Why is depth of field so shallow in macro photography?

Macro depth of field is shallow because at true close-focus magnification, the subject distance is only slightly longer than the lens's focal length — and the depth-of-field formula's near and far limits both collapse toward that focus point as subject distance approaches focal length, regardless of aperture. A 100mm macro lens focused at 35cm for a true close-up produces roughly 1.4mm of total sharp depth at f/2.8; the same lens focused at a normal 3-meter portrait distance produces meters, not millimeters, at the identical aperture.

It's Magnification, Not Just Aperture

The instinct to blame a wide aperture for shallow macro depth of field is understandable but usually wrong — even stopping down substantially at true 1:1 magnification only widens the sharp zone by a few millimeters, since it's still a razor-thin band by any normal photographic standard. The dominant factor is magnification itself: the closer you focus relative to your lens's focal length, the more dramatically depth of field shrinks, independent of whatever aperture you've chosen. See real millimeter-scale numbers for a specific lens and aperture on the 100mm f/2.8 macro depth-of-field page.

Why Focus Stacking Exists Because of This

Stopping down far enough to meaningfully widen a millimeter-scale depth of field runs straight into diffraction, softening the whole frame before it meaningfully helps. Focus stacking sidesteps the problem by capturing multiple exposures at slightly different focus points across the subject and combining the sharp regions of each in post-processing — a genuinely different solution from choosing a narrower aperture, and the standard technique serious macro photographers rely on rather than fighting the physics with aperture alone.

See exactly how much depth of field grows as you back away from true macro magnification in the DoF & Hyperfocal Calculator.