What is a long exposure? And how to create one
This post assumes basic knowledge of the exposure triangle. If you’re unfamiliar with the exposure triangle click here.
Long exposure photography can be truly stunning. Capturing a passage of time in a single image is something our eyes and brain just can’t do. To understand what a long exposure is we first have to understand what an exposure is. To help explain, I’m going to use an excerpt from lesson 1 of our Portraits Like a Pro photography course:
“In digital photography, the term exposure can be used in numerous ways. It describes the process of exposing an image sensor to light. It also describes the lightness of an image. For example, if an image looks as it should, it is optimally exposed; but if it’s too bright it, is overexposed, and if it’s too dark, it is underexposed. Exposure can also refer to a single shutter-cycle (the time between the shutter opening and closing).”
Here, we’re concerned with the first and third descriptions: the process of exposing an image sensor to light, and a single shutter cycle (the time between the shutter opening and closing).
When you take a picture, you are exposing the image sensor to light for a pre-determined duration of time; and a long exposure simply refers to the fact that the image sensor was exposed to light for a long duration in a single shutter cycle. The amount of time that elapses between the shutter opening and closing is called the shutter speed.
As well as determining the duration of exposure. The shutter speed controls the amount of movement in an image: a faster shutter speed like 1/1000 second will freeze motion, whereas a slow shutter speed like 1 second will cause motion blur because the sensor is capturing everything that is happening in front of it during the exposure time. So if something moves during the exposure then it will be blury. This motion blur is what you’re seeing in a long exposure photograph. The more something moves during the exposure, the more it’ll blur.
As you can see in the first two photographs, the relatively short exposure times of 1/100 and 1/160 have frozen the motion of the water. In order to blur the motion of the water, much longer shutter speeds are needed.
With longer exposure times of 10 and 8 seconds, the motion of the water has been blurred, while the rest of the scene remains still.
In long exposure photography, it is often desirable to blur the motion of only 1 aspect of the scene while everything else remains perfectly frozen. To achieve this, the camera must be kept perfectly still throughout the exposure time. For the photograph of the waterfall with the 8 second shutter speed I simply placed the camera on a rock, and for the one with the 10 second shutter speed I used a basic tripod. You can see how I captured it in this video.
Remember, the sensor is capturing everything that is happening in front of it during the exposure time, and the more something moves during the exposure, the more it’ll blur. The water blur is pleasing because it’s constantly moving fast. With these cars driving down the road, a longer exposure time of 30 seconds was required to capture their journey across the entire image. If the cars were moving too slowly, or I used 8 seconds like the waterfall, the lights would’ve stopped midway into the picture.
Finally, in order to achieve a long exposure, the same rules of the exposure triangle apply. If you’re unfamiliar with the exposure triangle and how to balance exposure then click here to access our fun and comprehensive Portraits Like a Pro photography course for free. If you enjoyed this blog and found it useful, then the course is definitely for you.