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 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.
Picture Style options
Surprisingly on the EOS 50D all Picture Styles now use an identically shaped tone curve. (On the 40D there was a slightly more contrasty curve for Standard, Portrait, Landscape and Monochrome Picture Styles and a slightly flatter curve for Neutral and Faithful Picture Styles). Highlights and shadows clip roughly at the same points for all tone curves as well, so changing Picture Styles does not impact on the dynamic range or contrast of your images.
Image Highlight tone priority
The 50D features the same Highlight Tone Priority option as its predecessor. It's available via C.Fn II-3 and, once enabled, the usable ISO range becomes ISO 200 - 3200. In this mode the camera must be applying slightly less gain than normal (hence the feature is not available at ISO 100) combined with a different tone curve to deliver just over a stop (1.1 EV) more highlight range.
ISO Sensitivity and Dynamic Range
The EOS 50D produced a fairly consistent dynamic range of about 8.5 EV from ISO 100 to 1600 dropping to 7.6 EV at ISO 3200 and to a minimum of 5.5 EV at ISO 12800 (due to shadow noise). However, highlight range is consistent (around 3.5 EV) up to ISO 6400. While the figures for the highlights are in line with the results produced by the EOS 40D the shadow range is reduced, due to increased shadow noise on the much more pixel-dense sensor.
|Sensitivity||Shadow range||Highlight range||Usable range|
|ISO 100||-4.8 EV||3.5 EV||8.3 EV|
|ISO 200||-4.9 EV||3.6 EV||8.5 EV|
|ISO 400||-4.9 EV||3.6 EV||8.5 EV|
|ISO 800||-4.9 EV||3.6 EV||8.5 EV|
|ISO 1600||-5.0 EV||3.5 EV||8.5 EV|
|ISO 3200||-4.0 EV||3.6 EV||7.6 EV|
|ISO 6400||-3.0 EV||3.4 EV||6.4 EV|
|ISO 12800||-3.4 EV||2.1 EV||5.5 EV|
Dynamic Range compared
As you can see, due to its relatively steep tone curve, the EOS 50D produced slightly less highlight range than the D300 and A700. In terms of shadow range it is on par with most of the competition (but lags behind the K20D and the EOS 40D). Despite the comparatively small measured highlight range the 50D manages a fairly soft 'roll off' at the highlight end which results in less hard-clipped looking white highlights.
|Camera (ISO 100)||
|Canon EOS 50D||-4.8 EV||3.5 EV||8.3 EV|
|Nikon D300||-4.7 EV||4.1 EV||8.8 EV|
|Pentax K20D||-5.8 EV||3.2 EV||9.1 EV|
|Sony DSLR-A700||-4.9 EV||3.9 EV||8.8 EV|
|Canon EOS 40D||-5.7 EV||3.4 EV||9.1 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 the default Adobe Camera RAW conversion delivers less dynamic range than JPEG from the camera (a more contrasty tone curve and less noise reduction in shadows). The best we could achieve was 11.6 EV of total dynamic range. This included 1.8 EV of extra highlight range.
- ACR Default: Exp. 0.0 EV, Blacks 5, Contrast +25, Curve Medium
- ACR Best: Exp. -1.0 EV, Blacks 0, Bright. 100, Contrast -50, Curve Linear
WARNING: 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 clip before others. This can be seen fairly clearly in the examples below. On the far right the 2.5 EV negative digital exposure compensation has revealed more detail in the clouds but has also generated a pinkish color cast. The first hint of the same discoloration is y visible in the central sample image where the negative digital exposure compensation was only 1.0 EV.
|Adobe Camera RAW default conversion||Adobe Camera RAW with -1.0 EV digital comp.||Adobe Camera RAW with -2.5 EV digital comp.|