Required stroke of DM1 (out of pupil) on THD2 (in units of nm) to reach a DH contrast of 10⁻⁹ with an HLC mask designed with option (c) described in the text. The strokes are given as a function of amplitude transmission, on the y-axis, and OPD in nm of wavefront, on the x-axis, of the HLC mask. This simulation assumes the two concrete DMs of THD2, and a correction at 700 nm, which is the worst case in terms of the DM1 actuator stroke out of the three simulated wavelengths (700 nm, 740 nm, 780 nm). Using the same specs as Roman (1.57% transmission and 2.87 rad phase) for an HLC on THD2 requires a DM1 stroke of 380 nm ptv, and thus still leaves margin for aberration corrections. For easier manufacturing, the HLC for THD2 deploys a slightly lower OPD, while still meeting the specs (for details, see text).