Updated · 3 min read
Two questions decide every focus stack: how big can each focus step be, and which aperture should you shoot at? Get them right and the stack is seamless. Get them wrong and you see soft bands or a picture that’s soft all over.
Plan your focus stack
For flowers, insects and small objects. Start with your framing and the depth you want sharp.
From the nearest detail to the furthest, not the subject’s height or width.
The real-world width covered by the entire photo at the subject. Include any space beside it.
Includes one extra frame at each end.
- Focus step
- 0.32 mm
- Sharp depth per frame
- 0.48 mm
Focus position: -0.32 mm from the nearest detail
Magnification: 1× · Effective aperture: about f/16
Stopping down reduces the frame count, but diffraction can reduce fine detail. Compare a test frame at a wider aperture.
A starting estimate, not a guarantee. Uses the close-up formula below, two-thirds of a frame’s sharp depth per step, and a pupil ratio of 1. Close inspection halves the usual circle of confusion. Actual lenses and camera step scales vary: shoot a test and check for gaps. Not for landscapes or microscope objectives.
Why the steps must overlap
Each frame is sharp in a zone around its focus distance. If the next frame’s zone starts where this one ends, everything is covered, but only just: the edge of each zone is only acceptably sharp. If there’s a gap, the stack shows a soft band across the subject at that distance. A step of about two-thirds of the depth of field keeps every part of the subject in the sharpest part of at least one frame.
A simple way to work it out
For close-up work, total depth of field is about 2 × N × c × (1 + m) ÷ m², where N is the f-number, c the circle of confusion (0.03 mm on full frame, about 0.02 mm on APS-C and 0.015 mm on Micro Four Thirds) and m the magnification. For stacking that will be viewed closely, use a smaller c, say half, to be safe.
Depth of field per frame
At 1:1 and f/8 on full frame: 2 × 8 × 0.03 × 2 ÷ 1 ≈ 0.96 mm.
Step
Two-thirds of that: about 0.65 mm.
Frames
A 10 mm deep subject: 10 ÷ 0.65 ≈ 16, plus a frame at each end: 18 frames.
Camera bracketing modes use numbered steps (1–10) instead of millimetres, and the size of each number changes with aperture and focus distance. Do one test series, check where the soft bands appear, and note the setting that works for each lens.
Choosing the aperture
A smaller aperture gives each frame more depth and so needs fewer frames. But light spreads as it passes through a small opening (diffraction), and that softens the whole image. Close up, the effective aperture is smaller than the number on the lens: roughly N × (1 + m). At 1:1, f/8 behaves like f/16.
| Subject | Magnification | Aperture |
|---|---|---|
| Landscape | Far away | f/8–f/11 |
| Product, food | 0.1–0.3× | f/8–f/11 |
| Flowers, larger insects | 0.5–1× | f/5.6–f/8 |
| Small insects, eyes | 2–3× | f/4–f/5.6 (effective f/11–f/16) |
| Microscope objectives | 5× and up | Fixed by the objective |
Can you have too many frames?
Extra frames don’t hurt the result much, but they cost shooting time, card space and processing time, and give a live subject more time to move. Frames beyond the subject’s nearest and furthest points add nothing. Detalia points those out after stacking, with the frame to start or stop at next time.
Questions
- How many photos do I need for focus stacking?
- Subject depth divided by about two-thirds of the depth of field per frame, plus one or two at each end. Landscapes often need 2 to 5, macro at 1:1 around 15 to 30, and high magnification hundreds.
- What is the best aperture for focus stacking?
- The aperture just before diffraction softens fine detail: around f/8 to f/11 for landscapes, f/5.6 to f/8 for macro at life size, and wider at higher magnification.
- What focus step setting should I use on my camera?
- Bracketing step numbers aren’t standard. Start around 3 for macro and 5 for landscapes, shoot a test, and make the step smaller if you see soft bands.