Demystifying Shutter Speed

By: Adam Welch

One of the most crucial factors of making any photograph is the selection of the shutter speed. It is not always an easy task to decide what shutter speed you should select, to correspond to the aperture or ISO setting you have chosen. It can be a little overwhelming, and sometimes discouraging, to learn how to select the proper shutter speed to produce whatever your desired photo may be. You might still be shooting in full auto just because you can’t seem to have any luck with manually selecting your exposures. Luckily, once you understand the basic concept of shutter speed in relation to photography, this aspect will become much easier and almost intuitive.

Let’s take a look at what shutter speed really is, and how to better understand it, so you can begin to have more control over your photography.

What is shutter speed?

First things first, what exactly do photographers mean when they say “shutter speed”? This refers to the amount of time that the shutter of the camera is open. Shutter speed can be easily compared to blinking. Close your eyes, then open them for about one second. Now close them again. You have just performed a one second exposure with your eyes. Though very simplified, the exact same thing happens inside your camera when you press the shutter release button. The shutter opens, and remains open, for whatever duration you have set your camera to expose. This lets in light through the lens which interacts with whatever receptor you’re using (film or digital sensor), in order to produce a photograph. In reality, it might help you to refer to shutter speed as shutter time.

How does shutter speed affect a photograph?

As I have said, shutter speed is one of the biggest assets you can control in order to produce the type of photograph you want. Now, the shutter is not to be confused with aperture. Aperture has nothing to do with the amount of time that light is allowed to enter your camera. Aperture simply refers to the size of the opening through which the light passes when the shutter opens. The larger the opening is, the more light that enters your camera. The shutter speed, on the other hand, controls how long light is allowed to linger in order to make the photograph. Got it? Good.
So since shutter speed is related to time, it naturally means that it will directly affect how motion is recorded by your camera. This is where an infinite amount of creativity can be applied to your photographs. You may have heard a photographer say, “I used a really fast shutter speed to freeze the motion.” What they means here is that he or she used a shutter speed that was much faster than whatever motion was happening in the scene. The faster the motion, the faster the shutter speed will need to be, in order to arrest the movement. This is the very reason beginner photographers can become frustrated when photographing sports, children, or pets. They simply don’t understand that the shutter speed must be set in relation to the subjects motion to produce a desired outcome.
Take a look at this quarter that I froze mid-roll by using a fast shutter speed of 1/1250th of a second.

The flipside of the shutter speed coin comes into play when you want to impart a sense of motion, or to intentionally use blur within your composition. There is no better illustration of this than when working with moving water and waterfalls. Photographers will often use a long shutter time in relation to the speed of the water in order to produce that smooth, almost fog-like appearance that many of us love (or hate) to see. This again, comes down to relativity. A longer shutter time will be needed to blur a slow moving subject. A faster moving subject will not require as long of a shutter time in order to produce the same effect.
Here’s that same quarter shot at 1/50th of a second.

Things to keep in mind about shutter speed.

As with virtually everything else that has to do with photographic technique, there are not absolutes when it comes to how you choose to manipulate your shutter speed. It always comes down to whatever it is you are trying to express through your photograph. However, this doesn’t mean that there aren’t other things that you should know which are related to shutter speed. Two of the most important things you need to know is how aperture and ISO interact with shutter speed.

Aperture

Aperture is the best friend, and worst enemy of your shutter. As you have already learned, aperture controls the size of the opening in your lens and is measured in “stops”. Stops are indicated by the usage of f-numbers. Understanding how aperture is measured is the most difficult aspect of the subject. It is actually somewhat counter intuitive and that is why it becomes so confusing. Basically, the larger the f-number, the SMALLER the physical opening becomes. It might help to think of aperture as a window in your home. The larger the window the more light can come through. When shooting at larger apertures (smaller f-numbers like f/2.8, etc.) you have a lot of light coming into your camera so your shutter time doesn’t have to be as long in order to reach the desired exposure. The opposite is also true. When you are shooting at smaller apertures (bigger f-number like f/22) a longer shutter time will be required to produce the same exposure that was achieved at the larger aperture.
Here you can clearly see why less light can come through a smaller aperture.

Let’s say a certain shutter time at a certain aperture gives you a properly exposed image. You then switch to a higher f-number. If you don’t increase your shutter time, this image will be underexposed compared to the previous one because you have essentially made the window into your camera smaller. The take-away point here is that a change in aperture must also be accompanied by a change in shutter speed if you wish for the overall exposure to remain the same.
It should also be noted that aperture plays a key role in the perceived depth of field of a photograph…but that’s another article.

ISO

ISO is a measurement of light sensitivity. It is fairly straight forward to understand. The higher the ISO number, the more sensitive the camera sensor, or film, is to the light coming in through the lens. Although most modern cameras are capable of selecting ISO in smaller increments, when first learning about how ISO relates to shutter time it might be easier to use increments in powers of two; meaning ISO 100, 200, 400, 800, 1600, etc. Each time the ISO number doubles, the sensitivity to light also doubles. So ISO 200 is twice as sensitive as ISO 100.
We can then easily relate ISO to shutter speed using a one second exposure to simplify the math. Let’s say we find that a proper exposure of a scene requires ISO 100 and a one second exposure time. If we increase the ISO to 200 then we have doubled the sensitivity so we can now get the same exposure using half a second instead of one second. If we further increase the ISO to 400 then we can get the same results from a ¼ second exposure. As you have probably already deduced, increasing your ISO is an easy way to allow for an increase in shutter speed to compensate for subject movement, or for low light.
Take a look at these three images. I was able to get virtually identical results each time even though I decreased the exposure from 1 second to ¼ of a second just by increasing my ISO.



Be aware though, increasing your ISO will add grain (noise) to your final image to some extent depending on your camera and equipment. Still, it is almost always more acceptable to live with a little increased grain in an image, than to underexpose or miss the shot completely.
Understanding what shutter speed means to your images doesn’t have to be a complicated issue at all. Shutter speed, or more accurately shutter time, is simply a measure of how long you choose for light to enter your camera to make an image. Learning how shutter time relates to other aspects of photography is slightly more complex. That doesn’t mean that it should discourage you from experimenting and seeing first hand how ISO, aperture, and shutter time come together to produce different types of images.

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