Originally posted by keithlester F/8 and BE THERE
Handy rule that I've seen 8 million useless explanations for, plus the one it's actually referencing. At F8 on a fairly standard lens size from the film era, you can prefocus for just about everything that's in a useful range, so assuming you had appropriate film (or are set to an appropriate ISO rating), all you have to do is point & shoot without messing with the focus or waiting for the autofocus and maybe losing the shot.
With a 24mm lens (on a pentax DSLR or any other 1.5x crop camera) pre-focused to 12 feet at F8, your depth of field is "everything that's more than 6 feet away from you"
On a film camera it would have been a 35mm camera, and 12 feet would have gotten you everything from about 7 feet to about 41 feet away, which is a pretty reasonable distance for a 35mm lens. (focus to 17 feet and anything more than about 8.5 feet away is in focus).
For other lenses, the DOF varies, but the same basic concept is pretty sound.
There's a great calculator for it here:
Online Depth of Field Calculator
Also, for many lenses, they're at their sharpest across the board around F8.
Conversely, a lot of cameras either won't autofocus at F8 or can only autofocus slowly and in the center of the frame), so this can be *terrible* advice if you want to rely on autofocus and have one of those cameras (Not sure if Pentax is one of them... the mailman needs to hurry up with my camera so I can start playing with it! I've been waiting for it all day!)