Though it appears fair­ly com­mon, this stere­o­scope holds a unique place in stereo­scop­ic history.
A hall­mark of ‘Hemdé’ view­ers was their wood­en slide trays, but their true inno­va­tion lay in the crank mech­a­nism. Using a clev­er­ly thread­ed rod, it both lift­ed slides into posi­tion and moved the tray, enabling smooth for­ward and back­ward nav­i­ga­tion. The mech­a­nism was patent­ed in 1907 by Paul Sorel, Émile Cuny, and Mau­rice Delécaille.
The view­er illus­trat­ed fea­tures both ele­ments, though it lacks any brand­ing. How­ev­er, its design sug­gests it pre­dates the patent. Com­pared to lat­er mass-pro­duced mod­els, the mech­a­nism of this view­er is stur­dier, with more wood­en struts — sug­gest­ing it was still in devel­op­ment. The strongest indi­ca­tion that it is an ear­ly, short-lived pro­to­type is its unique focussing method: by mov­ing the entire inside, a high­ly uncom­mon fea­ture among tray stereoscopes.