Description
Folding pocket stereo cigarette card viewer
Circa 1930
All Metal, Folding Viewer for PRINTS – Black metal viewer with glass lenses made in Germany in the late 1920s and early 1930s.
This folding viewer for individual stereoscopic pictures has a cut-out between the lenses to accommodate the user’s nose!
The original folding viewer was patented by J. F. Mascher of Philadelphia in March 1853 and was designed to hold stereoscopic portraits using the daguerreotype process.
Unfortunately, this was at the very end of the daguerreotype era, and originals are pretty rare.
Principles
A simple stereoscope is limited in the size of the image that may be used. A more complex stereoscope uses a pair of horizontal periscope-like devices, allowing the use of larger images that can present more detailed information on a broader field of view. The stereoscope is essentially an instrument in which two photographs of the same object, taken from slightly different angles, are simultaneously presented, one to each eye. This recreates how in natural vision, each eye sees the object from a slightly different angle, since they are separated by several inches, which gives humans natural depth perception. A separate lens focuses on each picture. Showing each eye a photograph taken several inches apart from each other and focused on the same point recreates the natural effect of seeing things in three dimensions.
A moving image extension of the stereoscope has a large vertically mounted drum containing a wheel upon which a series of stereographic cards form a moving picture. A gate restrains the cards, and when sufficient force is available to bend the card, it slips past the gate and into view, obscuring the initial picture. These coin-enabled devices were found in arcades in the late 19th and early 20th centuries and were operated by the viewer using a hand crank. These devices can still be seen and operated in some museums specializing in arcade equipment.
The stereoscope offers several advantages:
Using positive curvature (magnifying) lenses, the image’s focus point is changed from its short distance (about 30 to 40 cm) to a virtual distance at infinity. This allows the eyes’ focus to be consistent with the parallel lines of sight, significantly reducing eye strain.
The card image is magnified, offering a wider field of view and the ability to examine the detail of the photograph.
The viewer provides a partition between the images, avoiding a potential distraction to the user.
A stereo transparency viewer is a type of stereoscope that offers similar advantages, e.g. the View-Master.
Disadvantages of stereo cards, slides or any other hard copy or print are that the two images are likely to receive differing wear, scratches and other decay. This results in stereo artefacts when the images are viewed. These artefacts compete in the mind resulting in a distraction from the 3D effect, eye strain and headaches.
