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A9 focus fails

Ziggy99

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The first time I took the camera out I noticed that locks were often hard to come by with small birds. Nothing would get focus.
Some settings experiments and a firmware update later and I'm not seeing any improvement.
The bird can be in mid ground with little around to confuse the AF or it can be closer in amongst foliage with plenty to confuse the AF.
Yesterday for the first time I added the 1.4 TC to the FE200600 and this failure hit a new level. I lost four shots in a row.
I did a simple test: a sapling trunk that was in good light with plenty of contrast. I used Spot: Small, Medium, and Expand Flexible. The AF area was entirely or substantially over the bark.
First up was a failure to focus on anything at all. Then I found with repeated alternating between more distant foliage and the trunk, focus occurred but was slow. I suspect the camera has some ability to learn. I've found similar results with test locks on a horizontal power line - initial failures followed by some success if a nearby object was used to set the range.
Settings: Focus/release balanced; AF sens set at 4.
If this was a DSLR I'd be blowing the AF sensor out or getting it repaired.

ILCE-9       840mm    f/9.0    1/1000s    ISO 1000


ILCE-9       840mm    f/9.0    1/1000s    ISO 1250
 

Ziggy99

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I've done some more testing.

Thom Hogan suggested canting the camera - nope.
Forum members elsewhere suggested putting AF tracking sensitivity on 1 - nope.
A Sony rep suggested Expand Flexible Spot - nope.

Out in the field when it happened again I accidentally hit my BIF settings button and that worked; Tracking Zone. The bird was contrasty enough against the foliage.

I've come across two A7 series users reporting the same problem.
 

Ziggy99

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Matt Granger in his YouTube review of the FE 400 mentions several instances of complete focus failure during his soccer shoot.

I was out again yesterday trying to focus on a small still bird, in midground and good light, in the centre of the AF area and the frame, and got repeated failures (see a later success below). I'm wondering whether it's worse in firmware 6. In time repeated alternation of subject and distant AF calls seemed to train the AF and get a result, and as before, trying to focus on something nearby and transferring to the subject can work - if there's something nearby (there wasn't here) and the bird hangs around.

This was with the FE 100-400 & 2x TC. That combo worked fine on BIF.

Tracking: Zone worked and I have to test that further with a bird mixed up in foliage. It will depend on subject recognition obviously.

ILCE-9       800mm    f/11.0    1/800s    ISO 400


BIFs no problem

ILCE-9       600mm    f/11.0    1/3200s    ISO 6400
 

Ziggy99

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Here's another couple of tests, partly to add some horizontals into the mix as a line-type sensor should cope better with those.
These are with an AF Spot overlapping a post, wire or branch. A horizontal wire in the second pic didn't fare any better than a vertical.
EXIF showed no point in focus.
100-400 & 1.4 TC. at 560mm. Focus/release: balanced. Focus range: full. The branch was closest and the post was as close as the wires.

Branch on an angle
ILCE-9    ---    560mm    f/8.0    1/750s    ISO Array


The vertical in the middle is a star post about 10m away.
ILCE-9    ---    560mm    f/8.0    1/2000s    ISO Array
 

Ziggy99

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This is interesting.

Mathieu Gasquet of Mirrorless Comparisons:

As always with Sony cameras, single areas such as Flexible Spot, Center or Expand Flexible Spot tend to use contrast detection only which results in a slower acquisition time and the classic back and forth movements of the lens elements while the cameras “scan” the contrast of your scene to acquire focus. If you choose Zone or Wide Area, the chance of seeing the phase detection points increases.
In Continuous autofocus, phase detection points are used at all times and this is where the two cameras give you the best performance. In fact I often leave them to C-AF even for scenes that don’t require it, just to acquire focus more quickly.


https://mirrorlesscomparison.com/sony-vs-sony/a7r-iii-vs-a7r-iv/#autofocus

My experience with the CDAF on the otherwise excellent Panasonic G9 is that it would too often lock on something other than the subject - most commonly something further away.,
 

Ziggy99

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Took the new FE400 out yesterday for a morning's shoot (before it hit 44 C in the afternoon).
It's crisp and contrasty, and quick to focus and sticky in tracking, with one exception ...

With these oncoming Terns I wanted to start framing from a distance so I tried to push the AF to infinity by locking onto some hazy mountains in the distance. It repeatedly failed at that, whether CAF Zone or CAF Small spot. In one case there was even one dancing green square showing.

Murphy-Racey reports four instances of flat focus failure with this lens shooting sports at the press tryout, and Alex Phan reports a similar failure to mine.

With CAF and Zone, if Gasquet is right, this is trying PDAF.

ILCE-9       560mm    f/6.3    1/3200s    ISO 2000

The specks are midges which the Terns take in mid-air.
 

Ziggy99

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This is interesting.

Mathieu Gasquet of Mirrorless Comparisons:

As always with Sony cameras, single areas such as Flexible Spot, Center or Expand Flexible Spot tend to use contrast detection only which results in a slower acquisition time and the classic back and forth movements of the lens elements while the cameras “scan” the contrast of your scene to acquire focus. If you choose Zone or Wide Area, the chance of seeing the phase detection points increases.
In Continuous autofocus, phase detection points are used at all times and this is where the two cameras give you the best performance. In fact I often leave them to C-AF even for scenes that don’t require it, just to acquire focus more quickly.


https://mirrorlesscomparison.com/sony-vs-sony/a7r-iii-vs-a7r-iv/#autofocus

My experience with the CDAF on the otherwise excellent Panasonic G9 is that it would too often lock on something other than the subject - most commonly something further away.,
OTOH Thom Hogan says the two modes are both employed: PD first for speed, then CD for accuracy.
 

Ziggy99

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A test of the new A7R III shows the same episodic failure to get a small bird in the mid-ground with Spot AF modes.

If the bird is the closest object, Zone AF is worth trying.
 

Ziggy99

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When does the Sony deploy the AF modes, CD and PD?

According to this source, on the A7R III it uses both, except when the aperture is over f8 when CD alone is used. But CD needs good light to work well.
David Busch Sony Alpha a7R III Guide to Digital Photography
 

bdbits

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Ziggy, have you experimented with AF sensitivity as suggested by some on that page at FM? I didn't read beyond the one page, though.

On AF CD vs PD - It has been my understanding PD is only good up to F8 on all the Sony bodies. CD is used beyond F8, and I had thought it was also used in low light which seems somewhat contrary to what Busch wrote in your quote. Hmmm... I am also a little less than certain CD *always* kicks in as a 2nd check after PD but maybe it does. I am not sure Sony has ever said so themselves or not, too lazy to Google at the moment.
 

Ziggy99

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Yes, I have Bob.
Made no difference and probably that's because it's to adjust sensitivity while tracking which I'm not using for static shots.
Yes, it's said to be CD over f8.
I've done some searching on Sony's method. One Sony UK vid says both are used but not how.
 

Ziggy99

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Ah, so.... when the A7R II was announced -
Mr. Kimio Maki, Senior General Manager, Digital Imaging Business Group, Sony Corporation:
we are using a hybrid focus, so first we use the phase-detection focus to get close to the object. Then near the object, we start to use contrast AF to get a clear peak. Then we adjust the focus. Then in order to make very precise focus (because 42-megapixel means very very small pixels), and also the focusing point could be a very small one, therefore we phase-detection together with contrast AF, contrast focus.
https://www.imaging-resource.com/ne...the-must-have-sensor-tech-of-the-future#phase
 

Dan Euritt

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Ah, so.... when the A7R II was announced -
Mr. Kimio Maki, Senior General Manager, Digital Imaging Business Group, Sony Corporation:
we are using a hybrid focus, so first we use the phase-detection focus to get close to the object. Then near the object, we start to use contrast AF to get a clear peak. Then we adjust the focus. Then in order to make very precise focus (because 42-megapixel means very very small pixels), and also the focusing point could be a very small one, therefore we phase-detection together with contrast AF, contrast focus.
https://www.imaging-resource.com/ne...the-must-have-sensor-tech-of-the-future#phase
a7rii from 2015 is not the a9 from 2017, and contrary to that quote, the a9 has 24mp, not 42mp, so his claim that "because 42-megapixel means very very small pixels" does not apply to the a9.

Furthermore, it's 399 ospdaf points vs. 693 ospdaf points, and the a9 has a stacked sensor, so it can make a whole lot more actual pdaf measurements, it doesn't need to rely on a CDAF trim.

At 20fps af-c, there isn't enough time for any camera/lens combo to be doing a slow CDAF back and forth trim on every frame, the a9 was not designed to depend on CDAF.

When you use the LAEA3 or MC-11/unsupported lenses on the a9, it activates a menu where you are forced to choose between PDAF or CDAF, but never both. The af in that PDAF-only situation is stunningly accurate, which proves how well the a9 works without any CDAF functionality.
 

Ziggy99

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That's the only official data I can find, apart from a similar protocol used on one of the 6nnn.
Sony says the A9 uses hybrid AF, and CD in low light.
What's your Sony source for the body?
I don't know why you think CD is slow when the A9 body can sample AF and AE 60x a second, when CD is done in software and when the initial moves where and how far are informed by PD. It would be working just like Panasonic CDAF DfD which is very fast.
 

Dan Euritt

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I posted an example of where Sony never uses hybrid af, and I would suggest that you experience it for yourself, in order to understand how well OSPDAF works by itself, on the a9, CDAF is not needed.

I also indicated that CDAF is too slow for 20fps action shooting, perhaps we need to review how it works in order to understand why that is:

"Contrast detection autofocus – despite being the easiest, cheapest, and most accurate method of focusing – is also the slowest. If you’ve ever seen the autofocus motor “hunt” back and forth, kinda like you would do when manually focusing, this is contrast detection at work." https://www.jmpeltier.com/difference-phase-detection-contrast-detection-autofocus/

See the black square examples of CDAF having to hunt on both sides of the focus plane, by moving the focus element in the lens back and forth, in order to find the sharpest position. Waiting for a camera lens to move back and forth slows down the af process, regardless of how fast the sensor can do an af measurement and calculation, the body is waiting for the response from the lens.

That's why I stated that the a9 is not using a CDAF trim step at 20fps af-c, there just isn't enough time for the lens to do any CDAF hunting.

Panasonic DFD is not fast, because it's based on CDAF, it has the same failure mode of having to look at multiple images before it can pick out the best place to position the focus element of the lens. See that on page 50 of this Panasonic GH5 document, where it's talking about having to evaluate two images before setting the final position of the focus element in the lens: http://www.personal-view.com/downloads/GH5_Presentation.pdf

Sony is the only camera company that rates lenses by how fast they focus on a camera: http://support.d-imaging.sony.co.jp...ilce9/continuousshooting/en/index.html?id=spt
 
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