What is Focus Stacking?
Focus stacking is a photographic technique that enables a photographer to achieve virtually unlimited depth of field. It is accomplished by compositing a set of captures focused at different distances to create a single image with greater depth of field than any of the individual files. With today's photographic tools and post-processing computer technology, we can convey a subject with more visible detail than ever before. To me, this is one of the realizations of Canon See Impossible.
Focus stacking is applicable to all kinds of photography. The technique can be used to achieve a vast landscape that is tack sharp from foreground to horizon, or a macro subject with stunningly intricate detail, or high-magnification imagery that reveals fascinating characteristics that may not be discerned by the unaided human eye—such as the scales of a butterfly, or the complex design of a single snowflake.
The Basic Technique
For the most consistent results, the camera needs a steady platform, such as a tripod or copy stand. While maintaining the subject's position in the frame, the photographer captures overlapping slices of sharpness by manually changing the focus of the lens, moving the camera toward the subject through the plane of focus, or moving the subject toward the camera.
In a landscape composition with significant depth of field, the effect might be achieved with only a couple of captures at different manual focus points, while a small subject and/or high-magnification subject could require tens, or even hundreds, of captures. The composite is created in post-capture software that compiles all the images, retaining only "sharp" elements and discarding any information that is out of focus.
When photographing a focus-stacked image, keep in mind that you can easily have too few images to achieve a completely sharp composite, but seldom can you have too many.
Always take more images than you think are necessary, in overlapping increments that completely cover the entire subject.
The two different interpretations of garden flowers that accompany this piece were accomplished in the studio under controlled conditions. Each subject was positioned on a copy stand beneath a Canon EOS 5D MK IV camera with a Canon EF100mm f/2.8L Macro IS USM lens set to f/8 (the sharpest setting for this lens). The camera's movement for the focus stacking was precisely controlled using an automated focus stacking macro rail. A Canon MT-24EX Macro Flash was used for lighting. The resulting captures (shown here in screen shots) were composited in a computer using focus stacking software.
A Simpler Example
Focus stacking also can be accomplished simply in the field, with beautiful results. This rose was photographed in the garden using a tripod-mounted Canon EOS 5D MK IV and Canon EF180mm macro lens. Manual refocusing of the lens through the subject captured seven sharp slices which, when composited, rendered a completely in-focus close-up image of the rose, and one that can be printed large without loss of clarity. (Each capture: 1/180th sec. at f/11, ISO 800).
Focus Stacking at Higher Magnifications
The Blue Morpho butterfly is a truly beautiful creature, with the top of the wing a shimmering iridescent blue while the underside is a complex design in brown and gold. Depending upon your perspective, the two sides look like completely different beings.
At high magnifications, depth of field is infinitesimally small. Here's a focus-stacked image derived from 44 captures of just one of the tiny colored spots on the brown under-wing, photographed at 10X with the Canon EOS 5D MK IV camera, the Canon MP-E65mm f/2.8 1-5X Macro Lens, and a Canon 2X Tele-extender MK III. At such high magnification and close proximity to the subject, needed extra light is provided by the Canon MT-24EX Macro Flash. Achieving such extraordinary enlargement and depth of field reveals the complex construction of the individual scales that comprise the structure, color and design of the wing.
But how would you capture a larger segment, or even an entire butterfly wing, at high-magnification and total sharpness? A panorama, of course! Here, eight individual focus-stacked composites at 5X have been combined to reveal the intricate composition of the upper wing. Achieving this high-resolution image of what is still a very small area of wing scales required 637 individual captures. The first image below outlines the boundaries of the eight focus-stacked images, and the second shows the cropped, finished, photograph, which can be printed wall-sized with complete clarity.