Image selection by using an on-line fast shutter driven by tip-tilt signal

摘要

The possibility of improving the image quality of the Italian Telescopio Nazionale Galileo (TNG) by means of real-time on- line image selection by using a fast shutter is studied. The tip-tilt signal is checked against a user defined threshold to trigger on rejection of those images which would significantly degrade the long-exposure point spread function because of jitter broadening. The dependency of the achievable improvements on the rejection threshold, on the shutter opening and closing times, and on the atmosphere conditions (r$-o$/) is analyzed. The pros and cons of a ferroelectric liquid crystal shutter are discussed.