AE = r₂; AE′ = r′₂; B b = t″; BE = r₁ - r₂ = l
ε = the first angle of refraction b B′ k
η = the second angle of refraction B′ b C
ε′ = the first angle of refraction e E k′
η′ = the second angle of refraction e m C
α = the angle of emergence b C q
α′ = the angle of emergence m C q
i′₁ = BFA; i′₂ = EFA; i₁ = B′FA; i₂ = E′FA
e₁ = B b B′; e₂ = E e E′.
Proceeding exactly as in the case of the central lens we shall have