Incident metering is not restricted to simply matching normal film speed. Even in its most basic form it is not restricted to matching exposure to ISO (or 'factory') speed. It can be used to get a very good estimate of the scene or subject brightness range (what is also being called the 'contrast range' here). Minor White understood this - otherwise why would he have included it in the Zone System Manual. Like spot metering it needs to be used intelligently. Anyone with both types of meter, or a dual-purpose meter like the Sekonic L-508, L-758 etc, can do a comparison to see how incident metering can be used with the Zone System.
Best,
Helen
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