Depth of Field for Macro Photography
Macro is where depth of field stops being "a couple of meters" and becomes fractions of a millimeter. The math is different, the tools are different, and the workflow is focus stacking.
The magnification problem
At macro distances, depth of field follows DoF ≈ 2·N·c·(m+1)/m², where m is magnification (1:1 = 1.0). The m² term is the killer — each doubling of magnification quarters the depth of field:
| Magnification | DoF at f/8 (full frame) | Effective aperture |
|---|---|---|
| 1:4 (0.25×) | ~9.3 mm | f/10 |
| 1:2 (0.5×) | ~2.8 mm | f/12 |
| 1:1 (1.0×) | ~0.93 mm | f/16 |
| 2:1 (2.0×) | ~0.35 mm | f/24 |
| 3:1 (3.0×) | ~0.21 mm | f/32 |
An insect's eye sits maybe 1–2 mm from its wing — a 1:1 shot at f/8 can't hold both. And the effective aperture column shows the second problem: at 1:1, f/8 set is f/16 effective, losing two stops of light and gaining diffraction. Your exact numbers are in the macro DoF calculator.
Why stopping down fails
At 1:1, going from f/8 to f/16 doubles the DoF (0.93 → 1.86 mm) but the effective aperture hits f/32 — where diffraction has already softened everything to a similar blur as the DoF gain. The image looks "sharp" nowhere. This is why pro macro is done at f/5.6–f/11 with stacking, not f/32 single shots.
The focus-stacking workflow
- Rig it: camera on a rail (or tripod with a focusing rail); subject still. Focus ring moves the lens, the rail moves the camera — for 1:1+ use the rail.
- Shoot wide-ish: f/5.6–f/11 (f/8 typical) to minimize diffraction while keeping a usable step size.
- Step by 80% of the DoF: the calculator's stacking step output is exactly this — move focus that far between frames. Overlap 20–30% so the stacking software has matching detail.
- Merge: Helicon Focus or Photoshop (Edit → Auto-Blend Layers). Review edges for halos; if present, use a smaller step.
A 3 mm-deep subject at 1:1 with ~0.9 mm DoF needs roughly 4–6 frames. Live subjects (breathing, swaying) force a compromise: wider aperture, faster shutter, flash, and a smaller stack.
Lighting and exposure at high magnification
- Effective aperture light loss: your camera meters through the lens so exposure is usually right — but manual flash math must add the stops (at 1:1, add 2 stops).
- Diffusion beats power: a diffused flash near the lens (ring or twin-flash) gives the short, motion-freezing light macro needs; continuous light means slower shutter and more shake.
- Focus at working aperture: focus wide open to see, stop down to shoot, or use focus peaking if available.
Related tools & guides
Macro DoF Calculator
DoF, effective aperture, and stacking step for your magnification.
Open →Shutter Speed Chart
Handheld macro needs 1/200 s or faster.
Read →Exposure Equivalence
Recompute exposure when effective aperture bites.
Open →Macro DoF FAQ
Do I need a macro lens for focus stacking?
No — extension tubes, close-up filters, or reversing rings on a normal lens all work. What matters is controlled focus movement: a rail for 1:1+, or a lens with a smooth focus ring for lower magnifications.
Why does my 100 mm macro show more DoF than a 60 mm at the same magnification?
At the same magnification, focal length mostly cancels out of the macro DoF formula — the difference you see is usually working distance (100 mm lets you shoot from farther, which helps light and skittish subjects, not DoF).
Can I stack handheld shots?
Software can align handheld stacks, but success drops fast at 1:1 — the alignment quality suffers and steps become uneven. Tripod + rail until the subject forces you handheld, then burst-shoot and hope for 2–4 usable frames.