Wood­en slide trays were a hall­mark of ‘Hemdé’ view­ers, 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.
While the trade­mark ‘Hemdé’ was reserved exclu­sive­ly for Delé­caille and Sorel, Cuny was the sole man­u­fac­tur­er of the view­ers. He evi­dent­ly also dis­trib­uted view­ers under his own name, although only a small num­ber of such exam­ples are known. Some unbrand­ed view­ers are also known; how­ev­er, their dis­tinc­tive char­ac­ter­is­tics indi­cate that they dif­fer from the major­i­ty of Cun­y’s view­ers mar­ket­ed under the ‘Hemdé’ trademark.