A cross section through the model LBT modulation transfer function for the Brα filter, with perfect wave front correction and phase control. The MTF of a single 8.25 m aperture would consist only of the low-frequency peak, and go to zero power at approximately the equivalent of 0.5 au around the Altair system. The secondary maximum of the LBT MTF is at a baseline of B _CC, equivalent to 0.3 au. Green indicates the frequencies equivalent to radii of a face-on habitable zone as defined by Cantrell et al. (2013).