Question

the part of combination of two lenses x and y is 4d. if the focal length of x Is 12cm , calculate the focal length of y and nature of lens y

Answer 1

It depends on the distance between them. If their distance is d and the focal lengths of the lenses are f1 and f2, then the focal length f of the combined system is determined by

1/f = 1/f1 + 1/f2 − d/f1f2.

The thickness of each lens is neglected here.