The maximum crosshead travel is ±3.5 arcmin on the sky. The 10mm thick dichroic substrate produces a 5.”27 image shift, which vanishes when guiding off the substrate. Stars within a few arcsec of its edge will be split into two images 5″ apart, so the edges must be avoided when choosing guide stars. The figure shows the exact dimensions of the areas of constraint which affect the selection of guide stars.

Back to Acquisition and guiding in “Description”.