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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 May 21st, 2007, 08:35 AM   #1
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SI-2K and wide angle lenses

I've read of a potential problem with certain types of sensors and certain wide angle lenses that have a small exit lens. Fall off occurs because unlike film, CCD sensors are affected by the angle at which the light strikes them. Obviously this might be a problem affecting any sensor and might explain what I've noticed with some footage shot with WA stills lenses.

Is this issue likely with a CMOS sensor, if so any lenses we should avoid.
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Old May 21st, 2007, 12:39 PM   #2
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Hi Bob,

It's not quite a concern because of the back-focal distance being quite large in the case of PL-mount, and the sensor itself being only 2/3" rather than having to cover a 36x24mm rectangle like still-35mm-photography. With C-mount lenses though, it could be an issue with really wide-angle stuff. We have used 9.5mm lenses with no problems, so I'm sure you can go wider than that before any visual fall-off problems result . . . again, in the case of PL-mount, I'm not concerned, but the c-mounts might pose an issue at super-wide angles because the back-focal distance is so small.
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Old May 22nd, 2007, 04:35 PM   #3
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Thanks Jason,
one less issue to worry about as we're only going with PL mount lenses at this stage.
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Old May 23rd, 2007, 02:21 AM   #4
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Heh, I asked the same question but about fast lenses like my f0.95 a while ago.
Now I have an even faster f0.85 c-mount with 1" sensor coverage, I really hope someone in atlanta get's an SI-2k so I can test it out :)
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Old May 23rd, 2007, 07:55 AM   #5
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Wow, where did you get a c-mount with that wide an aperture? We've never tested a lens that wide . . . so not sure if there will be port-hole type effects with an aperture that wide. I do know though that you're typical >f1.2 apertures should have no problems.
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Old May 23rd, 2007, 06:06 PM   #6
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Quote:
Originally Posted by Jason Rodriguez View Post
Wow, where did you get a c-mount with that wide an aperture? We've never tested a lens that wide . . . so not sure if there will be port-hole type effects with an aperture that wide. I do know though that you're typical >f1.2 apertures should have no problems.
Jason, it's the Fujinon CF25L. Rated for 1.5 megapixel

Got it on ebay, paid a good bit. It's discontinued, but some places still stock it for around $400-$600
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