by Johan J Ingles-Le Nobel
Last updated July 27, 2014
Focus stacking is a photography term used to describe the process of combining photographs to obtain images with a much larger depth of field that would be possible in a single photo. Starting out with focus stacking isn't hard, can be done at any time and doesn't need to be expensive. All you need to start focus stacking is a stage, a flash, your tripod, software, and a good sprinkling of patience.
Focus stack studio shot of a sawfly using the Componon 35 f/4. This is a stack of 213 photos, finished off with CS4, NoiseNinja & Topaz Detail.
Focus stacking is done by amateurs, professionals and part-timers, has applications in entomology, science and astronomy and there's even a camera that focus stacks on the Mars Rover.
Focus stacking, also known as macro stacking, focal plane merging, z-stacking and focus blending, can be done inside on the kitchen table during winter and is fun to learn, opening new worlds and opportunities for photography.
Like anything, there's a workflow and certain amount of preparation that's done before shooting a focus stack.
Focus Stacking Software
There are two main vendors of focus stacking software: Zerene Stacker and Helicon Soft. Both give superb results in the right hands, although the software of choice does tend to be Zerene Stacker because of its retouching abilities (cloning between photographs). A free open source alternative is ImageJ, used by many science institutions. Photoshop can also be used for stacking using its merge functionality.
Focus Stack Workflow
Good focus stack preparation prevents a lot of work in post. Before starting your stack, clean, spread, card and pin the subject and have it ready to be moved into position. Switch on any equipment that needs to be on for a while before settling at the correct colour temperature. Read more.
Shooting The Focus Stack
Calculate your optimal step size and make sure that your batteries are fresh. Set up your lighting and diffusion, work the stage to the ends and as a very last step, actually mount the specimen that you actually wish to photograph. Read more.
Processing Your Focus Stack
Zerene Stacker software, the discerning software choice for extreme macro focus stacking. Zerene Stacker is available as a free trial and can be downloaded here.
Focus Stack Post Processing
Adjust levels if necessary, enhance detail, remove noise, remove dirt by cloning, carefully sharpen and fix for presentation. Focus stacks are rarely supremely sharp or beautiful before postprocessing work is done and this stage is usually an important part of the overall macro stack process.
Focus Stacking on a Budget
For a low-cost focus stacking setup that gets you up to 5:1 or so, you really don't need expensive equipment. It is better to start with flash rather than continuous lighting because you'll avoid the unsharpness that long exposures and continuous lighting can give you. If you already have a camera, all you need to diffuse the on-board flash is a sheet of tissue paper which makes a fine diffusion material. To move the camera use a Velbon Super Mag Slider and make your own dial for greater sensitivity. For a specimen holder, either use a helping hand or an old lens (which can be twisted to make an up/down platform), blu tack and a pin. Then stack using ImageJ, which is free!
Common Stacking Problems
Your first stacks will be your worst. They may very well exhibit one of these very common stacking problems, which we have all had at some point. There is nothing to be alarmed about if you get these and it is always best to concentrate on getting your equipment train and workflow in good order first before expecting excellent results. Stacking is a slow process and learning to avoid issues is just a small part of this.
Unsharp stacks are commonly caused by vibration during the stack when using long exposures and continuous lighting, but can also be due to a poor optic or high ISO. Solution: Use flash instead, low ISO, try another optic and add some gentle post processing sharpening.
Dark lines are caused by dirt on the sensor, compounded into a line because of the stacking process. Solution: test for sensor dust by shooting a high f/stop frame, then use a good sensor cleaner to remove. Photoshop cloning or Zerene retouching can rescue these in case of emergency.
Not uncommon, this is a "dead" or "hot" pixel, compounded into a line because of the stacking process. They often appear with long exposures (several seconds), and do increase with increasing sensor temperature. Usually they're too small to notice because they're just a single pixel. Solution: There maybe a pixel remapping mode on your camera. If not, just retouch from a single frame.
Your stacking software constructs a weird out-of-focus colour splodge. Caused by the stacking software getting confused by out of focus colour values and adding them into the in-focus composite. Or, if using photoshop, caused by photoshop selecting big blocky areas instead of tracking closely to the actual structure of the subject. Solution: Experiment with different dmap settings - change threshold values or use Pmax.
Semi transparent hairs are a common artifact that happen when you use a wide aperture lens that can look round foreground objects to see a focused background. If there is higher contrast detail in the background than in the foreground, then the stacking algorithm will show the background. Solution: Break the problem up into smaller parts and use substack slabbing.