Shutter speed : What it does and when to use it

Shutter speed controls the time that the sensor of the camera is exposed to the light coming in the lens and is measured in seconds or fractional seconds. I gave a basic explanation in the Exposure Triangle post from earlier and how the shutter speed is one corner of the exposure triangle and whilst it has it's own purpose, it does also impact on the other elements of the exposure triangle.

What does the shutter speed do?

Controlling the shutter speed allows us to control time. No, it won't let you travel back to the 80's, but it will give you control over how time can be perceived in your photographs, and can be a very subjective thing.

It gives you the control to decide if you want to show motion blur to convey the movement of the subject of the photo or if you want to freeze a moment as though it were dead still. If you took the same photo of the same subject at the same moment with one set to a slow shutter speed and one on a fast shutter speed, the end result would turn out very different. One would contain some motion blur because during the time the sensor was capturing the scene, the subject moved. One would be dead still with no sign of motion at all.

The slower shutter speed used in this photo means the movement of the people walking in front of the building is captured as motion blur against the building which doesn't move and is therefore still sharp. This movement helps convey to the viewer the hustle and bustle of a busy city street. Would it have the same impact if all the people were perfectly still?

Which one is best? Which one should I do?

That is totally up to you. Say you took those two photos and showed them to a dozen different people. I'm sure you would find that some like the one with the motion blur better and some would prefer the still version. Some might say that the one with the motion blur helps to convey to the viewer the speed of the object whereas some might say the motion blur ruins it and the still photo is better.

Ultimately, it's up to you as the photographer to make a choice about what you want to convey in the photo and choose the settings that will give that result the best.

How to use it?

Your camera most likely has a mode called "Shutter Priority". In this mode, the photographer can set the desired shutter speed they want and the camera will then adjust the other aspects of the exposure triangle automatically to try and get the best exposure for the photo.

It is called shutter priority because the photographer (you) are specifically controlling the shutter speed as it will be the deciding factor in the image you want to create. Just as there is also aperture priority mode which does similar for controlling that aspect.

When looking at the scene you're intending to photograph, think for a minute about what story you want to tell when a viewer looks at the photo later and decide if the movement (or lack of) is the important factor in the image. If not, it might be best to look at a different mode such as aperture priority.

Sometimes a fast shutter speed can freeze the motion in the image entirely and if composed well it can still convey movement and action but without any visible motion blur. If getting the sharpest detail from the moving subject is important then a fast shutter speed will freeze motion.