Calculator
Plotly Graph
The curve shows how optical power changes as radius varies around your chosen input.
Example Data Table
These sample rows help verify the formulas before using your own values.
| Method | Radius | Indices / Constant | Calculated Power | Note |
|---|---|---|---|---|
| Single Refracting Surface | 0.50 m | n₁ = 1.00, n₂ = 1.50 | 1.00 D | Useful for one curved interface. |
| Symmetric Thin Lens | 0.10 m | n_lens = 1.52, n_medium = 1.00 | 10.40 D | Assumes equal magnitude front and back radii. |
| Keratometry Approximation | 7.80 mm | K = 337.5 | 43.27 D | Common corneal curvature estimate. |
Formula Used
D = (n₂ - n₁) / R
Use this when light passes through one curved boundary separating two media. Radius R must be in meters for diopters to be correct.
D = 2[(n_lens / n_medium) - 1] / R
This is a simplified lensmaker-style form for equal magnitude front and rear radii. A positive radius produces positive power for a converging geometry.
D = K / r(mm)
Here K is often 337.5 and radius is entered in millimeters internally. This approximation is commonly used when converting corneal curvature to diopters.
How to Use This Calculator
- Select the physical model that matches your problem.
- Enter the signed radius and choose its unit.
- Fill in refractive indices or the keratometric constant.
- Set decimal precision and graph span if needed.
- Press the calculate button to show results above the form.
- Review optical power, focal length, curvature, and sensitivity.
- Use the graph and exports for reports or comparisons.
Frequently Asked Questions
1) What does diopter mean?
A diopter is the reciprocal of focal length in meters. A larger positive diopter means a stronger converging effect, while a negative diopter means diverging optical power.
2) Why does radius need a sign?
Optical sign conventions track surface orientation. Reversing radius sign can reverse lens power sign, so use the convention that matches your textbook, software, or design workflow.
3) Which method should I choose?
Choose single surface for one interface, symmetric thin lens for a simplified two-surface lens, and keratometry when converting corneal curvature using a fixed constant.
4) Can I enter millimeters or centimeters?
Yes. The calculator converts meters, centimeters, millimeters, and inches into meters internally, then applies the selected formula consistently for the diopter result.
5) Why is the result huge for a tiny radius?
Diopter is inversely proportional to radius. Very small radii produce very high curvature, which leads to large optical power values and steeper graph behavior.
6) What does the sensitivity value show?
Sensitivity estimates how quickly diopter changes when radius changes near your input. Large sensitivity means small radius errors can noticeably change optical power.
7) Is keratometry exactly the same as full lens power?
No. Keratometry is an approximation based on a standard constant. It is useful clinically, but it does not fully replace a complete physical lens model.
8) What if my focal length becomes negative?
A negative focal length indicates diverging behavior under the chosen convention. That usually corresponds to negative diopters and a virtual focal point.