Calculate focal length, object distance, or image distance for a thin lens.
Lens & Object Parameters
mm
mm
mm
Calculation Results
Enter two parameters to find the third
Quick Reference
fFocal Length
doDistance to Object
diDistance to Image
M-di / do
Overview
The thin-lens equation relates the focal length of a lens to the distances of the object being viewed and the image formed. It's fundamental for cameras, telescopes, and eyeglasses.
💡
Pro Tips
Use positive values for converging (convex) lenses, negative for diverging (concave).
Object distance (do) is usually positive.
A positive image distance (di) means a real image; negative means virtual.
!
Fun Facts
"The human eye behaves like a converging lens that can change its focal length."
"Lenses were used as early as the 5th century BC to start fires by focusing sunlight."
"The term 'lens' comes from the Latin word for 'lentil' because of the shape."
