Figure 1. This figure shows the tilts required to correct for the translation of the secondary mirror owing to the flexure of the secondary truss and the flexure of the secondary actuator supports as a function of telescope elevation angle. The translation of the secondary mirror with respect to the primary mirror causes coma in the telescope optics. The tilts shown here are those required to correct for the coma measured by the Shack-Hartmann sensor.

The squares show the tilts required in the y direction. There is no measurable variation of y-tilts as a function of telescope elevation angle. There is a small constant offset of about 5 arcseconds which is the result of errors in the initial collimation.

The circles show a clear variation of x-tilts as a function of elevation angle. This is the direction of tilt expected from sag in the telescope truss and secondary actuator supports. The solid line shows a fit to these data. The lower legend gives the form used for the fit. The coefficients m1 through m3 must be added to the current TCC tilt coefficients.