Long-exposure techniques have become increasingly popular, particularly in the realm of landscape photography. One key reason is the ability to capture scenes with enhanced softness and harmony compared to standard exposures.
With the rapid evolution of digital cameras, we can now take extended exposures without significant digital noise caused by sensor overheating. Additionally, advancements in neutral density (ND) filters mean we can shoot with minimal color cast and no loss of sharpness.
That said, ultra-long exposures are hard to pull off for a variety of reasons. In this article, I explain my stacking technique, which makes it far easier to capture long-exposure effects while avoiding conventional difficulties.
If you’re passionate about long-exposure photography, this is definitely a tool to add to your arsenal!
What is long-exposure stacking?
By taking multiple photos (usually at least 30 seconds each), you can blend them to create a final image with a total exposure time equal to the sum of the individual exposures.
This technique is especially useful for landscape photography but can also be beneficial in other photography styles that require extended exposure times for maximum quality.
Here are the main advantages of long-exposure stacking:
- Extended exposure time: Achieve longer exposure without a single long shot.
- Reduced noise and hot pixels: Shorter exposures result in less digital noise and fewer hot pixels.
- Decreased vignetting: Using a weaker ND filter per shot reduces vignetting.
- Minimized risk: Avoid wasting time and shots due to tripod shakes or sudden light changes.
- Flexible post-processing: You can decide the strength of the long-exposure effect later.
Of course, every technique has its disadvantages, and long-exposure stacking is no exception. Here are the main issues with this approach:
- Not a single exposure: Some competitions and contests may not accept stacked images.
- Requires post-processing skills: You need to know how to blend multiple exposures.
- Purist concerns: This technique might not appeal to photography purists.
When should you use long-exposure stacking?
I recommend this technique in a variety of scenarios:
- If you want to capture a very long exposure, stacking allows you to push exposure times to higher values without as much risk.
- If you are frustrated by the amount of noise in your long-exposure shots, stacking will help reduce noise by keeping the sensor from overheating.
- If you’re not sure how long you want the exposure to be, you can decide on the final exposure duration later by summing shorter exposures.
- If you’re photographing in rough weather or hostile conditions, stacking reduces the risk of wasting exposure time in challenging environments.
- If the light is changing quickly, stacking increases the likelihood of capturing the perfect moment.
With all that out of the way, let’s get on with the fun part: actually implementing long-exposure stacking!
Elevating your long exposures with stacking: the step-by-step approach
This technique is relatively easy, but it’s important to pay careful attention to each step if you want to get high-quality results!
Also, before trying this, there are at least a couple of required skills you should have (apart from the basics for taking pictures with your camera):
- Standard long-exposure photography know-how: Familiarize yourself with long-exposure basics.
- Basic Photoshop knowledge: Learn to use layers in Adobe Photoshop or similar software.
Step 1: Get the right gear
The equipment for this technique is the same as for standard long-exposure photography. If you’re new to it, here’s a short list:
- A camera that’s capable of long exposures.
- A lens that’s compatible with neutral-density filters.
- A sturdy tripod.
- A remote trigger (this is optional but recommended).
- Neutral-density filters. ND filters are essential for most long-exposure scenarios, but if you’re shooting in very low light, you can get away without them.
Step 2: Plan the shot
Never hit the shutter without properly planning your photo. Thorough planning plays a crucial role in capturing a great photo! Do not underestimate the power of planning your long-exposure shooting.
Everyone’s planning process is different, and that’s okay. However, it’s important to think about the lighting, the subject, and the necessary settings before you set up your camera. If possible, scout locations ahead of time and get a sense of what’s available to you!
While luck can help you occasionally, consistent preparation increases the likelihood of being ready when the right conditions present themselves.
Step 3: Take the shots
Once you’ve planned your photo and arrived at your location, focus on two key aspects: composition and exposure. Composition depends on your personal taste, while exposure involves a complex interplay of factors.
Before taking any picture, landscape photographers usually meter the light to determine the exposure time. The final exposure time is influenced by various factors such as wind strength, cloud movement, and water flow. The critical question is, “How long should I expose for?”
In situations with rapidly changing light or strong winds that could shake your camera or tripod, long exposures might not be feasible. That’s one of those times where the stacking technique proves invaluable.
For instance, if you aim for a total exposure of eight minutes, instead of taking a single long exposure, you can divide the total time into four consecutive shots of two minutes each. You can choose the length of each exposure and the number of shots as long as the time gap between shots is minimal for stacking purposes. Ensure you don’t move the tripod or camera between shots. After capturing your series of shots, proceed to the post-processing step.
Before shooting:
- Ensure your focus is accurate.
- Stabilize your tripod (avoid sand or uneven surfaces if possible).
After shooting:
- Check your histogram to confirm proper exposure or exposure to the right.
 |  |
 |  |
 |  |
Step 4: Stack your files
Now that you’re home or at your favorite cafe with your laptop and a coffee or beer, download your shots and select the ones you want to stack.
We’ll demonstrate the stacking process using Adobe Photoshop, although any software supporting layers can be used. Photoshop offers two methods for stacking files to simulate a longer exposure:
- Semi-automatic stacking
- Manual stacking
Semi-automatic stacking in Photoshop
This semi-automated method involves going to Files>Scripts>Load Files into Stack.
Next, select the individual long-exposure shots, and check the boxes so Photoshop automatically aligns the source images and creates a smart object:
Click OK, then wait for Photoshop to do its thing. Once the process is complete, select the Smart Object, then go to Layer>Smart Objects>Stack Mode>Mean. This process combines all images embedded in the Smart Object, resulting in a new image that simulates a single long exposure with a total time equal to the sum of the individual exposures.
You can see the result of stacking in the image below:
Manual stacking in Photoshop (or elsewhere)
The second method involves manual blending, which can be done with any software that supports layers. This process requires adjusting the opacity of each layer sequentially.
The mathematical rule is as follows: each layer’s opacity should be set to 1 divided by its position in the stack. Like this:
- First photo (bottom layer): 100% (1/1)
- Second photo: 50% (1/2)
- Third photo: 33% (1/3)
- Fourth photo: 25% (1/4)
- Fifth photo: 20% (1/5)
- Sixth photo: 17% (1/6)
- …
- Nth photo: 1/N
This method replicates the automatic Mean Stack Mode and yields identical results.
Step 4: Post-processing workflow
At this point, just follow your typical post-processing steps. Here’s what I like to do:
- Clean away dust spots, straighten, and crop: Remove any dust spots, straighten the image, and crop as needed.
- Recover detail: Use other exposures (e.g., 3 or 5 bracketed shots) to bring back detail in static parts of the image that were under- or overexposed.
- Adjust exposure and contrast: Fine-tune the exposure and contrast settings.
- Adjust colors: Modify the colors to achieve the desired look.
- Add finishing touches: Apply any final adjustments to suit your taste.
- Export: Save your final image.
Here’s my sample image once all of the above has been completed:
Capture breathtaking long-exposure photos!
This technique is highly flexible and can significantly enhance the quality of your final image. Stacking images reduces random digital noise, with a reduction proportional to the square root of the number of photos used.
For instance, stacking four photos results in a 50% reduction in random digital noise in static parts of the image, which is especially beneficial for underexposed areas. This technique is widely used in astrophotography and other fields where increasing the exposure time of a single shot is impractical.
So give it a try and see what you think!
Need further help or explanations? Don’t hesitate to leave questions below!
