Calculate diopter or focal length from the other value, with focal length in mm, cm, m, in, or ft and step-by-step results.
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Diopter To mm Formula
The following formula is used to calculate the focal length in millimeters from a diopter measurement.
Variables:
- FL is the focal length in millimeters (mm)
- D is the diopter measurement (diopters)
For a thin lens in air with nonzero optical power, take the reciprocal of the signed diopter measurement and multiply it by 1000. Zero diopters corresponds to infinite focal length; negative diopters gives a negative focal length for a diverging lens. This converts the measurement from meters to millimeters. For example, a 2-diopter lens would have a focal length of 1/2 meter, or 500 millimeters.
| Diopters (D) | Focal length (mm) |
|---|---|
| 0.25 | 4000.000 |
| 0.50 | 2000.000 |
| 0.75 | 1333.333 |
| 1 | 1000.000 |
| 1.25 | 800.000 |
| 1.5 | 666.667 |
| 2 | 500.000 |
| 2.5 | 400.000 |
| 3 | 333.333 |
| 3.5 | 285.714 |
| 4 | 250.000 |
| 5 | 200.000 |
| 6 | 166.667 |
| 7 | 142.857 |
| 8 | 125.000 |
| 9 | 111.111 |
| 10 | 100.000 |
| 12 | 83.333 |
| 15 | 66.667 |
| 20 | 50.000 |
| *Formula: Focal length (mm) = 1000 / D. Example: 2 D → 500 mm. | |
What Does “Diopter to mm” Mean?
A diopter is a unit of measurement used in optics to determine the optical power of a lens or curved mirror. It is equal to the reciprocal of the focal length measured in meters. Therefore, if you want to convert diopters to millimeters, you would take the reciprocal of the diopter measurement and then convert that measurement from meters to millimeters. For example, a 2-diopter lens has a focal length of 1/2 meter, or 500 millimeters.
How to Calculate Diopter To mm?
The following steps outline how to calculate the Diopter To mm using the formula: FL = 1000 / D
- First, determine the diopter measurement (D).
- Next, use the formula FL = 1000 / D to calculate the focal length in millimeters (FL).
- Finally, calculate the Diopter To mm.
- After inserting the value of D and calculating the result, check your answer with the calculator above.
Example Problem:
Use the following variables as an example problem to test your knowledge.
diopter measurement (D) = 2
