Understanding Exposure: Part 2

Shutter speed, another main factor of the mysterious exposure triangle, however the good news is that it is usually the easiest of the big 3 for beginners to master (it was for me anyway). Shutter speed can allow you to get a razor sharp shot freezing the action or the nice motion blurred image implying movement and motion. Whichever type of shot you are shooting, it is important to know how shutter speed works and how it's going to affect your overall exposure.

In the previous article, Understanding Exposure: Part 1, we learned about aperture. We took a look at what aperture was, how it works and how it is going to affect your overall exposures. In this article we'll look at what shutter speed is, how it works, how it will affect your exposures and finally how shutter speed and aperture work together.

Cameras work by having light travel through the lens and into the camera then onto the film or sensor (digital). However, the shutter and aperture blades are in between the lens and the sensor. The light must travel through the front glass of the lens, through the aperture, through the shutter and finally onto the film or sensor. The aperture blades (the size of the lens opening), which were discussed in Understanding Exposure: Part 1, can regulate the amount of light that reaches the shutter. The shutter is then basically a time measurement of how long the light is allowed to reach or "expose" the film or sensor. For example by setting the shutter speed to 1 second, you are allowing the film or sensor to be exposed to the incoming light for a duration of 1 second.

Now that we know that shutter speed is a timed duration of how long the light is going to be exposed to the film or sensor, we can then use this knowledge to help us make more creative images. The faster your shutter speed, for example say 1/400, the more likely it is that you will be able to freeze action. If you look at the image to the right, this image was taken with a 1/1000 shutter speed, enabling the small pieces of snow to be frozen in place. On the other hand, if your goal is to create an image that implies motion then you would use a longer shutter speed, allowing parts of the image to blur, implying motion. This can be seen in the image to the left where the Eastern Kingbird is taking off from a branch and his wings and tail are motion blurred.

• As a rule of thumb to follow when shooting handheld shots, take your focal length and reciprocate it to give you a general idea of how fast a shutter speed you need to created a sharp image. For example, if your focal length is 300mm, most people will need 1/320 shutter speed to get sharp images. Or if your focal length is 50mm, most people will need 1/50 shutter speed to obtain sharp crisp images.

Basically, when you want to freeze action, it requires a fast shutter speed, when you want to imply motion and blur action, then use a slower shutter speed. However, changing your shutter speed will also change your overall exposure (don?t forget about the exposure triangle). So how do you know what aperture to use when you want to stop action or imply motion? The image below will help you get an idea of how your settings should be set. This is by no means an exact model you should follow, but it will give you the general idea.

There are many different combinations of shutter speed and aperture that will give you the correct exposure, but the image above is meant to illustrate that each stop down goes in halves and each stop up doubles, the same as aperture. So when you use a small aperture, you will need to use a lower shutter speed to retain a correct exposure. However when you use a large aperture such as f/2, you are able to use a very fast shutter speed. This goes back to the previous article, when talking about "fast" lenses. The larger you can open the aperture, the faster the shutter speed you can use. But basically you just have to go out and experiment, it's the best way to learn.

To review, the shutter's part in the big 3 in controlling exposure is by allowing light to reach the film or sensor for a measured time interval. That should make sense. Faster shutter speeds freeze action while slower shutter speeds can be useful for implying motion. Finally, practice practice practice, it's the best way to learn!