How big should the focus step be?

Slightly smaller than the per-frame depth of field, so neighbouring slices overlap. The step equals DOF × (1 − overlap). A 25–35% overlap is a safe starting point for clean stacks.

What circle of confusion should I use?

Around 0.030 mm for full-frame, 0.020 mm for APS-C, and 0.015 mm for Micro Four Thirds are common defaults. Smaller values give finer steps and sharper stacks at the cost of more frames.

Why does higher magnification need so many frames?

Depth of field falls roughly with the square of magnification, so doubling magnification cuts DOF to about a quarter. Covering the same subject depth then needs many more, finely spaced frames.

Does diffraction affect my choice of aperture?

Yes. Stopping down increases DOF per frame but at high magnification the effective aperture grows and diffraction softens detail. Many macro shooters use f/4–f/8 and rely on more frames rather than a very small aperture.

Macro Focus Stacking Step Calculator

Q: How is depth of field calculated at macro magnification?

The calculator uses the macro DOF approximation DOF ≈ 2·c·N·(m+1) ÷ m², where c is the circle of confusion, N is the f-number, and m is the magnification. At high magnification the m² term makes DOF shrink dramatically.

The Macro Focus Stacking Step Calculator works out exactly how far to move focus between frames so your stack covers the whole subject with no soft gaps. It is built for macro photographers using a focus rail or in-camera focus bracketing.

How it works

At macro magnifications the depth of field at a single focus plane is tiny — often a fraction of a millimetre. The standard thin-lens macro approximation for total depth of field is:

DOF ≈ 2 · c · N · (m + 1) ÷ m²

where c is the circle of confusion, N is the f-number, and m is the magnification ratio. Because of the m² term, DOF collapses quickly as you push past 1:1.

To cover a subject of depth D you step focus by slightly less than the DOF so adjacent slices overlap:

step = DOF × (1 − overlap) and frames = ceil(D ÷ step) + 1

A 25–35% overlap keeps the sharp regions of neighbouring frames touching, which is what stacking software needs to blend cleanly.

Choosing aperture and overlap

Stopping down increases DOF per frame and reduces frame count, but at high magnification the effective aperture grows and diffraction softens fine detail. Many macro shooters settle around f/4–f/8 and take more frames instead of a very small aperture. If you see banding or soft seams between slices, increase the overlap and re-shoot.

Example and notes

At 1:1 (m = 1), f/5.6, with a circle of confusion of 0.020 mm, the per-frame DOF is 2 × 0.020 × 5.6 × (1 + 1) ÷ 1 = 0.448 mm. With 30% overlap the step is about 0.31 mm, so a 5 mm-deep insect needs roughly 17 frames. Use these numbers as a starting point and add a frame or two of margin at the front and back of the subject.