Enter Lens Values
Leave one field blank. The calculator solves the missing value using the lens relation and also reports magnification and optical power.
Formula Used
The calculator follows the Cartesian sign convention for spherical lenses. Enter two signed values and leave one field empty. It solves the missing term, then calculates magnification and optical power.
- Magnification: m = v / u
- Lens Power: P = 1 / f (when f is in meters)
- Real image: usually positive image distance
- Virtual image: usually negative image distance
How to Use This Calculator
- Choose the lens type and preferred unit.
- Enter any two signed values among object distance, image distance, and focal length.
- Leave the unknown value blank.
- Press the calculate button.
- Review the result card, magnification, power, and image description.
- Export the result as CSV or PDF if needed.
Example Data Table
| Case | u | v | f | Lens Type | Interpretation |
|---|---|---|---|---|---|
| 1 | -30 cm | 15 cm | 10 cm | Convex | Real, inverted, diminished image |
| 2 | -15 cm | 30 cm | 10 cm | Convex | Real, inverted, magnified image |
| 3 | -20 cm | -10 cm | -6.667 cm | Concave | Virtual, erect, diminished image |
Frequently Asked Questions
1. What does the lens formula calculate?
It relates focal length, object distance, and image distance for a thin lens. If you provide any two signed values, the calculator finds the third.
2. Why must one value stay blank?
The equation solves one unknown from two known inputs. Filling all fields can create conflicting values, while leaving more than one blank makes the problem incomplete.
3. What sign convention should I use?
Use the Cartesian convention. Typically, object distance is negative for real objects on the incoming-light side, and convex focal length is positive while concave focal length is negative.
4. How is magnification interpreted?
The magnitude shows size change. Values above one indicate magnification. The sign helps indicate orientation, while the result card also labels the image as erect or inverted.
5. What does lens power mean?
Lens power is the reciprocal of focal length in meters. It is measured in diopters and indicates how strongly the lens converges or diverges light.
6. Can I use millimeters or meters?
Yes. Select millimeter, centimeter, or meter. Keep all entered distances in the same unit so the formula remains consistent before the power conversion.
7. Why does the result show a sign warning?
The warning compares the calculated focal length with the selected lens type. If they disagree, your chosen signs may not match the intended optical setup.