Which material corresponds to n=1.523 and abbe value 58.9?

• A. Ophthalmic crown glass
• B. CR-39
• C. Polycarbonate
• D. Trivex

Answer: (A)

This question focuses on identifying a lens material from its optical constants: refractive index and Abbe (chromatic) number. The given values, n = 1.523 and Abbe = 58.9, point to ophthalmic crown glass because this material historically sits near n ≈ 1.523 with a high Abbe number around 58–59, indicating relatively low chromatic dispersion for its index.

Among common lens materials, CR-39 has a smaller index (about 1.498) and a similar Abbe, but the index doesn’t match as well. Polycarbonate has a higher index (around 1.586) but a much lower Abbe (roughly 30), indicating more dispersion. Trivex typically has n around 1.532 with an Abbe in the 40s, which again doesn’t align with the 58.9 Abbe value. The combination of a ~1.523 refractive index with an Abbe near 59 is characteristic of ophthalmic crown glass, making it the best match.