Fig. 1. Configuration of the freeform, dual-FOVs, dual-EFLs, off-axis, three-mirror zoom system.

Fig. 2. Layout of the initial planar system. (a) The system for the short-focus zoom. (b) The initial planar system for the long-focus zoom can be obtained after calculating Δ. The two zooms are overlaid in this figure. The red and green rays represent the rays in the short- and long-focus zooms, respectively.

Fig. 3. Scheme of coaxial three-mirror system.

Fig. 4. Scheme of coaxial dual-FOVs three-mirror system.

Fig. 5. Layouts of the system after each design stage. (a)–(c) show the layout of system after constructing freeform M1, M3, and M2, respectively. (d) The system after iterations.

Fig. 6. Distortion grids of both zooms after iterations. (a) The short-focus zoom. (b) The long-focus zoom.

Fig. 7. Layout of the final system for after optimization. (a) The layout of the system with two zooms overlaid in one figure. (b), (c), (d), and (e) show the individual zooms. The switch of the zooms (different FOVs) is achieved by rotating the M2 element along a rotational axis in the x direction (Figs. 7(b) and 7(c)) or the y direction (Figs. 7(d) and 7(e)).

Fig. 8. MTF curves and distortion grids for the two zooms after final optimization. (a) and (c) are for the short-focus zoom. (b) and (d) are for the long-focus zoom.