7 Replies Latest reply: Jul 17, 2011 9:59 AM by Jim Simon

Vertical rolling lines with DSLR and projector

I_don't_believe_it! Jul 15, 2011 6:04 AM

I used a DSLR (EOS 60D) as a B camera for wide shot on a shoot in a dark lecture room the other day. Vertical rolling lines were evident across the whole frame. Whilst similar to scan lines on a CRT the lines were not restricted to the projection display. I assume this is related to the shutter speed, but whatever speed was selected I could not get rid of the artefact.

Are there any post production solutions for this? Forunately I used another camera ( a proper video camera ) for the A roll and had much more control over the shutter speed. The B-roll is not crucial but would be useful.

TIA

1. Re: Vertical rolling lines with DSLR and projector

John T Smith Jul 15, 2011 8:37 AM (in response to I_don't_believe_it!)

First, to be sure your sequence matches your footage, try this...

See the 2nd post for a picture of the NEW ITEM pointer http://forums.adobe.com/thread/872666?tstart=0
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2. Re: Vertical rolling lines with DSLR and projector

I_don't_believe_it! Jul 15, 2011 10:12 AM (in response to John T Smith)

Thanks for this. It is visible on the rushes so not related to any setting in Premiere. I suspect it is related to the refresh rate of the projector and shutter speed of the camera. The problem was that whatever shutter speed I set on the camera I could not get rid of the vertical roll. I also wonder if it is related to the projector type (DLP/LCD).

I am not sure and have not seen this before.

Andrew
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3. Re: Vertical rolling lines with DSLR and projector

Jim Simon Jul 15, 2011 12:35 PM (in response to I_don't_believe_it!)

If you see the lines over the whole image, and not just on the projection screen, then they are not likely caused by a mismatch of scan rates. Something else is going on with your camera.
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4. Re: Vertical rolling lines with DSLR and projector

Bill Hunt Jul 15, 2011 12:48 PM (in response to Jim Simon)

Jim might be onto something here.

What is the light source in that lecture hall?

Good luck,

Hunt
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5. Re: Vertical rolling lines with DSLR and projector

Dave Merchant Jul 15, 2011 8:11 PM (in response to I_don't_believe_it!)

The question is, was the "dark" room lit by something other than the glow from the projection screen?

If it was, your camera frame rate was mismatched to the lighting frequency (e.g. 60Hz mains lighting, 25fps footage - old mag-ballasted fluorescent lighting is worst as it flashes at mains frequency with a wide amplitude, but compact electronic-ballasted fluorescents don't bother DSLRs as they flash at over 10kHz).

If the room lights were off, you're seeing the same effect but due to mismatch between the projector scan rate and the camera frame rate.

There's nothing you can do about it in post, you have to get it right during the shoot.
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6. Re: Vertical rolling lines with DSLR and projector

I_don't_believe_it! Jul 17, 2011 6:34 AM (in response to Dave Merchant)

Thanks for all the responses.

There was daylight from the right side of the room but the lights were down.

I think that as suggested the problem was a mismatch between the projector and camera. Unfortunately whatever shutter speed I used on the DSLR the problem was evident (another "I don't believe it!" moment) . I wonder if the projector was a DLP unit and the problem was the combination of wheel rotation on the projector and shutter speed on the camera. I could adjust the camcorder's shutter speed far more precisely than the DSLR's, so I am glad not to have had to rely on the DSLR as the only camera.

I was hoping that there might be a way to fix short sequences as cutaways, but maybe not.

Andrew
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7. Re: Vertical rolling lines with DSLR and projector

Jim Simon Jul 17, 2011 9:59 AM (in response to I_don't_believe_it!)

I think that as suggested the problem was a mismatch between the projector and camera.

If that were so, then the lines would only appear on the screen, not throughout the entire frame. If the lines appear across the whole frame, it's not a scan mismatch. (Assuming, of course, that the screen does not fill the entire frame, that there is other content besides the screen.)
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