Stanhope (optical bijou)
Stanhopes or Stanho-scopes are optical devices that enable the viewing of micro-photographs 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 micro-photograph at the end of a modified Stanhope lens. He called the devices bijoux photo-micro-scopiques or microscopic photo-jewelry. In 1862, Dagron displayed the devices at the Exhibition in London, where he got an "Honorable 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 micro-photograph 1 square mm (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 micro-photographs using a collodion process and a microscope converted to a camera. This resulted in a micro-photograph about 3 square mm (0.0047 sq in) in area. The main disadvantage of Dancer's method was that the viewing of the micro-photographs required a microscope which was at the time an expensive instrument. In 1857 Dagron solved the problem by inventing a method of mounting the micro-photographs 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.
The sectioned lens could magnify the micro-photograph three hundred times, so that the viewing of the micro-photographs no longer required a bulky and expensive microscope. The modified Stanhope lens was small enough to be mounted in all manner of miniature artifacts such as rings, ivory miniatures, wooden toys etc.
Dagron's efforts met with great success. The viewers were first introduced to the general public at the 1859 International Fair in Paris.
The success of his viewers enabled Dagron to purpose-build a factory dedicated to their production. As of June 1859, Dagron's factory was manufacturing the stanhopes, mounted in jewelry and souvenirs. In August 1859 he exhibited them at the International Exhibition in Paris where they met with great success. In 1862 he had 150 employees and was manufacturing 12,000 units a day.
In 1860 Dagron obtained the patent for his viewers under the title Bijoux Photo-micro-scopiques. Dagron also developed mail order marketing techniques for his viewers.