Olympus OM-D E-M5 Review
Olympus OM-D Dynamic Range (JPEG)
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-M5's lower noise levels than the 12MP PENs allow it to use a more gentle tone curve that offers greater dynamic range (because the bottom of the curve isn't so limited by shadow noise). The result is a camera that produces JPEGs with very competitive dynamic range, really making the most of what the sensor can capture. Switching Gradation to 'Auto' lifts detail out of the shadows, making it easy to create an image with a well-balanced tonal response, even in high contrast situations. And, indeed, in high contrast situations will lower the shutter speed to capture more highly detail and pull the rest of the image back up to the correct brightness.
The E-M5 is showing around 2/3EV more highlight range in the JPEGs than the PENs, or indeed the Panasonic G3, bringing it into line with the Sony NEX cameras. This is a significant improvement, and also means that you'll capture additional highlight detail when shooting RAW, unless you habitually override your camera's metering. This change is a sensible way for Olympus to optimize the use of the E-M5's improved sensor.
The E-M5's color modes have very little effect on its tonal response - only Portrait differs significantly, lifting the image brightness, adding a little contrast but with a gentle roll-off at both ends of the curve to prevent harsh jumps at either the highlight or shadow end of things. Instead, the dramatic changes in tonal response are achieved through using either the Gradation control's High Key and Low Key settings, or via the adjustable tone curve of the camera - both of which can be combined with color modes.
The gradation settings on the camera are really used for two things: to adjust the tonal response in the image to maximise the use of the captured dynamic range (Using the tone-balancing Auto mode), or to apply High or Low-Key special effects. The High and Low-Key modes affect the camera's metering as well as tone curve - with High Key using a brighter exposure and adding a more aggressive roll-off to highlight, and the Low Key setting doing the opposite.
This graph shows what the High and Low Key settings do, if the camera is allowed to set its own exposure: for instance the High Key setting makes a brighter image ('middle grey' in the scene is rendered at a luminance level of around 190, rather than the roughly 118 you'd expect with the Normal setting), with a very abrupt 'shoulder' at the top of the tone curve pushing lots of bright tones to near-white.
With the camera's adjustable tone curve now made so accessible, it's easy to use this an a bit of exposure compensation to recreate the effect of the High and Low Key settings and, indeed, better tailor the effect to your subject. With this capability so accessible, the High and Low-Key settings are best seen as simple presets if not entirely redundant.
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