My previous blog post showed an analysis of the left field AF problems of my Nikon D800. Last week I managed to ship the camera to the Nikon Service Point in the Netherlands for re-calibration. I did send it on Monday, and I got it back on Friday, effectively 4 days.
This blog post shows the results of the calibration, and a summary of the extensive phone discussion I’ve had with the engineer that did repair my camera.
2. Nikon Service Point – before and after calibration
The calibration procedure is normally performed with a dedicated calibrated 50mm/f1.4D lens (at f2.2). The engineer also used a 24-70mm/f2.8 and 24mm/f.14 lens, as the problem is (reported to be) more explicit with those lenses. The test card being used is shown below, it is always photographed from the same camera position, where only the AF points are changed:
The underlying crops show the difference before and after repair (you can click on the picture for a full-sized version). The left side of the picture show the situation before calibration (from top to bottom it shows the star just above the middle based on using the left, middle and right AF point). The right side shows the accompanying situation after calibration.
50mm/1.4D @ f2.2
24-70/f2.8G @ 50mm/f2.8
24-70/f2.8G @ 24mm/f2.8
As you can see, the results show a significant improvement after calibration. Nevertheless, there are still visible sharpness differences. Look at for instance in the 50mm/f1.4 picture; the right-most AF point still shows some unsharpness compared to the left-most and middle AF-point. For the 24-70/f2.8G @ 24mm the results look close to perfect.
3. Nikon Service Point – discussion
Directly after the repair on Thursday, I was contacted by the engineer who took care of my camera. We did have 20 minute chat, discussing the nature and expectations of the repair. He did read my blog and some forum posts. He was certainly interesed in informing the community about the backgrounds of the re-calibration procedure, so he agreed (and kind of hinted) to share his info. He also provided example pictures of his calibration efforts on the flash card, that I could use for that purpose.
Nikon Service Point in the Netherlands was the first service centre being be able to successfully repair the AF problems by re-calibrating the AF fields separately. This re-calibration repair has been invented by them by means of a special constructed hardware setup. It is now deployed by Nikon to service centers world-wide.
Nikon does not inform the service centers about the root cause for the AF problem!!! The engineer assumes it is some combination of the lens, the focal length, the aperture, the subject distance, the mount, the mirror and the AF-unit, and small fabrication deviations on any of these components that add up to a malfunctioning AF-system. The reason why only one side of the focus field is affected is therefore not understood.
The engineer warned about the effectiveness of the repair. I shouldn’t expect optimal results for all possible lenses and their use-cases. Some of the reasons are:
- Focus shift; you can only optimize the AF for a lens for one specific aperture value for a lens.
- Focus deviation; for zoom lenses the optimal focus distance differs for different focal lengths (e.g., a 24-70/2.8 which is normally calibrated and AF-fine tuned at 70mm, but then has the tendency to front-focus at 24mm, so the results at 24mm are generally less good).
- Live view is always intrinsically better than mirror-based focus. “Many people seem to understand and accept that live view has a better performance than mirror-based autofocus, but they have problems to accept that mirror-based autofocus is worse than live view”.
He agreed that my camera definitely had an AF problem. He considered mine to be “moderately affected”, and has seen cameras that were much worse. He talked about a couple of cameras already served by him. Hence, the AF problem is a common problem! He also mentioned people sending in cameras that did not have a problem at all, with no example pictures whatsoever. Obviously, there are also plenty of proper working cameras out there!
When I asked about the expected improvements, he stated that the results would be unpredictable, and I did have to check for myself. I was advised to first AF-fine tune all my lenses again (most didn’t need any fine-tuning for the middle focus point), because the focus may have shifted due to the re-calibration.
When I asked whether my 85mm lens (working perfectly before) would be negatively affected after this repair, his answer was “probably yes, it will be worse”. This concerned me a bit (I’m more into >= 50mm photography), so that’s why I’ve fine-tuned and tested (almost) all of my lenses again. The results of that are shown in the next chapter.
4. My own test
Back to the bookshelf again. After AF fine-tuning my lenses, I’ve checked the sharpness for the left, middle and right AF points using live view and viewfinder based focus. The underlying crops now show the results for live view on the left, and mirror-based autofocus results on the right. Again, the left-most focus point is on the top, the right-most focus point is on the bottom. Although you’ll find some compression artifacts because of the jpg translation, the quality is sufficient for relative comparison.
85mm/1.4G, f2.2, AF-fine tune +5: looks perfectly fine, with some minor variations on the right-most AF point.
50mm/1.4G f2.2, AF-fine tune -5: looks perfectly fine, with some minor variations on the right-most AF point
24-70mm/f2.8 @ 24mm/f2.8, AF-fine tune +5: very little unsharpness left, a bit more unsharpness right. Overall pretty good.
24-70mm/f2.8 @ 50mm/f2.8, AF-fine tune +5: not fully sharp at the left AF point
24-70mm/f2.8 @ 70mm/f2.8, AF-fine tune +5: a bit on the soft side everywhere, which is a property of the firstname.lastname@example.org, less sharp at the right AF point.
14-24mm/f2.8 @ 14mm/f2.8, AF-fine tune 0: suffers from front-focus at 14mm, and less sharpness at mid and right.
14-24mm/f2.8 @ 24mm/f2.8, AF-fine tune 0: good sharpness overall.
Overall the sharpness is not 100% accurate in all cases as predicted by the engineer at Nikon Service Point. There is however a significant improvement of the camera before it was repaired. I would call the repair an 85% success, much better, but not “perfect”.
5. Comparison with my D700
Many people claim that the D800 resolution is the cause for the sharpness issues. Comparison shows this is certainly not the case. I’ve performed similar tests on the D700, and for comparison I’ve scaled down the D800 images to D700 resolution, The following pictures shows crops from the D700 on the left side, and the D800 on the right side. As can be seen, the D700 shows consistent sharpness overall, the D800 does not.
This makes the idea of re-calibrating the 14-24 lens a bit suspicious, as how would it react on my D700 after repair? I’ll ask for advice at the NSP before drawing any conclusions.
The repair significantly improves the AF performance of the D800, and I can advice everyone who is impacted by the AF problems to send your camera to a Nikon Service Point.
The repair has some limitations though, there are still some sharpness variations, the significance depending on the lens.
My D700 shows more consistent results with the same lenses at a 3x lower resolution, and gives me a better confidence that I can rely on it for consistent AF. It’s a matter of time to see if daily usage of my D800 gives me a similar enjoyable experience before drawing a definitive conclusion about it’s current status.