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.
Picture Style options
As we have previously revealed 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.
Image Highlight tone priority
One feature new to the EOS 40D (although previously seen on the EOS-1D Mark III) is designed to deliver more highlight range. It's available via C.Fn II-3, once enabled the usable ISO range becomes ISO 200 - 1600 (ISO 100 and 3200 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 (0.9 EV) more highlight range, that's pretty impressive.
ISO Sensitivity and Dynamic Range
The EOS 40D produced a fairly consistent nine stops (around 9 EV) of dynamic range from ISO 100 to 1600 dropping to 7.4 EV at ISO 3200 (due to shadow noise). While these are higher figures (by some two thirds of a stop) than we are used to seeing from most other digital SLRs the EOS 40D's improvement is in shadow range, highlight range (that above middle gray) still clipping at around 3.4 EV. We can make some assumption that this improved shadow range is thanks to the new 14-bit processing pipeline.
|Sensitivity||Shadow range||Highlight range||Usable range|
|ISO 100||-5.7 EV||3.4 EV||9.1 EV|
|ISO 200||-5.7 EV||3.4 EV||9.1 EV|
|ISO 400||-5.5 EV||3.4 EV||8.9 EV|
|ISO 800||-5.5 EV||3.4 EV||8.9 EV|
|ISO 1600||-5.5 EV||3.4 EV||8.9 EV|
|ISO 3200||-4.0 EV||3.4 EV||7.4 EV|
Dynamic Range compared
As you can see the EOS 40D produced slightly more highlight range than the D200 and over a third of a stop more than the K10D. Its biggest advantage however is at the shadow end where it extends to almost six stops below middle gray compared to around five stops for the other cameras. The 40D also features a softer 'roll off' at the highlight end which will deliver less hard-clipped looking white highlights.
|Camera (ISO 100)||
|Canon EOS 40D||-5.7 EV||3.4 EV||9.1 EV|
|Nikon D200||-5.0 EV||3.2 EV||8.2 EV|
|Pentax K10D||-4.5 EV||2.8 EV||7.3 EV|
|Canon EOS 30D||-5.1 EV||3.3 EV||8.4 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 you can see the default Adobe Camera RAW conversion delivers less dynamic range than JPEG from the camera (a more contrasty tone curve and less noise reduction in shadows). The best we could achieve was nearly eleven stops (11 EV) of total dynamic range, more importantly almost a stop of that is in highlights (although with no guarantee of color accuracy).
- ACR Default: Exp. 0.0 EV, Blacks 5, Contrast +25, Curve Medium
- ACR Best: Exp. -1.0 EV, Shadows 0, Bright. 70, Contrast -50, Curve Linear
WARNING: Although ACR was able to retrieve the 'luminance' (brightness) of wedge steps which were previously clipped there's no guarantee of color accuracy as individual channels may clip before others. This can be seen fairly clearly in the examples below, on the right the negative digital exposure compensation has revealed some more detail in the background but this soon turns into gray as one or more of the color channels clips.
|Adobe Camera RAW default conversion||Adobe Camera RAW with -3.0 EV digital comp.|