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Size Matters ! (When it comes to CCD Image Sensors that is.)

Shocked like I was when you looked into your expensive CCD camera that was supposed to have a 1/2 inch image sensor in it and you saw this little shriveled up thing that was about half the size you expected? It's not a half inch across and it's certainly not a half inch high and it's not even a half inch diagonal. So what gives? Why is it called a half inch CCD image sensor?

Today in high end videography (2004) the most common inage size is called 2/3 inch or just under 17 mm. But the diagonal is just 11 mm, and there's nothing about a modern 2/3 inch imager that is 2/3 of an inch in size. Back when there were tubes the image size on a tube that was 2/3 inch in diameter was 11 mm and the 2/3 inch designation carried over to solid state imagers.

So called inch and a quater tubes (which were actually 30 mm in diameter) had a 21.4 mm image diagonal. One inch tubes (and later solid state imagers) had 16 mm diagonals. An 8 mm image diagonal could be found on half inch and 5/8 inch tubes. CCD chips with that image diagonal are called half inch!

A 1/3 inch video sensor chip has a 6 mm image diagonal, a 1/4 inch 4 mm, and a 1/6 inch 3 mm. Was there ever an imaging tube that had an outside diameter of just 1/6 inch (a bit over 4 mm)? No. But it's the consensus of image chip manufacturers that had there ever been one it would have had an image diagonal of 3 mm.


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