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 camera's) 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
As it is now common the K200D offers a Dynamic Range optimization feature. It is called D-Range and is designed to expand highlight range. It's got no effect on shadow detail and only works from ISO 200 to 1600. By using a higher sensitivity the sensor's photosites don't 'fill up' as much as they would at ISO 100. The resulting 'highlight headroom' can then be used by applying a tone curve that is flatter in the highlight area.
D-Range doesn't appear to interact with the camera's exposure metering, so users who shoot exclusively in RAW mode will not see any effect (it's a post-shot processing step so it only appears in JPEGs). The included software doesn't allow you to simply apply D-Range to RAW files. Pentax Photo Laboratory, which is based on Silkypix, features a highlight compensation slider which unfortunately does not appear to alter the image in any way.
As you can see in the graph enabling D-Range at ISO 200 gives you approximately one stop of additional highlight range. The sample shots below demonstrate what difference this makes in real life. We exposed both shots to get some detail on the brickwork of the dark tunnel. Naturally this results in an overexposure of the buildings you can see outside. As you can see in the crops D-Range managed to recover quite a bit of highlight detail that would otherwise have been lost.
|D-Range disabled||D-Range enabled|