The focus radius and the focus position need keep constant in the laser application. To control them, a flexible optical system is required. The system is equipped with variable focus mirrors S2 and S3. We can adjust f2 and f3 to keep the constant focus geometry with varied actual distance L3 between laser and focusing aid. In this paper, f2, f3-L3 curves are given with fixed parameters. There are two groups of f2, f3-L3 curves with the same part of L3 (only partial curves were given in other pa
