Multipass V-shaped system with a large relative aperture: stages of development.

In this review I describe the step-by-step development and update of an optical multipass system with a fixed path length and large relative aperture. The system has been researched off and on for 20 years. Contrary to acknowledged ideas, some of the models were designed using the ratio between the base length of a multipass system and the focal length of an objective equal to 1.5 (compared with 2 for the classical White system). Such an unconventional choice of 1.5f base length between opposite mirrors ensured the development of a cycle of six-pass single-objective systems with a large relative aperture. The described systems were used in various gas analytical equipment. Of special interest is an original scheme with an f-number of 3.7 to be used in high-resolution spectroscopy.