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doppler_fto Registered since 23rd Mar 2013Fri 03-May-13 07:19 AM
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"D7100: AF focuses on background a lot?"


US
          

Howdy, y'all

It's been 1.5 months and 5,000 frames with the D7100, and I've consistently found that it has a tendency to focus on the background when the AF area isn't filled by a foreground subject.

First and foremost, I'm curious if other folks are noticing/have noticed this.

Shooting style


I spend a lot of time covering events with two bodies, in a candid, journalistic style. Before the D7100s, I used a pair of D300 bodies for 5 years (~130k frmaes). In that time, I never noticed the D300 picking up the background with the same aggressiveness that the D7100 does.

AF style


I shoot exclusively with AF-ON triggering, in release priority and in AF-C mode. I strongly prefer single-area AF, because it lets me pick what the camera will focus on in complex scenes. On the D300, I've generally used AF-11 for speed in switching AF points, unless I had the camera on a tripod, at which point I would manually switch to AF-51 to reduce focus-and-recompose.

With the D7100, I started with single-area AF-11, at which point I noticed the focus-on-background issue. I tried switching to AF-51 for a few weeks (thinking that reducing the focus area size might increase its targeting precision). It didn't help noticeably. At this point, I'm starting to get very frustrated, because shots that _should_ be gimmes are ending up focused on the background

Things that I've tried


As mentioned, I've tried using AF-11 and AF-51 with no apparent difference. I've tried 9-point dynamic-area AF, and got frustrated at not being able to predict what the camera would focus on. As a result, I didn't use it long enough to determine if it helped noticeably. The next time I find this issue happening, I'll probably give it another go.

Things that aren't the problem


The camera isn't back-focusing, it is focusing accurately on the background in some situations. Please don't tell me to check AF micro-adjust.

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doppler_fto Registered since 23rd Mar 2013Fri 03-May-13 07:24 AM
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#1. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 0


US
          

I should note that the problem is especially bad using any of the non-cross sensors, but it still happens even when I intentionally use the center sensor to try to avoid the problem.

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Toby01 Silver Member Nikonian since 19th Nov 2012Fri 03-May-13 05:36 PM
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#2. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 0


El Sobrante, US
          

I have not had that problem with my D7100; in fact, I have been impressed with how quickly and accurately it acquires focus. I have had no focus problems in either AF-C or AF-S. I often use large apertures for shallow DOF, so I am sure I would have seen the problem by now if my D7100 were acting like yours.

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doppler_fto Registered since 23rd Mar 2013Fri 03-May-13 07:56 PM
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#5. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 2


US
          

Toby01: What kinds of subjects do you shoot? Also, what lenses do you typically use?

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Toby01 Silver Member Nikonian since 19th Nov 2012Fri 03-May-13 08:12 PM
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#7. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 5


El Sobrante, US
          

Thus far with my D7100, I have mostly shot kids T-ball games, the Scottish Highland games, and casual family portraits (indoors). For the outdoor events, I used my Nikon 70-200 f/4 VR, mostly at f/4. I also used the 16-85 on some shots. For the indoor stuff, I used a Tamron 28-75 f/2.8 at 2.8 and the Nikon 50 and 85mm f/1.8 G lenses, usually at f/2.

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JosephK Silver Member Fellow Ribbon awarded for his excellent and frequent contributions and sharing his in-depth knowledge and experience with the community in the Nikonians spirit. Nikonian since 17th Apr 2006Fri 03-May-13 07:25 PM
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#3. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 0


Seattle, WA, US
          

The only thing that comes to mind is that the actual focus points are bigger than the square on the screen so that it might be picking up an edge near what you are aiming for.

Any chance we can see an example file that is unedited and has all its EXIF data?

---------+---------+---------+---------+---------+
Joseph K
Seattle, WA, USA

D700, D200, D70S, 24-70mm f/2.8, VR 70-200mm f/2.8 II,
50mm f/1.4 D, 70-300mm f/4.5-5.6 VR, 18-70mm f/3.5-4.5 DX

  

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unclemikey Platinum Member Nikonian since 29th Apr 2013Fri 03-May-13 07:52 PM
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#4. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 3


Henrico, US
          

Only have my d7100 for a few months now and haven't put that many exposures on card but I don't see any problem with the focus. I shoot both an active 30month granddaughter and small insects and haven't had any problems in any of the focus points.

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doppler_fto Registered since 23rd Mar 2013Fri 03-May-13 08:11 PM
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#6. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 3


US
          

JosephK: Yeah, I was thinking of that. See here:
http://web.mit.edu/~xsdg/www/stuff/d7100-focus/

(Is there any good way to link to the images _without_ having the forum auto-load the images? I'd like to make them easier to click, but don't want folks' browsers pulling down 16MB of images automatically)

In 0929, I had a left focus point squarely on the white shirt guy, and the camera focused on the background. I figured "oh, hmm, must not be enough contrast. That's weird." Then I saw the guy with the detail-laden shirt walking toward me and figured I'd try the shot again. "His shirt has a _ton_ of detail, so it can't miss" I figured. But I was wrong. Focused on the background _again_. And I was chimping between those two shots, so it's not like it was locked onto the background during the entire period.

Also, as mentioned, I am positive that I had the indicated AF point squarely on the guy's shirt. I actually hit the shutter release on 0930 after I had been willing the AF to bite for a half-second or a second, so he was in the exact same position as 0929 when I started trying to AF on him.

For these shots, I'm confident (but not positive) that I was in AF-11 mode. So the focus point would have been the left (not far-left) vertically-centered AF point.

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unclemikey Platinum Member Nikonian since 29th Apr 2013Fri 03-May-13 11:25 PM
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#8. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 6


Henrico, US
          

>JosephK: Yeah, I was thinking of that. See here:
>http://web.mit.edu/~xsdg/www/stuff/d7100-focus/
>
>(Is there any good way to link to the images _without_ having
>the forum auto-load the images? I'd like to make them easier
>to click, but don't want folks' browsers pulling down 16MB of
>images automatically)
>
>In 0929, I had a left focus point squarely on the white shirt
>guy, and the camera focused on the background. I figured
>"oh, hmm, must not be enough contrast. That's
>weird." Then I saw the guy with the detail-laden shirt
>walking toward me and figured I'd try the shot again.
>"His shirt has a _ton_ of detail, so it can't miss"
>I figured. But I was wrong. Focused on the background
>_again_. And I was chimping between those two shots, so it's
>not like it was locked onto the background during the entire
>period.
>
From what you say, I'm wondering if there is something amiss with your particular camera? mb

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golfercat Silver Member Nikonian since 15th Sep 2012Sat 04-May-13 12:03 AM
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#9. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 6


Menifee, US
          

Looking at the first photo, I find the focus is on his left hand, fore arm and shirt. The exif data shows the aperature is F2.8. That is going to give a very shallow DOF.

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doppler_fto Registered since 23rd Mar 2013Sat 04-May-13 04:17 AM
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#11. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 9


US
          

In 0929, the focus should be on the guy in the white; he is completely out of focus. It was in 0930 that I was attempting to focus on the guy in the checkered blue shirt. In both images, the camera actually focused on something in the distance, rather than on the intended subject.

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km6xz Moderator Awarded for his in-depth knowledge in various areas, including Portraits and Urban Photography Nikonian since 22nd Jan 2009Sat 04-May-13 12:03 AM
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#10. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 6


St Petersburg, RU
          

There are many ways for the AF to misread your intentions. Were you using AF-C Release Priority?
Had you focused on a more distant subject while still having your thumb on the AF-On button when you then selected the person in the foreground?
If the AF in AF-C, 11 point was locked on another focal plane, with the AF-On button down, and recomposed, even with AF-C, the AF would have still being holding tracking of the first subject it locked onto. If in doubt, release the AF-On button and re-acquire focus lock on the new subject.
As was mentioned above, the focusing point sensors are larger than the box outline in the VF so if a better target was on an edge of the selected focal point but at a more distant focal plane, you would get shots like what you did.
Stan
St Petersburg Russia

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doppler_fto Registered since 23rd Mar 2013Sat 04-May-13 05:13 AM
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#14. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 10


US
          

I was using AF-C and release priority, yes. I had already developed the habit of releasing and re-pressing the AF-ON button when the camera isn't focusing on what I want it to, so I'm pretty sure I was doing that, although I can't say for sure — it's an ingrained habit, so I don't think about whether I'm doing it or not.

I don't believe the recomposition thing is my real problem (although it could be compounding whatever is going on). The real problem is that the AF locks on the background, even when the background should only be a tiny portion of the active AF area, if that, and even when the subject I'm trying to focus on has plenty of contrast. I mean, there are plenty of explanations why the camera could be behaving this way, but I can't think of any good reasons why a well-behaved AF system should behave this way.

Either way, I'll try decreasing setting a3 (Focus tracking with lock-on) from 3 (Normal) to 2 or 1 and see if that helps.

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    that people love.

  

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golfercat Silver Member Nikonian since 15th Sep 2012Sat 04-May-13 05:57 AM
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#16. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 14


Menifee, US
          

It may be a mute point. Since you are using AF-C and release priority as opposed to Focus priority, there is no guarantee that the picture will be in focus when the shutter release is depressed. You might want to consider using Focus Priority. Otherwise you get what you get. Shooting continoious in CH would give you a better chance of getting a picture that is in focus.

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JosephK Silver Member Fellow Ribbon awarded for his excellent and frequent contributions and sharing his in-depth knowledge and experience with the community in the Nikonians spirit. Nikonian since 17th Apr 2006Sat 04-May-13 04:24 AM
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#12. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 6


Seattle, WA, US
          

Assuming I have overlayed the focus grid correctly and interpreted the EXIF data correctly -- not necessarily a safe assumption -- it could be just a matter of missed focus.







---------+---------+---------+---------+---------+
Joseph K
Seattle, WA, USA

D700, D200, D70S, 24-70mm f/2.8, VR 70-200mm f/2.8 II,
50mm f/1.4 D, 70-300mm f/4.5-5.6 VR, 18-70mm f/3.5-4.5 DX


Attachment #1, (jpg file)
Attachment #2, (jpg file)

  

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doppler_fto Registered since 23rd Mar 2013Sat 04-May-13 05:00 AM
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#13. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 12


US
          

Aah, indeed. I posted those in a hurry this morning, and now that I have a chance to look at the exif, it does look like that was during the period when I was giving Dynamic AF a go

0929:
AF Area Mode : Dynamic Area (9 points)
Phase Detect AF : On (51-point)
Primary AF Point : D2
AF Points Used : D2

0930:
AF Area Mode : Dynamic Area (9 points)
Phase Detect AF : On (51-point)
Primary AF Point : C3
AF Points Used : C3

Of course, one might wonder whether Dynamic Area AF shouldn't generally choose to focus on the closer subject rather than the more distant one which also takes of less area in the focus zone.

Anyway, more examples forthcoming...

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  of moments
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doppler_fto Registered since 23rd Mar 2013Sat 04-May-13 05:50 AM
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#15. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 3


US
          

Next set of examples is uploaded. I've double-checked that these are all Single-Area AF (rather than Dynamic Area AF, like the first two).
JosephK: I'd appreciate if you could do the overlays again, at least for one or two of the images, just to confirm that the camera and I are on the same page about focus points.

Note that this is clearly happening on two cameras. 701_ prefix is one body, 710_ prefix is a second body. I bought the cameras in a single order, though, so if there were something amiss with their batch, it's possible that they're both affected.

Finally, I've drawn the red dot at the exact center of the image. Given that (I thought) I was using the center focus point, I would expect the red dot area to be in focus. Instead, the camera has clearly decided it'd rather focus on the background.

Images are here, sorted by upload time. Farther down is newer:
http://web.mit.edu/~xsdg/www/stuff/d7100-focus/?M=A

701_0404:
AF Area Mode : Single Area
Phase Detect AF : On (51-point)
Primary AF Point : C6 (Center)
AF Points Used : C6

701_0405:
AF Area Mode : Single Area
Phase Detect AF : On (51-point)
Primary AF Point : C6 (Center)
AF Points Used : C6

701_0517:
AF Area Mode : Single Area
Phase Detect AF : On (51-point)
Primary AF Point : C6 (Center)
AF Points Used : C6

701_1009:
AF Area Mode : Single Area
Phase Detect AF : On (51-point)
Primary AF Point : C6 (Center)
AF Points Used : C6

------------------------------------------------------------
I make prints
  of moments
    that people love.

  

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km6xz Moderator Awarded for his in-depth knowledge in various areas, including Portraits and Urban Photography Nikonian since 22nd Jan 2009Sat 04-May-13 01:53 PM
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#17. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 15


St Petersburg, RU
          

The only one I tried to download showed the focus point being walking man's right hand(camera left) and is not locked on. It appears that the focus lock was not obtained before the shutter was released, as Release Priority is supposed to do, release regardless of focus.

The dim light, underexposure, low contrast shirt target, if the moving person was the intended target, release priority and movement combined to make focusing less than assured.
If you want others to help it would be best to post 300k or less files directly on the thread. Few people would have the patience to download all those 30mb files from another web site.

What about your other photos, in other AF modes with good targets, are they also missing focus? I doubt this is a case of "missed focus" more like premature release.

Stan
St Petersburg Russia

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doppler_fto Registered since 23rd Mar 2013Sat 04-May-13 06:15 PM
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#22. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 17


US
          

>The only one I tried to download showed the focus point being
>walking man's right hand(camera left) and is not locked on. It
>appears that the focus lock was not obtained before the
>shutter was released, as Release Priority is supposed to do,
>release regardless of focus.
>
>The dim light, underexposure, low contrast shirt target, if
>the moving person was the intended target, release priority
>and movement combined to make focusing less than assured.

There's a difference between "focus is not assured" and "try as I might, I just can't get the camera to focus on my intended subject."

More to the point, it feels like you're calling my competence into question. I know how release priority behaves. I know how AF-C behaves. I know what it sounds and feels like when the AF system thinks it's locked onto something, versus when it's still focusing or has failed to lock onto something.

In particular, I've been using this lens for the last four years. I've been using AF-C and Release Priority since I was shooting with my D70 nearly 10 years ago. It's been long enough that I can tell when the camera's AF should be locked onto something.

I can assure you that in this case, the AF system did lock onto something; it's just that the "something" was the background rather than my intended subject.

>If you want others to help it would be best to post 300k or
>less files directly on the thread. Few people would have the
>patience to download all those 30mb files from another web
>site.

Will do so.

>
>What about your other photos, in other AF modes with good
>targets, are they also missing focus? I doubt this is a case
>of "missed focus" more like premature release.

At this point, I'm going to stick with single-area AF and play with other options. I can't imagine any of the other AF modes helping the camera to focus on things I want it to focus on; it's already clear that what it wants to focus on is the background.

That said, here's the next example. Shown is a 100% crop of the exact center of the image. The red circle depicts the center of the image. I think one could reasonably expect "oh, hey, this wedding ring has a lot of contrast, why don't I focus on that?" Instead, the camera focuses on the background. Again. Seriously?

Settings:
1/500s f/4.5 100ISO 32mm, shooting in broad daylight with the 24-70/2.8 lens

AF Area Mode : Single Area
Phase Detect AF : On (51-point)
Primary AF Point : C6 (Center)
AF Points Used : C6

http://web.mit.edu/~xsdg/www/stuff/d7100-focus/710_3898.center-crop.small.jpg

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kuzzy Silver Member Nikonian since 12th Dec 2005Sat 04-May-13 02:27 PM
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#18. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 15


Milford, US
          

In looking at 0404 and 0417 one issue may be with shutter speed and the movement of the drummer. If you look at his waist area and pants I think you will see that they appear to be better in focus than the upper body and head which would be moving more than his waist. The slow shutter speeds simply make it harder to determine if it is the cameras AF system. Especially if it is happening with 2 bodies.

The shutter speeds also seem a little low compared to the focal length. One of the things that became somewhat apparent with the introduction of the D7000 is that in order to get crisp images consistently you really need to be at 1.5 to 2 times the focal length with the shutter speed with the increased number of pixels unless your technique and hand holding is flawless. I am sure that is even more important with the even larger number of pixels on the D7100.

Looking at 1009 I am not sure what happened on that one as it is clear that the area in focus is the table behind the guy kneeling.

I think I would head outdoors with some good light and try doing some tests under those conditions using focus priority in AF-C single point and see what you get. If you still are having trouble you may have a problem at which point I think I would do a little more formal testing using a tripod, etc., in order to be sure of my results before contacting Nikon. Although, with it happening on both bodies I find that very unusual based on the track record of the D7100 so far, but anything is possible.

Marc
There are always two people in every picture: the photographer and the viewer.-Ansel Adams

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doppler_fto Registered since 23rd Mar 2013Sat 04-May-13 05:30 PM
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#21. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 18


US
          

>In looking at 0404 and 0417 one issue may be with shutter
>speed and the movement of the drummer. If you look at his
>waist area and pants I think you will see that they appear to
>be better in focus than the upper body and head which would be
>moving more than his waist. The slow shutter speeds simply
>make it harder to determine if it is the cameras AF system.
>Especially if it is happening with 2 bodies.

The reason his waist is in better focus is because it's closer to the wall which is what's actually in focus. Part of why I added 0517 to this set is to demonstrate definitively that the camera is focusing on the wall, and that the problem isn't motion blur or anything like that.

>The shutter speeds also seem a little low compared to the
>focal length. One of the things that became somewhat apparent
>with the introduction of the D7000 is that in order to get
>crisp images consistently you really need to be at 1.5 to 2
>times the focal length with the shutter speed with the
>increased number of pixels unless your technique and hand
>holding is flawless. I am sure that is even more important
>with the even larger number of pixels on the D7100.

I appreciate the advice, but this is pertinent to the issue at hand. If you're curious about my hand-holding abilities, the following post includes a number of images that I shot handheld at 1/15s with my 80-200/2.8. Remember that the 80-200 doesn't have VR:
http://blog.doppler-photo.net/2008/08/17-hours-of-street-photography.html

>Looking at 1009 I am not sure what happened on that one as it
>is clear that the area in focus is the table behind the guy
>kneeling.
>
>I think I would head outdoors with some good light and try
>doing some tests under those conditions using focus priority
>in AF-C single point and see what you get. If you still are
>having trouble you may have a problem at which point I think I
>would do a little more formal testing using a tripod, etc., in
>order to be sure of my results before contacting Nikon.
>Although, with it happening on both bodies I find that very
>unusual based on the track record of the D7100 so far, but
>anything is possible.

I'm still trying to get a better understanding of which situations provoke this behavior; I don't think I'm anywhere close to having a repeatable testcase yet. In particular, because I notice this when I'm actually trying to cover events, I don't have time to stop and troubleshoot; I just end up compromising on my desired compositions to make it easier for the AF system to do the right thing.

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JosephK Silver Member Fellow Ribbon awarded for his excellent and frequent contributions and sharing his in-depth knowledge and experience with the community in the Nikonians spirit. Nikonian since 17th Apr 2006Sat 04-May-13 06:41 PM
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#23. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 18


Seattle, WA, US
          

Marc may be right with the recommendation for some good-light testing.

The four new uploads show that the focus should have been on your red dot each time, assuming your were not doing a focus-and-recompose.

The kneeling drummer is an interesting example due to the table behind the drummer being in focus (not the far wall) at roughly the same distance back as the drummer and wall in 404 and 405. To me, this suggests a possible back-focus problem that should be tested for.

---------+---------+---------+---------+---------+
Joseph K
Seattle, WA, USA

D700, D200, D70S, 24-70mm f/2.8, VR 70-200mm f/2.8 II,
50mm f/1.4 D, 70-300mm f/4.5-5.6 VR, 18-70mm f/3.5-4.5 DX

  

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doppler_fto Registered since 23rd Mar 2013Sat 04-May-13 07:00 PM
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#24. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 23


US
          

I'll get there at some point, but I'm pretty sure I'm not to that stage of debugging yet; just trying to gather information and theories at this point.

That said, I have trouble believing that it's back-focus because there is pretty much always something in focus when this problem occurs. Beyond that, for the times when the problem doesn't happen, the focus is spot on:

http://blog.doppler-photo.net/2013/04/drops-of-jupiter.html
http://blog.doppler-photo.net/2013/04/byobw-2013-comin-in-hot.html


I'll keep playing and see what happens, though. I suspect that dialing a3 (Focus tracking with lock on) up and down when I'm running into this will be informative, since that'll tell help me figure out if any of the following might be the case:


  1. The camera is focusing on the intended subject and jumping to the background

  2. The camera is focusing on the background and just doesn't "see" the intended subject

  3. The camera is focusing on the background, and would jump to the intended subject with the lock-on set to lower duration.

  4. The camera's AF is "nervous," and is jumping around, which causes it to lock on to things other than the intended subject.


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jhearl Silver Member Nikonian since 16th Apr 2007Mon 06-May-13 03:27 PM
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#26. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 24


Milford, VA, US
          

I took a long look at 517 (the NEF file). Actually, I didn't see anything in the image that was in focus. The wall behind the drummer appears to be closer to being in focus than the drummer's face, but definitely not in focus. My two cents is that you really should investigate whether your 70-200 is back focusing. I own a D800E and with my 24-70 zoom, I have to set the AF Fine Tune to +18 to achieve proper focus. Other lenses have totally different AF settings.

I also looked at the other photos and, again, I just don't see any part of the image on any of them that is truly in focus so that makes it a bit harder to evaluate the problem.

You pointed to two other images where you say the subject is in focus (though it's hard to tell from those small images), but I do see that they were taken with a different lens. That lens may not be exhibiting the same back focus problem as your 70-200 (if indeed, that's what's going on).

One thing I found in moving from my D300 to my D800E was that I really could not hand hold at the same low shutter speeds I was used to due to the increased resolution. With my 24-70, I find I cannot hand hold at anything lower than 1/125th and get perfectly sharp images. I noticed that 517 was shot at 155mm at 1/160th and that VR was turned off as well. That may simply be too slow on the 7100.

And, finally, I'll mention that my shooting style at events is different than yours (we each develop our own style, of course) but I always use the center focus point and focus on the face. I don't mind focusing and recomposing simply because I find it ever so much easier than trying to move the focus point itself. But, that's just my style - not necessarily better than what you've come to prefer. For most of these images it seems that you would not have had to recompose much at all if you used the center focus point on the face.

In any case, I'd really encourage you to get into some good light and see if there's a back focusing problem with your 70-200. If not, at least you will have eliminated one of the variables.

Hope this helps a bit -
John


My Flickr page: http://www.flickr.com/photos/dancingtuna

  

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doppler_fto Registered since 23rd Mar 2013Mon 06-May-13 05:17 PM
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#27. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 26


US
          

I have two bodies and two lenses, and I never swap them. The 70-200 body/lens combo is focusing fine. See here:
http://web.mit.edu/~xsdg/www/pblog/2013-apr/byobw/701_1393.jpg

I am not a pixel-peeper and I don't shoot with a tripod. If an image is blurred in a way that's not visible (or is visible but doesn't detract) at my intended output size, then I simply don't care.

And this problem does continue to occur even while using the central focus point in single-area focus mode in good light and with a high-contrast subject that should be the only subject covered by the selected focus point. Revisit response #22:
http://www.nikonians.org/forums/dcboard.php?az=show_topic&forum=329&topic_id=27007&mesg_id=27007&page=#27056

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jhearl Silver Member Nikonian since 16th Apr 2007Mon 06-May-13 05:51 PM
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#28. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 27


Milford, VA, US
          

My initial response was meant to be helpful to the best of my ability and courteous, regardless, but apparently you didn't take it that way. So after this, I won't waste my time, but you comment that your 70-200 body/lens combo is focusing fine. From looking at the exif on 517, which indicates an FX focal length of 155mm, I'm guessing that's the lens you used for that shot. Which, if that's the case, apparently is not fine. You also refer me to a different photo (1393) that is in focus. I'm willing to bet that that photo was not taken at f2.8 - there is a great deal more depth-of-field in that image than in 517 and it was taken from farther away, which means you could have a back focus problem but it would be less obvious. However, since you are convinced you do not have a back focus problem even though you've never checked and seem reluctant to consider any of the suggestions you asked for from me or the other posters, then I guess you are on your own.

Cheers -
John

My Flickr page: http://www.flickr.com/photos/dancingtuna

  

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doppler_fto Registered since 23rd Mar 2013Mon 06-May-13 06:27 PM
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#29. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 28


US
          

My apologies for the curt response; I appreciate that you were trying to help.

From my perspective, I know for a fact that back-focusing is not the issue. Sure, the focusing might not be perfect, but it's also not so far off to cause this issue that I'm seeing. I specifically said "The camera isn't back focusing" because I know that to be the case. I had intended that part of my message to preempt well-meaning folks from suggesting that I should check if the body is back-focusing, because it isn't.

It is no coincidence that there is generally something in pretty good focus, regardless of the distance between the intended subject and that properly-focused background element. If the combo were back-focusing, this would not be the case — there would consistenly be cases where the body locks focus and nothing is actually in focus. But that does not occur.

As mentioned, I've already run a couple thousand frames through these cameras, including a bunch in low-light and at f/2.8. I know that I can get stellar results from both cameras and both lenses, I just want to see those results more consistently in situations where a properly-functioning AF system would deliver the goods without hesitation. Just because I'm only showing a handful of sample images doesn't mean that I haven't considered the problem in greater depth than may be apparent from the post.

So yes, I appreciate that you were trying to help, but I was frustrated because I already said explicitly in the original post that this kind of response would not be helpful. And true to form, it was not helpful, despite the good intentions.

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blw Moderator Awarded for his high level of expertise in various areas Nikonian since 18th Jun 2004Sat 04-May-13 04:49 PM
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#19. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 0


Richmond, US
          

You should review the images in ViewNX2, specifically to see which AF target is locked on. You may be surprised, especially in group dynamic mode.

_____
Brian... a bicoastal Nikonian and Team Member

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doppler_fto Registered since 23rd Mar 2013Sat 04-May-13 05:23 PM
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#20. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 19


US
          

I don't own a machine that will run ViewNX. Beyond that, there are a variety of examples in the thread (and one more forthcoming) that demonstrate this problem happening with single-area AF while focusing with the center point. Presumably, in that case, the camera shouldn't be letting other AF areas override the one that I specifically chose.

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Clint S Silver Member Nikonian since 02nd Jan 2011Sun 05-May-13 04:27 AM
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#25. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 20


Chula Vista, US
          

I had similar issues when I moved to the D7000. So I simply removed possile causes -

Use spot metering
Set
- autofocus mode to AF-S
- AF-Are Mode select Single point AF
- Set the center focusing point and lock the control
- a2 to Focus
- a3 - Off
- b4 - 6mm
- f4 - None (just use the shutter button)
- Turn on beep (d1)

try these settings with a couple of lenses

If your photos are regularly focused on the wrong area - then it is time to take a real good look at the camera

If your shots are cosnistently coming out focused as desired - then you have invested time correlating how this camera's focus and metering sytem works within your expectations. Start changing things like AF-S to AF-C 9 points, then change the metering to spot and matrix, etc.

Visit my Nikonians gallery - my Spare Time gallery

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nrothschild Silver Member Neil is an expert in several areas, including camera support Nikonian since 25th Jul 2004Tue 07-May-13 03:24 PM
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#30. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 0
Tue 07-May-13 03:30 PM by nrothschild

US
          

Hi Omari,

First, I want to say that long ago I shot a D2h, circa 2004. That camera has what I euphemistically call "most distant subject priority focus mode". The camera only has 11 AF sensors and they are very large, extending well beyond the focus reticle marks.

I determined, with careful tests, that given a choice of two subjects, one more distant than the other, the selected sensor would focus on the distant subject even if only a tiny part of the actual AF sensor was off the close subject.

When I upgraded to the D300 and added a D700 that problem went away. I have shot 200,000 images with those cameras and never suspected that there was any tendency to choose distant subjects. I believe this is an old problem Nikon long ago fixed.

I don't have your camera but I would be surprised if Nikon reverted to their old, poor logic. And that is supported by the fact that I don't see other complaints of this nature.

Carl Sagan is famous for suggesting that "Extraordinary Claims Require Extraordinary Evidence" or something to that effect. As I recall, it was in reference to UFO's but my experience is that it well applies to AF issues .

That is a joke of course. I know AF issues can be very troublesome and frustrating but they are very hard to pin down, and, more importantly, it is even more frustrating and difficult to convince others in the case where you think your camera behaves uniquely.

With that in mind...

I downloaded 6 of your NEF files from your FTP folder- 701_0404/405/517/1009, and 710_0929/0930.

I viewed each in ViewNX, displaying the active focus point. None of the 6 indicate a focus point. This, I think, is critical to your problem and your examples.

There are a number of reasons why the focus point is not indicated, and it varies somewhat from model to model. I just re-studied this issue and found variances in how my D300 and D700 deal with this. I don't know the "rules" for your camera.

However, in general, when using AF-C Release Priority Mode as I believe you did, and AF-On, the AF points should always be indicated if a) the camera believes the subject was in focus and b) you are actively focusing.

Actively focusing means that in the case of using AF-On only (shutter button does not focus), the Af-On button was pressed at the instant the image was captured.

If the AF-On button was not pressed when the shutter fired then some models will indicate an AF point if the active sensor saw a focused target, but others will not. Neither of my cameras will indicate the active focus sensor info if focus is locked, for example, with a programmed focus lock button. You would have to test your own model to get to the bottom of that.

You said that you are not using a tripod. If you tripped the shutter without pressing AF-On, you may have recomposed by accident. You may have something in your shooting style that is confusing the issue. Remember what I said about extraordinary claims .

I am not suggesting you did or didn't shoot these correctly. I am, though, suggesting that you need to at least reproduce the problem with sample images that have an active AF sensor indicated in the EXIF. Otherwise you could not convince me, and likely no one else, without doing that.

I would not accept images without that EXIF confirmation even if I shot them. So don't take that personally. From long experience, I never question images that do not have that EXIF indication. I know in that case I likely did something "wrong", in some sense.

Access to ViewNX may be problematic for you, but I think you need to work something out in order to solve this problem. You need that feedback.

Afterthought: even if you can not get ViewNX working, your camera should have an LCD playback option to display the active and used sensor (if it indicates anything). That is just as useful as ViewNX except you are looking at a tiny 3" image instead of something easier to drill down into on a large screen. Check your camera menus; it may not be turned on by default.

For the sake of process of elimination, one possibility, in principle, is that your actual AF sensors are out of line with your viewfinder reticle indicators. A test is fairly simple:

1. Set your camera on a tripod. You MUST use a decent tripod for this test. You need to eliminate any possibility of accidental focus/recompose.

2. Find a target, something like a stop sign, with simple geometry, and with a fairly distant background such that focus is absolutely unambiguous. I think I used a tree trunk for my initial D2h tests but followed up with better targets to confirm my theories on that camera.

3. Now take different shots, some squarely on the target, and some bordering the target. You may not even need to take shots, except as extraordinary proof to convince others. What you see in the viewfinder should tell you all you need to know.

You will also learn the extents of the actual focus sensors verses the viewfinder reticle indicators. I find very little overflow on my D300 and D700 but others seem to think there is more than I do.

_________________________________
Neil


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nrothschild Silver Member Neil is an expert in several areas, including camera support Nikonian since 25th Jul 2004Tue 07-May-13 07:37 PM
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#31. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 30


US
          

The plot sickens

I took a close look at the image exif using ExifToolsGui. ExifTools indicates "AFPointsUsed=C6 (Center)" for image 701_1009, for example.

Looking at one of my D300 images that do NOT show a focus point in ViewNX2, it indicates "AFPointsUsed=(none)"

From that I can only conclude that at least my own install of ViewNX2 is not displaying focus points for your images although it works for my D300/D700 images. And apparently you did get focus points on at least most or all of those shots?

Presumably your camera playback is doing a better job of that.

I'd be curious if anyone reading this, and having a D7100, can confirm or deny that my ViewNX2 situation is normal here. I did a fresh install of ViewNX2 2.7.1 and Capture NX2 2.4.1 in February.

I am having other issues with your files. If I open an image in ViewNX2 and zoom in to 100%, and then click other thumbnails, sometimes I get "Unupported File Type". It always works with the normal zooom to full screen setting (the widest zoom setting).

In addition, I cannot open any of your files in Capture NX2 2.4.1. I get a message box indicating "Cannot Load file: {file path/name}. Sigh. I think I have seen other posts with these problems, and the solution was to uninstall and re install the Nikon apps. But I just did that.

Just to say I may not be much help here until I get this straight.

I would suggest you do the focus point positioning test I mentioned previously. If My analysis of the EXIF is correct, it is hard to figure out 701_1009, for example. It would be tough to miss that one.

_________________________________
Neil


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kuzzy Silver Member Nikonian since 12th Dec 2005Wed 08-May-13 01:51 AM
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#32. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 31
Wed 08-May-13 01:55 AM by kuzzy

Milford, US
          

Neil, The latest version of View NX2 is 2.7.5. I had an older version on my computer and tried to view the NEF's and got the same message. You probably just need to upgrade your copy as I have since done and they now are working just fine.

The focus points are visible on the 3 NEF's I downloaded, 0404,0405 and 1009 (also just did 0517). I really had a hard time understanding 1009 until I just looked at the RAW image and looked at the carpet. It would appear that the carpet on a plane with the focus point, the drummers mid section, is in focus and not the table leg behind him as it appears at first blush. Looking at the carpet it looks like focus was much more accurate than originally suspected. Unfortunately there are no similar reference points to look at in the other images so it is more difficult to say on those. I believe that most of the issue here is caused by 24 Million tiny little pixels as opposed to 12 million in the D300. The extra pixels add more resolution both good and bad. I believe what you see is motion blur from the drummer moving with a shutter speed of 1/100. I would tend to agree with Omari that he does not have a backfocus problem or a problem created by less than perfect hand holding technique at these rather slow shutter speeds.

I think some controlled testing is the only way to narrow this down.

Your stop sign test is a good idea for locating the sensors. I have thought that my D7000 is off on the right side of the center focus point in particular but I have not had the inclination to try an elaborate test. Your idea sounds simple and it should give one a pretty good idea of exactly where the sensor is. Thanks for the idea.

Omari, some nice street shots on you blog. I really like the reflection shot.

Marc
There are always two people in every picture: the photographer and the viewer.-Ansel Adams

http://500px.com/WhatISaw
http://kuzzy.smugmug.com

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nrothschild Silver Member Neil is an expert in several areas, including camera support Nikonian since 25th Jul 2004Wed 08-May-13 09:41 AM
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#33. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 32


US
          

Hi Marc,

Good observation on the carpet. I was looking at that keyboard just behind and left of the subject, thinking that seemed to be more in the vicinity of focus.

I thought I was fully patched up but now I am for sure and both Nikon apps work properly. I installed Capture 2.4.2 - that may have been released just yesterday?

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Neil


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elec164 Silver Member Nikonian since 15th Jan 2009Wed 08-May-13 04:22 PM
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#34. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 33


US
          

>Good observation on the carpet. I was looking at that
>keyboard just behind and left of the subject, thinking that
>seemed to be more in the vicinity of focus.

I think you both are right (if I percieve the image correctly).

As I see it, the drummer is kneeling and the photographer was standing. If that's the case then the camera is pointed down at about a 20 degree angle, placing the plane of focus at angle instead of perpendicular to the floor.

If thats the case then with image 1009, if the focus point was placed where the red dot indicated then the focus plane would extend from the floor just in front of the drummer through his mid-section to the top of the keyboard support beam.

Again if that is the case then with the narrow DOF it would indicate a short coming in technique and not a camera error/fault.

Pete

Pete

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nrothschild Silver Member Neil is an expert in several areas, including camera support Nikonian since 25th Jul 2004Wed 08-May-13 05:24 PM
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#35. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 34


US
          

Good point, Pete. At 19.5 foot working distance (per the EXIF focus distance) and f/2.8 at 70mm, the DOF is 12 inches behind and 13 inches in front of focus. Raises questions.

The 70-200 was shot with VR *off*, per the EXIF. The 1/100s shutter speed is marginal per the general 1/fl rule of thumb, adjusted for DX but applicable only to screen size viewing, not drilling into the image.

So there are potential issues of camera shake, subject motion, and even DOF here. That is why I suggested that "stop sign" test. Which would hopefully be done in bright light within 2 stops or so of sunny/16, at lower ISO and reasonable shutter speeds.

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Neil


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doppler_fto Registered since 23rd Mar 2013Thu 09-May-13 08:55 AM
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#36. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 35


US
          

nrothschild: Thanks a lot for the stop sign suggestion. I had considered trying to do some repeatable tests, but couldn't figure out what kind of test might be useful, given that I can't (yet) reliable predict when this behavior will occur.

That said, as mentioned elsewhere in this thread, I think the following link explains my decision to hand-hold without VR at slow shutter speeds:
http://blog.doppler-photo.net/2008/08/17-hours-of-street-photography.html


kuzzy: thank you for the compliments; I appreciate it.

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nrothschild Silver Member Neil is an expert in several areas, including camera support Nikonian since 25th Jul 2004Thu 09-May-13 09:57 AM
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#37. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 36
Thu 09-May-13 10:09 AM by nrothschild

US
          

Hi Omari,

I see a huge difference between the quality of the images in that blog and the images you posted. Not sure the point you are trying to make there.

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nrothschild Silver Member Neil is an expert in several areas, including camera support Nikonian since 25th Jul 2004Thu 09-May-13 10:40 AM
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#38. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 36
Thu 09-May-13 10:42 AM by nrothschild

US
          

Let me put it another way. You made available 6 NEF files. In at least 5 of the 6, your subject of interest is obviously moving, and you shot these at a shutter speed very susceptible to subject motion

In the 6th image (701_1009), focus was not where it should have been- the subject's face.

None of the images are razor sharp anywhere. You did a credible job (with one exception) under the circumstances but I don't think it's "good enough" for these purposes, simply due to the circumstances and challenges of that venue.

That is NOT an assessment of your skills. It is simply a statement that this is not a good set of images for the purpose of supporting your claims.

I don't think you got the point I tried to make about "extraordinary claims" and "extraordinary evidence". If you want to find agreement with your claims, you need to eliminate all doubt on our part, and you cannot expect others, via forum discussions, to thread fine needles while assessing a problem like this. You need slam-dunk impeccable images. That simply cannot be done hand held, in a poorly lit room, of obviously moving subjects, at 1/100s and 80mm.

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FutureLook Silver Member Nikonian since 30th Dec 2003Thu 09-May-13 11:38 AM
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#39. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 38


Miami, US
          

Sorry to see that you have experienced this back focus problem. I have shot many pics with mine in combination with my 18-300 without any problems. My first experience was in Costa Rica where I put this camera and lens through a wide variety of conditions and it came out smelling like roses. I used just about any focus combination that the camera can offer and I was amazed with the accuracy. I have plenty to see in my website showing the quality and great performance of this camera.

Visit my website: http://www.futurelookphotography.com

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doppler_fto Registered since 23rd Mar 2013Thu 09-May-13 06:12 PM
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#40. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 38


US
          

Just to be clear, I am absolutely in agreement that a repeatable test would both be even more convincing and would also help qualify what exactly is happening.

>Let me put it another way. You made available 6 NEF files.
>In at least 5 of the 6, your subject of interest is obviously
>moving, and you shot these at a shutter speed very susceptible
>to subject motion

The point of my previous response was to demonstrate that I have sufficient dexterity that hand-holding at 1/80s is no big deal. The self-portrait was 80mm at 1/15s with no VR and was fine.

Given that the post was 5 years ago, it should also suggest that, as I typically shoot at these shutter speeds, I am very familiar with how well or poorly a camera should focus at these shutter speeds. The D300 would knock 'em out all day long.

>In the 6th image (701_1009), focus was not where it should
>have been- the subject's face.

I'm not an idiot. I wasn't expecting the camera to focus on the guy's face when the focus point was clearly on his abdomen. I was expecting the camera to focus on his abdomen, though, which it did not.

>None of the images are razor sharp anywhere. You did a
>credible job (with one exception) under the circumstances but
>I don't think it's "good enough" for these purposes,
>simply due to the circumstances and challenges of that venue.

I think the disconnect here is that I see no real link between the quality of the final image and the AF performance during the capture of that image. Yes, I've been posting images that aren't very good. And? The fact of the matter is that the images are poorly-focused in such a way that the AF system is clearly focusing on something that isn't the intended subject.

Think about it from this perspective: The D7100 AF system is rated to operate down to -2 EV. ISO only affects the image sensor, and so high-ISO noise or noise-reduction blurring do not impact the AF system whatsoever. Moreover, all of the sample images were taken at well above that minimum light level. Even in cases where the subject is moving, AF-C should be tracking that moving subject. I mean, that's why I picked AF-C instead of AF-S. That's why I paid for two of the fastest-focusing lenses in the Nikkor lineup. And I can assure you that my D300 behaved as expected — plenty of noise, but the focus was dead on.

So the point is that I don't see how anyone could look at 0517, or 3898, and conclude that the AF system is doing the right thing. The shutter speed that I choose doesn't magically cause the AF system to focus on the background. (And even if it did, 3898 is in bright sunlight, and the central focus point is above an _extremely_ high-contrast target).

>That is NOT an assessment of your skills. It is simply a
>statement that this is not a good set of images for the
>purpose of supporting your claims.
>
>I don't think you got the point I tried to make about
>"extraordinary claims" and "extraordinary
>evidence". If you want to find agreement with your
>claims, you need to eliminate all doubt on our part, and you
>cannot expect others, via forum discussions, to thread fine
>needles while assessing a problem like this. You need
>slam-dunk impeccable images. That simply cannot be done hand
>held, in a poorly lit room, of obviously moving subjects, at
>1/100s and 80mm.

I am a mathematician and an engineer. I understand your point. Moreover, I write test-related software for a living, so I also understand the concept of a minimal test case. But I also understand that a sufficient burden of proof can demonstrate that a problem exists, even if it doesn't fully narrow down the cause of the problem. I believe that the test images (and associated context from my explanations) demonstrate that something is misbehaving with the AF systems on my D7100 cameras, although I don't yet know what it might be.

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nrothschild Silver Member Neil is an expert in several areas, including camera support Nikonian since 25th Jul 2004Thu 09-May-13 06:32 PM
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#41. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 40


US
          

There are two reasons I think image quality matters...

1. A generally sharper image in good light would have more clearly delineated the DOF. It just makes it easier to assess the image.

2. In a very general sense, many here have been here a long time, and over that time have seen dozens if not hundreds of "camera focus error" threads.

And I suspect most have, like me, noticed that images taken in similar situations, with complaints of focus hardware problems, more likely than not turn out to be operator error. It is purely a statistical thing. And remember, we do not know you. You are relatively very new here.

Now, you have a very difficult swim against a roaring current if you are trying to convince anyone that you have a camera problem and that problem is a fundamental design problem shared by all D7100's.

That leaves only one possibility: If you believe your specific camera has a problem then I'm not sure why it is important that you get "group confirmation" on that. Send it in for repair. Perhaps after doing my "Stop Sign Test".

You are fully convinced that your expertise is such that you cannot be doing anything wrong. That only leaves one of the two options above, I think?

I'm just trying to come to some conclusion here without going round and round with what has already been said. I'm really trying to help, as is everyone else participating here.

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nrothschild Silver Member Neil is an expert in several areas, including camera support Nikonian since 25th Jul 2004Thu 09-May-13 06:37 PM
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#42. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 40


US
          

An afterthought to answer some questions...

The reason I think shutter speed matters is that I would prefer to isolate motion blur from focus errors. It simply cannot be clear to me exactly how out of focus your moving subjects are. Just basic test procedures. Separate and isolate variables and work with one at a time.

If I thought your images didn't display some sense of a *potential* problem I would not have suggested testing real verses reticle focus sensor position. Everything else I said about image quality was to encourage you to isolate those variables like low or poor light, shutter speed, and etc.

I'm not sure why this argument is continuing. I think you need to do that test and then come back with the results. Forget the last set of images. Go forward

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nrothschild Silver Member Neil is an expert in several areas, including camera support Nikonian since 25th Jul 2004Thu 09-May-13 09:47 PM
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#43. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 40


US
          

>> ...I wasn't expecting the camera to focus on the guy's face when the focus point was clearly on his abdomen. I was expecting the camera to focus on his abdomen, though, which it did not.

Regarding that image 701_1009...Now that I have more time to fully respond to this...

There are at least two of us here, who think the carpet is in sharpest focus at just about your subjects knees, or perhaps a few inches in front.

That is probably consistent with the 20 degree downward shooting angle previously suggested. And if we are correct that that point in the carpet is in focus, then the subject's abdomen, on which you focused, is also likely in focus.

Now, if the carpet immediately in front of the subject is in focus, why is the abdomen "out of focus"? If it's really in focus, as we believe, it must be a tiny touch of motion blur softening it up. And if something is moving, which? The subject or the carpet?

That is why I questioned the 1/80s shutter speed. You may not have moved when you shot that self portrait 5 years ago, but perhaps your subject did?

If you disagree with the above then please tell me where you think the carpet is in best focus. If this is an example of your camera "background focusing" then it must be in sharp focus somewhere well behind your subject. If you can find that sharp carpet then maybe you will have a convert.

One other important question. During the 7+ hour interval spanning just those images, you shot well over 400 frames. What percentage of the images have the problem you report?

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doppler_fto Registered since 23rd Mar 2013Sun 12-May-13 11:24 PM
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#44. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 0


US
          

A Breakthrough


Okay, after another frustrating start to a shoot yesterday, I finally figured out a large part of what's going on.

The breakthrough was that I noticed that I get out-of-focus images when manual focusing as well as when auto-focusing. Since the numbers in my viewfinder are sharp (demonstrating that my dioptre is set properly), this almost definitely means that my mirror angles are mis-calibrated.

See here for how Phase-Detect AF works:
http://photographylife.com/how-phase-detection-autofocus-works

Note that the secondary mirror is hinged off the back of the main mirror (and if you carefully open your DSLR while it's off and flip the main mirror up, you can see the secondary mirror flip up behind it). So if the main mirror angle is off, the secondary mirror angle may also be off.

Assuming the secondary mirror is off, that could easily cause the image to be misaligned with respect to the AF sensor. This could explain why the camera appeared to focus on the background so frequently — the part of the image falling on the selected AF sensor wasn't the part of the image that should have been hitting it.

But wait...


That said, an interesting aspect of this problem in my case is that it appears that the AF system and the focus screen are calibrated the same. That is, when I AF on a subject, that subject appears to be in focus when looking through the viewfinder. If I manual-focus on a subject, it appears to be equally well in-focus.

It's unclear what exactly that means. One extremely unlikely possibility is that the image sensor is the wrong distance from the lens mount. Another extremely unlikely possibility is that the AF is calibrated via some mechanism that attaches through the viewfinder (or, perhaps more likely, they assemble the mirror box, stick it into the calibration rig, and then stick it into the camera frame?). I really don't know, but it certainly feels like more than coincidence.

So, what now?


At this point, I have a definitive testcase which clearly demonstrates that one of my cameras is seriously miscalibrated (and the other is probably more subtly miscalibrated). I'll probably do some small tests (like swapping lenses) to see what I can see, but really, I'd love to have some confidence in the AF system when shooting, so it'll be off to Nikon pretty soon. I'll probably send one-at-a-time just so I'm not without a low-light option in case anything comes up while it's gone.

If my current hypothesis is correct, then I believe I should see the accuracy of manual-focus differ at different heights in the incoming image, so I'll double-check that. I'll also try using all of the AF sensors to see if there are any strong correlations there.

If you have any other tests you'd like me to do, or alternate hypotheses, please let me know. I haven't yet, but I'm still planning on running nrothschild's stop sign test as well.

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JosephK Silver Member Fellow Ribbon awarded for his excellent and frequent contributions and sharing his in-depth knowledge and experience with the community in the Nikonians spirit. Nikonian since 17th Apr 2006Sun 12-May-13 11:52 PM
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#45. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 44


Seattle, WA, US
          

When you are manually focusing in these tests, what are the "focus dot" and rangefinder arrows telling you?

---------+---------+---------+---------+---------+
Joseph K
Seattle, WA, USA

D700, D200, D70S, 24-70mm f/2.8, VR 70-200mm f/2.8 II,
50mm f/1.4 D, 70-300mm f/4.5-5.6 VR, 18-70mm f/3.5-4.5 DX

  

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doppler_fto Registered since 23rd Mar 2013Mon 13-May-13 12:47 AM
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#47. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 45


US
          

Great question. Which leads to an unsatisfying answer: I'm really confused.

Now that I'm home, I tried replicating a behavior that was obvious yesterday, and now it's not happening. It feels like there's some relevant variable that I'm missing.

Anyway, I'll keep trying to repro and then answer your question. Part of what's so confusing is that the whole thing seems to behave so inconsistently. If it were just back-focusing, or just focusing on the background or (be still, my beating heart) just working properly, it'd be pretty straightforward to figure out what's going on. Instead, it appears to be some combination of the behaviors.

nrothschild: your question definitely touches on consistency, and I'm sorry I haven't been able to answer it yet. I'm only just getting time to go through photos (including the ones from yesterday's shoot, as well as the ones you mentioned). Definitely on my list, though, because I'm really confused.

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nrothschild Silver Member Neil is an expert in several areas, including camera support Nikonian since 25th Jul 2004Mon 13-May-13 12:54 AM
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#48. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 47


US
          

If the AF is mis-calibrated then it will misfocus with the same unerring consistency that it has when it focuses correctly for most other people. Just food for thought.

Also consider that your NEF samples came from both your bodies. More food for thought.

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nrothschild Silver Member Neil is an expert in several areas, including camera support Nikonian since 25th Jul 2004Mon 13-May-13 12:35 AM
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#46. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 44


US
          

You did not answer the question I posed:

"During the 7+ hour interval spanning just those images, you shot well over 400 frames. What percentage of the images have the problem you report?"

I think the answer is important, in light of your current thinking.

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asoka Registered since 14th May 2013Tue 14-May-13 10:10 PM
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#49. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 46
Tue 14-May-13 10:15 PM by asoka

RO
          

Hi!
I own an d7100 from the first date when was shipped on 14 march. I have some 10000 photos taked in all possible condition.
I noticed the same predilection of focus jumping to background...even in most easiest condition for it in high contrast full daylight. In single point, single focus and with many focus confirmations in a row before taking the pictures.
Even on the old d7000 I noticed something similar.
With the both body I was in trouble to obtain focus consistency in controlled condition with reikan focal on his focus target.
I have owned an d5100 an d7000 (that in the second day of purchasing was sended in service for calibration and returned with -25 compensation writed in firmware) and now an d7100 and on all the bodies the focus was inconsistent and hard to control...
Another thing on d7100 with brand new tamron 70 300 usd ...when I put external flash on the hot shoe ...bang major back-focusing (when the light is dim enough) take off the flash bang everything is ok...
And another ugly problem...banding...a lot of banding if u take -2,-3 underexposed jpg-s...like an blue storm sky just when the sun is going under horizon and try to capture the dramatic deep blue dark clouds.

  

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doppler_fto Registered since 23rd Mar 2013Wed 15-May-13 05:52 AM
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#51. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 49


US
          

Hey, asoka. When and where did you get your camera? Also, if you don't mind sharing, what's the serial number? Mine are 2500702 and 2500845.

For others: I'm off gathering more data, so all quiet on the western front.

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km6xz Moderator Awarded for his in-depth knowledge in various areas, including Portraits and Urban Photography Nikonian since 22nd Jan 2009Wed 15-May-13 05:25 AM
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#50. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 0


St Petersburg, RU
          

I think this thread has run its course and no new information can be gleaned from the test files offered.
If you would like to set up a less variable infused test that isolates AF or now you say some were manual focus, from the other uncontrolled conditions, feel free to post another question in a new thread.
Be sure to post the images in the thread instead of requiring people trying to help to download 100mbs of files on another site.

Getting used to the camera and the vast differences in resolution over your D300 will likely be the key element in coming to a satisfactory conclusion to this problem. Personally, I feel there is no problem, just too many marginal conditions and settings to get what you intended. The very slow shutter speed for example, might have been fine on a D300 or D90 but you are using a camera with much higher resolving power which means motion blur will be seen at low speeds that is not seen by 12mpx and smaller sensors at the same speed.


Stan
St Petersburg Russia

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km6xz Moderator Awarded for his in-depth knowledge in various areas, including Portraits and Urban Photography Nikonian since 22nd Jan 2009Wed 15-May-13 08:44 AM
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#52. "RE: D7100: AF focuses on background a lot?"
In response to Reply # 0


St Petersburg, RU
          

I am locking this thread since it had wandered off of the original question and new questions should be asked in a new thread so readers and responders can follow the new topics easier.
Stan
St Petersburg Russia

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