Dynamic Range and the Zone System


Today’s Question: We hear about cameras having a dynamic range of 14-15 stops. Ansel Adams’ zone system was 1-10, I assume a form of dynamic range. I wonder how and where the elongation of the classic zone system has taken place? Also, how is the range determined?

Tim’s Quick Answer: Dynamic range has improved as a function of advancements in image sensor technology, with many cameras now offering greater dynamic than was possible with film photography. Note, however, that the zone system doesn’t truly relate to a specific dynamic range, but is rather more of a concept related to tonal distribution in an image.

More Detail: In the context of photography dynamic range is a measure of the range between the brightest and darkest values. For a digital capture the dynamic range indicates the number of stops of light between the darkest value and the brightest value that can be recorded in a single exposure.

We often think of the brightest value in a photo as being white and the darkest value as being black, but in reality it isn’t quite so simple. Think of the difference between “white” for an image that includes bright white clouds in the sky compared to a photo that includes the sun in the frame, which would be considerably brighter.

With film photography we were able to capture a range of around five stops with slide film and around eight stops with negative film. Today’s digital cameras are often capable of capturing a range of about ten stops, with the top cameras reporting a dynamic range of around fourteen stops.

There are a variety of factors that impact dynamic range capabilities for an image sensor, including the size of the individual photodiodes, microlens arrays used to focus more light at each pixel site, improved amplification technology that minimizes noise, and more. And, of course, you can create a photo that represents a greater dynamic range than a camera can record in a single photo by bracketing exposures and assembling them into a high dynamic range (HDR) image.

The zone system typically covers a range of eleven shades ranging from pure black (zone 0) to pure white (zone 10). I think it is fair to say that the emphasis of the zone was the photographic print, where zone 10 for example related to paper white. So, this isn’t a true measure of dynamic range in the context of variable photographic conditions, but rather how a scene was interpreted in the final print. Also, it is worth noting that even treating zone 10 as paper white is a little misleading, considering different papers will have a different effective brightness or whiteness value.

Because the zone system is something of an abstract concept rather than something directly tied to specific luminance values in the real world, the concepts related to the zone system can be applied to digital photography even though digital cameras have exceeded the capabilities of film in terms of dynamic range, and that the zone system was developed in the context of film photography before digital cameras had arrived on the scene.