Pentax K-5 Dynamic Range (JPEG)
Our 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 clipped white point down to black (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' (defined as 50% luminance) 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 above middle gray the camera can capture before it clips to white. Shadow range is more complicated; in our test the line on the graph stops 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.
Custom image modes
At default settings (Bright) the K-5's tone curve is more or less identical to its predecessor, the K-7. It measures a total dynamic range of 8.5 EV, just 2.9 EV of which are in the highlights with a rather abrupt clip to white. The Bright, Natural, Portrait, Landscape, Vibrant, and BW settings use essentially the same curve and therefore produce the same amount of dynamic range. The Muted setting uses a more linear, less contrasty curve. Bleach Bypass and Reversal Film on the other hand create images with more contrast. However, all the settings clip highlights at the same point.
The tone curve remains essentially unchanged across the ISO range (all ISOs clip at the same point) but at higher settings shadow dynamic range is limited by shadow noise.
Expanded Dynamic Range Function
The K-5 features a highlight expansion function which applies to both JPEG and RAW; shadow expansion can also be applied to the camera's JPEG output. With Highlight correction activated ISO 160 becomes the minimum sensitivity setting, and the tone curve is flatter in the highlights giving an extra stop or so of highlight range. If you compare the K-5's dynamic range curve with hghlight correction turned on against the Nikon D7000's default output, you can see that they match almost exactly. Since the two cameras share closely-related sensors, this strongly suggests that the Nikon is essentially performing an equivalent to highlight correction by default. The noise floor of both cameras is low enough to do so without any serious penalty in noise levels, and for this reason we'd recommending keeping highlight protection activated on the K-5.
With our dynamic range test setup we could not trigger the K5's shadow correction functionality and therefore we can unfortunately not provide any measurements for this feature. In normal use, shadow correction has a very subtle effect, but it does help lighten shadows slightly in contrasty scenes.