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Nikon D500 Focus Bug

August 19, 2017

I was exploring some D500 focus options when I discovered something was definitely amiss.  It turns out that I’m not alone.


Nikon has, for many years, offered auto-focus options that help you keep the subject in focus, even when the subject leaves your selected focus sensor.  One set of focus options, in continuous-focus mode, is called “dynamic-area AF”.  These modes have names such as [9-point, 21-point, 39-point] and [25-point, 72-point, 153-point] depending upon the camera model.

 


 


Mode selection

 

 


The general idea is to choose a bigger-numbered point when the subject gets harder to track.  For a very erratic-moving subject, you’d want to use the D500 “153-point” dynamic-area AF mode, since it covers nearly the entire field of view.  Right?  Wrong.


If you choose the 153-point mode and your subject moves off of your selected focus sensor, the D500 (and the D5) will simply re-focus on the background as soon as the time has elapsed according to your selection of the “Blocked Shot AF Response” and “Subject Motion” values in the “A3 Custom Settings” menu.


This is an obvious bug!  It’s easy to test, by simply pointing the lens slightly off-target while continuously focusing.  The focus will shift to the background nearly immediately, ruining your shot.  The selected in-viewfinder focus sensor never updates with dynamic-area mode, so you have to view the photograph to see which sensor was used (little red square).  You’ll find that the camera isn’t switching focus sensors to keep up with the subject. 


I’m seeing the same problem with “D72”; it won’t track the subject when it moves off of the selected focus sensor but is still within the ‘box’ of 72 sensors.  I always use the back-button for focus (the AF-ON button or whatever button you assign focus to).  I haven't seen this focus bug on any other Nikon models, so it appears to only affect the D5/D500 models.


I am using the firmware version 1.13 (the latest to date).  I found out that Nikon was informed of this problem many months ago by multiple users, but each time has responded like they never heard of the problem.


Here are some of the links on this bug I found from other users, after I decided to go on a web search:

 

DpReview

FredMiranda



Note that in the “FredMiranda” link that his sample shots mention “d513” when he really means “d153”.  A simple little dyslexia-type mistake.  Steve used the Nikon D5 to demonstrate the exact-same bug I’m seeing with the D500.


We can only hope that enough complaints will shame Nikon into finally fixing this firmware bug.  By the way, their other camera models don’t have this bug.

 

 

Sample shot by Steve Perry (from Fred Miranda link above). D5 has the same “d153” focus bug.

 

 

The best substitute for 153-point


3D-tracking is the closest (functional) option to follow subjects all around your viewfinder.  You start by putting your desired beginning focus sensor like usual (in continuous-focus mode) over the subject.  Then you start focusing (presumably with the AF-ON button).


3D-tracking will use color information and then show you the automatically-selected focus point anywhere in the frame as the subject jumps around in your viewfinder image.  If your subject moves quickly, they recommend you also set “3D-tracking watch area” to “Wide” in the “Custom Settings” (pencil) A5 menu.


For quick response, Nikon also has the “Custom Settings” A3 menu to set both “Blocked Shot AF Response” and “Subject Motion” values.  For these settings, a lower number is for quicker reaction to changes, although in 3D-tracking note that 1=2=3 for the “Blocked Shot AF Response” setting.


If your subject is the same color as its background, then this mode will probably fail.
On the D5/D500, this 3D mode has the advantage of actually showing you the selected focus sensor as it tracks the subject around the frame.  I think their dynamic-area mode should do the same thing, since it gives you real-time feedback about what it is doing (or not doing).

 

Update 9-24-2017

 

Steve Perry (mentioned above and in the Fred Miranda link) has been pursuing this issue, and wrote more updates about the focus problem.  He thinks that Nikon fundamentally changed how dynamic-area AF works on the D5/D500, but didn't document it.  Rather than paraphrase Steve, I'm including his comments (from page 9 of the Fred Miranda site link) below (in blue font). Steve attempted to reverse-engineer what the focus algorithm must be doing.

 

OK, I think I finally have an answer. Before I lay it out though, I wanted to thank everyone who helped by posting to this thread and PM’ing me. A extra-special thanks to Snapsy and Keith for their help on this. Literally couldn’t have done it without them 

So, here’s what I think is happening, not sure if it’s 100% correct or not, but it seems to fit the facts and behaviors as we know them. Also, I reserve the right to revise this as time goes on : )

First, we know for sure that the D5/D500’s Dynamic area is not the same as the previous generation of bodies, no question there. In the past, you would typically acquire the target with the primary AF point, and then if the target slipped off that point, another AF point would jump in and take over – and it would track like that indefinitely. 

The new system on the other hand seems to let go of the target and go for whatever is under the primary AF point – almost like Dynamic wasn’t even there. This tends to appear broken since when viewing the images in View NX-i or on the back of the camera, the system never seems to move the AF point – it always shows the selected point. (In the past, you could see the point it used.)

According to the EXIF data though, it actually is selecting different AF points as the subject leaves the primary point. However, it’s reporting it like Group AF does – just showing you where the selected area (point) is and not the actual AF point that was used. As Snapsy said, you can verify this with the EXIF Tool. The camera is unquestionably selecting different AF points as needed. 

So, after looking at far too many lines of EXIF code and finally seeing a pattern, here’s how the new system works (I think  )

It locks on with the primary AF point and begins tracking. If the subject falls away from the primary AF point, the system will switch to one of the auxiliary points in the selected Dynamic area. However, unlike the old system, the new system has a bias for the primary AF point. After a brief delay, the camera tries the Primary AF point again. If there is a good target under the primary AF point, it will go for that. If there is not a good target under the primary point, it will go back to using the auxiliary points. It will continue to go back and forth like that until it can get a lock with the primary AF point again – or you stop focusing. 

Two notes - 

Note that it MUST be a good AF target for the system to switch – just a target that it can technically focus on isn’t good enough. I have tested this with poor targets the camera could just barely focus on. While the camera could technically get a lock, it would stutter a little trying to keep it. I would then switch to Dynamic and focus on a printed box with the poor AF target in the background. When I move my primary AF point over the poor AF target, it would stay with the first one indefinitely. Field tests also seem to confirm that it needs a good target in order to switch points – sadly, there are a LOT of those out there. 

Delay time – In the past, the camera would not invoke the delay time (Blocked AF Response) specified under A3 unless the target had completely left the AF area. However, that’s not the case now. 

The camera will start the countdown as soon as the target leaves the primary AF point (as a poster noted above) and use the auxiliary points until the time runs out – at which point it will try again with the primary AF point. 

Usage

So, if this is the new normal, we have to adjust to the change. For some people, this system is actually an advantage, for others, not so much. 

The advantage favors more experienced shooters. In the past with Dynamic, if the system switched to a different AF point, it would tend to stick with it – but sometimes that’s a problem. 

With the old system, if I’m photographing a bird coming at me at a 45-degree angle, I would go for his head. However, if I accidently slide the primary point off, the system would pick a new AF point. If it decides to go to the spot on the bird down by where the wing meets the body, it was an issue. The camera would lock on and just stick there until you refocused – even if for the rest of the sequence you kept the primary AF point on his eye. 

With the new system, it may still move to the wing, but if you keep the AF point on the eye, the camera will get the idea and switch back to it. 

The downside of course is that if you really are having a difficult time tracking, in the past Dynamic would really help. Just get the initial lock and fire away. Even if the primary AF point never revisited the subject, it would continue to track and not jump to the background. IMO this is the better method – less experienced shooters can use wider areas and more experienced shooters would use smaller areas to restrict where the camera could focus. 

So, the bottom line is this – with the new system, you need to do your best to keep the primary AF point on your subject. If you’re having a hard time, set the delay under A3 to 4 or 5. However, keep in mind even at “5” the delay is short. However, just knowing that it’s critical to keep the AF point on target may be enough to help some shooters. 

 

-- Steve Perry

 

There was this response, after more than a YEAR from Nikon:

 

I apologize for the delay, and for the confusion. According to our design group at Nikon Corp, the Dynamic Area AF function has been enhanced with the newest AF sensor, particularly for subjects moving toward or away from the camera.
Dynamic Area AF (9, 53, 72, or 153 point) does not track the subject, however it will expand the area the subject will remain focused should it BRIEFLY leave the initial focus point.
If the subject leaves the selected number of AF points, then the camera will refocus.
If the subject leaves the initial focus area and enough time has lapsed before the subject is recentered, the camera will refocus.
If peripheral data from initial target area has enough of a difference from the initial target (unspecified), then the camera may refocus as well. This is not the intent of the function, but it may happen at times.

Choose the numbered area based on your ability to keep the initial AF area on the subject, and also expected movement path, and always try to follow and center your subject during the burst. If the subject does refocus, and it may, then either let go of the button, reacquire the subject in the center AF area, and continue firing, or, depending on the quality of the subject (ability for the AF sensor to grab and hold), just keep firing and the lens will refocus on it's own. Success is dependent on a combination of subject contrast and user skill and speed of the user and the subject.

If you want you to allow the AF area to track your subject around the frame, then select 3D or Auto. 3D will follow around the subject using a single AF point and Auto will use several points.
The intended performance improvement, again, was for subjects moving toward or away the camera using information from surrounding points, that is one area where the enhancements were noted during testing with this new system.

(See more on this response from here).

 

Conclusion

 

It appears that Nikon chose to change the way dynamic-area focus works, but the majority of photographers who have used it don't like it (including me). You need to use the "exif tool" to query what the focus points are doing (Capture NX-D for instance doesn't give you a clue). There is no official Nikon documentation noting the change or how to cope with it, as of this writing.

 

I'd recommend that you try setting the "Blocked Shot AF Response" to the longest allowable (5), so that it waits a little longer before it picks a different focus sensor.

 

Most photographers seem to prefer "Group Autofocus", although be aware that this mode will always pick the nearest subject.

 

 

 

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