Step size decides how much the focus point moves between each frame of a macro focus stack, and getting it wrong shows up either as visible soft bands where frames fail to overlap or as an excessive frame count that wastes time without improving sharpness. This guide covers how depth of field sets a natural starting point and how to dial the number in with a quick test.
What Step Size Actually Means
Step size is the distance the point of sharp focus moves between one frame and the next in a stack, whether you control it by turning the focus ring a small amount, moving a dedicated focus rail a set distance, or letting in-camera focus bracketing handle the increment automatically based on settings you choose.
The goal behind choosing a step size is straightforward: each frame’s thin zone of sharp focus should slightly overlap the zone covered by the next frame, so nothing in the subject falls into a gap that no single frame actually recorded sharply.
Depth of Field Sets the Natural Step Size
At high magnification the zone of sharp focus in any single frame is extremely thin, which means small steps are needed to keep consecutive frames overlapping rather than leaving gaps between them. A narrower aperture number widens that sharp zone and lets you take fewer, larger steps to cover the same subject.
Stopping down too far to gain a wider sharp zone per frame introduces its own softness from diffraction across the whole image, so step size and aperture are really two sides of the same decision rather than separate settings to pick independently. The guide to how a macro lens works covers the underlying optics behind why depth of field behaves this way at close focusing distances.
Signs Your Steps Are Too Large
Oversized steps leave visible soft bands or a faint halo where the stacking software blends two adjacent frames that do not quite overlap, since neither frame actually recorded that thin strip of the subject in sharp focus. The guide to halos in a macro focus stack looks at this specific artifact in detail.
Fine texture on a subject, such as the facets on an insect’s eye or the detail on a textured surface, is often where missing coverage shows up first, since those areas have the least tolerance for a focus gap compared to a smoother, more forgiving part of the same subject.
Signs Your Steps Are Too Small
An excessive frame count for the magnification and subject slows down capture and increases the chance that a light flicker or a slightly moving subject ruins part of the set before the sequence finishes. A subject that only needed thirty frames but was captured in a hundred wastes time without adding any extra sharpness, since the overlapping zones beyond what is necessary do not improve the result further.
Processing time grows with frame count too, since blending software has to work through every extra frame during alignment and stacking. The guide to stacking extension tubes is a related read for anyone working at high enough magnification that frame counts start climbing quickly regardless of step size.
A Practical Way to Find Your Step Size
- Capture a short test stack of the actual subject at your planned aperture and magnification before committing to a full sequence.
- Check the preview for any soft band or halo between adjacent frames once the test stack is blended.
- Cut the step size roughly in half if gaps show up, then test again on the same subject.
- Increase the step size if the frame count feels excessive for a clean, fully covered result.
- Repeat the test with a new subject or a different magnification, since the right step size rarely carries over exactly from one setup to another.
Rail, Ring, or In-Camera Bracketing
A dedicated focus rail moves the whole camera a precise, repeatable distance for each frame, which gives the most consistent step size across a long sequence. Turning the focus ring by hand works for occasional, smaller stacks but is harder to keep perfectly even across many frames in a row.
In-camera focus bracketing automates the step size and frame count based on settings you select before shooting, though it does not always suit every macro situation. The guide to in-camera focus bracketing for macro covers where that automatic approach holds up well and where a manual rail still has an advantage.
Frequently Asked Questions
Generally yes, since a narrower aperture widens the sharp zone in each frame, but stopping down too far introduces diffraction softness across the whole image, so it is a trade-off rather than a free way to reduce frame count.
It can estimate a step size based on the settings you give it, though the result does not always suit every macro subject and magnification, which is worth checking against a quick test stack before trusting it fully.
A visible soft band or halo where two frames were blended, usually most noticeable on fine texture or detailed edges that fell into the gap between the two frames’ sharp zones.
It varies enormously with magnification and aperture, from a handful of frames for a modest close-up to well over a hundred for an extreme magnification subject shot at a wide aperture.
The Short Version
Let depth of field at your chosen aperture and magnification set the starting step size, then confirm it with a short test stack before committing to a full sequence. Cut the step in half if gaps or halos show up, and increase it if the frame count feels excessive for a clean result.