A new optical structure design method was proposed by forward-object lens, zoom lens, focus lens and behind-object lens with transmissive switch-zoom infrared system. And an alignment method of the above structure was proposed to assure the imaging precision. The larger caliber forward lens structure was designed to immovably axial with system axis, while the zoom lens structure was designed to three different structures by actual optical design for reducing system dimension. The focus lens structure was absolute configuration for the stabilization during focus. The rear lens structure was also designed to small radial clearance. A through-shaft type tooling was proposed to cooperate to adjusting and confirming of the system optical axis by exact boring machine. Experiment results showed that the alignment method can be assured precision and economized cost.
