Eleanor Radcliffe
Why One Frame Rarely Does the Job
Get close to a bluebell or a fly agaric and you will quickly meet the hard limit of depth of field. At 1:1 magnification, even at f/11, you might be working with a slice of acceptable sharpness barely a millimetre deep. Focus on the stamen and the petal tips dissolve into a soft wash; focus on the back of the cap and the gills lose their detail. Stop down further and diffraction creeps in, robbing the whole image of bite.
Focus stacking sidesteps the problem entirely. Rather than asking one frame to hold everything, you take a short sequence of frames, each focused a fraction further into the subject, then blend the sharpest parts of each into a single image with front-to-back crispness. For close-up nature work, it is one of the most useful techniques you can learn.
Kit That Makes Life Easier
You do not need exotic equipment, but a few items turn a fiddly job into a reliable one.
- A solid tripod with a head that lets you make tiny, repeatable adjustments. Flimsy legs will undo your best efforts.
- A macro lens that focuses manually with a smooth, well-damped ring. Focus breathing is less of a nuisance than you might fear, as most stacking software aligns frames automatically.
- A focusing rail if you plan to shoot at high magnification. Moving the whole camera in small increments is far more controllable than nudging the focus ring.
- A diffused flash or reflector to keep light constant across the sequence. Changing exposure mid-stack creates blending headaches.
- A plant clamp or small beanbag to steady the subject itself, which matters more than steadying the camera in a breeze.
Some camera bodies now offer in-camera stacking, which is a lovely shortcut for simple subjects. It is still worth learning the manual method, because it gives you control over step size and lets you handle awkward subjects.
Capturing the Stack in the Field
Set your aperture to the lens's sweet spot, usually somewhere between f/5.6 and f/8, and let stacking do the work that stopping down used to. Set ISO low and use flash or natural light to keep exposures consistent.
Focus on the nearest point you want sharp, then work backwards in small increments. A useful rule of thumb is to overlap each step by roughly a third of the depth of field, which at close range often means steps of half a millimetre to two millimetres. Too few frames leaves gaps that show as soft bands; too many simply means more files to blend, and rarely does any harm.
Take a few more frames than you think you need, extending past the rear of the subject. Shoot a handful of extra frames at the start and end, because losing the very front of a flower is far more noticeable than a slightly over-long stack.
Blending the Frames Afterwards
Import the sequence, check for any frames spoiled by vibration or a stray gust, and discard them. Most stacking software will align the frames, then blend only the sharp regions from each. Output as a 16-bit TIFF so you retain plenty of latitude for later adjustments.
Expect to retouch a little. Halos can appear where a sharp edge from one frame meets a blurred background from another, and translucent subjects such as petals or insect wings often need manual blending. Work at 100% and be patient; the results are worth the fuss.
Field Craft for Flowers, Fungi and Insects
Wind is the enemy. Early mornings are your friend, especially after a still, cool night when dew is heavy and the air has not yet stirred. Woodland interiors and the lee side of hedges offer shelter when the open meadow is hopeless. A simple diffuser held between subject and sun softens contrast and slows wilting.
Fungi are the ideal subject: they sit still, they are wonderfully textured, and their shape rewards a full front-to-back treatment. Get the camera low, almost at ground level, and stack from the leading edge of the cap to the furthest part of the stem.
Insects demand a different approach. Seek out torpid subjects on cool mornings, when bees, beetles and damselflies are too chilly to move. A shieldbug on a seedhead at dawn will often sit through a full sequence. If your subject twitches, be prepared to abandon the stack and try a single frame instead.
Where Focus Stacking Goes Wrong
- Movement: a swaying stem or a breathing insect ruins alignment. Steady the subject or wait.
- Changing light: drifting cloud or a passing shadow alters colour and exposure between frames. Use flash or shoot in even shade.
- Steps too large: soft bands appear where no frame was truly sharp. Tighten the increments.
- Over-processing: a stack that is sharp from front to back can look unnatural. Sometimes leaving the background soft is the more honest, more beautiful choice.
Practise on a static subject in the garden first, and you will soon find the rhythm. Once it clicks, a whole world of tiny detail opens up.
