Optical Crown Glass

In optical crown glass, a low-index commercial-grade glass, the index of refraction, transmittance, and homogeneity are not controlled as carefully as they are in optical-grade glasses such as BK7. Optical crown is suitable for applications in which component tolerances are fairly loose and as a substrate material for mirrors.

Optical Crown Glass Constants Constants
Abbé Constant
(nF - nC) = 0.0089
2.55 g/cm-3
Young's Modulus
7.15 x 109 dynes/mm2
Poisson's Ratio
Specific Heat Cp (20° to 100°C)
0.184 cal/g-°C
Coefficient of Linear Expansion (20° to 300°C)
9.3 x 10-6/°C
Stress Birefringence, (Yellow Light)
10 nm/cm
Melt-to-Melt Mean Index Tolerance
Transformation Temperature
Softening Point

Transmittance characteristics for optical crown are shown the figure below.

External transmittance for 10-mm-thick uncoated optical crown glass