METERING AND THE ZONE SYSTEM

 

The zone system, championed by Ansel Adams and others as a means of establishing the exposure required for an image is usually thought of as relevant to black and white photography and perhaps also film. However it has it's uses in the digital colour world as well.

 

Many digital photographers on workshops I have been on can be heard commenting that the image they have captured does not look like the scene that they remember. This is most often the case when the scene involves a high dynamic range and they have been full sensor metering to make their exposure.

 

Lets look at the effect of the dynamic range. The human eye can discern about 22 stops of  dynamic range; the best camera systems at present are restricted to about 15 stops. So there is always more shadow or light detail that the sensor cannot capture.

PUT IN SCALE IMAGE

In camera metering comes in a number of different forms depending on the area being metered. The most common types are;

- Matrix (Nikon) or Evaluative (Canon) which meters across the whole scene.

- Centre weighted meters a small area of the scene

- Spot meters a single point in the scene

The important thing to remember when using matrix/evaluative is the cameras programming will try to accommodate the widest dynamic range range that it can, and according to the way it has been programmed it will make a determination where to place the maximum highlight and work back from that. This may not - probably is not - the optimum exposure for the scene.

 

So the first thing is to work out what is optimal exposure. Where the scenes dynamic range is within the scale supported by the camera this is straightforward. Where it exceeds the camera's capability the photographer has some decisions to make;

- whether to use HDR or blending in editing and to shoot the scene making exposure changes to capture the full dynamic range over a series of shots.

- if a single shot is the option chosen where to place the camera dynamic range on the scene dynamic range, whether to accept blown highlights or lost shadow detail.

 

Here matrix / evaluative metering can lead to some errors as the cameras program may prevent capture of the best possible image or series of images by not exposing for the critical areas the photographer wants.

 

So how to make the most of the cameras dynamic range and work out how to get the best RAW image to process and get the most information from. One thing to understand is how the digital sensor captures data (read about this here)

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