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Archive 2015 · AF repeatability

  
 
patrick04
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p.1 #1 · p.1 #1 · AF repeatability


I bought my first DSLR a few years ago -- a D7000 -- and I've never been fully satisfied with the autofocus capabilities. The more I shoot it, the more I notice that the AF doesn't seem to be very repeatable.

I was doing some informal testing in the backyard today by taking pictures of the same subjects over and over again (re-focusing with AF between shots) and I noticed that only about 50% of the shots appear to be in focus. Others were a bit front-focused, and some were a bit back-focused, by enough that the subject appeared to be soft/not sharp on the LCD when zoomed in. Is this par for the course with AF? Or should I expect better repeatability? I don't have a good point of reference since I've never used any other DSLR.

(I used both the Nikon 35 f/1.8 DX and the Sigma 17-50 f/2.8 OS for my informal tests, in AF-S mode. The tests were outdoors in good light. They both behaved very similarly in terms of AF repeatability. All the shots were hand held, but I was careful to lock focus and not move the camera before releasing the shutter.)



Mar 22, 2015 at 07:48 PM
workerdrone
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p.1 #2 · p.1 #2 · AF repeatability


I've had better results leaving it in AF-C personally, can't remember the last time I actually used the S mode. I use back button and usually keep it held down while shooting


Mar 22, 2015 at 08:07 PM
SiMuMe
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p.1 #3 · p.1 #3 · AF repeatability


My D7000 AF behaves like that. Under testing, I can put it on a tripod and not move it one inch between shots but it still won't give repeatable results. Very noticable when you are used to bodies that don't behave that way.

Having said that, when I have used the camera in anger(e.g. event work) I've had enough keepers that this doesn't concern me. So, I just do less analysis and more shooting .



Mar 22, 2015 at 09:00 PM
Steve Perry
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p.1 #4 · p.1 #4 · AF repeatability


I had a D7000 and I don't recall the AF being unreliable. You might want to have it serviced. All my current Nikons (a pair of D810s and D4) are spot on each and every time. Missed AF is usually my fault.


Mar 22, 2015 at 09:06 PM
sjms
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p.1 #5 · p.1 #5 · AF repeatability


i think it has something to do about understanding and learning how to use the AF system under various situations too. patterns to use under what light and scenario.
review D7000 manual pgs 91-98 to start with the basics.



Mar 23, 2015 at 07:52 AM
CanadaMark
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p.1 #6 · p.1 #6 · AF repeatability


Do you have some samples with EXIF data? It's hard to diagnose anything based on your description.

Also, phase detect AF by nature will not be 100% the same every time you focus, but it should be very close. I second the recommendation to only use AF-C, as it will correct for minute movements both on your part and the subject's part if applicable, which could be enough to throw the image out of focus at wide apertures.

If you're really worried, set up some controlled tests using a tripod and a remote. Compare PDAF results to CDAF (live view) at a medium distance (10 ft or so) as a quick way to check AF consistency.



Mar 23, 2015 at 11:10 AM
trenchmonkey
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p.1 #7 · p.1 #7 · AF repeatability


My in focus rate is >98%...in ANY light.
It's all about the settings with over 200K
clicks on D7K's, you can trust me on this.

edit: FWIW I've never used AF-S, ever.
Sounds like you need to blow out the AF
sensor slits. That'll jack up repeatability.



Mar 23, 2015 at 11:18 AM
patrick04
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p.1 #8 · p.1 #8 · AF repeatability


Interesting idea to get it serviced. I'll keep that in mind if I can determine that the problem is not user error.

The D7000 manual was helpful in telling me what makes for a bad AF target, but it wasn't much help telling me what would make a good AF target for this kind of test. Any suggestions?



Mar 23, 2015 at 11:29 AM
patrick04
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p.1 #9 · p.1 #9 · AF repeatability


At this point I'm leaning toward user error/bad AF targets (I don't think it's the camera, but maybe it is). Dust might also be an issue. I'll try cleaning and then give AF-C a try with some new subjects.


Mar 23, 2015 at 11:32 AM
patrick04
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p.1 #10 · p.1 #10 · AF repeatability




Edited on Mar 23, 2015 at 11:33 AM · View previous versions



Mar 23, 2015 at 11:32 AM
patrick04
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p.1 #11 · p.1 #11 · AF repeatability





Mar 23, 2015 at 11:32 AM
wellsjt
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p.1 #12 · p.1 #12 · AF repeatability


Unless I missed it, I don't think you mentioned what AF mode are you using? Single point, dynamic, 3D, etc.? The auto modes where it chooses a focus point is often a recipe for incorrectly focused photos.

Also, you mentioned shooting some tests handheld. What were your shutter speeds like during this?



Mar 23, 2015 at 11:57 AM
patrick04
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p.1 #13 · p.1 #13 · AF repeatability


I was using AF-S with the single center point, and the shutter speed was in the 1/800 to 1/1600 range.

I'm going to do a second test with different subjects. I think that at least part of the problem is the subjects... But I'm still not sure what a good subject would be (although thanks to the D7000 manual, I know what bad subjects are).

I'll probably post some images soon with EXIF data if I can't resolve the problem by trying different subjects.



Mar 23, 2015 at 01:39 PM
runamuck
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p.1 #14 · p.1 #14 · AF repeatability


The ubiquitous brick wall is always popular.


Mar 23, 2015 at 01:54 PM
incrediblehark
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p.1 #15 · p.1 #15 · AF repeatability


It's been a couple years since I sold mine, but I agree with the others about AF-C performing the best on the D7000. I used 9 points and I kind of remember setting the A3 menu to "off" if I'm not mistaken.

Cheers,

Adam



Mar 23, 2015 at 05:53 PM





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