This very right. In 'The theory of the photographic process, 4 th edition' T.H.James this subject has been treated in detail. Nrelson in the tone reproduction , clarifies that zones are an approximation only ( crude). Elsewhere in the same book it has been shown that a tone as perceived by the human eye is not a simple thing like a zone; it will depend on the microstructure. A microstructure that will seen in modern photographic optics. But the human eye fails to see that. This called: ' Do not believe your eye'. The eye is misleading. A modern lens is not misleading. PE uses crude for this difference.
Originally Posted by Photo Engineer
All this is nothing new. Leonardo da Vinci knew already that de 'invisible' details are important. His brushstroke inthe Mona Lisa are hairthin and 2mm at a maximum.