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.
Dynamic Range Optimization feature
One feature we first saw introduced with the DSLR-A100 is 'Dynamic Range Optimization', designed to deliver lighter shadow areas by boosting the lower end of the tone curve. The A100 provided just three options (Off, Standard and Advanced), the A700 expanded this to Off, Standard, Advanced Auto and then five manual levels (Lv1 - Lv5). The A900 has the same options as the A700, although Sony says the algorithms have been improved.
As you can see from the graph below (using our standard step wedges test shot), like the A700, the A900 achieves this brighter shadow response by modifying the tone curve, each of its five levels enhancing this shadow boost - though the effect is less extreme than we saw on the A700. As you can also see from these plots the Standard setting had only a very small effect. Note that the big advantage to doing this kind of tonal manipulation in-camera is that it is applied to RAW data before it becomes a JPEG.
Creative Style options
The graph below shows the dynamic range response from each of the A900's thirteen Creative Styles. As you can se each has a very slightly different curve mostly due to changes in contrast and brightness for each. The important point to note here is that no single Creative Style delivers more dynamic range than the 'Standard' mode and of course because of more contrasty responses some actually deliver less.