We all are familiar with the concept of depth of field, which describes the range of distances over which an image is in focus. This is determined by the f-number at which the image is taken, smaller f-numbers (larger lens openings) yielding shallow depths of field, larger ones (smaller openings) yielding greater depths of field. Often we use a shallow depth of field to emphasize our subject; this is especially useful in portraiture. But sometimes we wish a large range of distances to be in focus, and this can often exceed what is possible using a large f-number, even using hyperfocal focusing. In addition, an unavoidable disadvantage of using a very high f-number is that diffraction begins to soften the image, and this cannot be removed completely in post-processing.
Fig 1. A typical frame from the stack.
Click for an enlargement
There are at least two methods to extend the range of in-focus subject distances that appear in an image. One is to use a tilt-shift lens, an expensive option, and one that requires some practice to use successfully. The other is to take a series of images focused over a range of distance and somehow stitch them together. This latter technique is known as focus stacking, and is the subject of this article. With any Nikon camera and lens, a tripod, computer software, and perhaps some additional reasonably inexpensive equipment, this is easy and fun to do.
The basics of focus stacking are straightforward. A series of images, each focused in a slightly different plane, are combined by specialized software that utilizes the sharpest parts of each image to produce a single image that is in focus over a wide range of distances from the camera.
No matter what technique you use to obtain a series of differently focused images, you will need computer software to stitch them together. In this article I discuss the use of three packages, Photoshop® (CS6), Zerene Stacker® (version 1.04), and HeliconFocus® (version 7.5.1). While this isn't a software review per se, I will touch on the strengths and weakness of these packages as I have used them. The last two programs each have more than one way to combine the images, and I will illustrate output from each.
Focus stacking can be effective in two very different contexts. The first is in taking landscapes, where the photographer wants to keep objects spanning a large range of distances in focus (this is a traditional domain of the tilt-shift lens). The second is in close-up photography, where we want to keep an entire object in focus. In this article I deal only with the latter.
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