2002-12-08 Here is something else you may find of interest. The vidicon tubes never had a 4/3 or even a 2/3 inch diameter. The diameter of the tubes was 1/1.8 inches or 0.5556 inches or about 14 mm.
See here: There seems to be much confusion amongst the public at large about the image sensors used in digital cameras. The figures the makers quote are basically meaningless unless you are "in the know" about what they mean when they say "it has a 1/1.8 inch sensor". The example of 1/1.8 inch type of measurement relates to a standard used starting in the 1950s about Vidicon tubes used in TV cameras. That example of 1/1.8" works out to 0.5555 inches (1 divided by 1.8 is what it means) and that is the diameter of the original glass Vidicon tube that had an image size similar to the image size in the digital camera they are talking about. Due to the internal workings of the Vidicon tubes the image area was less than the diameter of the tube, it is roughly 2/3 of the tube diameter. So in the case of the 1/1.8" tube the image area was 7.176mm x 5.329mm, the diagonal being 8.933mm which is regarded as the "normal" lens focal length to use with that image size. This is from: http://homepages.ihug.com.au/~parsog/Guy/sensors.html Note: The VIEWABLE AREA was roughly 2/3 (66.7 %) of the tube diameter. This does not mean the tube was 2/3 inches. Again, a falsehood is perpetrated. Unfortunately, like an urban legend, the inches persist in getting the credit. Even the Brazilians are describing it as an inch standard. See here: http://www.foto.art.br/noticias/43/ I hope Marcus writes them a letter to correct this blatant lie. John ----- Original Message ----- From: "Markus Kuhn" <[EMAIL PROTECTED]> To: "U.S. Metric Association" <[EMAIL PROTECTED]> Sent: Sunday, 2002-12-08 11:29 Subject: [USMA:23844] Re: New Four Thirds Inch camera standard > I finally learned about where the name "Four Thirds" of the new > Olympus/Kodak digital camera optics standard came from. > > http://www.dpreview.com/news/0209/02092410olydak43inch.asp > > CCD photo sensor chips are traditionally completely metric designs, > however, they are named after the outer glass tube diameter of an old > vidicon vacuum-tube image sensor that would have an equivalent imaging > area. The currently used CCD chips in digital cameras are described in > data sheets as 2/3-inch sensors, even though no single dimension of the > chip is actually 2/3-inch, except that they are compatible with optics > designed for vidicon tubes with 4/3-inch outer glass diameter. The > vacuum tube industry is still using inch-based designations for glass > dimensions. > > So in a sense, it is a repetition of the story of the 90 mm (3.5 inch) > floppy disk, a metric design with a historic inch name stuck to it, or > of the nomencalture for flat pannel displays, which are also still > widely labelled according to the glass dimensions of cathode-ray tubes > with equivalent image area. > > Markus > > -- > Markus G. Kuhn, Computer Laboratory, University of Cambridge, UK > Email: mkuhn at acm.org, WWW: <http://www.cl.cam.ac.uk/~mgk25/> >
