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/>
