Focus Stacking

I was recently talking to my sister about photography and I brought up the topic of focus stacking. It's hard to explain, so here's a demonstration.

Magnifying for Macro

The world of macro photography is fun - the more space on your camera's sensor you can take up with the image you want to capture, the more detail you can see on your subject. Normal zoom lenses can often do some macro-type work; some are designed to allow you to be close to your subject and still allow the lens to focus. Most typical zooms can't - you have to stand back from your subject in order for the camera to be able to focus.

With specially-designed macro lenses, you can get up close to your subject and magnify it such that details will show up in your images that you could never see with your naked eye.

Focus Stacking Example

Here's a picture of my macro photography setup:

Camera: Olympus E-M1 Mark II

Lens: Olympus 60mm f/2.8 macro lens

Tripod: Super cheap old tripod from Best Buy that came free with a camcorder, circa 2003.

Software: Olympus Capture. 

Here is a shot of the subjects with normal camera settings - a bolt, Red Cross donor pin, and the ruler portion of steel calipers. The dark base they're on is an old tablet computer. 

Olympus Capture

This software allows me to plug the camera into the computer and operate the camera through the software, instead of making changes on the camera itself. Here's a screen snapshot of the application running. 

Most of the options shown on the right side would normally be changed on the camera itself, but they can be changed here. On the bottom right are some chevrons (<<<, <<, < and >, >>, >>>) which can be used to tell the camera to zoom in or out a little or a lot at a time. This is the equivalent of my rotating the focus ring on the lens by hand. I use these during the process of taking all the shots that will eventually be stacked.

Getting Started

I started off by focusing the lens on the closest point to the camera and taking a picture. Note how little of the image is in focus (where the arrows are pointing).

The problem with macro lenses, and microscope lenses (objectives) for those who use them, is that magnifying at this level means that not much of your shot will be in focus. It has to do with the physics of light and the way the lens and camera process it. The "depth" of the in-focus portion of the image is referred to as Depth of Field, or Depth of Focus. As you can see, with this lens and camera set up the way they are, there is a very shallow depth of field. Here's a good explanation, if you're interested. 

Because it would be great to get a clear, highly-magnified view of this scene, I can't just set my lens at its highest magnification and take a picture, because the depth of focus is so shallow that I'll only get a little bit of the image in focus. This is where focus stacking comes in - stacking involves taking a picture, refocusing the lens to be slightly farther away from the camera, taking another picture, then repeating these steps until the lens is focusing on the very back of the scene, or the lens isn't capable of focusing any father away.

Each of these shots will include small slices that are in focus, and the rest will be out of focus. The "stacking" part is done by software, which can identify which parts of which image is in focus, and combine those in-focus parts with the other in-focus parts of the other images, and then combine them. (How does it do that? I have a vague idea but it's mostly magic.)

Moving the Focus Across the Subject

Let's continue to watch the focus change through the images as the focus is "moved away" from the camera and towards the back of the subjects.

This photo is about half-way through the focus's travels. The parts in focus are indicated. The parts of the first shot above that were in focus are now completely blurry.

The next photo is about 3/4 of the way through. Note that the focus is "moving" towards the back. Anything at a particular distance from the lens is in focus, even if the different objects in the picture are above or below each other.

Here is the final shot; only the very farthest reach of the subject is in focus.

Stacking the Images

Now that we have these shots, we can load them into Zerene Stacker or Adobe Photoshop to be stacked. The image below was created by Zerene Stacker, which is named for the one thing it does really well (and better than Photoshop): focus stacking.

The in-focus parts of each image were "found" by the software and included into the resulting image. You can see all the little imperfections of the steel in the bolt, the tiny marks on the face of the Red Cross pin, and the other flaws that are not visible without magnification.

Watching the Focus Move

I made a short video showing the progression of the focus - there are about 40 images total. This helps visualize the different steps.

Stacking Non-macro shots

It's possible to stack non-macro shots. It can be done with landscape photography, product photography for advertisements, and many other place - anywhere you can use a tripod to control the framing of the image you're taking. The idea is the same - the in-focus parts of the images you stack will be blended with the others. 

More Examples of Macro and Stacked Images

Here are a few links to stacked and macro images on the Photomacrography website, where amateurs and professionals alike gather to show off their work, learn from others, and trade ideas. Some of these images were made with microscope objectives, which exhibit a tiny depth of field as a tradeoff for the high magnification they provide.

• Yellowjacket wasp eye, stack of 335 shots. 
• Blue carpenter bee, 296 shots stacked.
• Tick, stack of 101 shots.
• Dissolving sutures macro shots. This page not only discusses the appearance of real-life sutures, but makes a conjecture about how they are tied by a surgeon. Then a surgeon who is also a photographer weighs in, and the photographer eventually presents the images to the surgeon who performed the operation. Photography, knots, surgery - all in one place! 
• Popcorn salt on top of a penny, 330 shots in a stack. Neat! Click here for the discussion, and here for the picture. 
• Robber fly parts, a few different stacks are shown. I believe this was done with a microscope objective, attached to the camera with other lenses or adapters.

This is a small sample of what's on the  forums, you can look around there to see other images of very small things, see people's setups, and so on.