Focus stacking is a photographic technique that digitally combines sharp, in-focus elements of a number of images, to produce one composite image which has a large number of elements in focus that it more than would be possible in a single image, regardless of the depth of field used for that single image. Focus stacking is a relatively new technique and is possible only because of digital photography: trying to combine the parts of several dozen negatives in the darkroom is simply not a practical task.
Focus stacking has various applications, from landscape photography that has already been covered in the previous article, but it is also one of the main up and coming techniques in macro photography. Macro photography has one especially notorious challenge, being the remarkably limited depth of field that macro photographers have to content with. Even at a relatively generous f./stop, ie f/22, macro photographers measure their depth of field in millimeters or fractions of a millimeter, and of course that’s no good when you’re trying to obtain a tack-sharp shot of a subject several millimeters long. Some photographers might be tempted to immediately suggest using an even more generous f/stop such as f/96, but unfortunately the laws of physics work against this, with a particular effect named “diffraction softening” actually making a shot at f/96 demonstrably softer than the same shot taken at f/22.
What is required for focus stacking?
At its core, there are really two requirements for focus stacking: the actual sequence of shots – of the same subject at the same scale from the same direction but at different points of focus – and a digital means to combine this series of images and to create that final stacked shot.
Focus Stacking Stages
Shooting a subject at the same scale from the same direction but at different points of focus requires an extremely steady hand, and whilst it is possible to do so hand-held, by and large the overwhelming majority of people use a tripod and stage (for outside shots) or a custom-built stacking rig (for studio shots). A stage can be something as straightforward as a Velbon stage, although most experienced macro stackers tend to use apparatus which can give smaller incremental steps, or even a precision electronic focus stage which can give micron focus steps (1/1000 mm).
Focus Stacking Lighting
Lighting these small images is a separate challenge on its own, but both flash and continuous lighting see use, but to obtain the most discerning of high quality focus stacking images some extensive research into effective diffusion of flash and continuous light is highly recommended. Just as flash diffusion is a holy grail for macro photographers of all genres, much the same is true of focus stackers.
Focus Stacking Lenses
In terms of the actual camera apparatus, just about any DSLR will do absolutely fine for basic focus stacking, as long as you can equip it with the appropriate optics. 1:1 macro lenses are a reasonable start in terms of the optics, but you’ll find that when you delve into more extreme macro such as 1:1 to 10:1, off the shelf macro lenses just don’t do the trick anymore, unless of course you are lucky enough to own a Canon, in which case the Canon MPE-65 is the single best lens you can purchase for extreme macro, giving you a range of 1: to 5:1.
That said if you don’t own a Canon don’t despair: there are all sorts of other relatively low-budget optical options available, many of which are covered at http://extreme-macro.co.uk/extreme-macro-lenses/ – and with the glut of phenomenal quality darkroom lenses, available on eBay there really are plenty of outstanding optics out there. From the JML21mm, to the epic Componon darkroom lenses, to the use of a 10x microscope objective.
Focus Stacking Software
Lastly, software. There is free software out there such as Picolay, ImageJ, Hugin Tools and the older CombineZP, but most stackers use one of two professional focus stacking packages: Zerene Stacker or Helicon Focus. Both packages give spectacular results in the right hands and have a variety of editions geared at amateur and professional users, but there are more third party addons developed for Zerene Stacker and the majority of high-end stacking is completed using Zerene. Adobe Photoshop should also be mentioned as it has some limited inbuilt stacking functionality that will at least give you a flavor of stacking before purchasing custom stacking software.
Focus Stacking Limitations
Whilst focus stacking for macro is becoming more and more mainstream, focus stacking is not the answer to everything, nor is it appropriate for every situation. Stackers need to move through planes of focus in a series of shots, and the specimen needs to be stationary. A full stack run can either be slow (ie manually incrementing a focus stage to take a shot every few seconds), or fast (filming a sequence moving through the planes of focus, then extracting individual frames from that film to stack them). Needless to say, an insect that’s buzzing about in the heat of the day rarely affords the dedicated macro photography the opportunity to take a leisurely stack of images. Until technology advances enough to give us better options to shoot a rapid stack, single shot macro at a high aperture is still the unavoidable norm for many an outdoor situation.
- Tripod if you’re stacking outside, you’ll want to mount your stage on a tripod to ensure stability throughout the stack sequence.
- Focus Stacking Stage – there’s a range of options from relatively cheap eBay imports to precision electronic stages
- Extreme Macro Lens – you can start out with a Raynox on a standard kit 50-200 zoom, but as you adventure into greater magnification, you may find yourself buying enlarger lenses on eBay or high-end Mitutuyo objectives
- Lighting – you’re likely to want to supplement natural light with flashes or some form of continuous lighting
- Software – there’s a range of free software out there that will do stacks, but for professional-looking results, Zerene Stacker or Helicon Focus can’t be beat.