What is the depth of field of a 100mm macro lens at f/2.8?
At 100mm, f/2.8, focused at 35cm on full frame — close to this lens's minimum focus distance for a genuine macro subject — total depth of field is roughly 1.4mm. That's not a typo: at true close-focus macro distances, the sharp zone genuinely collapses to a couple of millimeters, thinner than the depth of an insect's eye.
Why Macro Depth of Field Is a Different Regime Entirely
The standard hyperfocal-distance formula still technically applies here, but at this magnification the hyperfocal distance itself balloons to over 120 meters — meaningless at macro range — while the near and far limits sit almost exactly on top of the focus point. This is why macro photography is discussed as its own discipline with its own depth-of-field intuition rather than an extension of normal landscape or portrait DoF thinking: the underlying physics is identical, but the practical numbers are in a completely different scale.
What Changes This Number
Stopping down to f/8 nearly triples the sharp zone, to roughly 4mm; f/16 reaches roughly 8mm — both still measured in single millimeters, and both starting to risk visible diffraction softening on a high-resolution sensor. Backing away from true 1:1 macro magnification toward a more moderate close-up distance widens depth of field dramatically, since magnification itself, not just aperture, drives this calculation at extreme close range.
See how depth of field grows as you back away from true macro distance in the DoF & Hyperfocal Calculator, pre-filled with 100mm f/2.8 at 35cm.
Frequently Asked Questions
Why is macro depth of field measured in millimeters instead of meters?
Because true macro magnification (close to 1:1 reproduction) means the subject distance is only slightly longer than the lens's focal length, and depth of field shrinks dramatically as subject distance approaches focal length — the same formula that gives meters of depth of field at normal distances gives millimeters at true macro range.
Why do macro photographers use focus stacking instead of just stopping down further?
Stopping down enough to meaningfully widen a millimeter-scale depth of field (f/16, f/22 and beyond) introduces visible diffraction softening across the whole frame, so combining multiple exposures at different focus points in post-processing usually produces a sharper final result than any single small-aperture exposure could.