when high shutter speeds cause strobing effect... at DVinfo.net

Cal Johnson · July 17th, 2006, 10:30 AM

Is it correct that the cause of strobing or flickering when using really high shutter speeds in video is because there is less information being recorded to tape, so you're actually starting to see black, unrecorded portions of tapea? I know there is not an actual shutter in a video camera, but I've never been certain of the process that causes this effect.

Chris Barcellos · July 17th, 2006, 10:48 AM

I'll take a stab at it with my theory. I think it is because the individual frame does not have as much blur in it. The higher the shutter speed the more "frozen" the image will be, creating a greater distinction between each frame. With 30 FPS, it won't be as noticeable as with 24 fps, or the 15 fps provided for instance with the Sony VX progressive mode.

Boyd Ostroff · July 17th, 2006, 11:19 AM

I think you're right about the motion blur issue Chris, but in the last part of the paragraph you seem to be confusing frame rate with shutter speed. The shutter speed is independent of the number of frames per second which are captured. In other words, you could shoot at 1/1000 sec shutter speed on either an interlaced camera at 60i or a progressive camera at 30p.

So I think you need to put aside interlaced vs. progressive to answer the question which Cal asked. There is "less information" being recorded at a high shutter speed, but not less picture data; the number of pixels is still the same and the amount of color data is the same. But there's less "temporal data." In other words, at high shutter speed you are only capturing what happens for a small portion of the 1/30 second frame. With a slower shutter speed you capture more of the time slice, and any motion will be blurred. So with a fast shutter speed there's a little gap between what happens in each frame which can make movement look odd.

Now it has nothing to do with "black, unrecorded portions of tape" though. Just the amount of time which passes between when each image was captured.

Cal Johnson · July 17th, 2006, 11:46 AM

Thanks guys.

July 17th, 2006, 10:30 AM	#1
Cal Johnson Major Player Join Date: Oct 2004 Posts: 180	when high shutter speeds cause strobing effect... Is it correct that the cause of strobing or flickering when using really high shutter speeds in video is because there is less information being recorded to tape, so you're actually starting to see black, unrecorded portions of tapea? I know there is not an actual shutter in a video camera, but I've never been certain of the process that causes this effect.

July 17th, 2006, 10:48 AM	#2
Chris Barcellos Inner Circle Join Date: Nov 2005 Location: Elk Grove CA Posts: 6,838	I'll take a stab at it with my theory. I think it is because the individual frame does not have as much blur in it. The higher the shutter speed the more "frozen" the image will be, creating a greater distinction between each frame. With 30 FPS, it won't be as noticeable as with 24 fps, or the 15 fps provided for instance with the Sony VX progressive mode. __________________ Chris J. Barcellos

July 17th, 2006, 11:46 AM	#4
Cal Johnson Major Player Join Date: Oct 2004 Posts: 180	Thanks guys. Last edited by Cal Johnson; July 17th, 2006 at 12:39 PM.

July 17th, 2006, 11:19 AM	#3
Boyd Ostroff Wrangler Join Date: Dec 2002 Location: Mays Landing, NJ Posts: 11,802	I think you're right about the motion blur issue Chris, but in the last part of the paragraph you seem to be confusing frame rate with shutter speed. The shutter speed is independent of the number of frames per second which are captured. In other words, you could shoot at 1/1000 sec shutter speed on either an interlaced camera at 60i or a progressive camera at 30p. So I think you need to put aside interlaced vs. progressive to answer the question which Cal asked. There is "less information" being recorded at a high shutter speed, but not less picture data; the number of pixels is still the same and the amount of color data is the same. But there's less "temporal data." In other words, at high shutter speed you are only capturing what happens for a small portion of the 1/30 second frame. With a slower shutter speed you capture more of the time slice, and any motion will be blurred. So with a fast shutter speed there's a little gap between what happens in each frame which can make movement look odd. Now it has nothing to do with "black, unrecorded portions of tape" though. Just the amount of time which passes between when each image was captured.