Answer to Question #287056 in Optics for Elle

Question

A lens system is composed of two lenses. Lens A has a refractive power of +9.25 D and lens B has a refractive power of −3.75 D. An object is located 235 mm in front of Lens A. The focused image of the lens system is located exactly 30 cm behind Lens B. The lenses are suspended in air. Calculate the distance between the two lenses. (5 marks)

Answer 1

$F=\frac{fd}{f-d}=0.092~m,$

$\frac 1F=\frac1{F_1}+\frac 1{F_2}-\frac l{F_1F_2},$

$l=F_1+F_2-\frac{F_1F_2}F=15.4~cm.$