Stack It Up! – A Guide to Using the Focus Stacking Photography Technique

Shooting and editing macro photographs using the focus stacking technique.

When a single shot won’t get everything in focus, try stacking a series of differently focused shots of the same scene. It’s easy, it’s fun—and it can be very useful.

This technique is most often used for close-up macro work, but can be used in any type of photography where you want objects in the foreground, center, and background to be equally sharp.

This introduction to Focus Stacking centers on the manual method – available to anyone with a camera and a lens that can focus on all the items you want to be sharp in the final image. You can also capture layers through microscopes to use with this technique. Automated tools are also available, as discussed at the end of this blog post.

How to Create A Stacked Focus Image; Shooting before Stacking

In the image above, shot with a close-up lens at its optimal aperture, a particular point of the image is in focus, but much of the area behind and ahead of the point of focus is very soft. Using a smaller aperture would cause more of the image to appear sharp, but much of the image would still be out of focus.

You might try using a still smaller aperture , such as f/16, f/22 or even smaller, but image quality will begin to degrade as the lens is further stopped down, and even then, not all the image will come into focus. This is why we stack, to get the whole thing sharp. 

Find the Best Aperture for Each Lens Before Your Shoot

Every lens has an optimal aperture, which delivers the best possible results. It’s a really good idea to find out what your optimal aperture is when making focus stacks. Multiple lens testing services provide results online, showing what their tests reveal about the very best aperture for a particular lens, so it’s easy to look up. If you can’t find your particular lens reviewed, the general rule of thumb is to use an aperture 3 f/stops down from wide open. The images in this article were all created with a 105mm Micro-Nikkor lens, at f/10, the best aperture for this lens, for this kind of work.

How can you preserve the quality of the lens’s optimum aperture and yet get the focus depth desired? Shoot multiple images, focusing at multiple different points in the same scene, and stack them together in the computer.

For best results, use all the techniques you know to get a sharp image. A good tripod is essential to execute and deliver high quality stacked images, and a cable release is strongly recommended.

How to Shoot your Stack of Images

Compose your image carefully, using your tripod. Next, focus on the closest point you wish to have in focus, and make sure that the framing and composition are to your liking. This closest-focused frame shows the boundary of the final image. As you change focus from front to back, the field of view will widen. Since you want everything from front to back to be sharp, the extra part around the edges of the frame which appears as you focus further back won’t be included in the final image, because this extra area isn’t included in the first frames you shot focused most closely.

The image sizes will shift slightly, or a lot, as you focus. This varies depending on the distance between the lens and the you are to the object(s) you’re photographing. As you focus front to back, watch for all the points you want to be sharp. Shoot an image for each of those points, and all the areas in between. You’ll need to shoot enough steps in between to give Photoshop room to make smooth transitions. When in doubt, shoot too many rather than too few frames. You can always remove some frames from the stacking process, but it’s impossible to put sharp areas back in if you don’t capture them before stacking.

When Photoshop matches up the images you’ve created to stack them, it works in a two step process. The first step aligns all the images correctly. (Note: Photoshop will tell you if it can’t do the alignment. If that happens, check each frame to see if you’ve included a frame that doesn’t match the rest.) In step 2, Photoshop automatically finds and blends the sharpest points of each aligned frame, masking out the soft areas.

Photoshop compensates for the change in size of the various frames by scaling and skewing some frames to match others. There’s a point past which compensation can’t be done, simply because there’s not enough at the edges of the frames of the front of the stack to shrink into alignment with the images shot.

You can see this in the first image below. The screen capture shows the moment after all the frames are aligned, but before they’re blended. The area that’s brighter white will end up being the area of the final frame, and you can see that this frame very closely matches the most closely focused image shown earlier. When the stack is composited into one image, the areas outside the edges will show up as blurs, which can’t be fixed in Photoshop. If you can live with the crop, great. It is, after all what you saw as you composed and focused the first frame. If not, you’ll need to check out the advanced tools later in this article.

How to Stack your Shots into One Image

All of the images need to be opened into one file, in multiple layers. There’s an automated way to do this, and a tedious manual way. Here are the steps for the fastest method, with screenshots. You really don’t want to open each image individually and do this manually, do you? The images are of a single bolt I found in a wall in the ghost town of Rhyolite, near Death Valley.

1. Open Adobe Bridge.
2. Drag the folder of images to be stacked onto the icon of Adobe Bridge, or navigate from Bridge (File Menu/Open/folder…).
3. Highlight the images you wish to stack.
4. Under the Tools menu, select Photoshop/Load Files into Photoshop Layers.
5. Each image will open into the same file, into a separate layer, in Photoshop.
6. Once all the images are open, Save your file.
7. Open the Layers Panel, select the first layer, hold down the Shift key, and click on the last layer. This selects all the layers in between.
8. With all the layers selected, under the Edit Menu, select Auto-Align Layers.
9. In the Auto-align dialog that appears, select Auto, then OK.
10. Photoshop will align the layers; depending on the size of your files, and the speed of your machine, you may find this takes a bit of time. When aligned, Save again.
11. Next, under the Edit Menu, select Auto-blend Layers. All the layers in the Layers Panel must still be selected.
12. In the dialog that appears, select Stack Images, and be sure the checkbox for Seamless Tones and Colors is selected.