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Physics

Thin Lens Calculator

Find image distance and magnification for a thin lens using signed focal length.

SI units shown beside each fieldIdeal model explained below
Optics bench
Optics bench

Use a negative focal length for a diverging lens.

See the method

Set focal and object distances

Runs on your device

Image location

Your result

Let’s calculate.

Use the Calculate button to see your result.

Review the method below for assumptions and conventions.

How to use this tool

  1. Enter focal length, object distance.
  2. Select Calculate to view the result.
  3. Check the method and assumptions below before using the result.

The method, explained

1/f = 1/do + 1/di; di = f do/(do−f); magnification = −di/do.

A WORKED EXAMPLE

Using focal length = 10 cm, object distance = 30 cm, the result is 15 cm. Change these example inputs to match your task; use the method above to check each step.

Understanding your result

Real object and paraxial thin-lens approximation. Positive focal length means converging; negative image distance means a virtual image.

What to keep in mind

Real object and paraxial thin-lens approximation. Positive focal length means converging; negative image distance means a virtual image. An idealized educational model using the stated SI units. Real systems may need additional forces, losses or experimental measurements. Not a safety or equipment specification.

Common questions

How do I use this thin lens calculator?

Find image distance and magnification for a thin lens using signed focal length. Enter focal length in cm, object distance in cm. The starting example is editable; use values for the same system or project.

Which assumptions affect this result?

Real object and paraxial thin-lens approximation. Positive focal length means converging; negative image distance means a virtual image.

Methodology maintained by ClarityKit. How these tools are built and checked.