I recently bought a depth of field calculator. Until I bought it, the rules I used were: Buy really fast glass for portraits. If very close to my subject (maybe 3-5 feet or so), use 2.8 aperture on my 50mm. If a little further away, use f/2 or 1.4. That's as scientific as I got and the results were basically fine--well, sort of, but I wished for more control.
So, after I got my DOF calculator (for iPhone), I started doing some calculations. It appeared that I could, in fact, stand at 3 feet from my subject and shoot at f/8 and still knock my backgrounds out of focus and, at the same time, keep more of my subject in focus.
Tried to test my new-found knowledge and discovered that, standing 3 feet away from my subject and shooting 2 nearly identical shots at f/2.8 and f/8, the background blur was much stronger with at f/2.8. This is even though the background was "at least" 4 feet away from my subject and the DOF for both f/2.8 and f/8 were in the inches...not feet. Going to redo the test with the background considerably farther away (distance between subject and background much further than focal-plane to subject distance), but not anticipating vastly different results.
So, it looks like I need to go back to my original rules (use 1.4, 2 and 2.8 exclusively for portraits...regardless of what some calculator says).
So, here's my question: what have you found? Are most of you isolating subjects at only the widest apertures, or is there some way to use smaller apertures at close distances to subjects?