Lens Equation Calculator

A thin lens forms images according to 1/f = 1/do + 1/di, where f is focal length, do the object distance, and di the image distance. Enter any two to find the third.

Lens Equation Calculator

$\frac{1}{f} = \frac{1}{d_o} + \frac{1}{d_i}$

Solve for

Object distance (do)

Unit

Image distance (di)

Unit

Result unit

How to interpret the result

The lens equation ties the three distances together: move the object closer and the image moves farther out. A positive image distance means a real image (projectable on a screen); the sign and size of the result tell you where — and how — the image forms.

Assumptions

Thin lens (thickness negligible compared to focal length)
Paraxial rays: rays close to the optical axis, small angles
Sign convention: distances measured from the lens; this calculator uses positive values for real object/image distances