An Introduction to Modern Astrophysics · Problem 6.4

Binary Systems and Stellar Parameters — Carroll & Ostlie

Physics — Astrophysics · achromatic-compound-lens

Problem

(a) Using the result of Problem 6.3, show that a compound lens system can be constructed from two lenses of different indices of refraction,

n_{1\lambda}

and

n_{2\lambda}

, having the property that the resultant focal lengths of the compound lens at two specific wavelengths

\lambda_1

and

\lambda_2

, respectively, can be made equal, or

f_{\mathrm{eff},\lambda_1} = f_{\mathrm{eff},\lambda_2}.

(b) Argue qualitatively that this condition does not guarantee that the focal length will be constant for all wavelengths.