Peak strength of the effective extinction curve caused by a distant turbulent screen as function of the mean extinction (⟨ A_V ⟩ ) for given column density contrast (σ_{lnN/ ⟨ N ⟩} ) (left hand figure) and as function of column density contrast for given mean extinction (right hand figure). The curves in the right hand figure are labelled with log A_V [mag] . The critical column density is assumed to be  [N_H] _crit = 10²¹   cm^-2. The values in the limit of a non turbulent medium (σ = 0) are shown as grey lines, the value in the the theoretical limit of infinite column density contrast (σ → ∞) as dashed line. Also shown as dotted lines are peak strengths derived using the approximation Eq. (A.3).