Final alignment of the VLT

摘要

In a recent paper McLeod proposed and used measurements of the field dependence of third order astigmatism to collimate a Ritchey-Chretien telescope with the stop at the primary mirror. We adapt this method to the Cassegrain focus of the ESO Very Large Telescope (VLT), where the stop is at the secondary mirror and the telescope is only corrected for spherical aberration. In addition, we study the effects of the practical definition that the center of the field is the center of the adapter. We present measurements of the field astigmatism and discuss the accuracy of this collimation method.