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flicker free with fluorescent light on 36fps

flicker alexa shutter angle

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#1 Joe Saadeh

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Posted 11 October 2013 - 12:44 PM

Hello Everyone,
This is my first post here, and i hope you would be able to answer my question.
So in two days i'll be shooting a music video on the Alexa.
The director would want the looks of the fluorescent light inside the shot. We'll be filming this on 36fps so we get this somehow slow motion effect the fluorescent lamps are 50hz.

My question is what would the shutter angle be if were shooting on 36fps so i dont get filcker?
Thanks
Joe Saade


Edited by Joe Saadeh, 11 October 2013 - 12:49 PM.

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#2 Zac Fettig

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Posted 11 October 2013 - 12:48 PM

Wouldn't that depend on the ballasts for the fluorescents? If the ballasts are high enough frequency, you'll probably see nothing, with any shutter angle. The honest answer is you'll probably have to run a test.


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#3 Joe Saadeh

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Posted 11 October 2013 - 12:53 PM

the ballasts are 50hz... i know i should run a test but its not that of a high budget music video (although were shooting on an alexa)
Usually i shouldn't have problems and i could always add a preferable shutter angle on set to modify it with... but i thought there might be some sort of formula to get this.
Thanks for your reply


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#4 Zac Fettig

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Posted 11 October 2013 - 01:07 PM

theta=(360 degrees)*f/h where theta is the shutter angle, f is the frame rate (36 fps) and h is the light frequency (50 Hz). You should have an angle of 259.2 degrees. 

 

I think. If someone could check my math, I'd appreciate it.

 


Edited by Zac Fettig, 11 October 2013 - 01:07 PM.

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#5 Joe Saadeh

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Posted 11 October 2013 - 01:13 PM

That is correct!! ill then get the shutter angle of 1/50 which makes it safe for a 50hz ballast
Thanks


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#6 Zac Fettig

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Posted 11 October 2013 - 01:22 PM

For aliasing problems you can also use even multiples. So in theory, you could use 1/2 or 1/4 that shutter angle. So I think a shutter angle of 129.6 degrees might work also.

 

This all assumes that the light is at 50Hz. Most modern fluorescents run much higher frequency than the mains do, especially cinema fluorescents.


Edited by Zac Fettig, 11 October 2013 - 01:25 PM.

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#7 Joe Saadeh

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Posted 11 October 2013 - 01:27 PM

thanks a lot man ... that was really helpful


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