Photography for Testers Part 4: The Exposure Triangle and Shutter speeds

Welcome to Part 4 of our series “Photography for Testers”. This week we continue with our discussion of the exposure triangle. Last week we talked about ISO. This week is all about shutter speeds.


Shutter Speed


The second element of the exposure triangle is shutter speed. Shutter speed is the amount of time that the shutter stays open. Or, the length of time the sensor “sees” the scene you’re photographing. This time is measured in seconds or fractions of seconds. So, the bigger the denominator, the faster the shutter speed. For example, 1/500 is faster than 1/60.


We’ll take a moment here to talk about “stops”. Stops refer to a doubling or halving of exposure (light). This is how you refer to making a change in exposure. So, when you change one element of the exposure triangle, you refer to the change in terms of a stop. A full stop and half-stop are the most common, with some cameras capable of making changes in a third of a stop. For the sake of simplicity, I will only be referring to full stops.


With shutter speeds, full stops are as follows:

1/4000, 1/2000, 1/1000, 1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8, ¼, ½, 1s (s stands for second), 2s, 4s, 8s, etc.

On your camera, they will appear differently. 1/250 as 250, 1/8 as 8, 2s as 2”.

1/4000 is a really fast shutter speed and lets in very little light. 2 seconds (2s) is a really slow shutter speed and lets in a lot of light.



1/125 lets in twice as much light as 1/250. It can also be said that 1/250 lets in half as much light as 1/125. This change is one full stop. These numbers follow a logical sequence. Each will be either half the previous number or double the next. This is not the case with apertures, but we’ll talk more about that in the next section.


Only the shutter speed was changed in each photo to show how each stop affects the light let in. 


How do you know what shutter speed to use? That depends on what you are photographing and the effect you want? Are you taking portraits? Shooting a sports event? Taking landscape photos? How much light is let in is not the only reason you need to change your shutter speed. How you want to capture motion is also a factor. A fast shutter speed is going to freeze movement. A slow shutter speed will create blur. For example, if you’re taking photos of a model and they are not moving, you don’t have to have a super fast shutter speed. If, however, you are photographing your kids and they’re running around (like kids normally do), you’ll need a fast shutter speed in order to not get just a blur.


You can use shutter speed in creative ways, too. If you want to create a sense of movement, you can slow your shutter speed to intentionally create motion blur. Say you are photographing someone running. A fast shutter speed might capture the runner with both feet in the air, showing no indication of movement. Switching to a slower shutter speed will cause blur, which will show the movement of the runner. Another example is shooting running water or waterfalls. Using a fast shutter speed will freeze the movement of the water. You will see individuals drops if there’s any water spray. If you use a slow shutter speed, the water will appear silky and convey a sense of movement. There are so many ways you can use shutter speed creatively. Experimenting with different speeds is the best way to get a feel for how they affect your photos.


Another factor that will affect your choice of shutter speed is the focal length of your lens. The simple technical definition of focal length is the distance between the lens and the sensor. It is listed on your lens in mm. (18-55mm, 50mm, 85mm, 70-200mm) The lower the number, the wider the perspective. And the higher the number, the narrower the perspective. In regards to shutter speed, the longer the focal length, the harder it will be to keep it steady when hand-holding. The general rule is to choose a shutter speed with a denominator (bottom number of a fraction) that is equal to or larger than the focal length. For example, with a 50mm lens, 1/60 is usually okay. But, if you’re using a 300mm lens, you’ll need to choose 1/500 or faster. (1/500 is chosen because the next fastest shutter speed to 300 is 1/500) If you need to use a slower shutter speed, a tripod will be necessary to avoid blur.


To break it down:


Fast SS = less time open = less light let in = freezes motion

Slow SS = more time open = more light let in = motion blur


I hope this has been helpful for some of you. Feel free to ask questions here or in the PTP group! Next week will be about apertures (f/stops). After that, we will briefly discuss using your camera’s meter before we bring all 3 of the elements of the exposure triangle together.