Color shifting during interview footage, why?

S

shawn.w

Active member
Hey Everyone,

So i shot a sit down interview of a professor in his office, under what i assume were fluorescent lights. I white balanced and got it looking nice. However, in waves of about every 3 seconds, the color will slowly shift from the warmer yellow to a light blue tone. Does anyone know why this might be happening? There was no sunlight he was leaning back into or anything like that, it was as if it was happening in the camera. I can't figure it out as im almost positive i didn't have ATW on at the time so the camera should have been working under a solid color balance and not have been shifting. Also the fact that it happened in a consistent pattern until the end of the interview makes me wonder what camera function might have been doing this. I have other footage i shot that day from a classroom, not sure what kind of lights, and the color is consistent and fine. Let me know what you guys think might be the issue. Thanks!

- Shawn
 
You are not the first person to have this problem, and it may be nothing to do with the camera at all.

Some of the fluorescent lights on the market cannot be relied upon to give a constant color temperature and they do exactly what you describe, they slowly strobe between two (or more) different settings. The human eye is so good at dealing with color temperature changes that it's not noticeable, but cameras are not so clever.

I had a problem like this some time ago and I had to reshoot it in the end. I know I didn't use AWB either.
 
It's almost definitely the shutter speed. NEVER EVER EVER shoot with a shutter speed faster than 1/60* when working under fluorescent lights!**


*or 1/50 for PAL users


**unless you know for a fact that the lights are high-frequency electronic ballast lights
 
Barry_Green said:
It's almost definitely the shutter speed. NEVER EVER EVER shoot with a shutter speed faster than 1/60* when working under fluorescent lights!**


*or 1/50 for PAL users


**unless you know for a fact that the lights are high-frequency electronic ballast lights
Click to expand...


Would this be the same scenario for say a FootBall field's lights?
 
Panasoinic mentions this on page 46 of the manual.

With artificial lighting and especially fluorescent
lights and mercury-vapor lamps, the luminance
changes in synchronization with the power line
frequency. When this frequency is 50 Hz, mutual
interference will occur between the camera-
recorder’s vertical sync frequency (approx.
60 Hz) and the lighting frequency (50 Hz). This
means that the white balance may change
periodically.
​

It also says what Barry just said.

Not sure why they reference 50hz. This is from the NA manaual. But it's about the same regardless.

Basically if you notice any flicker under flouro's (try waving your hand quickly under fouro's) you are not under a high freq ballast.
 
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Denwa said:
Panasoinic mentions this on page 46 of the manual.
With artificial lighting and especially fluorescent
lights and mercury-vapor lamps, the luminance
changes in synchronization with the power line
frequency. When this frequency is 50 Hz, mutual
interference will occur between the camera-
recorder’s vertical sync frequency (approx.
60 Hz) and the lighting frequency (50 Hz). This
means that the white balance may change
periodically.
​
It also says what Barry just said.

Not sure why they reference 50hz. This is from the NA manaual. But it's about the same regardless.

Basically if you notice any flicker under flouro's (try waving your hand quickly under fouro's) you are not under a high freq ballast.
Click to expand...


Yea, saw that 50hz reference and that was what kinda threw me :(

Since I have your attention Barry, which one of your Scene files - bought your book - would be a good choice in a Football field type scenario? (day and night)
 
any other considerations i should take into account when shooting under fluorescents besides no shutter above 1/60?
 
Mixed temp flouro bulbs. A lot of places have a mixture of color temps. You can get anything form pretty close to 5600K+ (6500K?) and down to 3200K and some with a god aweful green tinge.

As long as they are all the same or pretty close you should be able to color balance. Also bad ballasts can cause flickering at a diff rate than the others but that should be really obvious tothe eyes (and often, ears).
 
Thomas Lew said:
Interesting. Never knew about the flourescent thing. So a slower shutter will solve this.. strange
Click to expand...
No, a CERTAIN shutter will solve it. It has to be a multiple of the line frequency (i.e., of 60). The easiest way to remember it may be to think of it in fractions based on 120 (double 60), so 1/120, 2/120 (1/60), 3/120 (1/40), 4/120 (1/30) and 5/120 (1/24).

Those are the safe shutter speeds. No others are safe when using a rolling-shutter CMOS camcorder.
 
Let's say that your shutter speed did affect what you shot.. That is, you're getting a purple, blue, green shift for every frame. Does anyone have any suggestions to correct this in post?

HVX-200
FCP 5
SHAKE
 
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