What is minimum focus distance?

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.

What is working distance?

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.

How does MFD relate to magnification?

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.

Can I focus closer than the rated MFD?

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.

PhotoCalcs

Minimum Focus Distance Calculator — Working Distance & Magnification

Find the working distance and maximum magnification at your lens minimum focus distance.

Focal Length

Lens focal length

Minimum Focus Distance

From sensor plane to subject

Sensor Width

e.g. 36mm for full frame

Lens Physical Length

Length of lens barrel

How We Calculate This

This calculator determines the magnification and working distance at minimum focus. Minimum focus distance (MFD) is the full distance D from the sensor plane to the subject, so the thin-lens relation D = f(1 + m)² ÷ m must be solved for the magnification m:

Magnification at MFD

m = [(D − 2f) − √(D² − 4fD)] ÷ (2f)

Where f = focal length and D = minimum focus distance (both in mm). A real image needs D ≥ 4f; at exactly 4f the lens reaches 1:1 (life-size).

Working Distance (estimate)

Working distance ≈ MFD − lens physical length

A rough front-of-lens-to-subject figure; the true clearance varies with lens design.

Subject Coverage

Subject width = sensor width ÷ magnification

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates based on standard optical and photographic formulas. Results may vary with specific equipment.