Shutter Speed Facts & Myths

Did you know that most picture-taking situations have at least six possible combinations of f-stops and shutter speeds that will all result in correct exposure? They may not all be creatively correct photographic exposures, but they will all be correct. More often, only one or two of these f-stop shutter speed combinations is the creatively correct motion-filled exposure.

Every correct exposure is nothing more than the quantitative value of an aperture and shutter speed working together within the confines of a predetermined ISO. For the sake of argument, let’s say that you and I are both out shooting a city skyline at dusk using an ISO of 100 and an aperture opening of f/5.6. Let’s also say that, whether we’re shooting in manual or Aperture Priority mode, the light meter indicates a correct exposure at 1 second. 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’ve cut the lens opening in half (from f/5.6 to f/8), we now need to double the shutter speed time to 2 seconds to record a correct exposure. On the other hand, if I suggest we use an aperture of f/4, what would the shutter speed now be? Since we’ve just doubled the size of the lens opening (f/5.6 to f/4), we now need to cut the shutter speed in half (to 1/2 sec.) to record the same quantitative value exposure.

Easy, yet hard, right? Here are the equations (which all yield the same quantitative exposure in this situation):

• f/4 for 1/2 sec. is the same as
• f/5.6 for 1 second, which is the same as
• f/8 for 2 seconds, which is the same as
• f/11 for 4 seconds, which is the same as
• f/16 for 8 seconds, which is the same as
• f/22 for 16 seconds

Add them up and what have you got? Six possible combinations of apertures and shutter speeds that will all result in exactly the same exposure. And by same, I mean the same in terms of quantitative value only! I can’t stress to you enough how important it is to be aware of this principle. It doesn’t matter if you’re shooting with a film-based camera or a digital camera; you must learn to embrace a simple fact: Every picture-taking opportunity offers you no less than six possible aperture/ shutter speed combinations. And why must you know this? Even though each combo has the “same” exposure, the motion captured by each may look radically different. Knowing which one or two motion-filled exposures is correct before you take the picture is the key. Once you are armed with this knowledge, you can begin to fully explore the truly endless road of creatively correct motion-filled exposures.

Since every picture-taking opportunity allows for no less than six possible aperture and shutter speed combinations, how do you decide which combination is the best? Think about what you want to do. Do you want to freeze the action? Fast shutter speeds – 1/250, 1/500, 1/1000 sec. – are the creative forces behind “frozen” images. Do you want to suggest motion via panning? Then you should call upon shutter speeds of 1/60, 1/30, and 1/15 sec. And, those super slow speeds (1/4 sec. to 15 seconds) are the creative force behind images that imply motion, such as a waterfall or the wind blowing through a field of summer wheat.

And keep in mind that when it comes to motion-filled subjects, you must first think about which creative shutter speed will convey the motion before you in the way that you want. Then and only then should you even begin to worry about the second-most-often-asked-question: Where should I take my meter reading from? I’ll get to that in another post, but the good news is that the build-in light meters found in today’s cameras do a fantastic job of rendering a correct exposer, even when using Aperture or Shutter Priority modes.

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