Often long exposure requires minimum movement on the camera and tripod is necessary in most of the cases. There are some situations that require only a few seconds of exposure time such as photographing waterfall, river, beach, moving water or fireworks. Longer exposure on moving water gives us sense of motion because it creates motion blur on water. To create silky/foggy water effect, usually tripod and ND filter are necessary to create steady long exposure shots.
For smartphone camera, there are ND filters designed as lens clips to be clipped on the smartphone cameras. If you don’t have ND filter or tripod, there is a way to simulate the similar effect on post-processing, and it is the Burst Mode.
During long exposure on moving water, the random reflection and refraction of light from water stream travels to camera’s lens and falls on the sensor. In burst mode, camera captures at a certain sampling rate depending on the bursting speed, it receives random reflection and refraction pattern of light from water in every frame over the bursting duration. By averaging all these shots in post-processing, similar long exposure effect can be simulated. The effect will look closer to actual long exposure when there are more images(more light data) to be processed.
Getting the images
Burst mode is available in most of the smartphones nowadays, usually there is a limit on the number of shots. One set of burst shots will be enough to create the effect, but more is better. While hand holding the phone as steady as you can, press and hold the shutter button until it hits the limit. Repeating for a few times and we will have a lot of images for post-processing. If the camera has optical image stabilization (OIS), it will certainly help to compensate slight movement of your hands.
Post-processing
For the post processing, image aligning needs to be done before stacking the images. In Photoshop, select “Auto-Align Layers” under “Edit” drop-down menu and Photoshop will do the work. After aligning the images, select all the image layers and convert to smart object. We want to average the layers, so mean filter is what we need. By stacking the layers with Mean Filter (Layer menu > Smart Objects > Stack Mode > Mean), we are able to get the result below.
More images will give better result since there are more data but it also contributes to longer processing time. Here is the difference between 20 stacks and 60 stacks of burst shots.
It depends on your needs and what kind of result you want to create, some may prefer short shutter time to capture water splash, some prefer long exposure to create foggy effect, but both are achievable with smartphone camera technology. With burst mode and post-processing, it is possible to create similar effect as long exposure photography on certain situations. There are situations that are not possible with this technique such as night sky photography, motion blur on clouds which require significantly longer exposure time from tens of seconds to tens of minutes, but it certainly works on photographing moving water.