The Rainwater Memorial Calibration Facility for X-Ray Optics
Figure 8
Sketch of finite source distance implications. The dotted box contains lines parallel to the optic axis (full line) and the X-ray axis (dotted line) in each of the four cases. (a) Ideal situation with beam parallel to optic axis. (b) Reflection overshoot occurs when beam divergence causes reflected beam to miss second mirror. (c) Shell shadowing may also occur, but the distance between mirror shells in the NuSTAR optic means it does not contribute here. (d) Pseudoparallel illumination compensates for the beam divergence by adjusting the yaw of the optic. The divergence of the beam in this approach is determined by the radial size of the subgroup under investigation rather than the radial location of the subgroup.
