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.
'Optimize Image' presets
As you can see from the graph below the different 'Optimize Image' parameter presets do deliver different dynamic range / tone responses, this is as we would expect as they do obviously also adjust the gamma curve and contrast. The Softer setting delivers quite a bit more shadow detail and a flatter high tones response. None of these settings however change the highlight range (that above middle gray) which was always around 3.3 EV.
In addition to presets you can manually adjust image parameters. Here we have tested the extremes of the contrast setting from -2 to +2. As you can see the -2 setting does indeed deliver quite a bit more shadow range (because it lifts shadows above our cut-off point) but does not extend highlight range.
ISO Sensitivity and Dynamic Range
We were pleasantly surprised by the D40X's performance, it delivers a solid eight and a half stops of dynamic range virtually all the way from ISO 100 to ISO 800. That's over half a stop more than the D40, 0.4 EV of that in the all important highlight range (which could be the difference between getting a blue sky or a white washout). It just goes to show that dynamic range isn't just about pixel pitch it's also about sensor technology, we presume the 6 MP sensor in the D40 is 'older tech' than the 10 MP sensor in the D40X.
|Sensitivity||Shadow range||Highlight range||Usable range|
|ISO 100||-5.2 EV||3.3 EV||8.5 EV|
|ISO 200||-5.2 EV||3.3 EV||8.5 EV|
|ISO 400||-5.1 EV||3.2 EV||8.3 EV|
|ISO 800||-5.1 EV||3.2 EV||8.3 EV|
|ISO 1600||-4.3 EV||3.2 EV||7.5 EV|
|ISO 3200||-3.0 EV||3.2 EV||6.2 EV|
Dynamic Range compared
The graph below tells a very interesting story, the D40X delivering approximately the same overall dynamic range as the Canon EOS 400D and more than the D40. The biggest advantage however came over the Olympus E-410 which scored about two thirds of a stop (0.7 EV) less highlight range than the D40X.
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 you can see from the graph below there's at least another stop of extra information available, the overall gain using our 'Best' settings was almost three stops (including extra shadow information).
- ACR Default: Exp. 0.0 EV, Blacks 5, Contrast +25, Curve Medium
- ACR Best: Exp. -1.0 EV, Blacks 0, Contrast -50, Curve Linear
WARNING: One thing to bear in mind is that 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.
|ACR default conversion||ACR with -2.00 EV digital exp. comp.|