constringence
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constringence
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 | ||||||||
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann