The Exposure Triangle Reloaded

Now that we have explored ISO, Aperture and Shutter Speed in a bit more detail let us take another look at how these three things interact and how to get the most out of them for your everyday photography.

ISO is the sensitivity of the camera's sensor to light. The higher the sensitivity - the bigger the number - the more light is absorbed. BUT, the downside of high ISO is that it tends to be noisy and our images will look less pristine. So we want to use the lowest ISO practical in any given situation.

Aperture is the size of the opening in the lens that lets light through to the sensor. The wider open the aperture, the more light goes through. Aperture is our most frequently used creative tool because with it we control how much of a scene is in focus. With a narrow aperture, most of the scene - the foreground and the mountains in the background - could be in focus. When we use a small number for aperture, the opening in bigger, but the range that is in focus is limited - background blurred. This is a good way to achieve subject isolation.

Shutter Speed is the time during which the sensor is exposed to light. The longer the shutter stays open, the more chance there is for movement either by the subject or by the camera, resulting in blur. Maybe the blur is intentional, and that's good for creativity. Often we would rather have crisp, sharp photos, so use faster shutter speeds.

It's a balancing act.

My technique is as follows. But first, this is the way I do it most of the time, which may or may not suit you, and certainly will not be adequate in every situation. I'd encourage you to try it, use it, and then also learn other technique so that you can adapt and improve your own shooting style. We'll cover some other techniques soon.

Ready? 

  1. Set your camera to Av mode. This means you manually control the Aperture (and ISO), while the computer in the camera automagically determines the Shutter Speed.
  2. Set your ISO for the prevailing environment. Inside? ISO 1600. Outside on a cloudy day? ISO 400. At the beach? ISO 200.
  3. Set your Aperture for the creative control you want in this photo. F/4 is a good start for a stationary or slow moving subject. F/8 is sometimes better for faster moving or large (car-size) subjects. (Because the Depth of Field at f/8 is wider, meaning more in focus, allowing flexibility in where you focus.)
  4. Now comes the balancing. Framing your subject as you would like them in the viewfinder, check the Shutter Speed.
  5. Is it below 1/100, or the other tolerable value you have determined? If so, you need to get it faster. Increase the ISO to make the sensor more sensitive.
  6. Is the Speed above 1/1500? Is so, you will probably get away with going a bit slower. Decrease the ISO to make the sensor less sensitive and thus less noisy.


Now you have creative control of your photo. The numbers are guides. As you try different things, with different subjects, in different environment, you will learn what works for you. It may sound daunting and a lot of effort, but remember that we want to apply the intellectual component to the practical creation of your photographs. Keep doing it and muscle memory will prevail!

“The single most important component of a camera is the twelve inches behind it!” - Ansel Adams

Your Challenge

Get a photo outdoors that depicts the current season.  It could be wind, snow, beach, flowers blooming - anything you like, but use Aperture Priority mode and be creative.