Ah, yes. It do get confusing. For a treatise on sensor size
designations which does come from the old vidicon tubes see:
<http://www.dpreview.com/news/0210/02100402sensorsizes.asp>
The confusion arises from that fact that the vidicon 4/3" designation
(meaning the external diameter of the glass vidicon tube) also had a 4:3
aspect ratio and size specified as 18 x 13.5 mm.
Olydak have adopted this designation and stated the sensor size as 18 x
13.5 mm. See the official Oly site at:
<http://www.four-thirds.com/about.htm>
This page at one point does actually say: 4/3". However, if you take
the time to read the details here and elsewhere you will see that the
emphasis is on the 4:3 aspect ratio. Oly makes a point that images are
often cropped to fit a computer screen or other format (such as 8x10)
such that the 3:2 aspect ratio of 35mm film throws away a lot of the
image area. If you have a fixed number of pixels on a digital sensor
they want to arrange the aspect ratio such that most of those pixels
actually end up on the final image instead of being cropped away. Not
sure I agree with this with HDTV in the future but that's what they say.
Now for the final teaser. I had read this before but it didn't sink in.
See: <http://www.four-thirds.com/pdf/FourThirdsSystem.pdf> item 10 at
the top of page 4 which says:
"However, with the Four Thirds System, in contrast to 35 mm film
cameras, the diameter of the lens mount is designed to be
approximately twice as large as that of the image circle. This
gives wide adaptability among a variety of image sensors and
greatly expands the flexibility of lens design."
What does "a variety of image sensors" imply?
Chuck Norcutt
Woburn, Massachusetts, USA
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