Camera Obscuras

 

The technical principles of the camera obscura have been known since antiquity.

The earliest existant written record of the camera obscura is to be found in the writings of Mozi (470 to 390 BC), a Chinese philosopher . Mozi correctly asserted that the image in a camera obscura is flipped upside down because light travels in straight lines from its source.

. In the 4th century BC, Aristotle noted that "sunlight travelling through small openings between the leaves of a tree, will create circular patches of light on the ground."

Ibn al-Haytham (AD 965–1039), also known as Alhazen, described a 'dark chamber' and experimented with images seen through the pinhole.

Leonardo da Vinci (1452–1519), was familiar with the work of Alhazen in Latin translation and after an extensive study of optics and human vision, published the first clear description of the camera obscura.


The 17th century Dutch Masters, such as Johannes Vermeer, were known for their magnificent attention to detail. It has been widely speculated that they made use of such a camera, but the extent of their use remains a matter of considerable controversy.

The term "camera obscura" was first used by the German astronomer Johannes Kepler in 1604. The term is based on the Latin camera, "(vaulted) chamber or room", and obscura, "darkened"

 

How does it work?

The Camera Obscura consists of a darkened, octagonal shaped room with an inverted funnel shaped ceiling. Mounted in the funnel spout is a fixed lens above which is a rotating mirror set at an angle of approximately 45 degrees. In front of the mirror is an optical glass screen which protects both the mirror and the lens without affecting the true colour of the objects being viewed or distorting their image. The lens is solidly mounted below the rotating axis of the hood thus eliminating vibration. Beneath the lens is a floor-mounted, saucer shaped viewing table. Focal adjustment is obtained by raising or lowering and tilting the table.

Technical Information

  • Height of viewing window above seal level is 655ft (196.5m)
  • Lens 7 ins. (179mm) diameter of achromatic combination
  • Lens - focal length - 8ft.9ins. (2667mm)
  • Lens, f factor - f15
  • Table, diameter - 4ft 6ins. (1372mm)
  • Table, radius of curvature of concavity - 6ft. (1829mm)
  • Room dimensions : octagonal floor of internal diameter 12ft. (3.658m)
  • Clearance between walls and table - 3ft. 6ins. (1067mm)
  • Headroom - from floor at edge of table - 8ft. (2438mm)
  • General note : the value of the lens is the ratio of the lens diameter to its focal length. In our case it is 10ins/7ins. = f15