A camera’s shutter is just a mechanical curtain that stays closed, covering your camera’s sensor, until you press your shutter button. When the shutter button is pressed, the shutter opens and allows light to fall onto the camera’s sensor. Based on the settings used, the shutter stays open for a certain amount of time until enough light has been collected for a correct exposure, and then closes again preventing any more light hitting the sensor.
The amount of time the shutter allows light to hit the sensor is referred to as shutter speed. The slower the shutter speed, the longer it stays open and therefore more light is allowed to hit the sensor for longer. A faster shutter speed means that it stays open for a much shorter period of time and light only hits the sensor for a very brief moment. Shutter speeds can vary over a large range, from many minutes all the way up to a very brief 1/8000th of a second.
Motion and blur Although shutter speed is one setting that helps control your exposure, it also has another quality that can dramatically enhance, or indeed ruin, your photos. For example, if you are photographing waves against rocks using a fast shutter speed of 1/640th of a second in bright conditions with a handheld DSLR, anything that is moving will appear to be frozen in place.
Any movement of the camera whilst you are holding it will not be recorded either since the shutter was only open for such a brief period of time. However, if you are taking a similar shot but in lower light conditions with a shutter speed of around 1/4 of a second, to make sure you are capturing enough light for a good exposure, the movement of the waves will be noticeable since the shutter is open for a much longer period of time compared to the first example.
Now the waves will be blurred in the direction they were moving. Again, since you are shooting handheld, any movement imparted by you to the camera during the exposure will create even more blur and possibly ruin the shot. Care needs to be taken when using slower shutter speeds where camera shake is a danger.
Use a tripod A tripod becomes essential if you want to take photos with long shutter durations. The problem also becomes magnified if you use longer focal length lenses. A wide angle lens of about 14mm is less of an issue when compared to a telephoto lens of 400mm, where even the slightest movement of the camera creates a large amount of movement in your subject – as seen in the viewfinder.
Much faster shutter speeds are great for capturing and freezing fast action but do need plenty of light. Slower shutter speeds are perfect for turning moving water into mist but you will need a tripod.