constringence

A positive number (symbol: V) which specifies any transparent medium. It is equal toV = n_d − 1/n_F − n_Cwhere n_D, n_F and n_C 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