Pick-off mirror

Due to the poor reflectivity of the Standby pick-off mirror ($\sim$60% measure at 4700Å) and the fact it was not possible to get it re-coated by the ING a new mirror was acquired with a bare aluminium coating, so it can be re-coated at the observatory. Initial measurements show an overall improvement in sensitivity of StanCam of $\sim$45% in V, $\sim$30% in R and $\sim$0% in I. Comparing to other instruments, the reflectivity of the new mirror appears to be what is expected for the aluminium coating, but that makes the reflectivity curve of the old mirror hard to understand.

Thomas Augusteijn 2006-05-08