dioptre
1. A unit proposed by Monoyer to evaluate the
refractive power of a lens or of an optical system. It is equal to the product of the refractive index in the image space and the reciprocal of the focal length in metres. (
Symbol: D.) Thus a lens with a focal length (in air) of 1 m has a power of 1 D, one with a focal length of 1/2 m, has a power of 2 D, etc.
2. It is also incorrectly used to represent a unit of curvature, being equal to the reciprocal of the radius of curvature expressed in metres.
See curvature of a surface;
myodioptre;
fundamental paraxial equation;
refractive error;
vergence.
Fig. D3 Effect of an 8 Χ prism
| Table D3 Relationship between dioptres and focal length (in air) |
| | focal length |
| dioptre value | | (cm) | | (in) |
| 0.25 | | 400 | | 157 |
| 0.50 | | 200 | | 79 |
| 1.00 | | 100 | | 39 |
| 1.50 | | 67 | | 26 |
| 2.00 | | 50 | | 20 |
| 2.50 | | 40 | | 16 |
| 3.00 | | 33.3 | | 13 |
| 4.00 | | 25 | | 10 |
| 5.00 | | 20 | | 7.9 |
| 6.00 | | 16.7 | | 6.6 |
| 7.00 | | 14.3 | | 5.6 |
| 8.00 | | 12.5 | | 4.9 |
| 9.00 | | 11.1 | | 4.4 |
| 10.00 | | 10 | | 3.9 |
| 12.00 | | 8.3 | | 3.3 |
| 14.00 | | 7.1 | | 2.8 |
| 16.00 | | 6.2 | | 2.4 |
| 20.00 | | 5.0 | | 2.0 |
| Table D4 Relationship between prism dioptres and degrees |
prism
dioptres (Χ) | | degrees (º) | | minutes (′) |
| 1 | | 0.573º | | 0º34′ |
| 2 | | 1.14º | | 1º8′ |
| 3 | | 1.71º | | 1º43′ |
| 4 | | 2.28º | | 2º17′ |
| 5 | | 2.85º | | 2º51′ |
| 6 | | 3.43º | | 3º26′ |
| 7 | | 4.0º | | 4º0′ |
| 8 | | 4.57º | | 4º34′ |
| 9 | | 5.14º | | 5º8′ |
| 10 | | 5.71º | | 5º43′ |
| 15 | | 8.57º | | 8º34 |
)