The optical imager Galileo (OIG)

The present paper describes the construction, the installation and the operation of the Optical Imager Galileo (OIG), a scientific instrument dedicated to the 'imaging' in the visible. OIG was the first instrument installed on the focal plane of the Telescopio Nazionale Galileo (TNG) and it has been extensively used for the functional verification of several parts of the telescope (as an example the optical quality, the rejection of spurious light, the active optics and the tracking), in the same way also several parts of the TNG informatics system (instrument commanding, telemetry and data archiving) have been verified making extensive use of OIG. This paper provides also a frame of work for a further development of the imaging dedicated instrumentation inside TNG. OIG, coupled with the first near-IR camera (ARNICA), has been the 'workhorse instrument' during the first period of telescope experimental and scientific scheduling.