BTZS is based on incident metering because measuring ambient light is not subjective but an absolute. Basing an exposure on a reflected reading always involves some degree of subjectivity.
Originally Posted by Flauvius
One can not actually take an ambient meter reading of non-accessible objects so you must assume that the light falling on it is of the same quality as the light falling on an accessible object in a similar lighting situation. This usually works well enough but not always. If in doubt I will take a reflected reading on non-accessible objects as a check on the assumption.
The basic advantage of using the incident system in photographing outdoors is that it is less prone to misinterpretation than reflected readings. The result is that it is virtually impossible to make a serious mistake in exposure which ensures a higher percentage of negatives that have received optimum exposure, at least from a technical point of view.
The disadvantage of the incident system is that it does not lend itself quite as well to interpretative metering as the zone system, at least on the surface. But people who understand BTZS find ways to creatively apply the system.
Most people who use BTZS came to it after first using the zone system and tend to use both systems depending on circumstances. That is true in my case. I used the zone system for years before learning BTZS and don't hesitate to take a reflected reading if I think it will help make a better negative. But for the great majority of situations the incident system is kind of a no brainer because the results are so consistent and reliable.
Last edited by sanking; 09-18-2004 at 03:38 PM. Click to view previous post history.