To illustrate how much dynamic range you can pull out of the shadows in RAW conversion with the Canon EOS Mark III's images we have taken the base ISO RAW shots of our studio test scene and developed them in Adobe Camera RAW with a +3.0EV digital exposure compensation to lift the shadows. We've then taken crops in the darkest areas of our scene to compare the level of shadow noise on the EOS 5D Mark III, its predecessor, the Mark II, and its arguably closest rival, the Nikon D800. Applying the digital exposure compensation makes shadow noise more visible and at 100% magnification it becomes clear that the Nikon D800 produces noticeably less shadow noise than the two Canons which are on a similar level.
|Canon EOS 5D Mark III||100% crop|
|Canon EOS 5D Mark II||100% crop|
|Nikon D800||100% crop|
Take a look at the real-life sample below to see what the test above means in day-to-day shooting. The image below was taken on a sunny day against a bright sky without any exposure compensation which resulted in a nicely exposed blue sky but an underexposed subject. The hull of the plane is very dark with very little visible shadow detail. Converting the raw file in ACR 6.7 and applying some 'Fill light' brightens up the subject, bringing out color and detail, but there is also a lot of chroma noise in the affected image areas.
|JPEG - default||ACR 6.7 - Fill Light 60, NR default|
|JPEG - NR Off / Sharpness 5||100% crop|
Unfortunately, at a pixel level the 5D Mark III's low ISO JPEG output looks a little soft and mushy with poorly rendered low-contrast detail. For example the camera's JPEG engine seems incapable of of rendering the subtle contrast required to represent the texture of distant foliage. We suspect this is mainly due to the application of luminance noise reduction (even with noise reduction switched to 'Off') at base ISO. The results you can achieve from the same image files in raw conversion (see below) would support this suspicion.
|JPEG - default (NR Standard / Sharpness 3)||100% crop|
|JPEG - NR Off / Sharpness 5||100% crop|
|ACR conversion - custom sharpening||100% crop|
The sample above was taken with the 28-70mm L-lens at F10 and default JPEG settings (NR Standard, Sharpness 3). We then re-processed the raw file in-camera with noise reduction switched off and the sharpness increased to level 5. Despite Canon saying in the manual that noise reduction is applied at all sensitivity levels the former has, at base ISO, no visible impact on the rendition of low-contrast detail or other aspects of image quality.
Increasing the sharpness gets you a little more 'crispness' in the image but no additional detail is revealed. You also get a quite unpleasant 'digital' look with visible sharpening halos in some image areas (look of the white flowers of the tree in the center of the frame). Overall playing with the camera's JPEG parameters can help tuning the JPEG output toward your personal taste but none of the settings are capable to reveal the sensor's true potential.
This can only be done by processing your images in a raw converter. The last image above was processed in Adobe Camera Raw with custom sharpness settings (amount 33, radius 0.5, detail 81) and the difference to the out-of-camera JPEGs is staggering. The fine sharpening reduces artifacts and squeezes a significant amount of additional low-contrast detail out of the camera's raw files. In the 100% crop above the individual needles of the tree have become visible and the rendition of other fine detail such as the grass in the foreground has visibly improved.
Admittedly you only need to be concerned about pixel-level detail if you want to display your images at large sizes or crop them significantly, but in any case, if you want the best possible image quality out of your 5D Mark III you will have to add an extra step to your workflow and process your files in a raw converter.
Overall Image Quality
When talking about the Canon EOS 5D Mark III's image quality you have to distinguish between the camera's JPEG output and the raw data it captures.
With its 22MP sensor the Canon EOS 5D Mark III is capable of capturing large amounts of detail but when examining the Canon's out-of-camera JPEGs at a pixel level it becomes clear that the JPEG engine isn't making full use of the sensor's potential. Even at base ISO some visibly destructive noise reduction is applied which results in a slightly mushy appearance of the image and a loss of fine low-contrast detail. Combined with a fairly aggressive default sharpening this means the Canon JPEGs can look a little over-processed up-close. At base ISO turning off the noise reduction does not make any difference and the in-camera sharpening parameter does not give you any control over the sharpening radius which means it's pretty much impossible to squeeze any additional detail out of the camera's JPEGs by modifying the image parameters.
Processing the camera's raw files however makes a big difference. Reducing the noise reduction and applying some customized, small-radius sharpening reveals unexpected levels of detail and shows what the 5D Mark III's sensor, in combination with a good quality lens, is really capable of. We've printed some ouf our sample images and in low-contrast detail the difference between a converted raw and out-of-camera JPEGs becomes visible in prints larger than 8x12in.
At higher ISOs the Canon EOS 5D Mark III continues to apply strong noise reduction which results in comparatively clean images but also a loss of fine detail. When shooting at ISOs lower than 25600 we would recommend to disable the in-camera noise reduction. This doesn't actually mean that no noise reduction is applied (even with NR disabled there is a base level that cannot be switched off) but it gets you some additional low-contrast detail. Only at the very highest sensitivities does the chroma noise become sufficiently intrusive to make the 'Standard' noise reduction setting the better option. Like at base ISO processing raw files can get you better results than the out-of-camera JPEGs. The 5D Mark III's raw noise levels are comparable to other cameras in this class and if you have the time, a customized mix of chroma and luminance noise reduction in post-processing gets you high ISO images with better detail and a more pleasant 'grain' than Canon's JPEG engine can manage.
Overall the Canon EOS 5D Mark III's JPEG output across the ISO range offers good colors, tonality and dynamic range with a very smooth highlight roll-off. Both metering and auto white balance are consistently reliable. However, if you want the maximum detail at a pixel level you have no other choice but to shoot in RAW mode and spend a little time processing the files. Ultimately we would expect a large proportion of the EOS 5D Mark III's 'target audience' to shoot and process raw anyway, not only to get maximum detail out of the images but also for the added flexibility that raw files offer when making more 'in-depth' tonal adjustments on a computer.