Macro Photography Calculator

This calculator works out the practical tradeoffs of shooting at high magnification, where ordinary depth-of-field and exposure rules stop applying cleanly. Magnification is estimated from how much of the frame your subject fills (sensor width divided by subject width), then adjusted upward if you've added extension tubes, since each millimeter of tube adds tube-length/focal-length to your magnification. As magnification climbs, the effective aperture reaching the sensor grows darker — the calculator multiplies your set aperture by (1 + magnification), which is also the source of the light-loss figure reported in stops (2×log2(1+M)). Depth of field is derived from a magnification-aware formula using your chosen circle of confusion, and it shrinks fast: at 1:1 life-size magnification, DOF measures only millimeters even at moderate apertures.

Working distance approximates how far the lens's front element sits from the subject at the resulting magnification. Finally, the calculator checks whether you've hit the diffraction limit by computing the Airy disk diameter from wavelength (assumed at 550nm, green light) and effective aperture, then comparing it to your circle of confusion — if the Airy disk exceeds the CoC, diffraction is already softening the image more than any focusing error would, meaning stopping down further won't buy more sharpness. The most common misunderstanding here is confusing nominal aperture with effective aperture: your lens is still physically f/8, but at high magnification it behaves like a much smaller aperture for both light and diffraction purposes.