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Shutter angle for filming a tv at 25fps


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#1 Christophe Collette

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Posted 24 January 2007 - 07:32 PM

Hi, I will be shooting a video for a french singer shortly, the director wants a shot of a tv included, I know the angle for a tv here (60 hz (I don't know if it matters actually but I'd rather mentionning it) ) shooting 24fps is 144 degrees, What would the angle be shooting 25fps? the same, 144?

Thanks a lot!

C
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#2 Daniel Christie

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Posted 24 January 2007 - 08:17 PM

Shooting a 50Hz source at 24fps requires a 172.8º (or alternativly 86.4º, 259.2º or 345.6º) shutter as apposed to 180º at 25fps. May I ask more detail? Where will it be shot (mains power frequency)? What type of monitor are you shooting (LCD, CRT, Plasma)? What format/framerate will you be finishing at?

These factors will all affect your options and your needs in terms of sync boxes etc.

Daniel

Edited by Daniel Christie, 24 January 2007 - 08:19 PM.

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#3 Christophe Collette

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Posted 24 January 2007 - 09:57 PM

Hi there, I'll just reformulate my question here, all my lighting is flicker-free, the problem is the TV, regular cathodic screen tv, I know that when I usually shoot a tv, I set my shutter angle to 144 degrees at 24 fps, what do I set it at when shooting 25fps?

Thanks
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#4 David Mullen ASC

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Posted 25 January 2007 - 02:20 AM

You're shooting a 60i NTSC monitor at 25 fps? Or a 50i PAL monitor at 25 fps?

You do realize that even shooting a 60i monitor at 24 fps with a 144 degree shutter does not eliminate roll bars, only makes them thin lines instead of thick bands. They still roll unless you shoot at 23.976 fps, and even then, you can't get them out of the picture, so you end up with this thin line in the image.

In theory, a 150 degree shutter at 25 fps will give you a 1/60th shutter speed, just as a 144 degree shutter at 24 fps will. So you'd use a 150 degree shutter when filming an NTSC monitor at 25 fps to make the roll bars thinner. But they would still drift.
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#5 Christophe Collette

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Posted 25 January 2007 - 11:20 AM

Thanks a lot David, again! I understand better what Daniel meant.

I will be shooting a 60i NTSC monitor (cathodic screen) at 25 fps, I am shooting for PAL but in Canada. I asked for a synchronisator to be added to my camera list but will it solve the problem entirely?

While I am at it, I also heard that plasma screens don't have the pulsation when you film them at 24fps 180 degrees, is that correct?

Thanks!!
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#6 David Mullen ASC

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Posted 25 January 2007 - 11:29 AM

No, a synchronizer will probably get your roll bars to stop rolling after the shutter change gets them to be smaller lines, but the only way to get rid of the lines completely is to shoot at the true speed of the monitor (29.97 fps in the case of NTSC) or bring in a monitor that runs at the camera rate (for 25 fps, a PAL monitor, in the case of 24 fps, a special 24 fps monitor & playback system -- actually 23.976 fps.)

LCD screens don't flicker/pulse. Plasma screens might pulse but if you shoot at the same Hz speed, then it probably will be OK. So I'd see if a 150 degree shutter at 25 fps would get rid of the 60 Hz pulse in a Plasma screen that is showing NTSC.
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#7 Paramvir Singh

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Posted 25 January 2007 - 12:39 PM

i live in a 50Hz PAL country and shooting a PAL monitor at 25FPS (180 shutter) is pretty easy. You quickly switch the old Arri III on and off a couple of times, until the black bar goes out of the monitor. Then you roll!!
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