2010 April 29
Several days after installing NIRI on the telescope the beam splitter wheel began to have problems getting into position. The beam-splitters are flat mirrors which send light to the science detector and allow the surrounding field to go to the OIWFS. Each mirror is sized to match the field of view of the associated camera. The f/32 beam splitter mirror is the smallest, only sending a 22 arcsecond field through the instrument. The f/14 mirror sends a 51 arcsecond field, and the f/6 mirror is the largest, sending a 2 arcminute field. Since the OIWFS is currently not being used it is possible to use the largest beam splitter (f/6) to direct light to all three cameras. The obvious disadvantage to using an oversized beam splitter is that extra light is directed into the f/14 and f/32 cameras, which will result in higher background and possibly internal reflections. We have compared GCAL flats taken with the normal beam splitter and the oversized f/6 beam splitter and the inrease in background is minimal.