First things first: We realized we should learn the definition of "f-stop" before setting out to find the origin of the term. We headed to the Yahoo! Education's Reference section where we searched the American Heritage® Dictionary for "f-stop" and found the following definition: A camera lens aperture setting that corresponds to an f-number. Okay, so now we knew what an "f-stop" was, but what about the origin of the f in f-stop? After a bit of research, we found several intriguing hypotheses about the origin of the term on the easy-to-search photo.net forums. One post references a biography of Ansel Adams, and attributes the italicized f notation to Adams himself, circa 1932. Sometimes f-stop (or f/stop) and f-number are used interchangeably to indicate the relative size of the lens opening. The f-number series is a geometric progression -- each number in the sequence is multiplied by a factor of 1.4. According to the Lens FAQ on photo.net, f-stop refers to both maximum lens aperture and to the aperture opening selected in a specific situation
for optimal brightness and depth of field. The term "stop" originated in the early days of photography when aperture opening was selected by turning a wheel with different sized holes to let more or less light reach the film. While we're on the subject, here's another handy factoid: depth of field decreases with larger apertures and increases when the f-stop is higher and the aperture smaller. Confused? Automated point-and-shoot cameras do the calculations for you.
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