Joe’s How-To Focus Stacking
exposures (e.g., a field of waving grasses and wildflowers). I’ve found the most success with close-up images of relatively stationary objects. For this column I’ll use a recent photograph of oyster mushrooms I found in a forest north of Trinidad, California.
By Joe Doherty
One of the earliest things I learned when I picked up a camera was the relationship between aperture and depth of field. The rule was pretty simple – a smaller aperture meant that more was in focus. So I shot everything at the smallest aperture possible. But that didn’t work out so great, and it took me a while to learn why not. At some point every lens hits a point of diminishing returns for sharpness. Smaller apertures lead to more diffraction, or blurring. A photo could be sharp with shallow depth-of-field at f8, or un-sharp with great depth-of-field at f22. That was the trade-off.
It’s important to know something about your lens before you start shooting. Specifically, you should know at what f-stop diffraction starts to become noticeable. On my lenses that’s typically around f8 or f11, depending on the focal length. Given that, I try to shoot all of the images I intend to focus stack at around f8 or f11. This gives me frames that are as sharp as possible along with depth of field that makes blending easier. It takes a lot of trial and error to determine how many frames you need to shoot. It boils down to two things: how far apart are the nearest and farthest things you want in focus; and how much does the depth of field overlap across the frames. Before making any exposures I use the manual focus ring on my lens to get a feel for how much I need to turn it in order to get both ends of the stack in focus.
In addition, even with a small aperture not everything was in focus. The lack of infinite depth of field required me to make both technical and artistic choices. When photographing a wildflower it was important to maneuver the camera into a position where all of the important bits of the subject were in the same plane relative to the camera, so that they would be sharp as the foreground with the background blurred away. Creativity is how the we react to such constraints.
From experience I have an idea for how much I can turn the ring and stay within the depth of field of the previous shot. There are probably tables and guidebooks that tell how much that should be, and that’s good background information, but in the field it’s better to have an intuitive feel for it. There is no substitute for experience.
Today that constraint is at least partially gone, relieved by digital imaging and the technique of focus stacking. It is now possible to produce images with an amazing depth of field at the maximum sharpness of a lens. This is accomplished by shooting multiple frames of the same subject, changing the focus between frames, and blending them together using software.
Some cameras (my Nikon D850) can be set to automatically change the focus between shots. Nikon calls it “focus shifting,” and it allows me to choose how many frames to shoot (up to nine) and how much to shift the focus in between exposures. I found this very
Some subjects are difficult to focus stack because parts of them move in-between 22
22
