A feeling for f-stops
You don’t have to understand what they mean to know how they’ll affect shots
If you’re just starting out with an SLR, the numbers may not seem too intuitive, going from f/2.8 to f/4 to f/5.6 and so on, but you soon get used to them. The lower the number, the wider the aperture and the more light that reaches the sensor.
The most typical maximum aperture is f/2.8, but faster lenses can reach f/2, f/1.4 and even f/1.2, usually for a hefty price premium. They’re called faster because they enable a faster shutter speed to be set at the maximum aperture: so a lens with a maximum aperture of f/5.6 might struggle in low light, because even wide open, at f/5.6, it might require a shutter speed of, say, 1/8 sec for a correct exposure… in other words, too slow to shoot handheld in most situations. An f/2.8 lens set to f/2.8 would require a shutter speed of 1/30 sec for the same exposure, so much faster.
For the mathematically inclined, this sequence is a geometric progression, rounded out to make it easier to remember, based on powers of the square root of 2. For everyone else, it’s a matter of getting familiar with certain f-stops delivering a certain degree of depth of field. You’ll find that, soon enough, f/5.6 comes to mean just enough depth of field for an average subject, f/11 is comfortably deep, and f/16 reliably deep. These are rough-and-ready judgments, as it depends on whether you’re using a wide, standard or telephoto lens, but as there’s usually little time to calculate these things, having this kind of basic feeling for the numbers is useful.
1/60 sec at f/5.6, ISO4600 In this image of a woman frying corn arepas, I knew in advance exactly the kind of shot I wanted: wide angle, close enough to see her hands moving as she cracked an egg into the arepa, and with her hands in sharp focus. My judgment said the aperture needed to be medium-open, which by my definition is around f/5.6. The background could go soft as long as it was still clear what was going on; 1/60 sec was just fast enough
to freeze the slower parts of her hand movement, as at this moment.