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What is the common practise for using CC Gels + Color "theater" Gels

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#1 Daniel Reed

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Posted 26 May 2014 - 05:57 AM

When adding a flavor of color theatrical gel what is the best practice when being cautious of white balance?

 

Ex.

 

Say I'm using an odd HMI lamp as the key and it's reading 5400K via a sekonic c-500 meter.

The desired White Balance is... lets say 3200.  My pCam app says the the mired shift is 127.

I toss a Rosco 3401 Sun 85 gel or perhaps a 3/4 CTO gel to get me mostly there (either gel is rated at 131 mired)

 

Great... but now the art director/dp/client/boss says they want the light to be green...?

 

Do I then add a green filter on top of that...
...or do a magic trick w/ thinking of green as being somewhere around 4500K and use just one gel to accomplish the shift from 5400K.
Using just one gel I imagine should reduce light loss. So once again back at the pCam app and it says the mired shift from 5400 to 4500K is 37...
...so am I right in thinking i should just throw on a 1/4 CTO?  If so, how do I control the density of the green - add/sub green gels?

 

What about if they say they want the color to be purple, red or even yellow?

 

If there is a common consensus in terms of methodology, please let me know.  
I'd prefer not re-invent the wheel or get dumb looks from crew.
It's very possible this may have already been explained to me in a lecture, but my taxed brain was overloaded.

I am by no means a pro (I'm a part-time film student working a full time day job).

 

Thank you for taking the time to read all of this.

 

I recently made a scene remake from Blade Runner using the school's only HMI light graciously received as a donation from DTC w/ mixed tungsten lamps and got a bit of a headache trying wrap my brains around gels for both correction and color:  http://vimeo.com/nextbooth/blade

 

 

 

 


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#2 Brian Drysdale

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Posted 26 May 2014 - 06:45 AM

Basically you decide on what you're going to use as the "correct" colour temperature to give you a neutral white or grey.

 

Which colour.temperature is used. can depend on the circumstances, but usually it's either tungsten (3,200k) or daylight (5600k). Using this you can start adding colour gels onto lights that match this particular colour temperature.

 

Of course, when using tungsten lighting, HMI's will appear blue, while with daylight lamps,, uncorrected tungsten will appear to be orange.

 

To gave a certain colour you add gels of the appropriate colour, the manufacturers supply gels in a range of colours.  When shooting digitally you usually can see the results in a correctly set up monitor.


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#3 Daniel Reed

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Posted 26 May 2014 - 07:03 AM

Thanks Brian. To clarify, color correct the light first... then add color. Yeah?

Basically you decide on what you're going to use as the "correct" colour temperature to give you a neutral white or grey.

 

...

 

To gave a certain colour you add gels of the appropriate colour, the manufacturers supply gels in a range of colours.  When shooting digitally you usually can see the results in a correctly set up monitor.


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#4 Brian Drysdale

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Posted 26 May 2014 - 07:25 AM

Set up the lights to match your correct colour temperature, then add the colour effect gels. That's unless the light's normal colour temperature gives the colour effect you're after without putting on gels..


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#5 Stuart Brereton

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Posted 26 May 2014 - 01:13 PM

When adding a flavor of color theatrical gel what is the best practice when being cautious of white balance?

 

Ex.

 

Say I'm using an odd HMI lamp as the key and it's reading 5400K via a sekonic c-500 meter.

The desired White Balance is... lets say 3200.  My pCam app says the the mired shift is 127.

I toss a Rosco 3401 Sun 85 gel or perhaps a 3/4 CTO gel to get me mostly there (either gel is rated at 131 mired)

 

Great... but now the art director/dp/client/boss says they want the light to be green...?

 

Do I then add a green filter on top of that...
...or do a magic trick w/ thinking of green as being somewhere around 4500K and use just one gel to accomplish the shift from 5400K.
Using just one gel I imagine should reduce light loss. So once again back at the pCam app and it says the mired shift from 5400 to 4500K is 37...
...so am I right in thinking i should just throw on a 1/4 CTO?  If so, how do I control the density of the green - add/sub green gels?

 

What about if they say they want the color to be purple, red or even yellow?

 

 

The Mired system is designed to measure color temperature on the Blue/Red axis. Any corrections you make will be with CT gels. Alterations to the Green/Magenta axis will be with CC gels, which are not measured by Mireds. I'm not saying you can't estimate Color bias, such as leaving an HMI slightly cool and then adding green, as in your example, just saying that Mireds are not the correct measurement for them.

 

As Brian says, common practice would be to correct to 'white' first, then add color effects. Obviously, the more gels you stack on the lamp, the less output you get, so you would generally try to start with a lamp that has the correct color temp for your scene.

 

One other point. You should be careful when using CTO on HMI lamps. It's designed for correcting daylight which is as close to a perfect color source as you can get. HMIs, particularly older lamps, can have a green spike in their output. When you put CTO on them, it cuts the blue frequencies, but leaves the green, making the spike much more noticeable. Both Rosco and LEE manufacture an amber gel that is specifically designed for correcting HMIs.


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#6 Daniel Reed

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Posted 26 May 2014 - 05:33 PM

Awesome info, thank you Stuart!

 

What is the common practice for measuring the Green/Magenta axis and knowing the amount of CC gel to use?

In terms of color tools I have a Sekonic C-500 color meter, pCam iphone app and the SMPTE one shot color chart.

 

I'm trying to nail down controlling color on the fly as much as possible during principal photography. 

The Mired system is designed to measure color temperature on the Blue/Red axis. Any corrections you make will be with CT gels. Alterations to the Green/Magenta axis will be with CC gels, which are not measured by Mireds...


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#7 Daniel Reed

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Posted 26 May 2014 - 06:19 PM

from the Sekonic C-500 manual on page 12...

"1 CC index = 2.5 CC filter number" 

 

So... if i get a 2M on the color meter, I take that to mean I need a "5 magenta" CC filter number...

 

...I would then look at a LEE filter CC filter chart such as:

http://www.leefilter...ur-compensating

 

I would then need a CC05M gel to color correct for the M/G axis shift. Yeah? =)

 

 

 

If I understand this all correctly, then a common practice when gelling for color would be:

 

1 - WB the light along the mired shift axis and apply appropriate CT gel (if applicable)

 

2 - Adjust M/G shift based on meter CC reading and apply appropriate M/G gel (if present)

 

3 - Add color theater gels per taste/aesthetic/art preferences or boss/client "color" requests (if desired)

 

 

...then finally I would do the normal diffusion/scrim/lens focus/move light tango dance for exposure intentions.  Yeah Yeah?

 

 

Awesome info, thank you Stuart!

 

What is the common practice for measuring the Green/Magenta axis and knowing the amount of CC gel to use?

In terms of color tools I have a Sekonic C-500 color meter, pCam iphone app and the SMPTE one shot color chart.

 

I'm trying to nail down controlling color on the fly as much as possible during principal photography. 


Edited by Daniel Reed, 26 May 2014 - 06:20 PM.

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#8 Stuart Brereton

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Posted 26 May 2014 - 07:18 PM

 

If I understand this all correctly, then a common practice when gelling for color would be:

 

1 - WB the light along the mired shift axis and apply appropriate CT gel (if applicable)

 

2 - Adjust M/G shift based on meter CC reading and apply appropriate M/G gel (if present)

 

3 - Add color theater gels per taste/aesthetic/art preferences or boss/client "color" requests (if desired)

 

 

...then finally I would do the normal diffusion/scrim/lens focus/move light tango dance for exposure intentions.  Yeah Yeah?

 

 

Correct. Or just use a tungsten lamp...

 

Seriously though, in my experience, the occasions where I am adding effects gels to lamps are night scenes, INT or EXT, or studio shoots, where I generally try to use tungsten lamps. Unless you need the high output of an HMI, it's generally easier and cheaper to use tungsten.


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#9 Daniel Reed

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Posted 26 May 2014 - 08:16 PM

Absolutely, I was using the HMI and WB + color targets as an example.

I'm in search of clarification on common best working practices as a theory i can apply in various scenarios.

This has helped me a ton already.  Thanks so much.

 

I can't help but wonder now... is it common to have at least one grip per light setup in a budgeted professional job?

In terms of setups, I can easily see it taking a decent amount of time for each light. 

 

 

Correct. Or just use a tungsten lamp...

 

Seriously though, in my experience, the occasions where I am adding effects gels to lamps are night scenes, INT or EXT, or studio shoots, where I generally try to use tungsten lamps. Unless you need the high output of an HMI, it's generally easier and cheaper to use tungsten.


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#10 Stuart Brereton

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Posted 26 May 2014 - 09:35 PM

 

I can't help but wonder now... is it common to have at least one grip per light setup in a budgeted professional job?

In terms of setups, I can easily see it taking a decent amount of time for each light. 

 

 

Grips don't set lamps, electricians do. And no, it's not common to have one per lamp, unless you are working in Asia, where due to the cheap cost of labor, G&E teams are often huge.


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#11 Daniel Reed

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Posted 27 May 2014 - 12:41 AM

Thank you for taking the time to answer my silly novice questions - I really appreciate it.

Grips don't set lamps, electricians do. And no, it's not common to have one per lamp, unless you are working in Asia, where due to the cheap cost of labor, G&E teams are often huge.


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