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.
Offering about 9 EV, about 3.5EV of which is in highlights, the Pentax K-5 II has a curve that closely follows that of the Nikon D5200, while the Canon 650D - with its more compressed range, curves a little more subtly as it aproaches the highlights, but clips earlier. The Olympus E-M5, for its part, has a half-stop wider range and an even shallower curve in the highlights.
At default settings (Bright) the K-5 II's tone curve is more or less identical to its predecessor, the K-5. It measures a total dynamic range of 8.5 EV, just 3 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 incorporate 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.
Dynamic Range Modes
The K-5 II 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 of highlight range at the expense of approximately 2/3 stop of shadow detail.