The Uni­ver­sal-Stere­o­be­tra­chter is designed to sup­port mul­ti­ple stere­oview for­mats. When unfold­ed, the device con­sists of two sec­tions mount­ed on a base plate. The front pan­el con­tains the lens­es. Dur­ing focus­ing, the entire front pan­el moves for­ward or back­ward. The device has an oblique view­ing angle, which facil­i­tates posi­tion­ing the eyes in front of the lenses.
One dis­ad­van­tage is the small focus­ing knob, which is part­ly inte­grat­ed into the base plate. This con­struc­tion con­tributes to the com­pact dimen­sions of the view­er but makes focus­ing more difficult.
(from: Com­pendi­um of Stereoscopes)