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Before reading this post, I recommend you to read our post on the parts of a camera for better understanding. But I will try my best to keep it simple.

All pictures are essentially made up of light.

The Shutter is an internal part of the camera that opens and closes to allow light to enter the camera and get captured by the sensor.

The following gif shows how, when clicked, the shutter opens and closes. The green reflective plane that is exposed when the shutter is opened is the sensor which forms the image.

The three main parts in question are the mirror, shutter and the sensor. They are arranged as shown.

Before a click, the mirror is used to reflect the light to the viewfinder. None of the outside light is able to pass through the mirror and shutter to reach the sensor.

When the button is clicked, first the viewfinder moves up followed by the shutter. This is the reason why the viewfinder goes blank while taking a shot. After the mirror and shutter have moved away from the path of the sensor, light reaches the sensor and the sensor forms an image of the light.

After the image is formed the shutter closes followed by the mirror.

This is the crux of the process of capturing an image.

Now, shutter speed, simply defined, is the amount of time for which the shutter is open( or the amount of time light falls on the senor). It is measured in seconds.

However, the amount of time in question is generally very small. Usually, a fraction of a second. The shutter opens and closes in less than a second(most of the time).

A faster shutter speed means less amount of time; a slower shutter speed means more amount of time.

In most DSLR cameras the shutter speed can be adjusted between 30 seconds and 1/4000th of a second. You are likely to have a slider that can control the shutter speed.

For simplicity and for lack of space, shutter speeds that are less than one second are denoted as just the denominator. For example 1/100th of a second shutter speed is shown as 100, and 1/4000th of a second is shown as 4000. Shutter speed that are a second or more are denoted with a quotation mark. For example, 2 second long shutter speed is denoted as 2", and 10 second long shutter speed is shown as 10".

Light

Shutter speed can be used to adjust the amount of light in a picture(brightness). This is because more light enters the camera if the shutter is open for longer and vice versa. In other words the lower the shutter speed, higher the brightness; higher the shutter speed, lower the brightness.

When shooting pictures in low light decrease the shutter speed for brighter pictures.

Motion

Another important aspect of shutter speed is motion. One second is a very long time in photography. Since the image is continuously forming on the sensor, any movements of objects will result in a blurry picture.

In both the pictures the skateboard was in motion. However the two pictures look entirely different because of a difference in shutter speed.

For the first picture the camera was set at a shutter speed of 1/30th of a second. That means the image was forming for 1/30th of a second. During that time, the skateboard moved a long enough distance for it to look blurry.

For the second picture the camera was set at a shutter speed of a faster 1/100th of a second. In that time the skateboard did not cover a significant amount of distance and therefore, was sharp in the image.(Also, notice the difference in brightness of the two images).

You may have seen pictures where light is elongated such as car light trails. These are taken by setting a slow shutter speed.

This picture was taken at a shutter speed of 3/10th of a second.

Tripod

Using a tripod is the most important thing if you want sharp images. It becomes even more indispensable when shooting at lower shutter speeds. We know that when objects move we get a blurry image; the same is true when the camera moves.

Always use a tripod when shooting at shutter speeds slower than 30.

What if I don`t have a tripod?

If you don`t have a tripod then a simple hack is to place the camera on a stable surface and click slowly.