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Silicon Imaging SI-2K
2/3" 1080p IT-integrated 10-bit digital cinema w/direct-to-disk recording.


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Old November 11th, 2006, 09:52 AM   #1
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720p120 (1/2 - inch optical format)

720p120 (1/2 - inch optical format) , What does that mean? Does it mean that at 720p mode we will not be using the whole chip, thus being cropped into the frame slightly and essentially multiplying our lens by approx 1.4? i.e. will an 18mm then become a 24mm equivilant ?

or am I barking mad....

http://www.altasens.com/data/4562_datasheet.pdf
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Old November 11th, 2006, 03:59 PM   #2
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I’m afraid you are right Tomas (unless SI have changed the way they plan to do it) – for 720p they use a ‘window’ to capture less info so your field of view is narrower, about the same as a ˝ inch chip. So your 18mm lens field of view changes from about 29 degrees to about 22 – it is still an 18mm lens with an 18mm depth of field but you see less.
It makes getting those wide angle, slo-mo shots a bit tricky.

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Old November 11th, 2006, 04:58 PM   #3
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720P Optical Format

Here is another way to look at it:

The image area for 720P (1280 x 720) with a 5um pixel pitch is:

1280 x 5um = 6.4mm
720 x 5um = 3.6mm

The 1/2" optical format was defined for 4:3 to cover a 6.4 x 4.8mm area or 8mm diagonal.

If you use a lens designed for 2/3" (11mm diagonal), the image circle projected by the lens is larger that the area of the sensor (although you get to use the sweet spot or sharpest part of the lens). You see a cropped area of the projected image which will seem like you put on a more telephoto lens. The effective magnification is the ratio of the format covered:

11mm / 8mm = 1.375x


More details on the standard lens formats:

http://www.siliconimaging.com/Lens%2...%20formats.htm
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Old November 16th, 2006, 10:56 AM   #4
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This is a shame I think.

I suspect I will be reverting to the normal shoot 1080i and spilt out each field to make a vertical resolution of 540p but at 60fps for high speed stuff.

I really don t like the idea of

- increasing my DOF for a set shot (having to use a wider lens to equate the same FOV)
- reducing lens flexibility for my wides.

However it s horses for courses. If a chip comes up that can shoot 720p over the whole chip instead of windowing it please consider it.


N.B. please make sure there is a run button
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Old November 16th, 2006, 10:22 PM   #5
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Thomas

Run Button...Yes!

We will be sure to look at wider coverage 720P solutions for future products.

Keep feeding us the input.
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