2002-12-08
In fact, here is some further information:
Note that the 18 x 13.5 mm image area has an aspect ratio
of 4:3 (4/3 system). The 22.5 mm is the diagonal distance of the image
area obtained by the formula: (18^2 + 13.5^2)^0.5. Note that the APS and
35 mm standard has an aspect ratio of 1.5 (3:2). You will notice that the
3:2 aspect ratio is the INVERSE of 2:3. This is the meaning behind
your mention of the 2/3 sensor. Again, ABSOLUTELY nothing to do with
inches.
And if someone insists it has something to do with inches
demand the proof. You have the proof right here that it doesn't. In
fact involving inches makes absolutely no sense whatever. Does it to
you?
If you still are not convinced and still need further
proof and references to convince you that we are not speaking of some ancient
inch vacuum tube, but a unitless aspect ratio, please check out Google or some
other search engine. Here is a place to start:
These are the results when one enters the term "4/3
system" into the search box.
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
> 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/>
>
