It is a replica built in the style of the small "mousetrap" cameras designed by William Henry Fox Talbot in the mid 1830's . They were simple wooden boxes with a single lens used to expose paper negatives, sensitized by silver nitrate (the calotype or Talbotype process). Exposures often took hours, and Talbot had several of the cameras made by a local joiner near his country home in Laycock, Wiltshire. This replica was built by Wilhelm E. Nassau to demonstrate the loading and exposing of light sensitive paper in an early camera type. In the sliding holder the sensitive paper could be inserted into the camera and exposed for several minutes. The paper slide can be replaced by a matt screen. The lens is a simple achromatic design.