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.
Color Mode setting
As previously noted the D40 uses the color mode IIIa by default which has very slightly more contrast than mode Ia as used on other Nikon digital SLRs such as the D80. As you can see from the graph below the difference is primarily in the shadow range and changing color mode does not alter the highlight range 'clip point'.
In addition to color mode there are also obviously a range of image parameters which can be adjusted, however only Contrast would affect the final image dynamic range. 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 steps above our cut-off point) but does not extend highlight range which is always clipped around 2.9 EV.
ISO Sensitivity and Dynamic Range
The D40 delivers almost eight stops of dynamic range at ISO 200 and 400, dropping to about seven and a half stops at ISO 800 because of increasing shadow noise. After this range drops progressively as shadow noise grows, note that the highlight range is always between 2.8 and 2.9 stops.
|Sensitivity||Shadow range||Highlight range||Usable range|
|ISO 200||-5.0 EV||2.9 EV||7.9 EV|
|ISO 400||-5.0 EV||2.9 EV||7.9 EV|
|ISO 800||-4.7 EV||2.9 EV||7.6 EV|
|ISO 1600||-4.0 EV||2.8 EV||6.8 EV|
|ISO 3200||-2.1 EV||2.8 EV||4.9 EV|
Dynamic Range compared
As you can see the D40 has the same shadow range as the Canon EOS 350D (Digital Rebel XT) but clips the highlight range earlier. Compared to the K100D it delivers more shadow range with as good as identical highlight range (well 0.1 EV advantage to the K100D to be more specific).
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. We normally use Adobe Camera RAW for this comparison however as, at the time of writing this review, it doesn't yet support the D40 we have instead used Nikon Capture NX.
As you can see from the graph and wedges below NX in default mode returns just slightly less dynamic range (nothing to be concerned about though). The best we could achieve was just over 10 stops total dynamic range (although with no guarantee of color in highlights).
- NX Default: Default settings
- NX Best: Exp. -2.00 EV, Tone: Low, Levels: 0/2.0/255
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 sky and roof but there is no color information so the sky turns from cyan to gray.
|NX default conversion||NX with -2.00 EV digital exp. comp.|