The Zone System - Part 2
Understanding Exposure Meters
Everything about exposure comes down to the amount of light reflected by objects. Exposure meters measure this light and provide exposure recommendations.
The industry has used a universal standard for exposure meter calibration - this is an important point to understand if we are to take full advantage of the zone system.
Light meters come in two general types: meters that measure what is called incident light and meters that measure reflected light.
Incident light meters measure the light that falls on the subject from the source of light.
Reflected light meters measure the light that bounces off the subject to the camera.
To use the zone system we need to use a reflected meter that not only reads the contrast of a scene but that is also able to read a small area of a subject.
Imagine you are photographing a landscape, (Picture above) if you use a wide-angle reflected meter, such meter will make it impossible to read specific areas of the scene accurately. You will be able to use a wide-angle meter if you can get close enough to the subject to measure the contrast.
Light meters have no way of actually seeing the objects they measure. An exposure meter is a device that measures quantities of light.
For example: On a bright sunny day a dark wall might read 1/60 sec at f/8 - but so might a light wall on a cloudy day. To our eye, the walls are very different but to the meter they both measure the same, 1/60 sec at f8.
The light meter is responding to the change in incident light, but our eyes seea great difference, the dark wall should print Zone lll and the light wall as Zone Vll. (This will be explained in part 3)
All light meters are programmed to give a 18% gray exposure for whatever amount of light they are measuring. So, in the Zone System language, all light meters will automatically place any reading in
Zone V - THIS IS A KEY POINT TO MEMORIZE.
In practice this means that if we get a meter reading of a dark tree trunk that would fall in Zone lll and accept the meter reading without adjustment, the result will be disappointing - the bark of the tree will print a lighter tone than what we see in reality because the light meter related that dark tree as Zone V, medium gray.
If on the other hand we are photographing a snow scene and take a meter reading of the snow - if we accept the meter reading we will get not white snow but a muddy gray snow for the same reason explained above.
So, in a sentence what this means is that the light meter sees everything in relation to Zone V .
