What essential conceptual structure, foundational to later film photography, did Herschel introduce alongside the term 'photography'?

Answer

The distinction between negative and positive

Herschel introduced the terms 'negative' and 'positive,' establishing the distinction essential to understanding nearly every photographic process invented since the 1840s, allowing for infinite reproduction.

What essential conceptual structure, foundational to later film photography, did Herschel introduce alongside the term 'photography'?
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