The article I referred to is by Ctein, not Mike Johnston. An opinion that Johnston's blog is "pretty" doesn't make Ctein wrong.
I posted this: http://www.apug.org/forums/forum206/...tml#post824775 to a similar thread earlier, which was a way of checking the stated 'rule' against the depth of field spreadsheet provided by Schneider Optics. It supports Ctein's observations.
There are apparently a couple of folks posting to this thread who are on my ignore list, so I should bow out and let you guys carry on. No need for me to create a lot of confusion and cross-talk. People who are concerned can research things for themselves.