Let’s investigate the use of stacking in post to create a long exposure look from a burst of images. It’s a very esoteric technique, but can prove very useful in certain circumstances: you could, for example, find yourself in a situation where you want to achieve a long exposure look to some water, but don’t have either a means of stabilisation or any ND filters to cut down the light for a slower shutter speed.
In such circumstances, you can instead capture a series of images of the subject using a regular shutter speed. For best results, it’s a good idea to keep the framing as consistent as possible. You then (optionally) align these images before grouping them into a stack, where you can perform statistical operations to determine the final result. Mean and Median operators, for example, will average content between the images, and it’s exactly this approach that achieves a simulated long exposure look.
Watch the video above to see live footage examples of how to set up your shot for a successful result.
To achieve this kind of effect, you’ll need the following:
- Digital camera, preferably with a burst shooting mode, but you can take single shots spaced apart too.
- (Optional) Stabilisation, such as a tripod or other solid mount point. You can shoot handheld but the results will need to be aligned in post.
- Image editing software that can align and ‘stack’ images, e.g. Affinity Photo. Note: this is not the same as focus stacking. A stack is a group of images which you can then perform a statistical operation on.
Here are some key tips and things to look out for when you’re trying this technique:
- A tripod isn’t necessary, as most software will have auto-alignment capabilities, but if you can I’d recommend using one (or some form of stabilisation). This minimises the chances of alignment failing and can result in a more consistent framing of the shot.
- Experiment with the shutter speed you use whilst shooting the images: as demonstrated for the second example in the video, by using a high shutter speed I had a choice between using one image (for crystal clear water) and a stacked result (for blurred water). If you only shoot with lower shutter speeds (around 1/50 to 1/200) you may limit your options in post.
- Contrary to what I would suggest when shooting long exposures, don’t be afraid to raise the ISO if you need a faster shutter speed. A great by-product of stacking is that you increase the SNR (signal-to-noise) ratio, and random noise is significantly reduced. On most modern cameras you could probably shoot at ISO 1600 and still achieve a fairly clean result if you needed to.
- If you don’t have a high-speed burst mode on your camera, don’t worry! You can get results just by shooting image after image manually—the burst shooting is more for convenience and also to maintain consistent framing between shots.
- As mentioned in the video, this technique is a great way around the restrictions of using an ultra wide angle lens (for example, 11-14mm on most APS sensors, or 7-14mm on micro 4/3). UWA lenses typically require larger filters and a larger filter holder—both of which can be expensive, and hard to justify on a budget if you’ve already spent money on filters for your other lenses.
- Finally, don’t forget to experiment with other stack operators. In the video, I experiment with using Maximum, which blends the brightest pixels to give the water an intense look. Give Minimum and Mid-Range a try too.