The Camera Obscura is an ancient optical device. In its most basic form it is, quite simply, a dark
room with a small hole in one wall. On the wall opposite the hole, an image is formed of whatever is outside. This image is
upside-down (inverted) and back to front (laterally transposed).
The size of the hole has a great effect on the picture that is being projected. A small hole produces a sharp image, which is dim, while a larger hole produces a brighter picture which is less well focused.
This happens because light travels in straight lines, a property known as the rectilinear propagation of light.
Observations of and experimentation with camera obscura have taken place since very early times. The first recorded evidence of this effect was by Mo Tsu, a Chinese thinker in 500bc.
Widely used by astronomers for observing the sun without causing damage to the eyes, the camera obscura remained largely unchanged until around 1550 when a man called Cardano replaced the pinhole with a lens as described in his book De Subtilitate Libri. This increase in aperture size resulted in a far brighter picture but meant that the picture needed focusing. This was achieved by moving the viewing surface or the lens, this became necessary as lenses have a fixed focal length. Things in the foreground focus further from the lens whilst distant objects focus closer to the lens.
This was a major step forward in camera obscura development. The brightness and clarity of image that the lens introduced made it a practical tool for artists like Vermeer and Canaletto and perhaps encouraged more experimentation.
Camera obscura exist in two main forms. Rooms where the viewer is inside the camera looking directly at the image and box types where the image is projected onto a screen which is viewed from outside. The screen is often made of ground glass and normally requires a cowl or hood to block out ambient light.
During Victorian times they reached their pinnacle of popularity. With improvements in manufacturing it is likely that lens quality increased and costs were reduced making the lens less exclusive. Many were built at seaside and tourist resorts as a popular entertainment. Today, although the camera obscura is largely forgotten about, there are still some open to the public.
Our camera obscura is built in the room style with a lens mounted horizontally in the ceiling and a mirror at forty five degrees placed above it, the whole lens and mirror can be turned offering a complete 360 degree view. Our F16 rated lens produces a good image even on a dull day.
For instruction on making your own Camera Obscura go to the Building Information Page.