Jump to content


Photo

sodium vapor flickering test


  • Please log in to reply
6 replies to this topic

#1 Delorme Jean-Marie

Delorme Jean-Marie
  • Basic Members
  • PipPipPipPip
  • 513 posts
  • Cinematographer
  • paris, france

Posted 28 November 2006 - 06:23 AM

hi
prior to film a test of a sodium vapor betwen 16 and 20 fps at 180° in europe, i wonder if you've done it already?
did you notice any flicker problem?
  • 0

#2 Chris Pritzlaff

Chris Pritzlaff
  • Basic Members
  • PipPipPip
  • 187 posts
  • Gaffer
  • Los Angeles

Posted 28 November 2006 - 08:07 PM

I got flicker at 24fps with 180deg shutter. Don't know if that helps you any.
  • 0

#3 Michael Nash

Michael Nash
  • Sustaining Members
  • 3330 posts
  • Cinematographer
  • Pasadena, CA

Posted 30 November 2006 - 12:17 AM

Sodium vapor lights usally flicker at the rate of the power cycle (60Hz. in the US and 50 Hz. in Europe). Following "HMI safe" frame rates and shutter angles usually does the trick.
  • 0

#4 Zulkifli Yusof

Zulkifli Yusof
  • Guests

Posted 01 December 2006 - 08:25 AM

Sodium vapor lights usally flicker at the rate of the power cycle (60Hz. in the US and 50 Hz. in Europe). Following "HMI safe" frame rates and shutter angles usually does the trick.


In other words, framerates below 24/25fps will usually cause flicker right? I have a similar question pertaining to flicker issues with practicals in my thread within the Lighting sub forum. Michael, perhaps you can help me with it? Thanks
  • 0

#5 Michael Nash

Michael Nash
  • Sustaining Members
  • 3330 posts
  • Cinematographer
  • Pasadena, CA

Posted 03 December 2006 - 02:10 AM

In other words, framerates below 24/25fps will usually cause flicker right?


No, not exactly. Discharge type lights such as HMI's, sodium & mercury vapor, fluorescent and others "flicker" or pulse at a rate that either matches or doubles the frequency of the power supply (depending on the type of light). So, to avoid a visible flicker you have to shoot at frame rates that synch with that pulsing. There's an easy mathematical formula that lets you figure out what these frame rates are, and there are also charts where you can look it up. Or, you can just memorize them ;)

The formula is called the "twice the frequency rule," which says that any frame rate that can be divided evenly (whole number) into twice the frequency of the power supply, is a "safe" frame rate at any shutter angle.

In the US the power cycle is 60Hz. Twice that is 120. 120/24=5. Therefore 24 fps is considered "safe." I'll let you do the math to figure out what the other rates are, but I'll give you a tip: there are more of them between 1-24 than there are between 24-120. ;)
  • 0

#6 Delorme Jean-Marie

Delorme Jean-Marie
  • Basic Members
  • PipPipPipPip
  • 513 posts
  • Cinematographer
  • paris, france

Posted 03 December 2006 - 06:56 AM

if i remember my charts it will be 16,666 fps
  • 0

#7 Stephen Williams

Stephen Williams
  • Sustaining Members
  • 4708 posts
  • Cinematographer
  • Europe

Posted 03 December 2006 - 07:11 AM

Hi all,

50 Hz Speed in fps at any Shutter Angles :-

100.000 50.000 33.333 25.000
20.000 16.666 14.285 12.500
11.111 10.000 9.090 8.333
7.692 7.142 6.666 6.250
5.882 5.555 5.263 5.000
4.761 4.545 4.347 4.166
4.000 3.333 3.125 2.500
2.000 1.250 1.000


60 Hz Speed in fps at any Shutter Angles :-

120.000 60.000 40.000 30.000
24.000 20.000 17.143 15.000
13.333 12.000 10.909 10.000
9.231 8.571 8.000 7.500
7.058 6.666 6.315 6.000
5.714 5.454 5.217 5.000
4.800 3.750 3.000 2.500
2.000 1.875 1.500 1.000

Stephen
  • 0


Media Blackout - Custom Cables and AKS

CineTape

Rig Wheels Passport

Wooden Camera

Willys Widgets

Broadcast Solutions Inc

rebotnix Technologies

Tai Audio

Metropolis Post

Abel Cine

FJS International, LLC

Ritter Battery

Gamma Ray Digital Inc

Technodolly

Glidecam

Aerial Filmworks

Paralinx LLC

Visual Products

Opal

The Slider

CineLab

Technodolly

Paralinx LLC

Metropolis Post

Tai Audio

CineLab

CineTape

Broadcast Solutions Inc

Wooden Camera

FJS International, LLC

The Slider

Rig Wheels Passport

Abel Cine

rebotnix Technologies

Glidecam

Opal

Willys Widgets

Ritter Battery

Aerial Filmworks

Visual Products

Media Blackout - Custom Cables and AKS

Gamma Ray Digital Inc