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Old January 30th, 2008, 02:51 AM   #1
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24p at 1/60th - interferences in PAL land

I tried to test record in HQ 24p, and with shutter off got quite nice resluts inside my house, with only some regular bulbs on (was able to keep gain at 0 dB). However, when I switched the shutter on, I was astonished to see those horizontal waves, rolling on the LCD from top to bottom! That was with 1/60th (here in Poland we have 50 Hz mains); when I switched to 1/48th the effect was gone.

Since 1/48th is the "right" shutter with 24p anyway, I don't worry too much - but are those interferences normal with 1/60th shutter speed? I realize it might be perfectly normal - all my previous cameras being PAL-only, I never saw anything like it - but would like to know which situations should be avoided (of course I have yet to decide whether I'll be using 24p at all, or stick to the closest thing i.e. 25p).
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Last edited by Piotr Wozniacki; January 30th, 2008 at 03:36 AM.
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Old January 30th, 2008, 03:41 AM   #2
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You will see the rolling bars everytime you shoot under artificial light if you have a shutter speed and / or framerate that is not in sync with the power supply. Outside is obviously not a problem, but when it starts to gets dark will see the effect being generated by anything that is artificially lit.

When over cranking under lights you can only go up to 50fps, going any higher will result in the same effect.
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Old January 30th, 2008, 03:43 AM   #3
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Thanks for confirmation, Paul :)
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Old January 30th, 2008, 04:22 AM   #4
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Just out of curiosity what are the reasons people use 24fps instead of 25fps? 24 is for film and 25 is for dvd, tv etc. Right?

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Old January 30th, 2008, 04:48 AM   #5
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Sami,

The main reason is that neither BD, nor HD DVD officially support 25p.

Nevertheless, I managed to burn several BDs with 25p material from my V1E. However, didn't try them on a stationary BD player yet; on the PC they play perfectly.

This is why I'm still not sure which progressive framerate to use with my new EX1 - 25p or 24p. Those filming for broadcast in Europe will certainly go with 50i or 25p, though (or 720/50p of course).
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Old January 30th, 2008, 05:04 AM   #6
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Quote:
Originally Posted by Piotr Wozniacki View Post

The main reason is that neither BD, nor HD DVD officially support 25p.
Wow, new info again :) OK, well I think that might be a good thing for the future.

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Old January 30th, 2008, 05:06 AM   #7
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Shoot 25p. If you need 24p for distro for some reason I think you know how to change it in Vegas to 24p :).

I have another camera that shoots 24p, same thing with 50Hz lighting unless you use HF ballasts but sometimes that isn't possible.
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Old January 30th, 2008, 05:15 AM   #8
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Shoot 25p. If you need 24p for distro for some reason I think you know how to change it in Vegas to 24p :).

I have another camera that shoots 24p, same thing with 50Hz lighting unless you use HF ballasts but sometimes that isn't possible.
Yep. I'll tell you Bob that if I decide to keep my V1E (love it so much it's difficult for me to part with it), I'll certainly be using 25p as the common framerate between the two. If I sell the V1E, however, AND it turnes out that 25p BD's do not play back on any BD player out there - well, I guess I'll have to seriously consider shooting 24p vs transcoding 25p to 24p in Vegas... Especially now, when it has the smart rendering capability, which I couldn't use should I need to transcode everything!
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Old January 30th, 2008, 06:40 AM   #9
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I don't think it would be too difficult for someone to write some code that'd convert 25p mpeg-2 to 24p without decoding and encoding. Possibly nothing more than the frame rate in the header would need to be changed. The audio would have to be stripped out of the stream, resampled and muxed back in I guess but that's not impossibly difficult.
After all this is dead easy to do with a projector, just change the speed of the motor.
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Old January 30th, 2008, 03:18 PM   #10
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A workaround to rolling bars (and technical note about working with artificial lights):

If you use normal light bulbs, the flickering effects will appear when not in sync with the mains power frequency. But if you use studio lights, you won't notice it.

Why? Because studio spotlights are designed to run hotter than normal lightbulbs, and this, apart from giving a light with higher color temperature, prevents the filament of the light to cool down when the cycle of main power is at its low peak (which is what causes the flickering), so it will emit a more stable light, avoiding the flicker caused by the AC.
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Old January 30th, 2008, 04:03 PM   #11
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Went to the movies today to see the new Paul Haggis movie In the Valley of Elah. Theres a scene where the main character goes into a hardware store and guess what! Fluorescent flickering! And it looked good! Added to the realism and mood in my opinion.

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