Today’s Question: I would appreciate an explanation of focus stacking and if it is easily usable by the average photography enthusiast.
Tim’s Quick Answer: Focus stacking is a method for capturing a series of images with overlapping depth of field, and then blending those photos together into a final image that includes expanded depth of field. It is not too complicated, and it can be very helpful when achieving adequate depth of field can be difficult or impossible, such as with closeup and macro photography.
More Detail: Achieving full depth of field for a photo becomes particularly challenging when you are focusing very close to a subject. With macro photography, for example, it is very common to only be able to achieve a depth of field that is a fraction of an inch because by the nature of macro photography you are focusing very close to the subject.
To overcome situations where you’re not able to achieve adequate depth of field, you can use focus stacking. Some cameras include an automatic focus stacking feature, which can be tremendously helpful. There are also accessory devices that can automate the process for you. However, you can also manually capture focus stacked images.
The basic process involves capturing a series of photos with overlapping depth of field. You’ll want to configure the camera settings to maximize depth of field to the extent possible, to help minimize the total number of images you need for the focus stacking. I generally start at the front of the scene and work my way back, so I start by capturing a photo with the focus set at the very front of the range I want to include in the depth of field for the final image.
You can then adjust the focus in small increments to move the depth of field range backward. You want to make sure that you’re overlapping enough that all areas of the subject will be included within the depth of field range with no out of focus areas.
As a simple example, let’s assume you are photographing a ruler that is aligned with the lens, and that your camera settings only enable you to achieve one inch of depth of field. I would start with the sharpest area of focus set at the very front of the ruler. I would then adjust the focus so that the center of sharpest focus is at around the half-inch mark or so, in order to ensure that the area of full depth of field overlaps from frame to frame. Continue adjusting the focus for each photo until you have captured a range of images that include the full subject in focus. In other words, the last photo would have the far end of the ruler at the middle of the sharpest area of focus.
You can then assemble these focus stacked images into a final result that includes maximum depth of field. While you can assemble a focus stacked image in Photoshop, my experience has been that considerably better results can be achieved with other software. My preferred tool for assembling focus stacked images is Helicon Focus, which you can learn more about here: