Mirror & Lens Equation Calculator

About this calculator

This calculator solves the thin lens/mirror equation, 1/f = 1/do + 1/di, relating focal length f, object distance do, and image distance di for a lens or curved mirror, and derives magnification as m = −di/do — a negative m means an inverted image, while |m| > 1 means the image is magnified relative to the object.

This single equation, with a sign convention distinguishing converging from diverging elements, predicts whether a lens or mirror produces a real or virtual image, upright or inverted, and how large — the exact same physics that determines how a camera lens focuses light onto a sensor, how a magnifying glass or telescope eyepiece works, and how a concave shaving mirror produces an enlarged upright image at close range.

Physics students working through optics problems, optical engineers designing camera and telescope systems, and photography and astronomy enthusiasts curious about how their equipment forms images all use this calculator, entering focal length and object distance.