So here's an amusing bit of somewhat-related trivia:
Originally Posted by LiamG
On Nikon cameras, you can only set the aperture in 1/3 stop (or larger) intervals using the command dial. If you set the aperture with the aperture ring on the lens, then in principle you can set any f-stop, but the camera only reports full-stop changes. However, if you fix the aperture ring at wide-open aperture on a variable aperture zoom (or macro) lens, then as you zoom (or focus) in, the camera will report the true f-stop in much finer steps. For example, on my f/4.0-5.6 "plastic fantastic" zoom, I get true apertures reported as: f/4, 4.2, 4.5, 4.8, 5, 5.3, 5.6.