constringence (redirected from V- value)

constringence 

A positive number (symbol: V) which specifies any transparent medium. It is equal to

V = n_d − 1/n_F − n_C

where 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