This was Geoffrey Crawley's summing up of the terms in his precis of his longer article on Film developers published in 1960/1 "Notes on Present-day Monochrome Emulsions and their Development".

" Sharpness " - the overall impression of a print or projected image, measured scientifically as "acutance ", seen from normal viewing distance.

" Definition " - the extent to which fine detail is recognisably rendered in a print, etc. When acutance of fine detail is good, then definition is good.

" Acutance " - the contrast at the edge of significant detail, a scientific measurement of the density gradient at that point.

" Resolving Power " - the scientific measurement of the actual fineness of detail recordable by a lens, film, or developer, or any combination of these three.