A feel­ing for f-stops

You don’t have to un­der­stand what they mean to know how they’ll af­fect shots

NPhoto - - Nikopedia -

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.

Newspapers in English

Newspapers from Australia

© PressReader. All rights reserved.