Voigtlander stereo duplicator

Stereo slide duplicator (1907-1937)

Stereo slide duplicator 4.5x10.7
(photo shows two devices : one opened and one closed)
This wooden accessory was used to obtain two positive pictures on paper or glass, by direct contact from a stereo negative plate.

The picture taken through the lens of a camera shows the subject upside down.
Turning it over makes a right to left inversion which must to be restored to keep the 3D effect of stereo pictures.
This device was used to overcome this problem.

To use the duplicator :
1- Do a left positive copy on the right half of the unexposed plate by direct contact of the original slide.
2- again by direct contact, expose the right positive side of the copy on the left of the unexposed plate by sliding
    the plates inside the duplicator one opposite to the other, facing the central window.

One could obtain a glass or paper stereo photography where right and left were correctly kept.