Jump to content


Photo

Whats the effect of doubling up gels?


  • Please log in to reply
13 replies to this topic

#1 John M

John M
  • Basic Members
  • PipPip
  • 24 posts
  • Other

Posted 20 June 2012 - 04:27 PM

Does doubling up gels just add stops? Or will it also alter color temperature? I.e I have a Lee 442 Straw filter that changes 6500K to 4300K. If I doubled that up would it bring the temperature even lower? Or am I just losing more light?

Thanks
  • 0

#2 Jax McLennan

Jax McLennan
  • Basic Members
  • PipPip
  • 11 posts
  • 1st Assistant Camera
  • Melbourne, Australia

Posted 20 June 2012 - 06:31 PM

Yes it would - two 1/2 CTBs combined create a full CTB, for example.
  • 0

#3 Sean Elder

Sean Elder
  • Basic Members
  • PipPip
  • 76 posts
  • Cinematographer
  • Houston, Texas

Posted 20 June 2012 - 10:32 PM

Yes doubling a filter will decrease the amount of light that passes through the gel also it will change the value of the light as well. I'm sure there is someone on this forum that can give a a far more technical answer than what I have given.
  • 0

#4 Kyle Reid

Kyle Reid
  • Basic Members
  • PipPip
  • 23 posts
  • Industry Rep
  • Baton Rouge, LA

Posted 22 June 2012 - 08:27 PM

It's completely additive, if you double a gel you will see double the effect of that gel (color and exposure).
Although it would be good to note that two halves do not make a full when we are dealing with color temp gels. For example 1/2 CTB creates a MIRED shift of -79, however, full CTB creates a MIRED shift of -137. So if you use two sheets of 1/2 CTB over a light source you will create a MIRED shift of -158, but full CTB only creates a MIRED shift of -137. Gels work in a linear fashion, whereas color temperature does not.

Edited by Kyle Reid, 22 June 2012 - 08:28 PM.

  • 0

#5 Conor Stalvey

Conor Stalvey

    New

  • Basic Members
  • Pip
  • 8 posts
  • Gaffer
  • NJ/NY

Posted 14 August 2012 - 08:40 AM

It's completely additive, if you double a gel you will see double the effect of that gel (color and exposure).
Although it would be good to note that two halves do not make a full when we are dealing with color temp gels. For example 1/2 CTB creates a MIRED shift of -79, however, full CTB creates a MIRED shift of -137. So if you use two sheets of 1/2 CTB over a light source you will create a MIRED shift of -158, but full CTB only creates a MIRED shift of -137. Gels work in a linear fashion, whereas color temperature does not.


Thanks Kyle, I was not aware of the numerical values. Learn something new everyday.
  • 0

#6 Mei Lewis

Mei Lewis
  • Basic Members
  • PipPipPipPip
  • 347 posts
  • Other
  • UK

Posted 15 August 2012 - 03:52 PM

It's completely additive, if you double a gel you will see double the effect of that gel (color and exposure).



What does 'double' mean there? I guess it doubles the light loss, but in terms of color what number gets multiplied by two?
  • 0

#7 Chris Millar

Chris Millar
  • Basic Members
  • PipPipPipPip
  • 1642 posts
  • Other

Posted 15 August 2012 - 06:59 PM

It is not additive in the way some of you might interpret that - in some headspaces it's more multiplicative.

Think about it this way - imagine you had an ND gel that took away %50 of light and your original light source had a value of '1' - you'd end up with 0.5 units of light out of it, if it were additive you'd end up with 0 light with the second gel - and you know that aint correct

The math would be as follows:

1 x 0.5 = 0.5 (first gel)

0.5 x 0.5 = 0.25 (second gel)

maybe use the word 'sequential' instead

To set up a function with respect to number of gels as you're working in discrete units I think you'd need something like a recurrence relation or otherwise - not enough coffee to do that at the moment Posted Image
  • 0

#8 Chris Millar

Chris Millar
  • Basic Members
  • PipPipPipPip
  • 1642 posts
  • Other

Posted 15 August 2012 - 07:07 PM

ok, had my coffee -

oh gawd, its not as creepy as recurrence relations at all Posted Image


x = number of gels

% light output = 100(2-x)




  • 0

#9 Chris Millar

Chris Millar
  • Basic Members
  • PipPipPipPip
  • 1642 posts
  • Other

Posted 15 August 2012 - 08:55 PM

Should say that that function is only valid for each frequency band (which in an ND should be all visible light) - when looking at something with a colour correction on it you'd have to apply that function to every point along the response curve. Easy if you have a tabulated version in excel or some similar spreadsheet...
  • 0

#10 Stuart Brereton

Stuart Brereton
  • Basic Members
  • PipPipPipPip
  • 3054 posts
  • Cinematographer
  • Los Angeles

Posted 15 August 2012 - 11:34 PM

What does 'double' mean there? I guess it doubles the light loss, but in terms of color what number gets multiplied by two?


If you using Color Correction gels then it's the MIRED shift that doubles. If it's other colors, then you would just say that effect doubles in strength (although I am sure there a mathematical way of describing it).
  • 0

#11 Justin Dombrowski

Justin Dombrowski

    New

  • Basic Members
  • Pip
  • 6 posts
  • 1st Assistant Camera
  • Atlanta, GA

Posted 15 August 2012 - 11:57 PM

Another fun thing to try with stacking gels..
If your ever in a situation where you have a full CTB and no halves or quarters. You can apply the Full CTB & counter act the color temp with a 1/4 or 1/2 CTO.

Had this on a shoot where we needed to correct 2 tungsten 650w and we had limited gels. So we put a 1/2 CTB on one and a Full CTB paired with a 1/2 CTO on the other.


Now I know the light output and color temp wasn't perfectly matched but, it was close enough and served its purpose well.



Are there any other gel combinations that get interesting effects?
  • 0

#12 Sean Elder

Sean Elder
  • Basic Members
  • PipPip
  • 76 posts
  • Cinematographer
  • Houston, Texas

Posted 04 September 2012 - 09:02 AM

Here's a question! (Yes, I know that sentence was a statement.) How would you determine the falloff or mired shift for diffusion? Is there a formula for that or is that something that the diffusion manufactures set? Also is this based on one particular light source(i.e.: a scientifically preset and calibrated light fixture) or a general light source(i.e.: a open-faced quartz light, HMI, Par, Fresnel, Etc.)?
  • 0

#13 Stuart Brereton

Stuart Brereton
  • Basic Members
  • PipPipPipPip
  • 3054 posts
  • Cinematographer
  • Los Angeles

Posted 04 September 2012 - 11:09 AM

How would you determine the falloff or mired shift for diffusion? Is there a formula for that or is that something that the diffusion manufactures set?


Diffusion generally doesn't have a Mired shift. It's designed to soften light, not to change its color. Exceptions to this would be gels like LEE's Cosmetic series which combine a light diffusion with subtle color tints.
  • 0

#14 rsellars

rsellars
  • Basic Members
  • PipPip
  • 17 posts
  • Cinematographer
  • Portland, OR

Posted 12 September 2012 - 12:57 PM

Diffusion generally doesn't have a Mired shift. It's designed to soften light, not to change its color. Exceptions to this would be gels like LEE's Cosmetic series which combine a light diffusion with subtle color tints.


Stuart & Sean, while Lee & Rosco might not publish mired shift numbers for diffusion material, nearly all diffusion material does make light sources warmer. You can see it with your eyes and you can measure it with a color temperature meter. It varies slightly with each type of material, but I have found that a true 3200 tungsten source aimed through diffusion material averages around 2900 K. I'm not sure what the mired shift is. This is one of the reasons why Kinoflo offers 2900K tubes for their units. This "warmer" tungsten matches better with tungsten studio lights that are softened with diffusion material or bounced off white boards (which also warm light).
  • 0


Metropolis Post

Wooden Camera

CineTape

FJS International, LLC

rebotnix Technologies

Willys Widgets

Broadcast Solutions Inc

CineLab

Glidecam

Media Blackout - Custom Cables and AKS

Ritter Battery

Gamma Ray Digital Inc

Technodolly

Opal

Rig Wheels Passport

Visual Products

Tai Audio

Aerial Filmworks

Paralinx LLC

The Slider

Abel Cine

Gamma Ray Digital Inc

Visual Products

rebotnix Technologies

FJS International, LLC

CineTape

Glidecam

Tai Audio

Wooden Camera

Paralinx LLC

Rig Wheels Passport

Metropolis Post

Media Blackout - Custom Cables and AKS

Aerial Filmworks

Broadcast Solutions Inc

The Slider

Willys Widgets

Abel Cine

CineLab

Opal

Ritter Battery

Technodolly