Cam White Balance vs. Lighting Color Temperature

[Manuel Troendle]

Hey everyone, 

Will be doing tests on this topic soon, but i was just too curios hearing your experiences on this one: 

Lets say you want to shoot a blue-looking-cold night interior. option A: You use a Light with a temperature lets say 5600k and balancer your camera to like 700k (or just grade the RAW colder), so the scene looks now cold. 

B: You stay at a Camera white balance of 5600k, but i use a light that has a Color Temperature of 7000k, so now the picture is cold. 

How does this affect the color, tonal range and the overall feel of the picture? Will maybe the shadows/highlights be cleaner in option B? I think the main difference is that OptionA makes the whole picture bluer, and Option B only where the light hits/bounces to is blue the rest remains balanced and "white/grey". 

Really curious to hear about everyones experience on this one. 

 

 

 

[David Mullen ASC]

I don't know anyone that would go as low as 700K, that would really be pushing the blue channel! "Full blue" (Full CTB color) would be to shoot in 5600K light at 3200K on the camera.

Your two scenarios are quite far apart in the amount of blue color because you aren't calculating the MIRED shift values.

Using 5600K light on a camera setting of 3200K, which is the equivalent of putting Full CTB gel on a tungsten lamp, is a MIRED shift of -134.

Gelling a light to 7000K for 5600K setting on the camera is only a MIRED shift value of -36, which is hardly any increase in blue, it's like gelling a 3200K light to 3600K when the camera is set to 3200K.

You'd have to gel a light to 22,000K to get a 5600K camera setting to look as blue as a 5600K light looks on a camera set to 3200K. However, again, it's the same gel, Full CTB, so yes, you could put a Full CTB gel on a 5600K light, set the camera to 5600K, and get the same blue color as a 5600K light on a camera set to 3200K.

If this is the only light in the scene so no mixed sources, then in theory the blue channel would be cleaner when the camera is set to 5600K instead of being set to 3200K. This is because the "native" color sensitivity of most sensors is close to daylight-balance. However, if your camera is fairly clean at 3200K, then it's not much of an issue. Also depends on what base ISO you want to work at.

[David Mullen ASC]

Think of it this way:

In Scenario #1, you have a 5600K light at night and you set the camera to 3200K for a blue effect. Your lens is wide-open at, let's say, f/2.0 and your camera is at ISO 800.

In Scenario #2, you put Full CTB gel on the 5600K light and set the camera to 5600K for the same blue effect. But since Full CTB gel loses 2-stops of light and you're already wide-open at f/2.0, you have to set your camera to ISO 3200 to compensate. 

So any improvement in blue channel noise from working at a 5600K setting on the camera is negated by switching from ISO 800 to ISO 3200.

 

[Manuel Troendle]

21 minutes ago, David Mullen ASC said:

Think of it this way:

In Scenario #1, you have a 5600K light at night and you set the camera to 3200K for a blue effect. Your lens is wide-open at, let's say, f/2.0 and your camera is at ISO 800.

In Scenario #2, you put Full CTB gel on the 5600K light and set the camera to 5600K for the same blue effect. But since Full CTB gel loses 2-stops of light and you're already wide-open at f/2.0, you have to set your camera to ISO 3200 to compensate. 

So any improvement in blue channel noise from working at a 5600K setting on the camera is negated by switching from ISO 800 to ISO 3200.

 

Thanks David for your detailled answer and describing the 2 scenarios, really helped me to understand what you are trying to say! Now lets Say that you are not gelling, and you have an LED Light that does not loose output by dialing it to a 7000k color temperature, and you dont have to adjust your ISO. Which option would you now go for, #1 or #2? 
And to clarify: In my Post above i meant 3200k, not 700k, just copy-pasted that wrong. Sorry for the confusion. 

[David Mullen ASC]

Again -- setting a light to 7000K and the camera to 5600K is like setting the camera to 3200K and a light to 3600K, it's hardly much blue added. Certainly nowhere near as blue as setting a light to 5600K and a camera to 3200K.

If your light is 7000K, you'd have to set your camera to 3600K to get a MIRED shift of -134, the same as using a 5600K light on a camera set to 3200K. 

So yes, you'd slightly gain some improvement in the blue channel from setting the light to 3600K instead of 3200K. But hardly.

You just have to realize that a shift from 5600K to 7000K is hardly much of a change, it's same as a change from 3200K to 3600K. That's why the MIRED system was developed because the change is not linear.