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.
The E-520's gradation setting produces images in low or high keys, it does so by both modifying the tone curve as well as the exposure. The gradation setting does not have any impact on highlight dynamic range but using the low key option will slightly reduce dynamic range in the shadows, while the auto setting will increase it a little.
As you can see from the graph the auto mode does some serious lifting of the shadows. It can also introduce noise issues, and we'd advise shooting raw if you want to do this kind of tonal adjustment.
Here we have tested the extremes of the contrast setting from -2 to +2. As you can see the +2 setting does slightly decrease shadow range (-2 and normal settings are almost identical) but highlight range is always clipped around 2.8 EV.
ISO Sensitivity and Dynamic Range
Highlight range is consistent across all sensitivities but you lose some shadow range at ISO 800 and 1600. At base ISO the E-520 delivers a total dynamic range of 8.0 stops. This drops to 6.7 stops at ISO 1600.
|Sensitivity||Shadow range||Highlight range||Usable range|
|ISO 100||-5.2 EV||2.8 EV||8.0 EV|
|ISO 400||-5.1 EV||2.8 EV||7.8 EV|
|ISO 1600||-3.7 EV||3.0 EV||6.7 EV|
Dynamic Range compared
The Olympus E520 does make the expected step forward from the E510 (it's exactly what we saw with the E410/E420), but is still behind the other cameras in its class. The Sony A350 trumps them all, with the 450D putting in a pretty credible performance. The difference is around 1 stop and this is the kind of difference that you will see in real-world situations. This will result either in blown-out highlights or noisier shadows if you choose to under-expose and pull the tone curve about.
|Camera (ISO 100)||
|Olympus E-520||-5.2 EV||2.8 EV||8.0 EV|
|Canon EOS 450D||-5.1 EV||3.6 EV||8.7 EV|
|Pentax K200D||-6.0 EV||3.0 EV||9.0 EV|
|Sony A350||-4.9 EV||3.7 EV||8.5 EV|
|Olympus E-510||-4.6 EV||2.7 EV||7.3 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).
With many cameras, there's around an extra stop of dynamic range that can be pulled out of the raw files. This isn't really the case with the E520, which does a great job of including everything it is capable of, in its JPEGs. The downside is that this simply isn't as much as the competition.
The most we could achieve using Adobe Camera RAW was a total dynamic range of 9.4 EV although the last stop of this appears to have almost no color information.
- ACR Default: Exp. 0.0 EV, Blacks 5, Contrast +25, Curve Medium
- ACR Best: Exp. -1.25 EV, Blacks 0, Contrast -50, Brightness +85, 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 more detail on the chimney but because at least one channel has completely clipped we end up with a magenta cast to those 'recovered' areas.
|ACR default conversion||ACR with -3.0 EV digital exp. comp.|
The amount of additional detail than can be recovered from shooting RAW is distinctly limited. Beyond -0.5EV digital exposure compensation, no additional detail is revealed and that which is, is often clipped and suffers from distorted color. From a philosophical perspective, this is admirable, because it means JPEG shooters are getting all there is to get out of the sensor. Unfortunately, the E520 already lags behind the competition in terms of dynamic range in JPEG mode - this shortcoming is further exposed when well-processed RAW files are compared.