A positive number (
symbol: V) which specifies any transparent medium. It is equal to
V = nd − 1/nF − nC
where
nD,
nF and
nC are the refractive indices for the Fraunhofer spectral lines d (587.6 nm), F (486.1 nm) and C (656.3 nm). A material with a high constringence (e.g. V = 50) produces less chromatic aberration than one with a low constringence (e.g. V = 30). The reciprocal of the constringence is called the
dispersive power.
Syn. Abbé's number; V-value.
See dispersion;
crown glass;
flint glass;
Fraunhofer's lines.
| Table C8 Constringence (V) of some transparent media (index of refraction n) |
| | n | | V |
| glass | | | | |
| spectacle crown | | 1.523 | | 59 |
| dense barium crown | | 1.620 | | 60 |
| lanthana crown | | 1.713 | | 54 |
| zinc crown | | 1.508 | | 61 |
| light flint | | 1.581 | | 41 |
| dense flint | | 1.620 | | 36 |
| extra dense flint | | 1.706 | | 30 |
| titanium oxide | | 1.701 | | 31 |
| polymer | | | | |
| PMMA | | 1.492 | | 57 |
| CR-39 | | 1.498 | | 59 |
| Polycarbonate | | 1.586 | | 30 |
| Polystyrene | | 1.590 | | 31 |
| Water (at 37ºC) | | 1.331 | | 56 |
| Aqueous and vitreous (at 37ºC) | | 1.334 | | 56 |