Fig. 1. Design method

Fig. 2. Schematic of the zoom lens

Fig. 3. 2D structural diagrams of the optical zoom system. (a) Short focal length position (focal length 25 mm,F4); (b) middle focal length position(focal length 550 mm,F4); (c) middle focal length position (focal length 900 mm,F4);(d) middle focal length position (focal length 900 mm,F5.5); (e) middle focal length position (focal length 1050 mm,F5.5);(f) long focal length position (focal length 1200 mm,F5.5)

Fig. 4. MTF. (a) Short focal length position (focal length 25 mm,F4); (b) middle focal length position (focal length 550 mm,F4); (c) middle focal length position (focal length 900 mm,F4); (d) middle focal length position (focal length 900 mm,F5.5); (e) middle focal length position (focal length 1050 mm, F5.5); (f) long focal length position (focal length 1200 mm,F5.5)

Fig. 5. Aberration curves. (a) Short focal length position(focal length 25 mm,F4); (b) middle focal length position (focal length 550 mm,F4); (c) long focal length position (focal length 1200 mm,F5.5)

Fig. 6. MTF of different focal length position after temperature focusing. (a) Short focal length position (focal length 25 mm,F4,-40 ℃); (b) short focal length position (focal length 25 mm,F4,+60 ℃); (c) long focal length position (focal length 1200 mm,F5.5,-40 ℃); (d) long focal length position (focal length 1200 mm,F5.5,+60 ℃)

Fig. 7. Tolerance analysis

Fig. 8. Zoom data. (a) 25-900 mm;(b) 900-1200 mm

Fig. 9. Compact mid-wave infrared zoom imager

Table 1. Design specifications for zoom optical system

Table 2. Focusing amount of zoom lens at long focal length position

Table 3. Focusing amount of zoom lens at short focal length position