Our new Dynamic Range measurement system involves shooting a calibrated Stouffer Step Wedge (13 stops total range) which is backlit using a daylight balanced lamp (98 CRI). A single shot of this produces a gray scale wedge from (the cameras) black to clipped white (example below). Each step of the scale is equivalent to 1/3 EV (a third of a stop), we select one step as 'middle gray' and measure outwards to define the dynamic range. Hence there are 'two sides' to our results, the amount of shadow range (below middle gray) and the amount of highlight range (above middle gray).
To most people highlight range is the first thing they think about when talking about dynamic range, that is the amount of highlight detail the camera can capture before it clips to white. Shadow range is more complicated, in our test we stop measuring values below middle gray as soon as the luminance value drops below our defined 'black point' (about 2% luminance) or the signal-to-noise ratio drops below a predefined value (where shadow detail would be swamped by noise), whichever comes first.
Highlight Tone Priority
In common with most of the latest generation of EOS SLRs the Mark III sports Canon's new Highlight Tone Priority, designed to deliver more highlight range. It's available via C.Fn II-3 and, once enabled, the usable ISO range becomes ISO 200 - 1600 (ISO 100 is no longer available). In this mode the camera must be applying slightly less gain than normal combined with a different tone curve to deliver almost a whole stop more highlight range. The difference is subtle in most real world cases, but as there doesn't appear to be any penalty for using it (beyond the reduced ISO range) it's worth leaving it on if you're shooting JPEG.
As we have previously seen the various Picture Styles use either one of two tone curves, the first more contrasty curve for Standard, Portrait, Landscape and Monochrome Picture Styles and a slightly flatter curve for Neutral and Faithful Picture Styles. Neither curve delivers more dynamic range and they both clip highlights at the same point.
The graph below shows how the camera's tone curve and dynamic range is affected by the wide range of contrast settings. The lowest contrast setting (-4) is almost linear for at least two thirds of the range and offers the widest dynamic range, but only by a whisker.
ISO Sensitivity and Dynamic Range
The EOS-1Ds Mark II has an indicated base sensitivity of ISO 100 and the top setting by default is ISO 1600 (ISO 50 is indicated as 'L', ISO 3200 is indicated as 'H'). As you can see from graph below the compromise at ISO 50 is highlight range which falls nearly a stop (0.9 EV) short of the highlight range seen from ISO 100 upwards.
Using the default JPEG settings the Mark III delivers somewhere in the region of 8.6 stops of dynamic range from ISO 200 to 800, dropping slightly at ISO 1600 and by more than a stop at ISO 3200.
|Sensitivity||Shadow range||Highlight range||Usable range|
|ISO 50*||-5.1 EV||2.7 EV||7.7 EV|
|ISO 100||-5.1 EV||3.5 EV||8.6 EV|
|ISO 200||-5.1 EV||3.5 EV||8.6 EV|
|ISO 400||-5.1 EV||3.5 EV||8.6 EV|
|ISO 800||-5.0 EV||3.8 EV||8.5 EV|
|ISO 1600||-4.7 EV||3.5 EV||8.2 EV|
|ISO 3200*||-3.7 EV||3.6 EV||7.3 EV|
* Non-standard sensitivities
Dynamic Range compared
There's a not a lot of difference between any of the cameras near the top of the market; all offer somewhere in the 8.5 stops region, with Canon's slightly harsher tone curve clipping highlights a little earlier. The older EOS 5D doesn't do quite as well in the shadows as the Mark III, but considering it was launched over two and a half years ago there's no shame in that.
|Canon EOS 1DS Mk3 (ISO 100)||-5.1 EV||3.5 EV||8.6 EV|
|Nikon D3 (ISO 200)||-4.7 EV||3.9 EV||8.6 EV|
|Canon EOS 5D (ISO 100)||-4.7 EV||3.5 EV||8.2 EV|
The wedges below are created by our measurement system from the values read from the step wedge, the red lines indicate approximate shadow and highlight range (the dotted line indicating middle gray).
Experience has told us that there is typically around 1 EV (one stop) of extra information available at the highlight end in RAW files and that a negative digital exposure compensation when converting such files can recover detail lost to over-exposure. As with previous reviews we settled on Adobe Camera RAW for conversion to retrieve the maximum dynamic range from our test shots.
As usual the default Adobe Camera RAW conversion delivers less dynamic range than JPEG from the camera (the same contrasty tone curve and very little noise reduction in shadows). Simply switching to 'Auto' in the ACR conversion dialog reaps huge rewards, increasing the dynamic range to around 10.5 stops. The very best we could get out of a raw file manually was around 11.3 EV, which is pretty good (though not quite up to the standard set by the Nikon D3 or the Fujifilm S5 Pro).
- ACR Default: Exp. 0.0 EV, Blacks 5, Contrast +25, Curve Medium
- ACR Auto: Exp. -0.1 EV, Recovery 33, Brightness 0, Contrast 0, Curve Linear
Although it won't bring back grossly overexposed shots the Mark III's sensor gives you more than a stop of usable headroom to play with if you shoot raw. As the examples below show, even at -2.0 EV you'll often get something usable (though if you look closely at the second example you'll see areas where the highlight are completely clipped). Note: all the samples below have been converted from raw at a reduced file size to speed up downloads.
|Adobe Camera RAW default conversion||Adobe Camera RAW with -1.5 EV digital comp.|
|Adobe Camera RAW default conversion||Adobe Camera RAW with -2.0 EV digital comp.|
Once you start to really push the files you start to see channel clipping but even so it's pretty impressive to be able to get even this much tonal detail out of a sky so heavily over exposed.
|Adobe Camera RAW default conversion||Adobe Camera RAW with -4.0 EV digital comp.|
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