Dynamic Range (contd.)

ISO Sensitivity and Dynamic Range

The Alpha 700 offered impressive dynamic range and the Alpha 900 pulls off the same impressive trick, managing to squeeze almost nine and a half stops into a JPEG in the ISO200-400 'sweet spot'. Now you may argue that some of this is down to the rather heavy-handed noise reduction giving Sony an unrepresentative advantage in the shadow region of the curve, but you can't argue with the A900's superb highlight range - well over four stops above mid-grey in the ISO 200-800 region.

At ISO 200 the A900 delivers almost nine and a half stops of dynamic range, more importantly that over four stops of this are highlight range (compared to the more typical three and a half stops for most DSLRs).

Sensitivity Shadow range Highlight range Usable range
ISO 100 -5.1 EV 3.5 EV 8.6 EV
ISO 200 -5.1EV 4.2 EV 9.4 EV
ISO 400 -5.1 EV 4.3 EV 9.4 EV
ISO 800 -4.7 EV 4.4 EV 9.1 EV
ISO 1600 -5.1 EV 4.1 EV 9.2 EV
ISO 3200 -4.3 EV 4.1 EV 8.4 EV
ISO 6400 -3.4 EV 3.8 EV 7.2 EV

Dynamic Range compared

At ISO 200 the A900's JPEG highlight range extends considerably further than either of the Canon models in our comparison and even manages to squeeze past the Nikon D3 thanks to its very gentle curve roll-off. We've been consistently impressed with Sony's ability to hold onto highlight detail and - as our real world experience with the Alpha 900 showed - the dynamic range has real, visible benefits in contrasty conditions.

Shadow range
Highlight range
Usable range
Sony DSLR-A900 (ISO 200) -5.1 EV 4.2 EV 9.4 EV
Canon EOS 5D (ISO 100) -4.7 EV 3.5 EV 8.2 EV
Nikon D700 (ISO 200) -4.4 EV 3.4 EV 7.8 EV
Nikon D3 (ISO 200) -4.7 EV 3.9 EV 8.6 EV
Canon EOS 1DS Mk3 (ISO 100) -5.1 EV 3.5 EV 8.6 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).

RAW headroom

Experience has told 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. As with previous reviews we settled on Adobe Camera RAW for conversion to retrieve the maximum dynamic range from our test shots.

As you can see the default Adobe Camera RAW conversion delivers less dynamic range than JPEG from the camera (a more contrasty tone curve and less noise reduction in shadows). Adobe's 'auto' setting increased dynamic range by just under 1.5 stops in the highlight region and just under a stop in the shadows. By flattening out the curve we were able to squeeze a total of 12.6 stops out of the sensor (of course a curve of this shape doesn't represent anything you'd ever use in real life but it does show the potential for digital exposure compensation when shooting RAW with the A900). All the lab results tied in with our observations when using the A900 in the field; JPEG dynamic range (and particularly highlight range in the region over 'mid gray') is excellent, and there's even more in the raw files if you need it. Impressive stuff.

  • ACR Default: Exp. 0.0 EV, Blacks 5, Contrast +25, Curve Medium
  • ACR Best: Exp. -2.65 EV, Blacks 0, Brightness + 114, Contrast -50, Curve Linear

WARNING: 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. In our tests with real world shots the A900 consistently allowed us to pull back up to 2 to 2.5 stops of highlight information from overexposed (and apparently clipped) scenes, though once you get to -3.0 EV very little color information is recovered (check out the -3.0 EV example at the bottom of this page and you'll see that going beyond -2.5 EV adds only greyscale information.

Adobe Camera RAW default conversion Adobe Camera RAW with -2.5 EV digital comp.
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Adobe Camera RAW default conversion

Adobe Camera RAW with -2.0 EV digital comp.

Adobe Camera RAW default conversion

Adobe Camera RAW with -3.0 EV digital comp.

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