Focal Length Calculator

Calculate the focal length of a thin lens from image and object distances: 1/f = 1/do + 1/di.

cm
cm

Focal Length

10.00 cm

Lens Power10.00 diopters

Focal Length vs Object Distance

Voir la formule →

Formule

## Focal Length The focal length defines the converging or diverging power of a lens or mirror. ### Formula **1/f = 1/d_o + 1/d_i** Lens power in diopters is **D = 1/f** (with f in meters). Positive focal length = converging lens; negative = diverging.

Exemple Résolu

An object at 30 cm produces an image at 15 cm.

  1. 011/f = 1/do + 1/di
  2. 021/f = 1/30 + 1/15
  3. 031/f = 0.0333 + 0.0667 = 0.1
  4. 04f = 10 cm
  5. 05Power = 100/10 = 10 diopters