Pentax K10D Review
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.
Image Tone setting
The K10D provides two selectable image tones which define the tone curve and color saturation. The default Natural and optional Bright tones deliver the same amount of dynamic range, albeit with a slightly different tone curve.
In addition to the image tone options there are also obviously a range of image parameters which can be adjusted, only Contrast would affect the final image dynamic range. Here we have tested the extremes of the contrast setting from -3 to +3. In the shadow region (below middle gray) we see that the -3 setting delivers more shadow information before our cut-off point, and as we would expect the +3 setting the opposite. No setting changed the amount of highlight range (that above middle gray) which always clipped at around 2.8 EV.
The K10D had a very strange, contrasty tone curve, a virtual straight line from middle gray upwards with almost no roll-off in highlights and (just like the K100D) a lower than average highlight range (about a third of a stop less than the competition). At higher sensitivities the total range becomes limited by the amount of noise at the darker end of the range (shadow range).
|Sensitivity||Shadow range||Highlight range||Usable range|
|ISO 100||-4.5 EV||2.8 EV||7.3 EV|
|ISO 200||-4.5 EV||2.8 EV||7.3 EV|
|ISO 400||-4.4 EV||2.8 EV||7.2 EV|
|ISO 800||-4.0 EV||2.8 EV||6.8 EV|
|ISO 1600||-3.7 EV||2.8 EV||6.5 EV|
Dynamic Range compared
Again the K10D's contrasty tone curve is even more obvious here, giving up around a third of a stop in shadow range and a third of a stop in highlight range it actually delivers less dynamic range than we were expecting to see (obviously you could use a lower contrast setting to compensate, although this would only gain shadow range).
|Camera (ISO 100)||
|Pentax K10D||-4.5 EV||2.8 EV||7.3 EV|
|Nikon D80||-4.8 EV||3.2 EV||8.0 EV|
|Sony DSLR-A100||-4.8 EV||3.3 EV||8.1 EV|
|Canon EOS 30D||-5.1 EV||3.3 EV||8.4 EV|
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. As with previous reviews we settled on Adobe Camera RAW for conversion to retrieve the maximum dynamic range from our test shots.
As you can see from the graph below the Adobe Camera RAW default is actually quite similar to the camera JPEG, if anything there's very slightly more highlight range. The best we could achieve (with some pretty extreme ACR settings) was just over 10 stops total dynamic range, and more importantly about a stop more highlight range (although with no guarantee of color accuracy in highlights).
- ACR Default: Exp. 0.0 EV, Shadows 5, Bright. 50, Contrast 25, Curve Medium (Default)
- ACR Best: Exp. -0.85 EV, Shadows 0, Bright. 70, Contrast -25, Curve Linear
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 but there is no color information so the sky suddenly turns from cyan to gray.
|ACR default conversion||ACR with -1.25 EV digital exp. comp.|
Dec 15, 2006
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