Question

Two lenses are placed at a distance of f1 - f2. What is the focal length of the combination?

Options; a) infinity
b) 0
c) f1×f2 / 2f2
d) 2f2 / f1 × f2.

Answer 1

I think option c is right

Answer 2

c) f1×f2/2f2 is correct answer