Question

A lens of focal length f is divided into two equal parts and then these parts are put in a combination as shown in the figure below.

1. What is the focal length of L₁?
2. What is the focal length of the final combination?

Answer 1

(i) `1/"f" = (η -1) (2/"R")`

(ii) `1/"f"_1 = (η -1) (1/"R")`

F₁ = 2f

`1/"f"_2 = (η -1) (2/"R")`

F₂ = f