L 0.1[m] "Mirror-lens distance"
D 25[mm] "Mirror diameter"
f 0.5[m] "Lens focal length"
th 1e-3[deg] "Initial ray angle"
n 1.5 "Lens index"
R f*2*(n-1) "Radius of curvature (thin biconvex lens)"
T0 1[us] "Total computation time"
dt T0/100 "Time increment"