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May 9, 2012

LumoLabs: Nikon D800 AA filter vs. D800E

MTF curves for the Nikon D800 and D800E SLR full frame cameras.
Taken in the center with a Nikkor 24-70/2.8G lens at 50mm f/4.0 and critically controlled perfect focus, using studio flashes. Images taken RAW and processed in Lightroom PV2010 with default settings except for no noise removal and different sharpening settings: D800 sharpened with 1.0 px radius and 100% amount, D800E sharpened at 0.8 px radius and 70% amount. This results in both images having the same 10-90% edge rise width (1.32 pixels) and almost the same MTF50 resolution.

Ever since Nikon announced that the D800 will come in two flavors, D800 with a Bayer-AA filter and the D800E without one, people wondered how large the difference would be and what version to get.

Obviously, the D800 is meant for APS-C and 35mm full frame SLR crossgraders as all current such cameras with a Bayer sensor have a Bayer-AA filter. While the D800E is meant for medium format (or Leica M9) crossgraders as all current such cameras have no Bayer-AA filter. The latter makes sense because of the high resolution of the D800/E which at 36 MP touches what once was medium format territory (40+ MP).

However, don't believe for a second that Nikon created the two versions for technical reasons. They have not. They created two versions to serve two separate markets. It is this simple. So, don't expect Nikon has any clue what camera would be the better one for you. All they'll try is ask you questions to figure out which market you belong to. Not their business, not really helping in your decision.
If you want to know what's really in the boxes and how it really differs, you have to measure it. 

Which is exactly what my friend Dieter Lukas from panobilder.de and myself did and now want to share with you. You obviously need both a D800 and D800E to study the differences ;)

Results

We have prepared a detailed report about our findings and testing procedures which you are invited to read:
In a nutshell:

We determined the exact MTF of the Bayer-AA filter in the D800 and deduced the strength of the beam splitter (which such an AA filter really is). We determined its strength in the Nikon D800 to be rather weak, around 75% of what would be a full strength filter.

As a consequence, the difference between a D800 and D800E isn't as large as one may think: in a controlled environment, the D800 images can be sharpened to the level of the D800E. The downside is that it can produce some false colors too, although less likely and to a lesser extent.

As a rule of thumb, we found that (assuming 100% amount, in Lightroom terms) subtracting about 0.5 px from the sharpening radius used for a D800 image produces comparable sharpness and acceptable results. In practice, one may of course combine this with a larger radius and lower amount etc. We summarize this into the following headline:
D800: E = 0.5px sharper

Meaning, that with ~100% amount sharpening, the D800E should deliver comparable results with ~0.5 pixels less sharpening radius, compared to a D800. This also means that one should not refrain from sharpening when using the D800E. Just use weaker settings.

Examples

Below are two test chart 100% crops for the D800 and D800E, using the different sharpening settings as described above. To compare samples with identical parameters, please refer to the full report.

Nikon D800 sharpened with 1.0 px radius and 100% amount in LR3.
The edge blur width is 1.33 px.

Nikon D800E sharpened with 0.8 px radius and 70% amount in LR3.
The edge blur width is 1.30 px. The Nyquist limit is near the figure denoted "6".
As you can see, the results are pretty similiar, with a bit more sarurated false colors and false color moiré in the D800E (as to be expected). But the D800 is able to show a bit of false color moiré too (a phenomenon known from the Canon 5DmkIII too).

In the real world, we found false color moiré from the D800E not to be problem. We only spotted it in a very few shots so far and here is one rare example where it occured to us in the wild:
100% crop from a D800E image exhibiting a false color moiré pattern.
(Please, click on the image for the full size original image)
.
Your mileage may vary if you shoot man-made patterns (fabrics, buildings) for a life. The choice is up to you but it is our impression that either camera represents an excellent choice where differences don't matter as much as some may think (this statement includes video applications too).


Thanks for stopping by,

Dieter & Falk
by 31 comments:

May 8, 2012

LumoLabs: Nikon D800/E outer AF sensor accuracy

We found the Nikon D800 and D800E to be wonderful cameras. But there are some reports floating around the web that the performance of the outer AF detectors is subpar. Especially with a fast and/or wide angle lens like 24mm f/1.4 or 14mm f/2.8 where it may be considered broken. Especially with the leftmost AF point. We decided to evaluate the issue with the scrutiny of a laboratory test. And to compare two samples to figure out if the issue is consistent across units or isn't.

And this is what we found ...

Results

Required AF finetune adjustment value for accurate focus depending on the focus point for one sample D800/E.
Required AF finetune adjustment value for accurate focus depending on the focus point for another sample.
In the charts above, the "floor" represents the layout of the 51 AF sensors of Nikon's Advanced MultiCam 3500FX module. We evaluated the performance of 5 out of these 51 focus points, positioned according to the yellow bars. The larger the bar, the larger the focus error without an AF finetune adjustment. The bar denotes the required AF finetune adjustment to compensate for the focus error. Measurement done at 24mm, f/2.8, tungsten light and with 1.2m subject distance.

We conclude that the issue with the accuracy of the outer AF focus points of the D800 is real and probably affects all units out there to some (varying) extent. It is said to be pronounced at ultra wide angles. However, we found it to be (just) unacceptable at 24 mm as well. We guess that every camera with the "Nikon Advanced Multi-CAM 3500 FX" auto focus module is affected, i.e., D800, D800E and D4.

We evaluated the characteristics of the sample variation of the issue and found that the cause may not be consistent across units. There may be a mixture of a tilt problem (such as caused by a misaligned AF auxiliary mirror, possibly independent of the focal length) and a parallax problem (such as caused by a decentered AF relay lens, possibly dependent on the focal length) where both components contribute with variable strength from sample to sample (our statements about possble causes are speculative, our statements about tilt and parallax errors and sample variation are not).
Therefore, we express our concern if the issue can be cured by a simple firmware patch. As far as we can see, such a patch would require at least two additional calibration parameters. We rather see many units undergo a thorough re-calibration job at Nikon.

Breaking news: According to www.nikonians.org/forums/dcboard.php?az=show_topic&forum=430&topic_id=7054&mesg_id=7054&page=#7303 , a Nikon service center has been able to calibrate the outer AF points of one unit, much in line with our findings which suggest that each camera has to be cared for on an individual basis. It remains to be seen what procedure Nikon will propose to customers in general though.

Meanwhile, we recommend to be cautious when using all but the center 15 cross type AF points for any work relying on critical focus, at least on the wider end of focal lengths.

Further reading:

We provide full documentation of the lab testing which my friend Dieter Lukas from panobilder.de and myself did in order to classify the D800 outer AF sensor issue. Please refer to:
We strongly suggest you follow the above material before asking questions which are answered already ;)


Update (2012, June 20):

As detailed in our full document (cf. above), we used FoCal software from Reikan to determine the AF adjustment values required for each focus point (we had to use a trick to work around the FoCal limitation to only test for center AF point accuracy). We actually recommend their software for normal AF lens calibration.

Interestingly, Reikan is now producing a version of FoCal which is able to test for the consistency of all AF point. We highly recommend all D800 users to aquire and use this software (when out) in order to check for their own camera. Read more about it here:
Moreover, please feel invited to share your (then accurate) findings in the comments section. Thanks.

Meanwhile, we have officially asked Nikon Germany for a press statement about the issue but have received none to date. We'll keep you posted.

Update (2012, June 24):

There is an interesting blog article from hifivoice:
reporting about the status of repair attempts by Nikon Service Centers, and how Nikon Netherlands has taken a lead in the absence of clear directions from Japan yet. It becomes clear that the issue affects many, although probably not most, cameras. And that currently, a fix exists which cures most, although not all of the symptoms of the issue.


Enjoy the read and thanks for stopping by,

Dieter & Falk
by 8 comments:
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