Beginner’s Guide to Focus Stacking

You may or may not have heard the term “focus stacking” when it comes to digital photography.  Either way, it is a technique which helps one overcome the limitations of modern optics. In a nutshell, maximum “depth of field” is traditionally achieved with small aperture values such as f16, f22, and beyond if the lens allows. But depth of field is often defined as “an area of an image with sufficient focus”. Focus and sharpness are drastically different, especially as a lot of us are professional pixel peepers. And what may be sufficient for one person is not sufficient for another. That brings us to the question: why focus stack? First, you may encounter a scene where your lens’ smallest aperture still does not give nearly the depth to allow for front to back focus. To make matters worse, small aperture values introduce diffraction which ultimately softens fine, intricate details. Focus stacking allows one to use apertures which are the sweet spot for sharpness (often about 2 stop down from wide open), but lack the depth in any one frame. The process then becomes to dial in your composition, lock those exposure settings in, and focusing at different points throughout the scene and then merging together for a master file with complete depth and a high level of sharpness.

Field Example #1: In the images above, I wanted my composition, from the flowers directly in front of me all the way to the mountain in the back, to be in focus. I also wanted soft light after the sun had gone down. To make it even more challenging, there was a slight breeze. I needed a higher ISO of 800, and I opened my 12-24mm f4 lens at 12mm to an aperture value of f5.6. Ideally, I would have used f8 for better sharpness and the need for fewer stacked frames, but f5.6 allowed me to use a faster shutter speed to better freeze the swaying flowers. I focused at six different regions of my frame, starting at the bottom edge and moving systematically towards the top. Ultimately, I then waited for the stars to come out, and used my 24mm f1.4 lens to capture the stars and I blended that in using layer masks in Photoshop. If I had used f16 or f22, I may have achieved enough depth, but at the expense of sharpness and either a much higher ISO or a slower shutter speed. Both of which I did not want.

Field Example #2: This small section of rock had undulating folds and with a more mild telephoto focal length of 105mm, my depth of field was narrow. I needed many frames at f8 to insure I had enough depth to cover the whole scene. 20 frames in all. Telephoto lenses compress depth more than wide angle lenses do, so f8 on a wide angle will have more “depth” than f8 on a telephoto lens. Thus the need for more frames in this example. In this example, even using f32 on my macro lens would not have yielded enough depth in a single frame, and f32 has a high level of diffraction which softens all the fine details in the scene.

Most of the major camera manufacturers have added a way to automate the capture of focus stacked frames in their newest cameras of the past few years. Sony still has not. If you’re listening Sony, get on it! Most still require you to merge them together to get the final file. So the rest of this post is dedicated to the software side of getting your master file stacked and blended