φ = focal distance AF
t = thickness of the joint B b
t″ = B b
μ = refractive index of the glass
i₁ = BFA
i₂ = EFA
Then tan i′₁ = r₁φ; tan i′₂ = r₂φ
sin e₁ = sin i′₁μ; sin e₂ = sin i′₂μ
r′₁ = r₁ - t″ sin e₁; r′₂ = r₂ - t″ sin e₂
tan i₁ = r′₁φ; tan i₂ = r′₂φ