The focal plane unit consists of a heated iodine cell for wavelength calibration, and acqusition/guide camera for placing and keeping stars on the 50 micron spectrograph fiber, and a calibration channel for flat fielding and injection of ThAr calibration.

Initial plan is to use a Shelyak FIGU which has a 50 micron hole with circular fiber in a pickoff mirror with a guide camera imaging this focal plane, with a magnification of 1.5X (empirically could be 1.33X?). The guide camera is an Atik 414ex 531. It is normally controlled by APOsong through ASCOM Remote, although the PWI4 software also contains an ASCOM driver, which is useful for pointing models, etc.

The Shelyak is mounted on a Zaber X-LSM050a motorized stage with 50mm travel. From the Windows desktop, this can be controlled with the Zaber Launcher software, but normal usage for SONG is through the remote interface in APOsong (although it would be nice to write a quick ASCOM Focuser server).

The iodine cell is placed on a Thorlabs LTS150C motorized linear stage for moving it in and out of the optical path. From the Windows desktop, this can be controlled with the Thorlabs Kinesis software, but normal usage for SONG is through the remote interface in APOsong.

Temperature control is achieved using a Thorlabs TC300 controller with two heating elements for each half of the iodine cell. From the Windows desktop, this can be controlled with the Thorlabs TC300 software, but normal using for SONG is through the remote interface in APOsong.