The Janssen revolver ("Revolver Astronomique" in French) or Photo Revolver was invented by the French astronomer Pierre Jules César Janssen in 1874. It was the instrument that originated chronophotography, a branch of photography based on capturing movement from a sequence of images. To create the apparatus Pierre Janssen was inspired by the revolving cylinder of Samuel Colt's revolver.

The revolver used two discs and a sensitive plate, the first with twelve holes (shutter) and the second with only one, on the plate. The first one would take a full turn every eighteen seconds, so that each time a shutter window passed in front of the window of the second (fixed) disk, the sensitive plate was discovered in the corresponding portion of its surface, creating an image. In order for the images not to overlap, the sensitive plate rotated with a quarter of the shutter speed. The Shutter Speed was one and a half seconds. A mirror on the outside of the apparatus reflected the movement of the object towards the lens that was located in the barrel of this photographic revolver. When the revolver was in operation it was capable of taking forty-eight images in seventy-two seconds.

Pierre Jules César Janssen (22 February 1824 – 23 December 1907), also known as Jules Janssen, was a French astronomer who, along with English scientist Joseph Norman Lockyer, is credited with discovering the gaseous nature of the solar chromosphere, and with some justification the element helium.

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