SI-2K and wide angle lenses at DVinfo.net

Bob Grant · May 21st, 2007, 07:35 AM

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.

Jason Rodriguez · May 21st, 2007, 11:39 AM

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.

Bob Grant · May 22nd, 2007, 03:35 PM

Thanks Jason,
one less issue to worry about as we're only going with PL mount lenses at this stage.

Solomon Chase · May 23rd, 2007, 01:21 AM

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 :)

Jason Rodriguez · May 23rd, 2007, 06:55 AM

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.

Solomon Chase · May 23rd, 2007, 05:06 PM

Quote:

Originally Posted by Jason Rodriguez

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

May 21st, 2007, 07:35 AM	#1
Bob Grant Trustee Join Date: Nov 2005 Location: Sydney Australia Posts: 1,570	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.

May 21st, 2007, 11:39 AM	#2
Jason Rodriguez Trustee Join Date: Mar 2003 Location: Virginia Beach, VA Posts: 1,095	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.

May 22nd, 2007, 03:35 PM	#3
Bob Grant Trustee Join Date: Nov 2005 Location: Sydney Australia Posts: 1,570	Thanks Jason, one less issue to worry about as we're only going with PL mount lenses at this stage.

May 23rd, 2007, 01:21 AM	#4
Solomon Chase Regular Crew Join Date: Jan 2006 Location: Woodstock, Georgia Posts: 154	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 :)

May 23rd, 2007, 06:55 AM	#5
Jason Rodriguez Trustee Join Date: Mar 2003 Location: Virginia Beach, VA Posts: 1,095	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.