question_answer

Two lenses of focal length \[{{f}_{1}}\] and \[{{f}_{2}}\] are         available. What must be the separation                 between them so as to minimise, spherical         aberration ?

A) \[\frac{{{f}_{1}}+{{f}_{2}}}{{{f}_{1}}{{f}_{2}}}\]                  

B) \[{{f}_{1}}{{f}_{2}}\]

C) \[{{f}_{1}}+{{f}_{2}}\]                    

D) \[{{f}_{1}}-{{f}_{2}}\]