Editing Hyperfocal distance (section)

===Hodges 1895===
John Hodges discusses depth of field without formulas but with some of these relationships:<ref>{{cite book |first=John |last=Hodges |title=Photographic Lenses: How to Choose, and How to Use |location=Bradford |publisher=Percy Lund & Co |year=1895 }}</ref>

{{blockquote|There is a point, however, beyond which everything will be in pictorially good definition, but the longer the focus of the lens used, the further will the point beyond which everything is in sharp focus be removed from the camera.  Mathematically speaking, the amount of depth possessed by a lens varies inversely as the square of its focus.}}

This "mathematically" observed relationship implies that he had a formula at hand, and a parameterization with the f-number or "intensity ratio" in it.  To get an inverse-square relation to focal length, you have to assume that the CoC limit is fixed and the aperture diameter scales with the focal length, giving a constant f-number.