In the longitudinal chromatic aberration formula CA = D/v, what does D represent?

• A. Power of the lens
• B. Distance from the optical center
• C. Abbe value
• D. Wavelength

Answer: (A)

The main idea is that axial (longitudinal) chromatic aberration grows with how strongly a lens bends light and is reduced by how little the material disperses colors. In the formula CA = D/v, the symbol D is the dioptric power of the lens, i.e., the lens’s power measured in diopters (D = 1/f in meters). This shows that for a given material (fixed v), increasing the lens power increases chromatic aberration, while using a material with a larger Abbe number (larger v) reduces dispersion and thus reduces CA. The distance from the optical center and the wavelength are related concepts but not what D represents in this equation.