I experimented a bit with the focusing system, which introduces so much tilt that reversing focus direction introduces so many fringes that they can’t be resolved by the system. Keep in mind that it’s a double pass test so the beam reflects from the primary twice, which amplifies any tilt by a factor of two. Still, it appeared that the Strehl could be changed by as much as 0.1 by simply tilting the primary via the focus knob. This simply confirms the common knowledge that these systems should always be aligned and focused by turning the focus knob in the same direction (CCW.)