss the merits of focus modes start another thread.
 

Dan Euritt

TalkEmount Veteran
Joined
Jan 11, 2014
Messages
220
You were the one who brought up CDAF and DFD, not me. You made some claims about CDAF performance that were not true, and you keep trying to tie DFD to Sony. It was you that made this a focus mode discussion.

I tried to help you with things like that link to the soen software, which you evidently ignored, because actually learning what focus mode your a9 is using somehow doesn't fit your narrative here.

I got the a9 shortly after it was released, I've used it with all of the firmware versions, and I've never seen these mysterious "focus fails" that you keep referencing. So I'm trying to understand what you are doing.
 

Dan Euritt

TalkEmount Veteran
Joined
Jan 11, 2014
Messages
220
For anyone who is interested in figuring out what their Sony camera is doing, this is a screenshot of the Soen software, it reads data from the EXIF. The yellow boxes represent active PDAF points, and the blue bullseye is something called FocusLocation in the EXIF. AFAIK there isn't any CDAF focus point data in Sony EXIF, but if you want to look for it, try this link: https://fossies.org/linux/Image-ExifTool/lib/Image/ExifTool/Sony.pm

This was shot with the LAEA3, which as I mentioned earlier, does not use hybrid af, at all. MC-11/incompatible lenses emulate that, so it probably won't use hybrid af either.

Subscribe to see EXIF info for this image (if available)
 

bdbits

TalkEmount Hall of Famer
Joined
Sep 10, 2015
Messages
2,242
Real Name
Bob
This may only apply to the A7Riii I now have, but if you are in playback on the camera and hit the magnify button (just above the joystick), it will zoom to the focus point in the image you are viewing.

The A7info program is a pretty nice piece of software I see referenced from time-to-time. If you are looking for how to see the PDAF focus points, it's the fifth icon on the toolbar at the top of the window. I notice the sixth says "focus location" - perhaps that is for CDAF? Not sure.

There are a ton of options to exiftool, but it is not for those who abhor a command line. (Many programs - maybe A7info - use it under the covers to extract the EXIF data.) If you enter the command by itself, you'll get a dump of the many options, and there is more info on the exiftool home page. If you want to dump all the EXIF tags, I would suggest the following command line (for Windows): exiftool -all {yourpicturefilename} |more

Personally, I think you guys should just agree to disagree and move on.
 

Dan Euritt

TalkEmount Veteran
Joined
Jan 11, 2014
Messages
220
FocusLocation is not CDAF, because the LAEA3 can't use CDAF and PDAF at the same time, it is not capable of doing hybrid af, and since the Soen photo I posted is showing active PDAF points, it was not able to use CDAF there, but it had the FocusLocation bullseye.

I already discussed that back when I mentioned the menu item, here is one Sony reference for it: "A-mount lenses with SSM or SAM only. Choose phase-detection AF or contrast-detection AF in AF System menu." https://www.sony.com/electronics/interchangeable-lens-cameras/ilce-7m2-body-kit/specifications#features

The last time that I used the LAEA3 on the a9, it had that same menu, which is why I suggested that Ziggy99 try an adapted lens on his a9, so that he can understand that CDAF is not the issue with whatever problem he is having.

Edit: Here is that same menu item, referenced in the a9 version 4 firmware manual, not sure why it's not in the current a9 manual: https://helpguide.sony.net/ilc/1650/v1/en/contents/TP0001486847.html
 
Last edited:

Ziggy99

TalkEmount Veteran
Joined
Jan 25, 2019
Messages
330
Location
Australia
You were the one who brought up CDAF and DFD, not me. You made some claims about CDAF performance that were not true, and you keep trying to tie DFD to Sony. It was you that made this a focus mode discussion.

I tried to help you with things like that link to the soen software, which you evidently ignored, because actually learning what focus mode your a9 is using somehow doesn't fit your narrative here.

I got the a9 shortly after it was released, I've used it with all of the firmware versions, and I've never seen these mysterious "focus fails" that you keep referencing. So I'm trying to understand what you are doing.
What you do is Google and race through what you find looking for ammunition.

If you read it for meaning the results would be very different.

You're here just to score points, and that earns you a place on my ignore list.
 

Ziggy99

TalkEmount Veteran
Joined
Jan 25, 2019
Messages
330
Location
Australia
I just tried something else, sparked off by Garry Friedman's guide to the A9. He says that in tracking mode if the camera loses lock it will then try to focus on what's closest that has contrast in the AF area. In tracking mode, AF-C, single shot drive, with either Spot large or medium overlapping a branch or Spot small on a branch, it locked every time except one.
If this is consistent then maybe what's happening is that Tracking tells the camera to analyse the focus area and find something to recognise.
I'll need to do more before drawing a definite conclusion.
 

Ziggy99

TalkEmount Veteran
Joined
Jan 25, 2019
Messages
330
Location
Australia
Some more testing, using the rig that I found failures with the first time: A9, 100-400 + 1.4 TC. f8 (the max.), 1/500s.

This is a spot in a wetland where Swallows perch on some stakes and I've regularly had failures with various rigs. Today the birds were away and I shot the stakes from about 7 m away.

I'm again using Tracking Spot L and S.

The first shot, at the top of the blue stake, got a lock immediately. Bingo. With repetition it was possible to produce a fail on the top and on the middle but mostly it locked.

Subscribe to see EXIF info for this image (if available)


Subscribe to see EXIF info for this image (if available)


However, the top of the green stake, and the middle, almost always failed. Hello?

Subscribe to see EXIF info for this image (if available)


Subscribe to see EXIF info for this image (if available)


So what's the difference?
The green one is a little narrower and the background is different. The blue stake's background provides more contrast.

Observing the tracking box behaviour, it preferenced an edge when it locked. When it failed to lock on the green stake, it seemed to me it may still have been over an edge but wasn't adjusting focus.

I heard and saw no hunting so I doubt whether CDAF was the only focus mode.

The A7Info app shows what it calls Focus Location and also PhaseAF locations. In the blue stake fail, the former was on the stake, the latter were beside and behind it. In the success, both were on the stake. In the case of the green stake both appeared to be on the stake top in both the success and fail.
Using the Sony AF Visualizer app, it concurred in the case of the blue stake but showed no locks for either green stake image.

So all up, I got one different result but don't really know why. Other test subjects have failed with contrasty edges.
 

Latest posts

Links on this page may be to our affiliates. Sales through affiliate links may benefit this site.
TalkEmount is a fan site and not associated with Sony Corporation.
Forum post reactions by Twemoji: https://github.com/twitter/twemoji
Copyright © 2011-2019 Amin Forums, LLC
Top Bottom