Editing Hyperfocal distance (section)

===Piper 1901===
C. Welborne Piper may be the first to have published a clear distinction between ''Depth of Field'' in the modern sense and ''Depth of Definition'' in the focal plane, and implies that ''Depth of Focus'' and ''Depth of Distance'' are sometimes used for the former (in modern usage, ''Depth of Focus'' is usually reserved for the latter).<ref name="Piper1901">{{cite book |first=C. Welborne |last=Piper |title=A First Book of the Lens: An Elementary Treatise on the Action and Use of the Photographic Lens |location=London |publisher=Hazell, Watson, and Viney |year=1901 }}</ref>  He uses the term ''Depth Constant'' for {{mvar|H}}, and measures it from the front principal focus (i. e., he counts one focal length less than the distance from the lens to get the simpler formula), and even introduces the modern term:

{{blockquote|This is the maximum depth of field possible, and {{math|''H'' + ''f''}} may be styled the distance of maximum depth of field.  If we measure this distance extra-focally it is equal to {{mvar|H}}, and is sometimes called the hyperfocal distance.  The depth constant and the hyperfocal distance are quite distinct, though of the same value.}}

It is unclear what distinction he means.  Adjacent to Table I in his appendix, he further notes:

{{blockquote|If we focus on infinity, the constant is the focal distance of the nearest object in focus.  If we focus on an extra-focal distance equal to the constant, we obtain a maximum depth of field from approximately half the constant distance up to infinity.  The constant is then the hyper-focal distance.}}

At this point we do not have evidence of the term ''hyperfocal'' before Piper, nor the hyphenated ''hyper-focal'' which he also used, but he obviously did not claim to coin this descriptor himself.