Association of thin lenses

Each lens i is caracterised by its location and its convergence Cvi =1/f ' i.

To determine convergence Cv = 1/f ' of the association of two lenses we apply Gullstrand's formula (34) with N = 1 :

• The case of two lenses at distance e : Cv = Cv1 + Cv2 – e.Cv1.Cv2 being :

We thus deduct :

• The case of two joined lenses(Cv1 et Cv2) : e = 0 hence Cv = Cv1 + Cv2