Which material corresponds to n=1.498 and abbe value 58?

Which material corresponds to n=1.498 and abbe value 58?

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

Answer: (B)

When evaluating lens materials, two key properties guide you: the refractive index (n) and the Abbe value (V). The refractive index tells you how much the material bends light, which influences lens power and thickness. The Abbe value measures dispersion, or how much the refractive index changes with wavelength; higher Abbe values mean less chromatic aberration and crisper vision across colors. A material with n around 1.498 and an Abbe value near 58 fits CR-39, a common plastic lens material. CR-39 is known for its modest index around 1.498 and good dispersion characteristics with an Abbe value in the high 50s, which helps minimize chromatic aberration while keeping lenses lightweight and affordable. For comparison, ophthalmic crown glass typically has a slightly higher index (about 1.523) and a similar or slightly higher Abbe value, plastic options like polycarbonate have a higher index (around 1.586) but a much lower Abbe value (roughly 30), and Trivex sits between plastics with an index near 1.53 and a mid-range Abbe value (around 40–44). These differences explain why only CR-39 matches the given combination of n and Abbe.

When evaluating lens materials, two key properties guide you: the refractive index (n) and the Abbe value (V). The refractive index tells you how much the material bends light, which influences lens power and thickness. The Abbe value measures dispersion, or how much the refractive index changes with wavelength; higher Abbe values mean less chromatic aberration and crisper vision across colors.

A material with n around 1.498 and an Abbe value near 58 fits CR-39, a common plastic lens material. CR-39 is known for its modest index around 1.498 and good dispersion characteristics with an Abbe value in the high 50s, which helps minimize chromatic aberration while keeping lenses lightweight and affordable.

For comparison, ophthalmic crown glass typically has a slightly higher index (about 1.523) and a similar or slightly higher Abbe value, plastic options like polycarbonate have a higher index (around 1.586) but a much lower Abbe value (roughly 30), and Trivex sits between plastics with an index near 1.53 and a mid-range Abbe value (around 40–44). These differences explain why only CR-39 matches the given combination of n and Abbe.