Weird AF-S Thing - Different from every other Nikon I've owned

I'd been experiencing a rather strange phenomenon with my D750 (I'm putting together a review, and this will be in there) that I believe warrants separate mention.

I use AF-S mode a lot. It comes from my days shooting film where I'd focus and recompose, and while I've recently tried to really break myself of the habit and use focus points, I still do this a lot with static subjects. This hasn't been an issue for me until I got the D750. Let me explain.

I've changed all my cameras to back-button focus, which means that the AE-L/AF-L button is now set to AF-ON. This has never stopped me from focusing on a center point, reframe and fire. But I noticed very quickly that when I did this with the D750 it wouldn't fire. I had my AF-S Priority Select menu option set to Focus (vs. Release), just like every other camera I own, but when I'd reframe the shot wouldn't fire. When I was out today I decided to just not figure it out, changed the setting to Release and shoot away - thankfully everything worked out fine. So, when I got home, I started investigating why this was happening.

When I use AF-S, I use single point, and every camera (up to now) gives me a choice of a single point or an Auto selection. With the D750, however, when I choose AF-S mode I have a choice of modes (my word - I am without the manual as I type) that it operates in - Auto, S(ingle point) and Group. I assumed that Single Point would be appropriate as it is the only one that gives you a single AF point in the viewfinder. However, if you lock focus in on that point and then recompose, if the subject under that now-recomposed point isn't in focus the camera will not fire (with the AF-S Priority Select set to Focus)!! I have to tell you, it was making me crazy today. I verified this at home - choose a focus point, engage autofocus, recompose and attempt to shoot and it will not fire. But, if you change the mode to Group, which now surrounds the point with add'l focal points, it doesn't seem to matter how much or far you recompose, it will fire and retain the original focus point.

I need to do some digging on this. I did a lot of reading on this camera before buying and this is one of those things I never heard about, so it may be something new, and it may just be a "duh" thing that only I didn't pick up on. But regardless, I suspect others will run into this and I wanted to at least get it on the board here.

Looking forward to your review..Honestly I would just use the 51 points on S like you should..Why fix what is not broke..

Well, it does sound broken. Ever since we had had auto focus, cameras would lock focus and exposure if we held half press, so we could recompose at will (while holding). Even compact cameras do that. That's how, if the subject has a bright window behind them, you can focus at their feet (to exclude the bright), and hold it to bring it up to their face for a reasonable exposure. That is how D750 manual pages 129-130 describe it still working.

So there must be more to it, some other interference. I'm guessing something about AL/AE. See page 362, possibly AF-ON may disable it?




I already knew, but I just checked my D800. AF-S, focused up close, and holding half press, then if aimed far way, the green dot in viewfinder disappears, but the shutter still works, focus still locked close. That's just how they are supposed to work.

Jake, I don't know the d750, but I thought what you experienced was exactly how it is supposed to work. My d7000 does the same... to use back button focus with single point, I must use release priority or it may not fire upon recomposing if that single point falls on blur.

Now I ASSumed my d7100 worked the same way, but I just tested it and it fires no matter what the priority is set for. It was as if it ignores the priority setting and you get release priority all the time when af-on is set. I thought I would obsess about this all night, but a quick look in my d7100 manual, p77, confirms this is correct for the d7100. That is, if the back button is set for AF-on, the priority setting is ignored and you get release priority and you are free to recompose. So your d7000 should behave as your d750. Your d7100 behaves as you thought your d750 should. Not sure which side of the fence your other cameras fall on, but I'm sure you'll check it out.

Interesting that the d7000 and the d7100 handle setting the af-on setting differently.

Did the original point you focused on remain in focus when you recompose, (that is if you move a bit and the original point of focus is not fully in focus does the camera refocus that point or leave it as it is). The reason I ask is that in most of the systems when you move to recompose the original point of focus may not retain sharp focus, only camera I know of is the Hasselblad models with accelerometer which maintain the original point of focus perfectly in focus when you recompose.

May be in D750 AF-S expects the selected point to be in focus - this behavior is there in D3300 where unless the focus point selected is not in focus the camera will not fire, but the AF rectangle is pretty big in D3300, around 400x250 pixels (so slight recompose shift is fine) while that of D7500 must have been reduced to 50 pixels or less, hence the behavior you observe.

ShootRaw said:

Looking forward to your review..Honestly I would just use the 51 points on S like you should..Why fix what is not broke..

Click to expand...

Because, as has been confirmed, it IS broken if after focusing on one point of the frame you recompose and it now is over something out of focus, it should still fire. We all have our techniques, "right" or "wrong", that work for us. If moving the focus point around is something you should be doing then why they hell do they waste manual pages talking about it? Because it's a common technique many of us who predate the 51 point focus system have used for decades with great success. It's not "broke".

Here's the odd thing, I was able to reproduce it yesterday while typing the post, but can't seem to do it this morning in my office. I know which photos from yesterday have the issue and I'm going to dig down into the EXIF to see if I can find what any differences in camera settings there might have been with what's going on now. I'm headed out to shoot some as well so I'll see if it happens again. It was very strange, and uncharacteristic. I'm glad it's working properly now, but hate the idea that this may be some random thing.

Jake, just one question, was the back button set to focus or "focus lock"? I don't use the back button too often, but remember there are quite a few options in the focus menu on how to make this button work.

Just a thought.

aroy said:

Did the original point you focused on remain in focus when you recompose, (that is if you move a bit and the original point of focus is not fully in focus does the camera refocus that point or leave it as it is). The reason I ask is that in most of the systems when you move to recompose the original point of focus may not retain sharp focus, only camera I know of is the Hasselblad models with accelerometer which maintain the original point of focus perfectly in focus when you recompose.

May be in D750 AF-S expects the selected point to be in focus - this behavior is there in D3300 where unless the focus point selected is not in focus the camera will not fire, but the AF rectangle is pretty big in D3300, around 400x250 pixels (so slight recompose shift is fine) while that of D7500 must have been reduced to 50 pixels or less, hence the behavior you observe.

Click to expand...

This is precisely what I'm talking about. The original object I focus on remains in focus, but the point in the viewfinder is moved over something that is not in focus, and the camera will not fire because focus lock isn't achieved where the point is now located.

Playing around with it some more, it may be that the back-button disengaged somehow during recomposition (or at least the camera thought so) so that the AF-lock was lost and the camera thinks it needs to refocus? I've been using this technique for a long time, so I can't imagine I've suddenly lost the ability to leave my thumb on the button, but it could speak to an intermittent connection issue? I'm going to keep an eye on it.

aroy said:

Did the original point you focused on remain in focus when you recompose, (that is if you move a bit and the original point of focus is not fully in focus does the camera refocus that point or leave it as it is). The reason I ask is that in most of the systems when you move to recompose the original point of focus may not retain sharp focus, only camera I know of is the Hasselblad models with accelerometer which maintain the original point of focus perfectly in focus when you recompose.

May be in D750 AF-S expects the selected point to be in focus - this behavior is there in D3300 where unless the focus point selected is not in focus the camera will not fire, but the AF rectangle is pretty big in D3300, around 400x250 pixels (so slight recompose shift is fine) while that of D7500 must have been reduced to 50 pixels or less, hence the behavior you observe.

Click to expand...

I just tried with my D3300. Once AF has focused in at its point and I button-lock it, I can shoot anything anywhere, in focus or not, and it will fire. In any mode. Even when I take a step forward between focus and locking it, it will still fire. The lock just freezes the AF in its current state and overrules it.

BackdoorHippie said:

Playing around with it some more, it may be that the back-button disengaged somehow during recomposition (or at least the camera thought so) so that the AF-lock was lost and the camera thinks it needs to refocus?

Click to expand...

This is actually how I use back button is focus and release, at which point the shutter will fire as if the focus was locked.

Focus lock should be focus lock. Did you notice if the green focus indicator was constant when the no-fire situation occurred. If it was, the indication would be something else prevented the shutter release and just coincidental to when you were recomposing.

Eyelight said:

This is actually how I use back button is focus and release, at which point the shutter will fire as if the focus was locked.

Focus lock should be focus lock. Did you notice if the green focus indicator was constant when the no-fire situation occurred. If it was, the indication would be something else prevented the shutter release and just coincidental to when you were recomposing.

Click to expand...

In mine, if I select AF-on for the back button, it doesn't fire when out of focus but that's because this option simply shifts the AF from the trigger to the back button. It confused me at first until I understood it isn't a locking option.

Just got back from shooting and think I have it figured out. The D750 definitely behaves differently from the D610, which I'm assuming has everything to do with the different focusing systems. I have both cameras in AF-S Single Point and the AF-S Priority set to Focus, both with the AE-L/AF-L button set to "AF-ON".

With the D610, I use the back button to choose my focus point by pressing it in and achieving focus and I can then release the button, reframe and fire, with the camera taking the photo with no problem. With the D750, once the button released unless the focus point is over something that is also in focus the camera will not fire. In other words, I can focus on something, release the focus button, reframe, press the shutter release and nothing happens - it will not take the photo. But if I move the camera around with the shutter button down and as soon as I pass the focus point over an object in focus it will fire. If, however, I maintain pressure on the focus button everything works fine.

I went back and rechecked and every previous Nikon I've had will allow me reframe and fire without keeping the back button pressed - the D7000, D7100, D600 and D610 (but not the D800 since it has a separate AF button on the back that maintains the AF function of the shutter button, so if you reframe without maintaining pressure on the AF button it will refocus before firing).

I suppose it begs the question (for the curious at least), "Why did I start releasing the button during reframing?", and I suspect it had something to do with using AF-C mode with birding and then finding a static object I wanted to shoot and in reframe. In AF-C, focus would change during reframing because that's how the mode works once locked, so I likely learned to release when reframing a shot so being in the "wrong" mode wouldn't impact focus in a way I didn't want.

Summarizing, I am not saying the camera isn't working properly - follow the AF Lock reframing instructions in the manual and it works perfectly. What I am saying is that it does behave differently than the other cameras that do not have a dedicated AF back button. One more thing to remember. LOL I may ping Nikon with this question to see what they have to say.

BackdoorHippie said:

I went back and rechecked and every previous Nikon I've had will allow me reframe and fire without keeping the back button pressed - the D7000, D7100, D600 and D610 (but not the D800 since it has a separate AF button on the back that maintains the AF function of the shutter button, so if you reframe without maintaining pressure on the AF button it will refocus before firing).

Click to expand...

Was your d7000 set to focus priority for af-s? Because mine will not fire if using the back button and focusing/recomposing unless I select release priority. The d7100 however, will allow me to recompose with the back button held regardless of focus or release priority. More details of what I am thinking in my post #4 above.

nickt said:

Was your d7000 set to focus priority for af-s? Because mine will not fire if using the back button and focusing/recomposing unless I select release priority. The d7100 however, will allow me to recompose with the back button held regardless of focus or release priority. More details of what I am thinking in my post #4 above.

Click to expand...

Apparently the D7000 does not operate this way. Given that got mine IR Converted over two years ago it's likely that it gets very little use this way and I'd never encountered the issue.

Still strange that this would vary from body to body.

Is there a multi-plug for the accessory outlet, so that one could use cable remote & GPS simultaneously?
Thanks for any info.

willkommen said:

Is there a multi-plug for the accessory outlet, so that one could use cable remote & GPS simultaneously?
Thanks for any info.

Click to expand...

No. But you can always used an IR remote.

Jake: That was how my back button focus on my 610 started to malfunction. Then the malfunctioning "spread" to the shutter release button as i switched back and forth trying to figure out if it was me, or the camera. Could the autofocus be intermittently malfunctioning?
Eric

eal1 said:

Jake: That was how my back button focus on my 610 started to malfunction. Then the malfunctioning "spread" to the shutter release button as i switched back and forth trying to figure out if it was me, or the camera. Could the autofocus be intermittently malfunctioning?
Eric

Click to expand...

I'm the wrong person to ask. I know that I did side by side comparisons with my 610 and 750 while writing this and their behavior is described. My one comment would be that if you're using the shutter button for focusing then you better be able to recompose and shoot, but you're going to have to maintain the half-press or you'll need to reacquire focus before shooting as a natural part of pressing the shutter.

BackdoorHippie said:

I use AF-S mode a lot. It comes from my days shooting film where I'd focus and recompose, and while I've recently tried to really break myself of the habit and use focus points, I still do this a lot with static subjects.

Click to expand...

Pardon my (hopefully) dumb question, but why are you "relearning" how you focus and compose your shots?

Realize I'm new to all this, but I've been locking focus and recomposing. Is that somehow bad form?

RocketCowboy said:

Pardon my (hopefully) dumb question, but why are you "relearning" how you focus and compose your shots?

Realize I'm new to all this, but I've been locking focus and recomposing. Is that somehow bad form?

Click to expand...

Not all habits that yield good results are good habits. As a young musician I ignored some of the strong recommendations of my teachers regarding correcting bad left hand position (specifically thumb placement) on the guitar, primarily because I was more comfortable with the position my hand was in, and it posed no limitation to allowing me to play the things I was playing (likely the reason the teachers didn't persist in trying to get me to change it). Then, one day, I hit the wall where my left-hand technique prevented me from being able to execute a particular passage, or play a certain style. I had a choice - fix what was broken or bust my ass to try and figure out how to play it with bad technique.

We all run into them. It's why top tier pro golfers hire a swing coach and spend a year relearning their swing - because there's a hitch in their giddy-up and if they want to get better they need to break what they know and relearn. The other choice is just staying where they're at and learning to be OK with not getting better.

There's nothing wrong with recomposing the way I do, and the way I have. Thousands of successful photographers do it. But as I read articles by photographers who talk about using focus points the way they were intended I find benefits that can certainly be applied to the type of photography I love to shoot. Put a wild bird in a tree and they're not likely to wait while you grab them with the middle focus point and recompose so you get a nicely framed shot - they're flying away while you're recomposing and you wind up squeezing the trigger with both the camera AND the bird moving. Blown shot. There's a pair of kids with an ice cream cone and it's about to be empty with the ice cream on the ground, and with my technique I'm either going to get a poorly framed shot that needs to be fixed in post, or I'll miss another shot while reframing. So, I set my mind on trying another method and integrating it into my shooting to hopefully allow me to improve my photography - or at least improve my ratio of keepers to missed shots.

To your specific question, it is not bad form. I've watch great portrait photographers do it all the time during presentations, and they talk about precisely how to recompose when they've locked in with an 85mm f1.4 because that focal plane is so razor thin that improper recomposition means you no longer have the eye but instead have the cheek in focus. But only relying on that technique means you've limited yourself elsewhere, and that is what I'm trying to fix.