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Video - Our SLT/mirrorless experiences

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Post Options Post Options   Quote windhorse Quote  Post ReplyReply Direct Link To This Post Topic: Video - Our SLT/mirrorless experiences
    Posted: 16 March 2019 at 01:07
Originally posted by Photosopher Photosopher wrote:

My ex-wife looked less than human in the morning. Face detection didn't work very well on her.


Maybe the problem I ran into was also something to do with the hour of the morning? But in my case I suspect it was more to do with lack of coffee than the appearance of the subject.

However it did seem to work ok on Peter Gregg's poodle.
 



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Post Options Post Options   Quote Photosopher Quote  Post ReplyReply Direct Link To This Post Posted: 15 March 2019 at 23:17
Originally posted by jkp1 jkp1 wrote:

I guess this hunting have nothing to do w face detection or not. Seen the issue in other scenes as well...


It's a compound. It shares a piece of the pie simply by taking more processing power. But so does light, camera generation, AF tech, lens choice, and probably even how well the subject matches Sony's perfect face detection algorithm. My ex-wife looked less than human in the morning. Face detection didn't work very well on her.
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Post Options Post Options   Quote jkp1 Quote  Post ReplyReply Direct Link To This Post Posted: 15 March 2019 at 22:55
I guess this hunting have nothing to do w face detection or not. Seen the issue in other scenes as well...
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Post Options Post Options   Quote Photosopher Quote  Post ReplyReply Direct Link To This Post Posted: 15 March 2019 at 22:53
That's right, I remember now. And I believe you stated that you were shooting it at f4... Is that correct?

If so, I suggest the only thing that accomplished was to cripple your AF system by one f-stop. The depth of field difference between f2.8 and f4 will be negligible. And shooting crop mode makes up for that d.o.f. difference anyway. E-Mount AF tracking benefits greatly when used wide open.

Also, check your AF menu options for stickiness. Set to "Locked On" rather than normal or responsive. This will help camera stay on target without jumping to background or hands so quickly.

Otherwise, turn on focus peaking (try medium), get a good set of reader glasses, and practice some manual focus.

Consider that it is much much much much more acceptable for a subject to be seen moving out of focus plane a bit (here and there) than it is for any clip to show focus hunting from automation. Tell your talent to get comfortable in the position they will be speaking from, and not move around while talking. That's not an unreasonable request. Not only is it better for the focus plane, but it's more aesthetically pleasing to the viewer to have the speaker hold still.
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Post Options Post Options   Quote windhorse Quote  Post ReplyReply Direct Link To This Post Posted: 15 March 2019 at 22:00
Originally posted by Photosopher Photosopher wrote:

Excuse me if the question has been asked and answered, but what lens are you using?


In this case, Sony Zeiss FE 35mm f2.8 (in aps-c crop mode)
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Post Options Post Options   Quote Photosopher Quote  Post ReplyReply Direct Link To This Post Posted: 15 March 2019 at 21:46
Excuse me if the question has been asked and answered, but what lens are you using?
 



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Post Options Post Options   Quote windhorse Quote  Post ReplyReply Direct Link To This Post Posted: 15 March 2019 at 21:43
Originally posted by Photosopher Photosopher wrote:

Just out of curiosity, with all the effort spent on watching videos and corresponding with Dyxxum etc... Have you watched any of the How To Talking Head videos I linked? Have you practiced any manual focus? Have you looked into the camera manual?



Somewhat, however my main concern since I came across this problem a few days ago was to determine what is causing it. Thanks to input like yours I am not as confused about that as I was.
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Post Options Post Options   Quote Photosopher Quote  Post ReplyReply Direct Link To This Post Posted: 15 March 2019 at 21:29
Originally posted by stiuskr stiuskr wrote:

(no more than 60p and less is better)


Yes 120p disengages face detection, and although tracking still works, it is compromised when using wide AF and letting the camera pick the object. Better to use specified AF point when shooting 120p. Still pretty good on a99II though, on which I can't see any difference in face detection performance between 24, 30, and 60p. And 120p works great with specified AF point.

Yes I use the technology. But only for moving subjects, or when camera is moving along with subject. This short reel clip Is combination AF/MF. Should be obvious which shots benefit from it and which shots it is completely unnecessary.

Edited by Photosopher - 15 March 2019 at 21:33
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Post Options Post Options   Quote Photosopher Quote  Post ReplyReply Direct Link To This Post Posted: 15 March 2019 at 21:19
At :17 at the beginning of video, Dave says: "I'm not saying this is something you should try on an interview..." First advise of the video.

Just out of curiosity, with all the effort spent on watching videos and corresponding with Dyxxum etc... Have you watched any of the How To Talking Head videos I linked? Have you practiced any manual focus? Have you looked into the camera manual?

Earlier you mentioned that one of your considerations was to use AF to target the face, and verify it was accurate with focus peaking. I question why not just do that, and/or just use manual focus with focus peaking to do the same?

You'll notice that Gary and Dave videos only show hunting/breathing when they are demonstrating the technology. But the phenomenon doesn't show when they are making regular videos. I propose that's because they don't use face detection AF for their day to day professional workflow. Perhaps they use it for family videos though.
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Post Options Post Options   Quote stiuskr Quote  Post ReplyReply Direct Link To This Post Posted: 15 March 2019 at 21:10
From what I understand if Face Detection is enabled it will always be engaged if it can detect a face and it will focus on the next closest thing when it loses detection until it detects the face again. There are many variables that can cause it to lose detection or not engage in the first place such as video file format (no more than 60p and less is better), AF area used, locking sensitivity, Wi-Fi on and tethered to HDMI. What I've learned the most here is that the more the camera has to process the more likely it is to lose detection, have you tried Peter Gregg's settings, they seem to work very well.
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Post Options Post Options   Quote windhorse Quote  Post ReplyReply Direct Link To This Post Posted: 15 March 2019 at 19:38
Thanks a lot for this clear diagnosis!

If this is the case, is not the most plausible explanation that face detect autofocus was not engaged, the focus hunting was caused by the moving hands in the center focus area of the frame, and the focus breathing was caused by the focus hunting?
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Post Options Post Options   Quote sybersitizen Quote  Post ReplyReply Direct Link To This Post Posted: 15 March 2019 at 19:14
Originally posted by windhorse windhorse wrote:

Here is a link to crop from the video clip I am talking about. As you can see the autofocus is hunting and also the edge of the frame is moving, even though the camera is fixed on a tripod.

Any idea what is causing this?

The focus is rapidly changing (hunting) which results in the sudden changes in angle of view (breathing). Stop the hunting and you also stop the breathing. Or use a lens that is designed to have no breathing ... a focus change would still be evident, but no breathing would occur.

Just a thought: is it possible this problem has nothing to do with either focus breathing or hunting and is caused by the camera's in-built stabilising system that is switched on, even though the camera is stationary?

I think that would look different. But you can test it by keeping stabilization enabled and shooting a similar scene using both autofocus and fixed manual focus.
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Post Options Post Options   Quote stiuskr Quote  Post ReplyReply Direct Link To This Post Posted: 15 March 2019 at 19:13
That is focus breathing caused by focus hunting, why is the focus hunting is the question that needs resolved. Might be easier to answer if we could see the whole frame but from what I can see is that is a very animated subject, hands are moving almost non stop and he is rocking side to side from one foot to the other, the rocking motion shouldn't be enough to cause Face Detection to lose focus but it does look like the focus hunting is happening when his hands are moving. With the hands being the closest thing to the camera that's what it's picking up on when it loses FD. Thinking about what Peter Gregg says in that video, image stabilization could one of the contributing factors, the more things the camera has to process the less it can contribute to lock on face detection.

Edited by stiuskr - 15 March 2019 at 19:16
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Post Options Post Options   Quote windhorse Quote  Post ReplyReply Direct Link To This Post Posted: 15 March 2019 at 18:15
Originally posted by stiuskr stiuskr wrote:

Actually that is an example of focus breathing, where there is a small change in the field of view as the focus is adjusted from minimum to maximum focus distance without changing the focal length.


No wonder they say ignorance is bliss!

Here is a link to crop from the video clip I am talking about. As you can see the autofocus is hunting and also the edge of the frame is moving, even though the camera is fixed on a tripod.

Any idea what is causing this?

Just a thought: is it possible this problem has nothing to do with either focus breathing or hunting and is caused by the camera's in-built stabilising system that is switched on, even though the camera is stationary? However if that were the case, would not the movement be continuous rather than once in a while? And would I not see it in other clips recorded in the same way which I usually don't?

Edited by windhorse - 15 March 2019 at 18:18
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