optical crown(n = noun.substance) crown glass, optical crown glass - optical glass of low dispersion and low refractive index;
is a kind of optical glass
british crown, counsel to the crown, crown, crown beard, crown colony, crown daisy, crown fire, crown gall, crown glass, crown imperial, crown jewel, crown jewels, crown land, crown lens, crown monkey, crown of thorns, crown office, crown prince, crown princess, crown roast, crown saw, crown side, crown vetch, crown wart, crown wheel, golden crown beard, half crown, jacket crown, nero's crown, optical, optical aberration, optical activity, optical bench, optical cable, optical condenser, optical crown glass, optical device, optical disc, optical disk, optical fiber, optical fibre, optical flint, optical fusion, optical glass, optical illusion, optical instrument, optical lens, optical maser, optical opacity, optical phenomenon, optical prism, optical pyrometer, optical telescope, pinion and crown wheel, triple crown