Three thin lenses,each of focal length f,are placed in contact.What is the resulting focal length of the combination?

Question

Quizplus · Accepted Answer

When thin lenses are placed in contact, their focal lengths add. Therefore, the effective focal length of the combination can be found by adding the individual focal lengths:
1/f_eff = 1/f1 + 1/f2 + 1/f3
Since all three lenses have the same focal length f, we can substitute f for each f1, f2, and f3:
1/f_eff = 1/f + 1/f + 1/f
1/f_eff = 3/f
f_eff = f/3

Three Thin Lenses,each of Focal Length F,are Placed in Contact