In its simplest form, a camera obscura (Latin for 'dark chamber') is a large pinhole camera - ie, a box with a hole pierced in one of its walls. Light rays from outside are able to pass through this hole and form an inverted reduced image of the scene outside onto the opposite wall. If a sheet of paper is placed on this opposite wall one can faithfully reproduce the image by tracing. This procedure was used by several artists and was described in detail in 1569 by the Neapolitan thespian and physicist Giambista della Porta in his Magia naturalis.
The Middle Wallop camera obscura at the Museum of Army Flying, Middle Wallop, Hampshire, UK, was designed and built by Mr Bill Wakefield of Southampton and was considered to be one of the finest working examples in England. It was installed in 1997 for recreational purposes in the Interactive Science Centre and had no military function.
It used a 216mm crown flint lens (ex-U-boat1) with a focal length of 4.88m, whose image was projected onto a two-metre-diameter curved dish for focusing purposes. The radius of curvature of the dish exactly matched that of the lens, so that the image was in focus from the centre to the outside of the dish.
The viewing surface was made from white Malayan rubber - a very smooth and very white material which Mr Wakefield claimed was the finest reflective surface for this purpose that he had come across. The viewing surface had adjustable height to facilitate focusing.
The rotation of the mirror enabled the user to see around the adjacent airfield. Visitors could also operate the camera obscura using various buttons and switches to enable them to pan or tilt the periscope, thereby altering the view. The camera could therefore be used to view the surrounding countryside from a wonderful vantage spot, including nearby Danebury Hill (the site of an iron-age hill fort) and the activity on the adjacent airfield.
An audio system had been installed so that visitors could listen to a short pre-recorded talk.
Sadly, the camera obscura at Middle Wallop was dismantled around 2002 as the management found it a liability! For example, they found it difficult to keep the lens clean and also the focusing mechanism was not sufficiently robust to enable children to operate it safely. Most of the bits and pieces are stored in a hangar but, even more sadly, the lens has now gone missing.