The Zone System is a method used to take a scene as it appears to the eye and create an image to reflect the artist’s vision of it by controlling the exposure of lightness and darkness values. It’s a great method for achieving the highest dynamic range possible in one exposure, or to determine the proper way to composite an High Dynamic Range (HDR) image from multiple exposures. This will allow you to achieve correct, ideal exposures. It can be applied to film or digital in black & white or color.
Use the following scale for guidance in differentiating between the different values. Each zone is an increment of one stop.
In order to apply the Zone System, you must look carefully at your scene and decide what objects fit into the middle value, Zone V. Figure out what Zone you are metering on. To your camera, anything you meter on will be considered Zone V and the meter will give you settings for that. The point is to match what you visualize in the scene as belonging in Zone V with what the camera will capture as Zone V, or middle gray. You want the objects in the scene to fall into their designated zones as follows:
Zone 0: Darkest Shadows, night sky
Zone I: Very dark shadows.
Zone II: Pure black/dark surfaces, first instance of detail.
Zone III: Dark shadows, dark surfaces with textures: cloth, plastic, paper.
Zone IV: Blue sky, dark green foliage, shadows on dark skin or dark surfaces.
Zone V: Gray card, dark skin, green foliage, shadows on light skin & surfaces.
Zone VI: Average skin, yellow foliage, light stone.
Zone VII: Very light skin, soft shadows on white surfaces.
Zone VIII: White surfaces with textures: Paper, Sand, Snow, Cloth.
Zone IX: Pure white surfaces in direct light. On the digital scale this zone is synonymous with Zone X and appears pure white.
Zone X: Reflection highlights, direct sources of light.
For example, if you meter on a dark object that falls into Zone III, then you will have to compensate the exposure by stopping down by two [-2] stops. The reason being that the camera will give settings that will shift the Zone III objects into Zone V and cause over-exposure. To correct this, and move the Zone III objects back into Zone III you must adjust your settings to be 2 stops darker [Zone III - Zone V = -2 stops]. If your camera were exposing for Zone VII tones then you would need to adjust the exposure by two stops [Zone VII - Zone V = +2] to avoid under-exposure.