PERFORMANCE ANALYSIS FOR THEMIS IMAGE STABILIZER OPTICAL-SYSTEM .1.

This paper describes the performance of the optical image stabilizer s ystem developed for the franco-Italian T.H.E.M.I.S. telescope, which i s currently being built on the Canary Island Tenerife. T.H.E.M.I.S wil l be one of the largest solar telescopes, and will be the first to be manufactured with a real time tip-tilt correction system integrated in to its optical train. A new method is described here for measuring ima ge motions. This method is called granulation tracking. It is based on Fourier transform analysis. A servo-loop model is also proposed, base d on experimental measurements and the known time properties of atmosp heric turbulence, to deduce the image quality obtained after correctio n. Method sensitivity and accuracy under various terrestrial turbulenc e conditions are discussed.