Optics
Thin lens equation
The image distance for a lens of focal length f and object distance do.
The Formula
di = f x do / (do - f)
The image distance for a lens of focal length f and object distance do.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| f | Focal length | centimetres | Positive for a converging lens, negative for a diverging one. |
| do | Object distance | centimetres | The distance from the lens to the object. |
| di | Image distance | centimetres | The distance from the lens to the image. |
What Each Symbol Means
fcentimetres
Focal length
Positive for a converging lens, negative for a diverging one.
docentimetres
Object distance
The distance from the lens to the object.
dicentimetres
Image distance
The distance from the lens to the image.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to calculate a thin lens equation page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Calculate A Thin Lens Equation, filed under Science. Every number the guide produces comes from substituting into this one line.