Read about the Camera ISO noise tests in the help section to learn more about the tests and how they are conducted. A key take-away from that page is that noise reduction is completely off unless otherwise specified.
The files required to be downloaded to make all of the links in this review function properly are very significant in overall size - please be patient while they load.
Chuck Westfall emphasized that Canon's goal for the EOS 6D was cleaner pixel-level image quality. From what I'm seeing, they were quite successful.
Immediately noticeable in the comparison above is that the full frame sensors tested here deliver cleaner images than their smaller-sensored APS-C siblings. The Canon EOS 6D delivers noise levels similar to the smaller-sensor Canon EOS 7D and Canon EOS 60D at an ISO setting of over one stop higher. Compare the 6D's ISO 6400 to the 7D's ISO 3200 for example.
The Canon EOS 5D II is the camera that a lot of us have been waiting to compare the 6D to. In these results, it is not hard to see that the 6D indeed improves upon the long-time favorite. Up through ISO 400, it will be hard to see any difference in real-life results, but I start to see some 6D advantages starting at around ISO 800. The 6D advantage builds as the ISO setting increases. The difference becomes rather easy to see at ISO 3200 and the 6D's lead continues building until it leaves the 5D II in the dust at ISO 51200.
Obviously, the 6D has two stops of high ISO settings available that the 5D II does not have. Since the 6D's max shutter speed is 1/4000, I had to turn off two of the four hot lights to be able to step from ISO 25600 to ISO 51200 and had to narrow the aperture slightly for the ISO 102400 shot.
I again contend that these ultra-high ISOs are good for marketing purposes only. I don't know when I would have a use for images that look this bad. ISO 12800 and 25600 are still not looking very nice to me. I am shooting an indoor action event tonight - and expect to make heavy use of the 6D's ISO 6400 with an f/2 lens mounted. Update: had to go to ISO 8000. Images were noisy, but very usable at smaller print sizes.
The 5D III is a review-time-recent release. I have two of these bodies in my kit - and love what they do for me. But, I do think that the 6D is producing less noise than even the 5D III when compared at their native resolutions. You won't see much difference at lower ISO settings, but somewhere around ISO 800 to 1600, I can start to see a slight difference. The difference between these two cameras, even at very high ISO settings, is not significant enough to be a differentiator in my opinion.
The 6D up-sized images were output to 5D III resolution. The differences between these two cameras become harder to see at identical output resolution, but the 6D retains advantage at very high ISO settings. Other features such as price and AF systems are much more significant differentiators.
Differences in noise levels become easier to see when boosting image brightness during post processing.
As always, noise reduction is available via software - either in the camera or during post processing. Noise reduction is a destructive process - you throw some details away with the noise. I personally lean toward using only light amounts of noise reduction and show you such examples in the "6D NR" results.
Relatively new is Canon's Multi-Shot Noise Reduction. When using MSNR, four images are captured in a full-frame-rate burst with each shutter press. These four images are merged into a single JPG image in-camera. This is a great concept with solid improvement showing in the results - perhaps 1 to 2 stops of benefit in some comparisons.
Some of the downsides to Multi-Shot Noise Reduction include:
MSNR is currently available only with JPG output with oversharpened results using the Standard Picture Style with Sharpness set to only "1" (very low). I want MSNR added to DPP for RAW capture - perhaps as another HDR preset?
Multi-Shot Noise Reduction will not be so useful with moving subjects. Needing a still camera and still subjects removes some of the usefulness of this feature since you could just use a tripod and longer exposure at a lower ISO setting. Long exposure NR must be off to enable MSNR.
The 6D automatically reverts from MSNR to Standard NR in Basic zone modes, during video recording, in Bulb mode and when the camera is powered off. Flash is not supported in MSNR mode.
The camera remains "busy" for a brief period of time after the MSNR 4 shot burst - while it processes the merged image. Don't plan to take a quick follow-up shot.
Below is another comparison example that includes fine details. These samples were taken from the same shot and processing as described above. Fine details better-show resolution and better-hide high ISO noise.
The 6D delivers very clean results again in this comparison.
Notice that the Multi-Shot Noise Reduction samples do not appear oversharpened in the fabric area of the sample photo, but that many image details are being removed at higher ISO settings.
Back to the Canon EOS 6D Review.