Jump to content



Photo

CTO conversion


  • Please log in to reply
8 replies to this topic

#1 Mathew Collins

Mathew Collins
  • Basic Members
  • PipPipPip
  • 154 posts
  • Cinematographer
  • India

Posted 24 April 2017 - 02:07 AM

Hi,

 

Lee portal says,

 

Full CTO    Converts Daylight to Tungsten Light    6500K to 3200K
1/2 CTO    Converts Daylight to Tungsten Light    6500K to 3800K
1/4 CTO    Converts Daylight to Tungsten Light    6500K to 4600K
1/8 CTO    Converts Daylight to Tungsten Light    6500K to 5550K
3/4 CTO    Converts Daylight to Tungsten Light    6500K to 3600K

 

http://www.leefilter...lter=conversion

 

What would be the change in CT when we use these filters in front of a light with 5600K( say Arri PAR 4K)

 

Please share your views.
 


  • 0

#2 Michael Rodin

Michael Rodin
  • Basic Members
  • PipPipPip
  • 127 posts
  • Cinematographer
  • Moscow / Riga

Posted 24 April 2017 - 07:47 AM

Your HMI's color temp will be roughly 180 mired (= 1 000 000 / Kelvin CT). Then you find out the mired shift of a certain CTO and add it. Or subtract if it's CTB.

 

More mired - less Kelvin - warmer

Less mired - more Kelvin - colder


  • 0

#3 Mark Dunn

Mark Dunn
  • Basic Members
  • PipPipPipPip
  • 2279 posts
  • Other
  • London

Posted 24 April 2017 - 08:03 AM

Full CTO mired shift is about 159. So the new CT will be 1000000/(180+159)=2950K.

There's a chart on page 56 of the "Think Lee" download on that site under "resources". Just put a ruler across it.

http://www.leefilter...-resources.html


Edited by Mark Dunn, 24 April 2017 - 08:07 AM.

  • 1

#4 Mathew Collins

Mathew Collins
  • Basic Members
  • PipPipPip
  • 154 posts
  • Cinematographer
  • India

Posted 25 April 2017 - 10:52 PM

Full CTO mired shift is about 159. So the new CT will be 1000000/(180+159)=2950K.

There's a chart on page 56 of the "Think Lee" download on that site under "resources". Just put a ruler across it.

http://www.leefilter...-resources.html

 

 

Thanks much Mark and Michael.

 

When I calculated the required Miredshift, for converting 5600K to 3200K using the formula,

 

1000000/3200 -  1000000/5600 =133
 

1000000/3200=312.5

 

1000000/5600=178.5714285714286

 

I could not find a filter with 133 Miredshift in the pdf. But almost near one is 285 (Three Quarter CTO) with a value +124. 

 

Would this calculation is correct?
 


  • 0

#5 David Mullen ASC

David Mullen ASC
  • Sustaining Members
  • 19375 posts
  • Cinematographer
  • Los Angeles

Posted 26 April 2017 - 12:26 AM

626 LED conversion gel (Seven Eighths Digital LED CTO) has a 132 MIRED shift value.
  • 0

#6 Michael Rodin

Michael Rodin
  • Basic Members
  • PipPipPip
  • 127 posts
  • Cinematographer
  • Moscow / Riga

Posted 26 April 2017 - 08:45 AM

If you can't get it with one filter, use two. Or more. And if you want to apply a lot of correction to a big light (especially a PAR) it's better to add a couple spaced gel frames than a single dense gel.

 

The so-called LED gels shift tint, not only color temp. They're for daylight LEDs only, on HMIs they can give magenta color casts.


  • 0

#7 Mathew Collins

Mathew Collins
  • Basic Members
  • PipPipPip
  • 154 posts
  • Cinematographer
  • India

Posted 26 April 2017 - 12:06 PM

626 LED conversion gel (Seven Eighths Digital LED CTO) has a 132 MIRED shift value.

 

Would the LED conversion gel is OK for HMI PARs?


  • 0

#8 Stuart Brereton

Stuart Brereton
  • Basic Members
  • PipPipPipPip
  • 2778 posts
  • Cinematographer
  • Los Angeles

Posted 26 April 2017 - 01:40 PM

There's no need to get hung up on correcting your lamps exactly according to the Mired system. Most people do perfectly well with Full, 1/2 and 1/4 CTO and Full ,1/2 and 1/4 CTB


  • 0

#9 Mathew Collins

Mathew Collins
  • Basic Members
  • PipPipPip
  • 154 posts
  • Cinematographer
  • India

Posted 27 April 2017 - 09:30 AM

There's no need to get hung up on correcting your lamps exactly according to the Mired system. Most people do perfectly well with Full, 1/2 and 1/4 CTO and Full ,1/2 and 1/4 CTB

 

Hi Stuart,

 

Thanks much. Now I got the answer.


  • 0


Rig Wheels Passport

rebotnix Technologies

Pro 8mm

Technodolly

Willys Widgets

Visual Products

Broadcast Solutions Inc

FJS International, LLC

Media Blackout - Custom Cables and AKS

Paralinx LLC

Metropolis Post

ZoomCrane

Glidecam

Aerial Filmworks

Tai Audio

CineLab

Ritter Battery

Quantum Music Works

Abel Cine

CineTape

The Slider

Gamma Ray Digital Inc

ZoomCrane

Broadcast Solutions Inc

Metropolis Post

Ritter Battery

The Slider

Paralinx LLC

Glidecam

Rig Wheels Passport

Technodolly

Tai Audio

Pro 8mm

rebotnix Technologies

Abel Cine

Media Blackout - Custom Cables and AKS

Visual Products

Quantum Music Works

Aerial Filmworks

CineTape

FJS International, LLC

Willys Widgets

CineLab

Gamma Ray Digital Inc