Size
The size of video camera tubes is simply the overall outside diameter of the glass envelope. This differs from the size of the sensitive area of the target which is typically two thirds of the size of the overall diameter. Tube sizes are always expressed in inches for historical reasons. A one inch camera tube has a sensitive area of approximately two thirds of an inch diameter or about 16 mm.
Although the video camera tube is now technologically obsolete, the size of solid state sensors is still expressed as the equivalent size of a camera tube. For this purpose a new term was coined and it is known as the optical format. The optical format is approximately the true diagonal of the sensor multiplied by 3/2. The result is expressed in inches and is usually (though not always) rounded to a convenient fraction - hence the approximation. For instance, a 6.4x4.8 mm sensor has a diagonal of 8.0 mm and therefore an optical format of 8.0*3/2=12 mm which is rounded to the convenient imperial fraction of 1/2 inch. The parameter is also the source of the "Four Thirds" in the Four Thirds system and its Micro Four Thirds extension—the imaging area of the sensor in these cameras is approximately that of a 4/3 inch video camera tube at appromimately 22 millimetres (0.87 in).
Although the optical format size bears no relationship to any physical parameter of the sensor, its use means that a lens that would have been used with (say) a four thirds inch camera tube will give roughly the same angle of view when used with a solid state sensor with an optical format of four thirds inch.
Read more about this topic: Video Camera Tube
Famous quotes containing the word size:
“One writes of scars healed, a loose parallel to the pathology of the skin, but there is no such thing in the life of an individual. There are open wounds, shrunk sometimes to the size of a pin-prick but wounds still. The marks of suffering are more comparable to the loss of a finger, or the sight of an eye. We may not miss them, either, for one minute in a year, but if we should there is nothing to be done about it.”
—F. Scott Fitzgerald (1896–1940)
“It is very considerably smaller than Australia and British Somaliland put together. As things stand at present there is nothing much the Texans can do about this, and ... they are inclined to shy away from the subject in ordinary conversation, muttering defensively about the size of oranges.”
—Alex Atkinson, British humor writer. repr. In Present Laughter, ed. Alan Coren (1982)
“Our brains are no longer conditioned for reverence and awe. We cannot imagine a Second Coming that would not be cut down to size by the televised evening news, or a Last Judgment not subject to pages of holier-than-Thou second- guessing in The New York Review of Books.”
—John Updike (b. 1932)