There are three components to every exposure: shutter speed, aperture, and ISO speed. In order to get a correct exposure, each of these three values must be adjusted in a relationship. We’ll look at how that relationship works in a subsequent article, but for now, we’ll look at shutter speed.
The shutter on your camera controls two different aspects of each picture: the amount of light that can hit your film or sensor, and the amount of motion blur that may or may not result.
Let’s look at the light aspect first. Shutter speeds are notated by lengths of time, such as 1 second, 1/2 second, or 1/1000 of a second. The longer the shutter is open, the more light will be recorded on our film or sensor.
Let’s suppose that you’re thirsty, and that a 12 oz glass of water would be enough to quench your thirst. You can fill the glass slowly or quickly, but at some point the glass is full. This is the correct amount of water. If you leave the faucet open for too long, it will overflow and you’ll have wasted water. If you turn it on for too short, you’ll still be thirsty.
The shutter is very similar. If you open it for too long, too much light will enter your picture and it will be “blown out.” You’ll have wasted the photo. If you open the shutter for too short a length of time, you won’t have “poured” enough light into your photo and it will be too dark.
The second consideration we have about shutter speed is how it affects the blur (or lack thereof) in our picture. Let’s say that we want to take a photo of a jogger. Our camera tells us that a 1-second shutter speed is needed to get a proper exposure. If we keep the shutter open for 1 second, the jogger will have traveled several feet and our camera will have recorded the entire sequence in one big blur.
On the other hand, if we had used a shutter speed of 1/250 of a second, the jogger might not have traveled any distance. Consequently, our jogger will seem as though they’re frozen in time.
For most pictures, we don’t want any blurring to occur. In these situations, it’s important to use a fast shutter speed to freeze the action. Note that we humans often shake a little when holding a camera (heavy ones in particular), so we need to make sure our shutter is faster than our movement is. Many photographers try to use a shutter speed of 1/125 S or faster when hand holding their camera to prevent their shaking from blurring the photo.
In some cases, you want to imply motion, so you would choose a longer shutter speed. You might do this to make star trails at night or to record the paths of tail lights from cars. If you have the option, it’s often useful to use a tripod to minimize undesired blurring.