What is the approximate index of refraction and abbe value for CR-39 (Plastic)?

• 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: (B)

CR-39 is a common ophthalmic plastic with a modest refractive index and high dispersion resistance. Its typical values are about n ≈ 1.498 and Abbe ≈ 58, meaning it bends light moderately but has relatively low chromatic dispersion for a plastic. The pairing n ≈ 1.498 with Abbe ≈ 58 matches these well-known figures, so it is the best fit. The other options either imply a higher index that CR-39 usually doesn’t have, or a much lower Abbe value that indicates stronger dispersion than CR-39 exhibits.