Lens Equation Calculator
Calculate image distance from focal length and object distance.
Lens Equation measurements
Enter your values, then calculate.
Result
How to calculate lens equation
The thin lens equation relates focal length, object distance, and image distance for a simple lens — this calculator finds image distance from focal length and object distance.
How the calculation works
Image distance = 1 ÷ ((1÷Focal length) − (1÷Object distance)).
Example
A 10 cm focal length lens with an object 30 cm away: 1÷((1÷10)−(1÷30)) = 1÷(0.1−0.0333) = 1÷0.0667 ≈ 15 cm.
Frequently asked questions
How is Result calculated?
Result = 1 ÷ (1 ÷ [Focal length] − 1 ÷ [Object distance]).
Is the Lens Equation Calculator free to use?
Yes — every calculator on Simple Calculator Tools is free, runs in your browser, and does not require an account.
Lens Equation Calculator
Image distance = 1 ÷ ((1÷Focal length) − (1÷Object distance)).
Let's understand your lens equation result.
Calculate a result above and this guide will help you interpret it using this calculator's own formula and explanation.
Pro Tips for Lens Equation
- This uses the standard sign convention where distances are measured from the lens — double-check your specific convention if results seem unexpected.
- When object distance equals focal length, the denominator approaches zero and image distance becomes very large (parallel rays, no real image forms).
Common Lens Equation Mistakes to Avoid
- Using an object distance smaller than the focal length without recognizing this produces a virtual image (negative result), which behaves differently than a real image.
When to Use This Calculator
The thin lens equation relates focal length, object distance, and image distance for a simple lens — this calculator finds image distance from focal length and object distance.