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:
“Learn to shrink yourself to the size of the company you are in. Take their tone, whatever it may be, and excell in it if you can; but never pretend to give the tone. A free conversation will no more bear a dictator than a free government will.”
—Philip Dormer Stanhope, 4th Earl Chesterfield (1694–1773)
“To believe her limited in range because she was harmonious in method is as sensible as to imagine that when the Atlantic Ocean is as smooth as a mill-pond it shrinks to the size of a mill-pond.”
—Rebecca West (1892–1983)
“For truly I tell you, if you have faith the size of a mustard seed, you will say to this mountain, ‘Move from here to there,’ and it will move; and nothing will be impossible for you.”
—Bible: New Testament, Matthew 17:20.