Hi, Ed,
Thanks. Very interesting.
The technique is really a guide to know what level of detail will be discernable in the foreground for any given aperture when focus is set to full infinity.
This can also be calculated by my out of focus blur performance spreadsheet, available here:
http://doug.kerr.home.att.net/pumpkin/OFB_calculator.xls
It will show you, for focus at any distance (
e.g., infinity) the degree of blurring produced in the image for objects at any other distance. The blurring is quantified in terms of the diameter of the resulting circle of confusion (not to be confused with the maximum diameter of the circle of confusion that we consider allowable in depth of field calculations - the "circle of confusion diamater limit, or COCDL).
The COC diamater (C) is of course as it occurs in the image itself (on the film or digital sensor). You will need to conclude just what a certain size means by considering the size at which the image is expected to be viewed.
You can enter (as c) the COCDL (circle of confusion diameter limit) you consider useful in DOF calculations for the format size in use. Then the value B in right hand panel will interpret the COC diameter (for the blurring being studied) as a ratio to that COCDL (a concept pioneered by Leon Witwer).