Focus Stacking Step-Size Calculator for Macro Photography

To calculate the step size for macro photography, particularly when doing focus stacking, you need to determine the distance between each focal plane. This depends on the magnification ratio, the aperture, and the circle of confusion.

Here’s a simplified approach to calculate the step size:

Determine the Circle of Confusion (CoC)

The Circle of Confusion (CoC) is dependent on the sensor size. Generally accepted CoC values are 0.023 mm(APSC), 0.029 mm(FF), 0.015 mm(M4/3).

Calculate the Depth of Field (DoF)

Use the following formula to calculate the Depth of Field (DoF) at a specific magnification and aperture:

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DOF = \frac{2*f*CoC*(m+1)}{m^2}
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f = Nominal aperture (e.g., f/8)

CoC = Circle of Confusion

m = magnification ratio (e.g., 1:1, 2:1)

Calculate the Step Size

The recommended step size is usually 75% of the Depth of Field to ensure overlap between frames.

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Step\,Size = DoF*0.75
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Example Calculation

Let’s say you’re using an f/8 aperture, with a magnification of 1:1 (m=1) on a micro four thirds camera, such as the Olympus:

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Circle\,of\,Confusion\,(CoC)\,(M4/3)=0.015mm
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Depth\,of\,Field\,(DOF) = \frac{2*8*0.015*(1+1)}{1^2}=0.48mm
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Step\,Size=0.48*0.75=0.36mm
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This means you would set your focus stacking rail to move 0.36 mm (or smaller steps) between shots for a good balance between overlap and sharpness across the stack.