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Diopter Focus Calculator

Find the new minimum focus distance and magnification when you stack close-up diopters in front of your lens.

Pick a lens to begin

Choose a cinema lens from your catalog, or switch to manual to enter focal length and MFD by hand.

▸How this works

A close-up diopter is a magnifying filter that screws onto the front of your lens and lets it focus closer than its native minimum. Strength is rated in diopters (1/m): a +1 brings a lens set to infinity down to about 1 m, a +2 to 0.5 m, a +4 to 0.25 m. When you stack two or more diopters, the combined power depends on where each element sits along the optical axis — it isn’t a straight add. That’s why this calculator asks for every diopter’s distance from the sensor.

Under the hood, the math chains the thin-lens equation through each element at its actual position. When the diopters sit flush against the front of the lens, this collapses to the textbook formula MFD_new = m / (m · ΣD + 1), where m is the lens’s native minimum focus distance and ΣD is the total diopter power. Distances measured from the sensor are exact; values measured from the front of the lens or a diopter depend on the geometry you entered above.