The long-wave thermal imager has a zoom ratio of 20:1. It's focal length can be continuously varied from 18.5 mm to 367 mm by the mechanical compensation zoom approach. We designed the continuous zoom mechanism. In order to make optical axis error reaches requirements of the system, the inner linearity/parallelism of zoom mechanism, the parallelism between the zoom mechanism and the optical axis of the system needs to be adjusted accurately. By using thermal compensation table, temperature compensation and ...