Optical model of a four lens telescope, maker unknwon, 1752. Once belonged to Stephen Demainbray. A handwritten inscription on the base reads: 'Plan of Four Lens Telescope with Threads'.

This model is one of a series of optical models that were once owned by Stephen Demainbray and used by him in his lectures on natural philosophy. it is the most complex of his telescope models and shows the arrangement of the standard four-lens telescope that was popular at the time. It consists of an object, primary and a final image, four convex lenses, and an eye hole. Originally silk cords would have been used to represent the rays of light. Demainbray worked as superintendent at the King's observatory at Kew from 1768 and his collection of instruments and apparatus was absorbed into the King's own collection.