Atmospheric dispersion corrector

The Atmospheric Dispersion Corrector (ADC) is now fully installed and operational. First tests revealed problems with prism positioning which was found to be caused by too wide drive belts for the belt wheels. The positions of the 2 prisms have been calibrated and all operational modes verified. Sequencer commands to operate the ADC need to be made while the status and value of the ADC should be displayed on the FIES status display and added to the data FITS headers.

From on-sky tests it was found it has a 3.1 arcmin field-of-view and the measured throughput was found to be 88-91% in the optical, 85% J&H, and 67% in K. Although the ADC is primarily developed for use with FIES, it can for some cases be valuable for other instrument as well. The ADC is located under the 'roof' of the adapter, and swings into the telescope beam above the FIES and STANCAM pickoff mirrors.