Jump to content


Photo

HMI Flicker with different frame rates


  • Please log in to reply
3 replies to this topic

#1 Scott B. Jolley

Scott B. Jolley

    New

  • Basic Members
  • Pip
  • 3 posts
  • Cinematographer

Posted 13 April 2006 - 10:24 PM

When shooting with the different frames rates on the varicam and using HMI lighting, are there sync or flicker problems? Are electronic ballest needed? What is the math to figure it out?
Thanks
  • 0

#2 Michael Nash

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

Posted 13 April 2006 - 10:51 PM

Same rules apply as for film, except you adjust shutter speed instead of shutter angle.

You can follow the "HMI safe" frame rates derived from the "twice the frequency rule." Any number that divides evenly into 2x the power cycle is a flicker-free frame rate at any shutterspeed. That's 120/x for 60Hz. countries giving you: 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 20, 24, 30, 40, 60.

If you want to shoot at some other frame rate, you need to set your shutterspeed (through clearscan or synchroscan) to a number that matches or divides evenly into the power cycle. For example, 1/60 sec., or 60.0Hz. For the most natural-looking motion blur, pick the denominator or Hz. that's closest to double the frame rate.
  • 0

#3 Scott B. Jolley

Scott B. Jolley

    New

  • Basic Members
  • Pip
  • 3 posts
  • Cinematographer

Posted 14 April 2006 - 08:48 AM

Same rules apply as for film, except you adjust shutter speed instead of shutter angle.

You can follow the "HMI safe" frame rates derived from the "twice the frequency rule." Any number that divides evenly into 2x the power cycle is a flicker-free frame rate at any shutterspeed. That's 120/x for 60Hz. countries giving you: 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 20, 24, 30, 40, 60.

If you want to shoot at some other frame rate, you need to set your shutterspeed (through clearscan or synchroscan) to a number that matches or divides evenly into the power cycle. For example, 1/60 sec., or 60.0Hz. For the most natural-looking motion blur, pick the denominator or Hz. that's closest to double the frame rate.


  • 0

#4 Jeremy

Jeremy
  • Basic Members
  • PipPipPip
  • 112 posts
  • Cinematographer

Posted 18 April 2006 - 03:58 PM

HMIs actually have very strange color warping when you play with a shutter speed that catches the lights at a different frequency. By standard settings on the Varicam, this usually happens with 1/250 and up.
  • 0


Metropolis Post

Opal

Wooden Camera

rebotnix Technologies

Tai Audio

Aerial Filmworks

CineLab

Willys Widgets

Technodolly

Ritter Battery

CineTape

Media Blackout - Custom Cables and AKS

Glidecam

Abel Cine

The Slider

Paralinx LLC

Gamma Ray Digital Inc

FJS International, LLC

Broadcast Solutions Inc

Visual Products

Rig Wheels Passport

Abel Cine

Gamma Ray Digital Inc

CineLab

rebotnix Technologies

Rig Wheels Passport

Willys Widgets

Aerial Filmworks

Ritter Battery

Visual Products

Glidecam

Wooden Camera

FJS International, LLC

CineTape

Paralinx LLC

The Slider

Broadcast Solutions Inc

Technodolly

Media Blackout - Custom Cables and AKS

Opal

Tai Audio

Metropolis Post