For a refractive index of exactly 2.0, the image forms on the surface of the sphere, and the image may be viewed on an translucent object or diffusing coating on the imaging side of the sphere. Many of those few are either too brittle, too soft, too hard, or too expensive to for practical lens making ( columbite, rutile, tantalite, tausonite). Most clear solids used for making lenses have refractive indices between 1.4 and 1.6 only a few rare materials have a refractive index of 2 or higher ( cubic zirconia, Boron nitride (c‑BN & w‑BN), diamond, moissanite). The image is not directly accessible the closest accessible point is on the sphere's surface directly opposite the source of light. Ball lenses of extremely refractive glass įor materials with refractive index greater than 2, objects at infinity form an image inside the sphere. The further the camera lies from the ball lens, the better the background will come into focus. If the camera is close to the ball lens, the background around the ball will be completely blurred. The ball lens (or "lensball") is placed fairly close to the camera and the camera's own lenses are used to focus an image through the lensball. Lensball photography Įxperimental landscape photograph taken through a lensball by Danish photographer Hanstholm Fyrīall lenses are used by photographers to take novel extreme wide-angle photos. ![]() The image of the sun formed by a large crystal ball will burn a hand that is holding it, and can ignite dark-coloured flammable material placed near it. ![]() The omnidirectional burning glass effect can occur with a crystal ball that is brought into full sunlight. The device, itself fixed, records the apparent motion and intensity of the sun across the sky, burning an image of the sun's motion across the card. This effect is exploited in the Campbell–Stokes recorder, a scientific instrument which records the brightness of sunlight by burning the surface of a paper card bent around the sphere. Since a crystal ball has no edges like a conventional lens, the image-forming properties are omnidirectional (independent of the direction being imaged). The refractive index of typical materials used for crystal balls ( quartz: n = 1.46 window glass: n = 1.52 ), focus infinity to a point just outside the surface of the sphere, on the side of the ball diametrically opposite to where the rays entered. Ball lenses have extremely high optical aberration, including large amounts of coma and field curvature compared to conventional lenses. The same optical laws may be applied to analyze its imaging characteristics as for other lenses.Īs a lens, a transparent sphere of any material with refractive index ( n ) greater than air ( n = 1.00 ) bends rays of light to a focal point for most glassy materials the focal point is only slightly beyond the surface of the ball. In particular, a ball lens (or "lensball") is a bi-convex spherical lens with the same radius of curvature on both sides, and diameter equal to twice the radius of curvature. Art of scrying Ī crystal ball is an optical lens. Fortune tellers, known as drabardi, traditionally use crystal balls as well as cards to seek knowledge about future events. The use of crystal balls for divination also has a long history with the Romani people. Immediately before the appearance of a vision, the ball was said to mist up from within. ![]() Ĭrystal gazing was a popular pastime in the Victorian era, and was claimed to work best when the Sun is at its northernmost declination. He devoted much of his life to alchemy, divination, and Hermetic philosophy, of which the use of crystal balls was often included. John Dee was a noted British mathematician, astronomer, astrologer, geographer, and consultant to Queen Elizabeth I. By the fifth century CE, scrying was widespread within the Roman Empire and was condemned by the early medieval Christian Church as heretical. In the first century CE, Pliny the Elder describes use of crystal balls by soothsayers ( "crystallum orbis"). In more recent times, the crystal ball has been used for creative photography with the term lensball commonly used to describe a crystal ball used as a photography prop. It is generally associated with the performance of clairvoyance and scrying in particular. The Crystal Ball by John William Waterhouse (1902)Ī crystal ball is a crystal or glass ball and common fortune-telling object.
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