This work focuses on methods used in the mechanical design of infrared catadioptric lenses. Multiple lens designs are presented to allow elaboration on mirror design considerations, alignment, athermal principles, system focusing options and design ruggedization. Catadioptric lenses are commonly used in the infrared as a cost effective solution to their refractive design counterparts. Janos Technology Inc. has designed, fabricated, and tested many catadioptric systems and this paper draws from their history. A summary of the assembly and testing process is also included.