David Kilpatrick and the mysterious NEX autofocus issue!
David Kilpatrick noticed a “mysterious effect” of the NEX autofocus system. Look at the video above!
Nice catch David! By the way…I didn’t know you can play Benjo! 
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Comment from Steve Mullen: As I wrote in my eBook (Shoot Great Vide...
Comment from scdrawert: hey i agree this must have someting to d...
Comment from Owen.C: David said it could be because you could...
Comment from erwinkfoto: @Mattia: Yes, it is :)
I read somewhere...
Aj700
2 years ago |seen this. But I think if you just press shutter button, it will refocus. Never really thought it as an issue until now.
Chris
2 years ago |I don´t see the problem.. just looks like the camera doesn´t like his hand ^^
everything else he tried was perfect in focus : )
jarzon
2 years ago |I guess that issue is common for all autofocus systems. David’s scene is badly lit by one strong light source behind the subject and some ambient light. It’s normal, that the AF system will focus at brighter and more contrasty object instead of dull object in front. I suppose that with the lamp turned off the camera would focus properly.
70000
2 years ago |would the japanese think buyers are likely to take pictures of them selves, holding the camera with one hand? they might.
maybe the camera has a hand recognition feature alongside the face recognition.
JX
2 years ago |Just a guess on my part, but can this have something to do with face detection and the fact that his hand is, obviously, skin colored? Some kind of intelligence in the focus system to prevent accidental refocus if somebody temporarily blocks the view of what was originally in focus. (I.e.: What’d happen if David had sat with his back turned to the camera so that his face wasn’t visible, and then waved his hand?)
I don’t have a NEX so I can’t check this for myself, but that was what sprung to mind when I saw the video.
WillBfree
2 years ago |That is an excellent feature! So if a cop tries to block your lens, the scene you are recording will still remain in focus through his fingers. It seems like an intelligent feature, not a problem.
Bjorn
2 years ago |It’s because the camera works wit contrast autofocus. And there isn’t enough contrast in the hand. And my conclusion is that the 16mm en 18-55 pictures are not as sharp as they should be.
J Cornejo
2 years ago |… couldn’t it be a setting that is focusing on the face (i.e. face recognition) ?
Raz
2 years ago |BJourn, you are wrong. There are some very sharp pictures from 16mm and 18-55mm, see these threads
http://forums.dpreview.com/forums/readflat.asp?forum=1042&thread=35931097
Mattia
2 years ago |Wait a minute!! The hdmi output is working when you record video??
erwinkfoto
2 years ago |@Mattia: Yes, it is
I read somewhere that the HDMI Output isn´t even compressed!
But I´m not 100% sure
Owen.C
2 years ago |David said it could be because you could see his eyes and it was using face recognition, which is very good.
scdrawert
2 years ago |hey i agree this must have someting to do with the pretty advanced face detection technology. great feature and mighty intelligent to keep the focus on the face while a hand coveres most of it. rather impressive i think….
Steve Mullen
5 months ago |As I wrote in my eBook (Shoot Great Video with Sony NEX Cameras), “Because the NEX AF system is always seeking high contrast, should a subject or object with higher contrast enter the frame, the AF system MAY decide to lock on it.”
In David’s example, his hand has no greater contrast than his face — so a NEX will NOT change focus.
But, why the MAY?
There are 25 contrast detection zones — each of which checks the contrast in its own small area. A microprocessor checks these zones. One can think of each zone voting by declaring its amount of contrast. The central 15 zones get a stronger vote.
The microprocessor firmware — as has been the case on Sony products for half a decade — is “smart.” It monitors the zones and if several in the center have a nice high contrast — it will ignore the outside zones. This allows someone to walk through an AF shot and have the focus remain locked on the subject measured to have high contrast at the start of a shot.
Perform a pan, and focus will stay locked on the subject measured to have high contrast at the start of a shot until something on the edge has good enough contrast — and then focus will switch to it. (This has nothing to do with face recognition — although face recognition is an advance on smart AF.)
So the reason for the MAY is that the AF system is not simply looking at contrast — it is looking at patterns of contrast on the 25 zones. On the other hand, without contrast — the system cannot function well.
Clearly David’s room is well enough lit to obtain a good image. But, brightness does not mean high contrast. So his face is slower to focus on, than the B&W books that have super contrast.
PS: Smart isn’t always smart — “should your subject, for example, walk into a shadow and lose contrast while something else in the frame has high contrast, the camera MAY decide to focus on it.” Here the MAY depends on the time the subject becomes lower in contrast AND just how much contrast the “something” in the frame has.
To the microprocessor, it’s all numbers shifting over time.