Sony SLT-A57 In-Depth Review
JPEG Tone Curves / dynamic range
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.
Note: this page features our new interactive dynamic range comparison widget. The wedges below the graph 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).
The SLT A57 uses the same default tone curve as current and recent Alpha models. This means you get about 4 stops of detail in the highlights, with a smooth roll off rather than harsh clipping; overall the default JPEG settings cover about 9 stops. The A57's various color mode options serve mainly as contrast and saturation adjustments. For a look at how they affect dynamic range, see our Sony SLT-A55 review.
The A57 offers Sony's now-familiar dynamic range optimization (DRO) settings in various strengths. The effect of these settings differs depending on the scene, so this test, performed using our 18 step wedge, isn't necessarily an accurate indication of 'typical' performance with a real-world subject. It does clearly show, however, the way in which DRO is designed to work, extending by increments the amount of mid tones by lifting shadow areas to get the most detail out of these areas in a single exposure.
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