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-420's gradation setting produces images in low or high keys, it does so by both modifying the tone curve as well as the exposure. In our Dynamic range test we 'neutralize' the exposure compensation element by exposing manually in order achieve 'middle gray' on our selected step of the wedge. Therefore in the graph below you only see the impact of the tone curve adjustment. 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.
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.
The images below show a real world application of the Gradation setting. You can see that in the Auto setting the shadows are lifted while there is hardly any impact on the highlights. If you use the Olympus Master software to convert RAW files you can apply the same type of adjustment and control the strength of the effect. At the maximum setting you can see a large amount of image noise appearing.
|Gradation Normal||Gradation Auto||Olympus Master 100% tone correction|
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-410 delivers a total dynamic range of 8.2 stops. This drops to 6.8 stops at ISO 1600.
|Sensitivity||Shadow range||Highlight range||Usable range|
|ISO 100||-5.4 EV||2.8 EV||8.2 EV|
|ISO 400||-5.1 EV||2.8 EV||7.9 EV|
|ISO 1600||-4.0 EV||2.8 EV||6.8 EV|
Dynamic Range compared
Here you can clearly see the difference between the E-420 and the competition. While it is slightly better than the E-410 it is still not quite up to par with the competition. The E-420 offers roughly the same shadow range but has between 0.5 and 1.0 EV less highlight range than cameras such as the Nikon D60, Canon EOS 450D (Rebel XSi) or the Sony A350. Whilst you can counter this by reducing exposure when you take the pictures and lifting the shadows in post-processing, this does introduce noise issues.
|Camera (ISO 100)||
|Olympus E-420||-5.4 EV||2.8 EV||8.2 EV|
|Nikon D60||-5.7 EV||3.3 EV||9.0 EV|
|Canon EOS 450D||-5.2 EV||3.5 EV||8.7 EV|
|Sony A350||-4.9 EV||3.7 EV||8.6 EV|
|Olympus E-410||-4.5 EV||2.7 EV||7.2 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 tells 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.
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 -1.5 EV digital exp. comp.|
In comparison to other cameras in its class the E-420's RAW headroom is fairly limited and the samples below demonstrate this. Even a -3.0 EV negative exposure compensation in ACR can only get very little detail back into the bird's blown out plumage. The E-420 certainly does better than its predecessor when it comes to preserving highlights in JPEG exposures, but we'd suggest this isn't down to any improvement in the hardware itself, but is down to a more sensible tone curve.
|ACR default conversion||ACR with -3.0 EV digital exp. comp.|