Blackmagic Forum

Received my BMCC today, charged it up and threw on a Sigma 30 1.4. After playing around with it for a few minutes, I noticed something disturbing. When I had it pointed at my television (which was on) and framed it so that half the TV was in frame and the other half was the room, I noticed these unusual lines that seem to carry over from the brightest parts of the TV along the wall. Does anyone know what these are? I would try and take a photo, but I do not have a SSD yet.

Please if you have your camera, frame it like I stated above and let me know if you see the lines as well.

* EDIT - I turned the camera back on after typing this and the mysterious lines/blocks were gone. When I powered off and back on again, the lines were back!? Any help would be greatly appreciated.

Try changing your shutter angle and see if they go away. Sometimes when the shutter and a light source (like a tv) are cycling at slightly different rates, you get this effect.

Thanks for the reply Phillip. These are not lines caused by the cycling - they are not showing up on the TV screen itself, but off to the side on the wall. They seem to carry over horizontally from the brightest part of the TV - similar to the darker exposure in some areas that some were complaining about on here.

Jartanyon wrote:Thanks for the reply Phillip. These are not lines caused by the cycling - they are not showing up on the TV screen itself, but off to the side on the wall. They seem to carry over horizontally from the brightest part of the TV - similar to the darker exposure in some areas that some were complaining about on here.

Sorry, Jartanyon.. but this thread is pretty worthless without an example of some sort.

Something like this ?

http://johnbrawley.wordpress.com/2011/0 ... ind-trick/

jb

Yes John, exactly like that! Based on Kyle Mallory's comment, I guess that will have to be an accepted limitation of these particular CMOS sensors (haven't noticed this on my other cameras). Thanks for the help!

Damn I got something similar while filming natural light coming through a door, I tried all frame rates, and adjusted all the shutter angles, so it defiantly not a frequency problem.

arnoscene wrote:Damn I got something similar while filming natural light coming through a door, I tried all frame rates, and adjusted all the shutter angles, so it defiantly not a frequency problem.

Can you share that as a DNG?

Or show us a screen shot of the waveform before any grading is done?

Here is the original DNG

https://docs.google.com/file/d/0B9-7AVz ... sp=sharing

arnoscene wrote:Here is the original DNG

https://docs.google.com/file/d/0B9-7AVz ... sp=sharing

first of all, I will say that the shot looks is severely under exposed, I would expect to see these kinds of artefacts in such low light conditions.

Initially I thought it might be some kind of flare problem, but I notice that the shot isnt exactly level, but the lines are - so it seems to be happening at sensor level.

Do you see these lines when exposing in more appropriate circumstances?

no I only noticed this as I was experimenting with silhouettes if I had aperture control I would have made it even darker.

Under normal lighting conditions I have not seen this.

It's not just limited to CMOS and has been a problem to solve for a while.....and is called a smear :-

http://www.axis.com/products/video/camera/ccd_cmos.htm

"In addition, when there is a very bright object in the scene (such as a lamp or direct sunlight), the CCD may bleed, causing vertical stripes below and above the object. This phenomenon is called a smear."

Try and avoid when shooting and if not, fix in grading....or use film, where the sensor is replaced 24 times or so per second.

Edit - Quotes added

Hmmm... CMOS usualy don't smear, as far as I know.

Looked more like and underexpose problem to me.

Frank you are no doubt correct when it comes to the CMOS sensor itself but could this be related to the type of glass that is bonded directly in front of the sensor ?

arnoscene wrote:Damn I got something similar while filming natural light coming through a door, I tried all frame rates, and adjusted all the shutter angles, so it defiantly not a frequency problem.

It's the same issue that I linked to earlier. There is no defeating this when you have high contrast scenes with dark FG and hot BG's.

jb

I just got my camera today and see the lines in the sun peaking through a tree. There's also a burnt patch of pixels in the center of the sun.