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SORRY!!!! Posted in general, here it is again


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#1 Christophe Collette

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Posted 01 October 2006 - 09:24 PM

Hi everyone, I am totally new to this forum, I am a young photographer from Montreal, I will be directing the photography for a music video next tuesday, this is not my first video but I am still unfamiliar with the flicker thing as I did not study cinematography. The video takes place in an hotel room, looks a lot like the Richard Ashcroft "song for the lovers" video, (), in terms of lighting, just a little less moody. Lighting is a mix of Fresnels 300-650-1k, Open face 2K, kino flo 4x4 and 2x4 and practicals (up to 4 in the frame at times) and a window gelled with 1/2 CTO. I think everything is 60HZ in the room, I am quite worried about safe speed for all this. The director wants to shoot part of video at 18fps, which I believe is not a safe speed at all shutter angles and shutter speeds. I would rather not touch the shutter, am a bit too green for this! Should I suggest shooting at 20FPS, or 15FPS? Is 24 FPS a safe speed also? I do not want to mess this up and it is quite hard to do any tests prior to shooting, I will go along with my ass. cam tomorrow to try to run some test alongside his but I don't think I'll get to view it prior to tuesday. I'd like an insight from the pros! I am shooting on the Arri Sr3. 500T Vision2 and transferring on either Quadra or Spirit. Also, should I worry a lot about the practicals, I intend in putting a 25W lightbulb, maybe painting one side black or taping it, the lamps are not bare bulbs, I will never see a bulb really but I don't want to kill all details over around the lamps. I do not have access to dimmers for the practicals.

All suggestions are greatly appreciated, Sorry for this long post!! Thank you very very much!

Christophe Collette
www.christophecollette.com
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#2 David Mullen ASC

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Posted 01 October 2006 - 10:24 PM

The only lights you'll have problems with at non "safe" speeds are 60 Hz AC discharge lamps -- practical fluorescents (not Kinoflos), streetlamps, and HMI's with the older magnetic ballasts. So in terms of what you listed, you should be fine at the different frame rates and shutter speeds.
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#3 Christophe Collette

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Posted 01 October 2006 - 10:52 PM

The only lights you'll have problems with at non "safe" speeds are 60 Hz AC discharge lamps -- practical fluorescents (not Kinoflos), streetlamps, and HMI's with the older magnetic ballasts. So in terms of what you listed, you should be fine at the different frame rates and shutter speeds.


Thank you very much for your generosity David, however I still have a question, I have a few hotel lamps in some shots, are these what you call AC discharge lamps? What are the "safe speeds" below 24 fps with such lamps? 18 fps is not one I believe... Would 20 be fine? Sorry for not being well informed, as I mentionned, I am a photogapher at the basis. And also, while I am at it, I overheard a shutter angle of 45 degree at 24 fps could also be problematic with AC 60hz discharge lamps. I know about the 2 stops compensation but is it true that different shutter angles can generate different flicker responses...

Is there an easy rule for calculating flicker free speed based on the source??


Thank you very much!!!


Christophe
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#4 David Mullen ASC

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Posted 01 October 2006 - 11:09 PM

Thank you very much for your generosity David, however I still have a question, I have a few hotel lamps in some shots, are these what you call AC discharge lamps? What are the "safe speeds" below 24 fps with such lamps? 18 fps is not one I believe... Would 20 be fine? Sorry for not being well informed, as I mentionned, I am a photogapher at the basis. And also, while I am at it, I overheard a shutter angle of 45 degree at 24 fps could also be problematic with AC 60hz discharge lamps. I know about the 2 stops compensation but is it true that different shutter angles can generate different flicker responses...

Is there an easy rule for calculating flicker free speed based on the source??
Thank you very much!!!
Christophe


If the hotel lights are ordinary tungsten bulbs, these are fine at any speeds. If they are fluorescent compact bulbs, they might flicker at non-safe speeds and if possible, you should switch them to ordinary tungsten bulbs (also because of the color.)

Trouble with shooting AC discharge sources at a 45 degree shutter angle is not flicker but misexposure. At 24 fps / 180 degrees, you capture about two and a half AC pulses per frame; at 144 degrees, exactly two pulses. But at 45 degrees, you are capturing part of a single sine wave of light and everytime you trigger the camera, you may fall in sync with the peak or valley of the pulse (and thus be underexposed if at the valley). So basically, don't go below 90 degrees at 24 fps unless these are non-AC discharge (non-pulsing, i.e. continuous or super high-frequency) sources.

Here is a chart of safe speeds -- note that these speeds still have to be crystal-sync, not wild or constant, but crystal:

http://www.griptruck.....ng speeds.htm

The other technique is to pick a crystal-sync frame rate and shutter angle combo that add up to 1/60th of a second shutter speed per frame.
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#5 Christophe Collette

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Posted 02 October 2006 - 08:37 AM

If the hotel lights are ordinary tungsten bulbs, these are fine at any speeds. If they are fluorescent compact bulbs, they might flicker at non-safe speeds and if possible, you should switch them to ordinary tungsten bulbs (also because of the color.)

Trouble with shooting AC discharge sources at a 45 degree shutter angle is not flicker but misexposure. At 24 fps / 180 degrees, you capture about two and a half AC pulses per frame; at 144 degrees, exactly two pulses. But at 45 degrees, you are capturing part of a single sine wave of light and everytime you trigger the camera, you may fall in sync with the peak or valley of the pulse (and thus be underexposed if at the valley). So basically, don't go below 90 degrees at 24 fps unless these are non-AC discharge (non-pulsing, i.e. continuous or super high-frequency) sources.

Here is a chart of safe speeds -- note that these speeds still have to be crystal-sync, not wild or constant, but crystal:

http://www.griptruck.....ng speeds.htm

The other technique is to pick a crystal-sync frame rate and shutter angle combo that add up to 1/60th of a second shutter speed per frame.



Thanks a lot David! This made it really clear!
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#6 Mario C. Jackson

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Posted 02 October 2006 - 09:15 AM

Chris

If you dont have dimmers just by you some streaks and tips from a salon store/hair store. Just lightly or heavily spray them on your practical lights.
Hope this helps
Mario C. Jackson

Edited by Mario C. Jackson, 02 October 2006 - 09:15 AM.

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#7 Christophe Collette

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Posted 02 October 2006 - 10:42 AM

Chris

If you dont have dimmers just by you some streaks and tips from a salon store/hair store. Just lightly or heavily spray them on your practical lights.
Hope this helps
Mario C. Jackson



Thanks a lot Mario, I went to the hardware store this morning to purchase dimmers for the practicals, I also grab a can of black paint for BBQ, someone gave this tip on the forum, does this works as well as streaks and tips??

Thanks again!
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Willys Widgets

rebotnix Technologies

Wooden Camera

Tai Audio

The Slider

Abel Cine

Broadcast Solutions Inc

FJS International, LLC

CineLab

Metropolis Post

Technodolly

Glidecam

Gamma Ray Digital Inc