NX1 Face detection AF in not-so-good light

Hi guys,

I've been playing with my brand new NX1 +16-50 S for two days. If you remember it, I posted sometime ago my experience with another unit which had a backfocus issue. (The thread went wild, part of it was my culprit as I shouldn't have answered some people at all, and at the end was deleted by admin).

Nevertheless, although I really haven't had enough time to get used to the camera, I can say that this new unit doesn't suffer that general backfocus issue. Well, I *think* (but I'm not sure) it has an slight tendency to backfocus, but probably, it's just a design decision. Normally the targets you take pictures at are behind the point you focus at, so maybe slightly displacing the good in-focus area to the rear is a smart decision. (And also good DOF area is grater in that direction just because of physic behaviour).

Well, let's get on topic... Nevertheless I'm not writing this new post because of this. I'm writing it because I *think*, (again I'm not sure as I haven't had enough time to play with it), that NX1 might have a software trouble with Face Detection and AF specially in not-so-good light.

I explain, we all know that NX1 AF is not so good when the light goes down, and I think that this issue is specially relevant with face detection. The trouble seems to be that the pictures usually tend to be backfocused in most of the test I've quickly done. It's like if the camera is struggling to get AF on the eyes and then it gets AF on the contour of the face against the background which normally leads to a backfocused picture (with the eyes somehow a bit blurry). (If you shoot at maximum aperture with focus on the eyes, normally the face itself will be slightly blurry in its edge, as it is actually recessed). So maybe it will be a good idea if the software added an artificial slight frontfocus displacement when it was detecting that the focus it is getting is on the edge of the face.

If I disable face detection and I just use mutipoint AF, it actually seems to work better (when it locks on the face, obviously).

Is this a known behaviour? Or do you think I'm wrong (as I said, I haven't made enough tests)?

well, I don't think that any current mirrorless backfocuses, but I would believe it has more to do with the focusing looking for or locking on the more contrasty area that what is intended as for phase detection. my understanding is once the area or scenario shifts to a more challenging light scenario, the AF system also switches from phase detection to a contrast detection.

I don't want to start the "backfocusing" argument again. Please just believe me that phase detection AF could ALWAYS go wrong (it heavily depends on lens quality and/or defects). SLR just adds more chances over mirrorless because of possible AF sensor misalignments (which obviously cannot exist in mirrorlerss). Only Contrast detection is defect-free guaranteed.

My question about face detection mode is not about strict PDAF "backfocusing" but, as you've said, that I've got the feeling, that the camera focus in the wrong point. Instead of selecting the eyes, (because it is more difficult and light is not so good and we all know low light AF is not a virtue in NX1?), I *think* it selects the edge of the face. And this selection can lead to a "backfocused"-like picture.

But as I've said I'm not strictly sure so I wanted to ask other users if this is (or not) a known behaviour.

Well, after a week playing with my NX1, I *think* I'm starting to understand its AF peculiarities, (at least for still shots), and I do really think Samsung should do something about it.

As you can imagine I cannot be 100% about what I'm going to post..., but let's say I'm 85% sure.

• The camera struggles to get PDAF when light is not so god. (This is an absolute truth known by everyone).
• In a DSLR-like way, when you get a green focusing square, the selected and real AF point can be outside it. In a DSLR AF sensor, the sensor size is usually bigger than the AF squares shown in the viewfinder. In NX1 you don't actually know where its 205/209 AF points are located, and a "green square" can be focusing with a little offset around it.
• The previous statement seems to be true no matter which kind of AF flavour you use (Selection AF, Multi AF or Face Detection AF).
• The camera is reaaaaally prone to focus in high-contrast areas instead of the nearest detected targets or even whatever it is actually inside its "green squares".

And the combination of the last statement and the outside-green-square focus makes NX1 a very tricky camera specially with Face Detection in not so good light... Yes, you get a green square on the face, but the camera CAN actually focus around it. Its quite easy to focus in the face contour, (which is usually outside the green square although near to it), which is usually a high-contrast area instead of focusing on the eyes, nose or mouth which has quite less local contrast against the surrounding face. And what you get is a backfocused picture, with the focus plane around the ears...

There's also another quite easy test which NX1 usually fails. Pick a bottle, can, or any other cylindrical shape. Place it before a white background so you are sure that its edge is a really good and easy targeting point. Now use Selection AF with an adequate size against some not-so-good-and-contrasty detail on the can. And be sure that you don't actually touch the contour of the can with your AF square but be sure to stay NEAR it. Voilà, specially in dim light, it's quite easy to get backfocused pictures where the focus is actually placed on the contour of the bottle.

And finally another easy test NX1 usually fails. If you select Multi AF against people in not-so-good light, (and specially with a brighter/clearer/whiter background) again it's quite easy to get AF squares around their silhouettes. Much easier than getting squares OVER them. And this situation usually leads to backfocused-like pictures if you shot with big apertures, because people are NOT flat so their faces are nearer you...

As I say a really tricky camera. Samsung should improve its AF point selection algorithms...

Q: Do you think your NX1 focus' better than your 7d overall, and if you do, does it focus better than it in lower light?

PS I appreciate your effort in writing about your AF experiences.

ARSPR said:

I don't want to start the "backfocusing" argument again. Please just believe me that phase detection AF could ALWAYS go wrong (it heavily depends on lens quality and/or defects). SLR just adds more chances over mirrorless because of possible AF sensor misalignments (which obviously cannot exist in mirrorlerss). Only Contrast detection is defect-free guaranteed.

My question about face detection mode is not about strict PDAF "backfocusing" but, as you've said, that I've got the feeling, that the camera focus in the wrong point. Instead of selecting the eyes, (because it is more difficult and light is not so good and we all know low light AF is not a virtue in NX1?), I *think* it selects the edge of the face. And this selection can lead to a "backfocused"-like picture.

But as I've said I'm not strictly sure so I wanted to ask other users if this is (or not) a known behaviour.

Click to expand...

The NX1 uses both contrast and phase detection. So there is no "backfocusing". That is pretty much a DSLR problem. Most mirrorless cameras autocalibrate, although in some cases they allow you to offset the autocalibration. The NX1 allows you to do this manually btw.

What is happening is that the camera is focusing on something other than what you intend it to focus on.

Exactly. The camera focuses on the background very often, in my experience, even if the square is mostly on the target.

This is probably my biggest complaint about the nx1 (and something that never happened with the nx300).

Well, with my small experience with NX1, I still cannot be sure. I need more time.

7d has the typical behavior of "traditional" DSLRs which don't actually analyze the scene you are shooting at (as they don't actually "see" it). It just focuses on the nearest target it detects on its AF sensor points. And it does it pretty fast.

Of course it depends on the lens quality and specs. My expensive EF-S 17-55 performs much better than my cheap 55-250...

Another matter is the focus precision. Again it also depends on lens quality, available light and if you use the center AF point (the best one) or a peripheral one (the worst ones). But, no matter how much fine tuning I do with the AF micro adjustment and contrasty targets, I always have the feeling that PDAF is a bit off (when I open to f/2.8).

But it is a rather smooth process. Forgetting the FUBAR pictures you always get with any system, the rest of the pictures are more or less OK. And when you get a misfocused picture is something like "I've tried to do my best, but I just cannot get closer".

But my little experience with the NX1 is somehow different. It usually focuses perfectly. But it just selects the wrong place. It's something like "my PDAF needs contrasty targets, and I desperately look for one, even if it is not the adequate one". And the funny thing is that even while selecting wrong targets, in low light it ALSO uses some degree of CDAF and focus hunting therefore...

So, maybe I'm wrong but I *think* that:
+ If you use the camera as a Point and Shot one in not so good light, paradoxically the Canon 7D is going to perform better. It's going to be faster and it's going to get an acceptable number of focused pictures. NX1 is just going to focus to the wrong place one time after another...
+ But if you understand how NX1 focuses and its peculiarities, and you use point AF where you can actually select the correct target, (and avoid "dangerous" zones), NX1 is going to perform better but slower because CDAF is also involved and used somehow. At least till the light goes down the point its focus system just does not work at all...

As I said, even being a mirrorless and therefore a closer camera to a P&S one, I think NX1 is somehow a difficult handling camera, probably harder than a DSLR.

I agree with your observations for the most part. Some suggestions for backlit subjects:

1. change the focus priority to speed priority (not accuracy priority or release priority).

2. if you can use selection AF with a small AF point, that can sometimes help reduce the chance of focusing on the background.

3. if you can, turn on the AF assist lamp. I know it is very bright and distracting but oh well...

4. Try lock-on AF.

5. Try focusing on a highlight that is the same distance as the intended target. For example, if you want to focus on the eyes but the face is shaded, perhaps you can focus on a highlight on the shirt that is equidistant to the camera.

6. If you use multi-AF, half-press the shutter and wait until there are a large number of green AF points blanketing the subject.

creaDVty said:

I agree with your observations for the most part. Some suggestions for backlit subjects:

Click to expand...

The issue doesn't appear ONLY with backlit target. I appears quite frequently, specially when more or less dim light. It's quite frequent within indoor pictures.

creaDVty said:

1. change the focus priority to speed priority (not accuracy priority or release priority).

Click to expand...

I'll test it.

creaDVty said:

2. if you can use selection AF with a small AF point, that can sometimes help reduce the chance of focusing on the background.

Click to expand...

I've already done. But the problem is not focusing on the background but on the contour of your target instead of in the center of your target.

creaDVty said:

3. if you can, turn on the AF assist lamp. I know it is very bright and distracting but oh well...

Click to expand...

It's normally useless... because I'm speaking about situations where the camera still evaluates that there's enough light and it does not turn it on.

creaDVty said:

4. Try lock-on AF.

Click to expand...

I'll try but I feel it's going to useless... because my target is going to be tracked and then backfocused on its contour

creaDVty said:

5. Try focusing on a highlight that is the same distance as the intended target. For example, if you want to focus on the eyes but the face is shaded, perhaps you can focus on a highlight on the shirt that is equidistant to the camera.

Click to expand...

I would call it a hack, don't you think? Of course this is a known technique for demanding situations. But I wouldn't call it an easy-to-use camera, specially when the situation is not actually so demanding at all...

creaDVty said:

6. If you use multi-AF, half-press the shutter and wait until there are a large number of green AF points blanketing the subject.

Click to expand...

The problem is that you usually don't get squares OVER your target but AROUND it... But yes, I usually dismiss face detection AF and prefer using common multi AF because you retain more control about the real behavior of the camera.

creaDVty said:

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TTL Flash Tutorial and over 400+ other articles for taking better candid and family photos.
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Click to expand...

Imo, nx1 needs eye detection function. In fact when putting the square on the face, most of the time it will focus on the edges and not the eyes. It focuses on the eyes when the person's face fills most of the frame (thus is easier to put the square on the eye specifically) and is well lit.

tecnoworld said:

Imo, nx1 needs eye detection function. In fact when putting the square on the face, most of the time it will focus on the edges and not the eyes. It focuses on the eyes when the person's face fills most of the frame (thus is easier to put the square on the eye specifically) and is well lit.

Click to expand...

Exactly!

I wonder if this is entrenched a bit in the Samsung autofocus algorithms in that it gives up too easily and looks elsewhere. My Samsung EX2f was very bad here as even in macro mode with the object in the centre spot it would doggedly focus on the distant background. Other people did also report that problem on this forum.

tecnoworld said:

Exactly. The camera focuses on the background very often, in my experience, even if the square is mostly on the target.

This is probably my biggest complaint about the nx1 (and something that never happened with the nx300).

Click to expand...

Hi ARSPR. I think maybe you misunderstood my intention. I'm not denying that there are problems with the AF, nor am I saying they're limited to backlit subjects. I said as much in my review. The suggestions I gave are not intended to discount your observations (actually I made the same observations). The suggestions are just that -- suggestions. Call them hacks, workarounds, whatever. They don't fix the problem, nor do they work 100% of the time. But they can help. Here are some sample snaps where they worked:
















Again, none of them work all the time, but they can sometimes help. It's up to you if you want to use them or not, or if you've already concluded that they don't work.

Please, don't apologize. I'm really grateful of your hints.

I was just answering in a "technical" way. In no way I considered them any kind of "personal" attack or anything similar. (This is a true symptom of the strange aura this dpreview forum is contaminated by...)

In fact my "solution" about "back focused on the contour" issue is just using point AF in the correct place... (which you also hinted). But it's a pretty slow procedure even with the aid of the touchscreen...

Happily it really seems a software issue which has a lot of fine tuning room in future FWs, (if Samsung were interested... which I hope it's the case).