Lens Magnification Calculator

It relates focal length and the two distances as 1/f = 1/do + 1/di, where do is the object distance, di is the image distance and f is the focal length. Give any two and the third is fixed.

Linear magnification is m = -di / do. A magnitude above one means the image is enlarged and below one means reduced, while the sign tells you the orientation.

A negative image distance marks a virtual image on the same side as the object, as when an object sits inside the focal length of a converging lens. A virtual image cannot be projected onto a screen.

A negative magnification means an inverted, real image, the kind a projector or camera forms. A positive magnification means an upright, virtual image, the kind you see through a magnifying glass held close.

Distances in front of the lens and converging focal lengths are positive. Virtual images give a negative image distance and a positive magnification, following the standard real-is-positive convention.

Yes. Enter a negative focal length for a diverging lens. It always forms a reduced, upright, virtual image, so you will see a negative image distance and a positive magnification below one.

When the object distance equals the focal length, the outgoing rays are parallel and the image forms at infinity, so no finite image distance exists. The tool reports this rather than returning a misleading number.

Enter all three quantities in centimeters. Magnification is a pure ratio with no units, so it reads the same regardless of the length unit as long as you stay consistent.

No. The equation is solved in your browser, so the distances you enter are never uploaded.