Zooms—The Silent Killer

Despite endless technological evolution, one photography convention has endured for more than a century: Our numbering system for lens apertures. That is, the familiar “f-stop” scale:

1.4   2   2.8   4   5.6   8   11   16   22

This sequence is admittedly peculiar-looking, and it always confuses beginners. Why do larger numbers mean smaller-diameter lens openings?

But as many of you are aware, these numbers are actually “f/ratios“—that is, they’re the ratio of a lens’s focal length to the aperture diameter. Setting a lens to f/4.0 means its aperture opening measures one-fourth of the focal length.

F/Ratio Definition