# CTO conversion

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### #1 Mathew Collins

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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)

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### #2 Michael Rodin

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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

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### #3 Mark Dunn

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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.

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### #4 Mathew Collins

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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?

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### #5 David Mullen ASC

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Posted 26 April 2017 - 12:26 AM

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

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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.

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### #7 Mathew Collins

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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?

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### #8 Stuart Brereton

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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

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### #9 Mathew Collins

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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.

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