What is the approximate index of refraction and abbe value for Ophthalmic crown glass?

• A. n=1.523, abbe=58.9
• B. n=1.498, abbe=58
• C. n=1.586, abbe=30
• D. n=1.53, abbe=44

Answer: (A)

Ophthalmic crown glass has a refractive index in the low 1.5 range and a high Abbe number, meaning it bends light moderately but shows relatively little chromatic dispersion. The typical values are about n ≈ 1.523 and Abbe ≈ 58–59, which is why the match of n = 1.523 and Abbe = 58.9 is the best choice. This low-to-moderate index with high Abbe number distinguishes crown glass from materials with high dispersion (lower Abbe) or significantly different indices.