TSC 225 (1989-1991)This telescope is the only one Schmidt-Cassegrain made by Takahashi. The focal ratio is f/12 (f/3 for the primary and x4 for the secondary miroir). This optical design gives less field curvature and less of axis coma than US Schmidt-Cassegrain (which are f/2 x5 = f/10). The schmidt corrector plate is made from Schott BK7 optical glass. This telescope was produced in a very short time (between 1989 and 1991) and it seems that there are a little more that one hundred TSC-225 in the world.