The tent was ingeniously constructed using lightweight telescopic poles and a custom-built focusing mechanism. Derek designed a system of chains, cogs, and ropes that allowed the lens to be moved up and down, adjusting the focus. Setting up Derek’s tent camera obscura took about an hour, and it could be used indoors or outdoors—provided the weather was dry. Inside, about ten people could fit, although the experience worked best with five or six visitors, who could walk around the viewing screen as the image shifted.
Derek’s tent camera obscura was first tested on the quay at St Germans in 1985. It later appeared at various events, including a National Trust Association Fair at Cotehele House, where it was set up at the request of the local National Trust Association, of which Betty was a committee member. Derek also exhibited it in Liskeard, where visitors were particularly intrigued by the ability to see what was happening at the far end of exhibition halls.
