Apochromatic lenses are corrected for chromatic aberration at how many colors?

• A. One
• B. Two
• C. Three
• D. Four

Answer: (C)

Apochromatic lenses address chromatic aberration by aligning the focal points of three wavelengths, bringing red, green, and blue to the same focus. This minimizes color fringing across the spectrum far better than corrections that cover only two colors. The result is sharper, more accurate images, especially at high magnifications or wide apertures. In contrast, an achromatic lens corrects two wavelengths (typically red and blue), which reduces but does not eliminate chromatic aberration. Some ultra-specialized designs can target four wavelengths, but the standard apochromatic approach is three-color correction.