Focus stacking involves taking several photos of the same subject, shifting the focus plane each time, then blending them to produce an image whose depth of field goes beyond what a single shot can offer. It's the go-to technique in macro photography, but it's just as useful in landscape or product photography to keep everything sharp from the foreground to infinity.
The Focus shift tool calculates the number of shots to take and the focus step to apply between each shot, using two methods.
This mode matches the focus shift function built into some camera bodies (Nikon, Sony, Canon...), which automatically shifts focus by a fixed step between each shot.
Focal length and aperture: the lens settings in use.
Distance: the focusing distance to the subject.
Step width: the shift value set on the camera body (1 to 10 depending on the brand).
Lens calibration: the actual shift, in mm, that one camera step produces at a given reference distance. This value depends on the lens and must be calibrated once in the field.
The app shows:
Shots required: the number of frames needed to cover the requested subject depth.
Gap risk: an indicator that lights up if the chosen step is larger than the effective depth of field, a sign that a focus gap may appear between two consecutive shots.
Effective and total DOF: the depth of field per shot, before and after applying the safety overlap (percentage kept between two images for a clean stack).
Focus shift per shot and recommended max step, to fine-tune the step width.
The ruler angle corrects the calculation when the subject is photographed at an angle (for example with a tilted macro rail): the tighter the angle, the smaller the focus shift needed per shot.
This mode doesn't depend on any proprietary camera function: it calculates directly, from the lens's hyperfocal distance, the sequence of focus planes to photograph to cover the whole subject depth, with the desired safety overlap.
Standard: suits most subjects (landscape, product, close-up portrait).
Extreme macro: use this mode once magnification approaches or exceeds 1x. The depth-of-field calculation then switches formula and factors in the lens's pupil ratio, which affects the effective aperture at close range.
First focus plane: the focus point of the first shot in the series (by default, the subject distance).
The app shows the number of optical shots required, as well as, in macro mode, the effective aperture actually used. A diffraction-limit warning appears if the chosen aperture degrades sharpness despite high magnification, a sign that it's better to open the aperture and compensate with more shots rather than an aperture that's too small.
The Focus sequence table lists, for each shot in the series, the focus plane to set along with the near and far limits of its sharp zone.
Use a stable tripod and a remote shutter release (or the self-timer) to avoid any movement between shots.
Lock white balance and exposure in manual mode: they need to stay identical across the whole series.
Constant lighting (stable daylight, flash, or continuous light) makes blending the images much easier.
Then merge the series in a focus-stacking program (Helicon Focus, Zerene Stacker, or Photoshop's dedicated module).
In extreme macro, prefer several shots at a medium aperture (f/8-f/11) over a single shot at a too-narrow aperture penalized by diffraction.