Maximizing Dynamic-Range

2013.02.06

All cameras have a limited dynamic-range which they can capture in a single shot. Exposure is there mostly to choose which slice of a scene's dynamic-range makes it into an image. Everything brighter gets overexposed (clipped to white) and everything darker gets underexposed (clipped to black).

How much dynamic-range a digital camera can capture depends both on the particular camera and the settings used. Tests sometimes indicate that over 14 stops of dynamic-range can be captured but that is under ideal conditions. The primary control over how much dynamic-range gets recorded is ISO sensitivity.

The lowest native ISO for your digital camera has the greatest dynamic range. In most cases, the lowest ISO available is the native ISO but there are several cameras with a few lower ISO settings. The native ISO represents the intrinsic sensitivity of the image sensor. For most digital cameras it is 100 or 200.

Another setting which affects dynamic-range comes in different names. Canon calls it Highlight Tone-Priority while Pentax calls it Highlight Expansion. In either case, this setting influences the exposure system to capture a darker image and delays the clipping of highlights. Note that at the same time, shadows get clipped earlier because the exposure simply shifts. For RAW files, exactly the same amount of dynamic-range is captured. For JPEG images, more dynamic-range gets preserved during the internal conversion.

A RAW file keeps all that data. If you shoot JPEG, the data gets transformed according to your image parameters. To get the most dynamic range in JPEG mode you need to find which mode keeps the most dynamic range. This is usually one of the low contrast modes such as Natural or Muted, depending on the brand of camera.

While the suggestions above above allow the camera to keep the most dynamic-range. A few things can be done to maximize how

much dynamic-range is seen by the camera:

• Avoid flare. Veiling flare occurs when too much light bounces around inside your lens and causes a drop of contract. Use a lens hood and avoid strong light sources in the frame or just outside.
• Choose the right angle. The same scene can show much more dynamic-range from certain angles. Usually the trick is to find the angle when the scene contrast is high but still lower than the limit of your sensor (except for Exposure Fusion and HDR of course). If the sun is behind you, a scene gets illuminated evenly for the most part which results in less dynamic-range because the shadows are behind your subjects.
• Avoid extreme apertures. This only makes a tiny difference but it's here for completeness. Wide open lenses get soft. This also happens past the diffraction limit. When that happens, contrast gets reduced cause a slight loss of dynamic-range in the shadows.

Finally, if you cannot beat them, join them, as they say. Sometimes working with excessive dynamic-range can emphasize aspects and allow for more creativity.

• Digital Photography