Historical information

Multiplex mechanical stereoplotting equipment was used at the Army Survey Regiment, Fortuna Bendigo. c1950s. Multiplex equipment was imported from the UK in 1951 and introduced in the following year, to accelerate map production output covering CMF training areas at 1:25,000 map scale. Multiplex plotting was a productive advancement replacing the ‘Arundel’ method of graphical plotting planimetric detail that was expensive and slow, especially in timbered mountainous terrain. Air photos were made into small diapositives and mounted on racks in the exact position relative to when the aerial photos were taken. The technicians operated the Multiplex in a darkened room, with one photo projected with a green filter and the other through a red filter to form a 3D view of the overlapping photos. The 3D model projected onto a platen, which was a small platform that was raised up and down. The technician viewed the 3D image with special glasses fitted with red and green lenses. In the centre of the platen was a small pinhole that served as a floating mark, with a vertical pencil located exactly below the pinhole. This tracing table was moved to follow the topographic feature or contour line and draw it on the paper underneath. The technician raising or lowering the platform’s floating mark to match the height of the 3D terrain. It also replaced the slotted template method of mechanical adjustment of strips of aerial photography, however was restricted to each strip rather than between strips in the block. Although the Multiplex was phased out of production in 1968, it was used in the training of photogrammetry and aero-triangulation at the School of Military Survey located at Bonegilla, Victoria until the early 1990s. The history of the Multiplex is covered in more detail with additional historic photographs, in pages 50 to 51 of Valerie Lovejoy’s book 'Mapmakers of Fortuna – A history of the Army Survey Regiment’ ISBN: 0-646-42120-4. This instrument is only one of the projectors of a set and is unfortunately missing its platen coloured filters and coloured glasses.

Physical description

A black wooden box containing a Multiplex Unit Projector (incomplete). The Multiplex has a Lamp Head, Barrel Housing, Body of the Projector and a Platen which is missing.

Inscriptions & markings

WILLIAMSON MANUFACTURING CO, PHOTOGRAHIC ENGINEERS, SERIAL NUMBER 3437, TYPE MPC, LITCHFIELD GARDENS, LONDON AND READING.