The scenes and objects in the world around us contain an infinite range of colours and tonal values (brightnesses). In order to make it easier to interpret and visualise this vast range of brightnesses, Ansel Adams proposed that the infinite continuous tone range from pure black to pure white should be divided into 11 discrete steps, each step to be twice as bright as the previous step (moving from black towards white). Hence, each step is 'one stop' different from it's immediate neighbour.

He also proposed that the middle step in this 11 step sequence should be the same brightness value as the Kodak 18% grey card (this is now universally known as 'middle grey').

Ansel Adams called the steps 'zones' and named the complete sequence from black to white, the Zone Scale. He also gave each step on the scale a unique number to make it easy to identify and visualise. He began with black as Zone O and white as Zone X. The other zones are numbered according to their relative position on the scale. See image below. Middle grey is always Zone V. Ansel Adams proposed the use of Roman numerals for clarity when referring to the zone scale (this takes a little getting used to at first but soon becomes intuitive).

The full zone scale is from Zone O (Full black) to Zone X (Pure white). Within this full scale are two important zone ranges that you should become very familiar with, the first is the 'dynamic range' which is the range of zones from Zone I to Zone IX. The second is known as the 'texture range' which is the range of zones from Zone II to Zone VIII. The flashing red boxes on the graphic below show the limits of these scales.

Click on each zone above to see a description of that zone and examples of what subjects are likely to be represented by the zone.

Note: It helps to understand the descriptions of the zone values if you visualise the grey scale in three parts, Zones O to III are low values (dark areas), Zones IV to VI are middle values (where most detail is seen) and Zones VII to X are high values (light areas).

Note the use of the term 'high values' for the lighter zones. This is to differentiate them from 'highlights' (which many people incorrectly assume are the high values) which are actually 'specular highlights' i.e. direct reflections of the light source. An easy example of a highlight is the intense reflections seen on the surface of a lake looking into the Sun. Highlights are ALWAYS pure white in a print (they usually fall on zone XI or above). It is important when discussing the zone system that we use the correct terminology so that other system users know exactly what you mean!