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 camera's clipped white point down to black (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' (defined as 50% luminance) 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 above middle gray the camera can capture before it clips to white. Shadow range is more complicated; in our test the line on the graph stops 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-M10's default 'Normal' tone curve is pleasantly S-shaped with graudal rolloffs on both ends. Gradation Auto takes a drastic approach to shadow tones, though unlike previous Olympus cameras, doesn't necessarily change from the baseline exposure.
Low key and high key are exposure shifts rather than dynamic range expansion modes. Low gives preference to highlight tone, with a tone curve similar to 'Normal' shifted to the right in the chart above, and slightly more detail in the sky visible in our real world shot. High key shifts exposure for an extra stop or so in shadow tone, just losing the top of the Space Needle in the shot below as it clips the sky in highlights.
The real-world demonstration of dynamic range modes shows that Auto produces a somewhat flat-looking, lower contrast image than Normal mode produces. High and Low Key show their respective tone curve shifts, with High just losing the top of the Space Needle in highlights, and Low giving preference to the highlights in the background and the bright blue sky.
In the widget above you can seethe E-M10's default JPEG tone curve compared to those of the Canon EOS Rebel T5i/700D, Nikon D5300 and Panasonic GM1. They're all very closely matched, though the E-M10's includes slightly more tone before clipping to either extreme.
The E-M10's offers a base ISO of 200, with an extension to 100 below it. As seen in the comparison below, using the extension mode comes at the cost of a significant amount of highlight tone. Push processing the Raw files should reveal less noise if you attempt to brighten the ISO 100 image's shadows, but this difference is likely to be minor.
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