The spectrum of one of our targets (J18414143−0531378) observed with AF2 (top), at R = 4100 and with ISIS at R ≈ 16   000. At the AF2 resolution, many of the lines seen in the ISIS spectrum are blended into broad features. An interesting example is the 8514 Å blend (mainly Fe i) that appears as a single feature at the AF2 resolution. This feature is very strong in luminous supergiants (see Fig. 5).