Minimum Focus Distance Calculator — Working Distance & Magnification

Minimum focus distance (MFD) is the closest distance from the sensor plane to the subject where the lens can still achieve focus. It is measured from the sensor plane (marked with a symbol on most camera bodies), not from the front of the lens. A shorter MFD allows closer focusing and higher magnification.

Working distance is the physical gap between the front of the lens and the subject at minimum focus distance. This calculator estimates it as MFD minus the lens barrel length — a rough figure, because the true clearance depends on the lens design (internally-focusing and telephoto barrels vary). Working distance matters for macro, wildlife and product photography — too short and you may cast shadows or scare subjects.

Maximum magnification occurs at minimum focus distance. Because MFD is the full sensor-plane-to-subject distance D, the thin-lens relation is D = f(1 + m)² ÷ m, which solves to m = [(D − 2f) − √(D² − 4fD)] ÷ (2f). Macro lenses have short MFDs relative to their focal length, reaching 1:1 (1x) at D = 4× the focal length. Standard lenses typically achieve only 0.1–0.25x magnification.

Not optically. However, extension tubes, close-up dioptre filters, or reversing the lens can all reduce the effective MFD and increase magnification. Extension tubes maintain optical quality but reduce the focus range to infinity. Close-up filters are convenient but may reduce sharpness.