The shutter speed control regulates how fast the shutter curtain will open and close. For most lower-end cameras the shutter speed can be regulated in full stops of light from 1/4000 of a second to 15 seconds or even 30 seconds. However, higher-end cameras have as fast as 1/8000 of a second, and mirrorless typically can go as fast as 1/32000 of a second with the electronic shutter feature. The technical details of this are not so important here, what we should understand is that the shutter speed regulates two things: how much or little light we allow into the sensor, and how much motion we allow into the finished image.
When it comes to light, then we need to understand that the faster the shutter speed, the less light we allow into the sensor. This way we can use the shutter speed to regulate the exposure, either by preventing too much light in bright scenarios or to allow more light into the sensor in darker scenarios. If you are outside in the middle of a summer day, and the sun is high in the sky, you might want to allow less light into the sensor, since your image otherwise would be overexposed, that is, too bright. In this case, you would “stop down” the shutter speed, meaning making the shutter open and close faster. For example, if your shutter speed is at 1/250 of a second, you might want to stop it down to 1/1000 of a second, in order to allow less light into the shutter.
Each stop, halving or doubling the shutter speed, represents a non-defined amount of light. How much this amount is, is less relevant here. What we need to understand is that when we move the shutter speed one step down, for example from 1/250 of a second to 1/500 of a second, we are halving the amount of light. That means that stopping down one stop is doubling how dark the image will be. If we stop down one stop more – twice from the original exposure – there will be one-quarter of the light, which was at the original exposure (1/1000 of a second is one-quarter of the light of 1/250 of a second). Of course, when we are out in the real world, we won’t think about this a lot, unless in a situation where we are adjusting the other controls and we are not able to see the final result, something which is not the case today when we use digital cameras, but was something you would need to figure out back in the days when using film cameras. All we really need to understand today is that the faster the shutter speed, the darker the image. The slower the shutter speed, the brighter the image.
However, as stated, the shutter speed also controls the amount of motion, we choose to introduce to the image. This helps in our creative process, deciding whether we want to freeze the movement of the subjects in the image, or whether we wish to introduce some feeling of action through motion blur. For example, most of us are probably familiar with nighttime photos of light streaks on the streets, created by cars passing by, either toward us or away from us. This effect, the light streaks, is created by having a slower shutter speed, and that way keeping the shutter curtain open long enough that the light from the cars will pass through the image, creating this streak behind it.
Other times we might want to freeze the action, for example when taking photos of some kind of sports match. Here it is crucial to have a fast shutter speed, to prevent the motion of the players to be visible in the image. Imagine a photo of two soccer players jumping for a header, having them blurred out by the motion because the shutter speed was too slow.
But this of course can put us in a dilemma. What if we want to freeze the action, but it is during the evening, not offering us enough light? Or if we want to have motion in the photo, but the shot is done in the middle of the day, adding too much light to the sensor? That’s where we have to look at the two other exposure controls, the aperture, and the ISO. I will cover these two controls in later posts.
In the two photos added as examples of how to use the shutter speed control creatively, I have slowed down the shutter to allow motion to appear in the image. This was done to give a sense of movement, of life happening. In the first photo, I wanted to contrast the person sitting on the bench with the cyclist passing by. In the second photo, I wanted to incorporate the traffic on the highway, to give a sense of it, rather than freezing the movement of the cars, which I feel would have felt unnatural.