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
As we have previously seen the various Picture Styles use either one of two tone curves, the first more contrasty curve for Standard, Portrait, Landscape and Mono and a slightly flatter curve for Neutral and Faithful Picture Styles. Neither curve delivers more dynamic range and they both clip highlights at the same point.
Highlight Tone Priority is a feature designed to deliver more highlight range. It's available via C.Fn II-5 and, once enabled, the usable ISO range becomes ISO 200 - 12800 (ISO 100 is no longer available). In this mode the camera must be applying slightly less gain than normal combined with a different tone curve to deliver exactly a whole stop (1.0 EV) more highlight range, though as our real world examples later in the review show, don't expect miracles.
ISO Sensitivity and Dynamic Range
Although noise cuts the shadow range above ISO 1600 the EOS 500D's JPEG dynamic range (and tone curve) is pretty consistent across the range. The highlight range actually increases very slightly from ISO 3200 upwards but there's so much noise in the images you would hardly notice.
|Sensitivity||Shadow range||Highlight range||Usable range|
|ISO 100||-5.1 EV||3.4 EV||8.5 EV|
|ISO 200||-5.1 EV||3.5 EV||8.6 EV|
|ISO 400||-5.1 EV||3.5 EV||8.6 EV|
|ISO 800||-4.9 EV||3.6 EV||8.5 EV|
|ISO 1600||-4.9 EV||3.6 EV||8.5 EV|
|ISO 3200||-3.0 EV||3.8 EV||6.8 EV|
|ISO 6400||-3.0 EV||3.8 EV||6.8 EV|
|ISO 12800||-2.4 EV||3.6 EV||6.0 EV|
Dynamic Range compared
The EOS 500D is slightly lagging behind the competition in terms of highlight range in JPEGs. Both the Nikon and Olympus have almost a 2/3 EV advantage over the Canon. To a large degree this is due to the default tone-curve applied to the JPEG output but nevertheless at standard settings the competitors produce more highlight detail than the 500D. All in all though there is not an awful lot between these cameras with the best performer, the Olympus E-620, producing just 2/3 EV more than the Canon (most of this being at the shadow end). As the graph below clearly shows the EOS 500D is almost identical to its predecessor, with the only significant difference being a touch less highlight range.
|Camera (base ISO)||
|Canon EOS 500D||-5.1 EV||3.4 EV||8.6 EV|
|Nikon D5000||-4.8 EV||4.0 EV||8.8 EV|
|Olympus E-620||-5.3 EV||3.9 EV||9.2 EV|
|Canon EOS 450D||-5.1 EV||3.6 EV||8.7 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 or 1.5 EV (one to one and half stops) or so 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 but we have added a Canon Digital Photo Pro (DPP) conversion for comparison.
As you can see the default JPEG, the default Adobe Camera RAW conversion and the default DPP conversion all produce very similar tone curves, all of them clipping highlights at the same point and only slight differences in terms of shadow range (JPEG delivers slightly more than ACR and DPP default). The best we could achieve was just over 11 stops (11.1 EV) of total dynamic range, more importantly just over a stop (1.0 EV) of of the additional dynamic range is in highlights (although with no guarantee of color accuracy).
- ACR Default: Exp. 0.0 EV, Blacks 5, Contrast +25, Brightness 50, Curve Medium
- ACR Auto: Exposure -0.85 EV, Recovery 7, Brightness 0, Contrast 0, Curve Medium
- ACR Best: Exposure -1.35 EV, Brightness 105, Contrast 0, Curve Linear
- DPP Auto
The 500D did an average job when it came to recovering detail from highlights that would be clipped in JPEG shots. Pretty often you get some detail back even applying up to 3 EV of negative 'digital exposure compensation' but most of the time one or more of the color channels had clipped which resulted in color inaccuracies.
On the first two examples you can see how the negative 'digital exposure compensation' brings a lot of detail back but there is a purple color cast. The last shot is admittedly an extreme example but it shows that when things go completely wrong (and that's exactly what they did in this shot) even a -4.0 EV correction won't save you any highlight detail.
|Adobe Camera RAW default conversion||Adobe Camera RAW with -3.0 EV digital comp.|
|Adobe Camera RAW default conversion||Adobe Camera RAW with -2.0 EV digital comp.|
|Adobe Camera RAW default conversion||Adobe Camera RAW with -4.0 EV digital comp.|