Knowing that every picture taking opportunity offers you no less than six possible aperture/shutter speed combinations in and of itself may seem immaterial, but when you consider the impact of the creative possibilities influenced by the shutter speed (freezing actions, implying motion or panning) and aperture (a great depth of field, or a background of muted tones and/or out of focus foregrounds) you will have a much greater appreciation for why you are choosing that particular shutter speed and aperture combination. Again, why all the ‘fuss’ what difference does it really make which combinations of apertures and shutter speeds we use as long as the meter indicates a correct exposure?
If I suggest we use an aperture of f/8, what would the shutter speed now indicate as a correct exposure? If you said 1/500s, you are correct, which also means that you know at f/22 the correct exposure would be a 1/60s and at f/11 1/250s and at f/5.6 your shutter speed would now be 1/1000s.
Likewise, if we find ourselves taking an outdoor portrait at the park with our telephoto zoom, we find that with our aperture set to f/16 and with an ISO of 100, a correct exposure is indicated at a shutter speed of a 1/125 second (s).
I want to stress the word ‘same’ it is meant to mean the ‘same’ in terms of quantitative value only! The EquationsĪdd them up and what have you got? Six possible combinations of aperture and shutter speeds that will all result in exactly the same exposure. What other combinations of aperture openings (f/stops) and shutter speeds can we use and still record a ‘correct’ exposure? If I suggest we use an aperture of f/8 what would the shutter speed now be? Since we have cut the lens opening in half (f/5.6 to f/8) I will now need to double my shutter speed time to two seconds to record a correct exposure, (1 sec + 1 sec= 2 seconds.) On the other hand, If I suggested that we use an aperture of f/4 what would the shutter speed now be? Since we have just doubled the size of the lens opening (f/5.6 to f/4) I will now need to cut my shutter speed in half (1/2 second) to record the same ‘quantitative value exposure’.įor a refresher on these terms, take a look at Bryan’s intro article on Basic Photo Tips: Aperture, Shutter Speed, and ISO.
For the sake of argument we are both out photographing a city skyline at dusk, using a film speed of 100 ISO and an aperture opening of f/5.6 and whether we are shooting in manual mode or aperture priority mode the light meter indicates a correct exposure at 1 second. But only one, sometimes two, of these combinations of f/stops and shutter speeds is the creatively correct motion-filled exposure.Īgain, let’s review, that every ‘correct’ exposure is nothing more then the quantitative value of an aperture and shutter speed working together within the ‘confines’ of a predetermined ‘ ISO’. Perhaps you have already figured it out after reading the above, but if not, you will soon know that most picture taking situations have at least six possible combinations of f/stops and shutters speeds that will all result in a correct exposure not a creatively correct exposure but a correct exposure. Every picture taking opportunity allows you to record no less than six correct exposures!