Stanhope (optical bijou)

Stanhopes or Stanho-scopes are optical devices that enable the viewing of microphotographs without using a microscope. They were invented by René Dagron in 1857. Dagron bypassed the need for an expensive microscope to view the microscopic photographs by attaching the microphotograph at the end of a modified Stanhope lens. He called the devices bijoux photo-microscopiques or microscopic photo-jewelry. In 1862, Dagron displayed the devices at the Exhibition in London, where he got an "Honourable Mention" and presented them to Queen Victoria. In 1864 Dagron became famous when he produced a stanhope optical viewer which enabled the viewing of a microphotograph 1 square millimetre (0.0016 sq in), (equivalent in size to the head of a pin), that included the portraits of 450 people.

In 1851 John Benjamin Dancer invented microphotographs using a collodion process and a microscope converted to a camera. This resulted in a microphotograph about 3 square millimetres (0.0047 sq in) in area. The main disadvantage of Dancer's method was that the viewing of the microphotographs required a microscope which was at the time an expensive instrument. In 1857 Dagron solved the problem by inventing a method of mounting the microphotographs at the end of a small cylindrical lens. Dagron modified the Stanhope lens by sectioning the normally biconvex Stanhope lens and introducing a planar section so that the plane was located at the focal length of the convex side of the cylindrical lens. This produced a plano-convex lens, where Dagron was able to mount the microscopic photograph on the flat side of the lens using Canada balsam as adhesive. This arrangement enabled the picture to be focused.

The Stanhope optical viewers were also mounted inside the bows of violins by French violin maker Jean-Baptiste Vuillaume, probably using Dagron's methods and equipment. The violin Stanhopes featured the portraits of famous people such as Paganini, Tourte and Stradivari.

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