White Balance Issue

[Jeff Milligan]

I interviewed a person (head and shoulders view) at a desk under a mix of overhead fluorescent (sp?) lights and an on-camera 10 watt light. I did a custom white balance which seemed to work as usual. The EVF view also looked good. When I looked the clips afterwards on the editing monitor, there is a slow cycle of changing white balance from slightly cool to slighty warm that repeats throughout all of these clips. An interview right after that at another location with a mix of some diffused window light and the same on-camera light was fine.

I have not ever had this happen on the XL1s or the GL2. Does the XL2 continue looking for a balance after the WB indicator has stopped blinking? Any help would be appreciated. I want to prevent this from happening in the future. I also have to figure out how to deal with this in post production to use these clips.

[Kelly Wilbur]

Hi Jeff,

This isn't a white balance issue...it is a shutter speed issue. If your shutter speed is set high under flourescent lights, you will see the effect you got. You need to slow your shutter speed down in order to blend together the refresh rate of the lights.

This will only happen with flourescent lights. The same thing happens when you shoot a TV with a high shutter speed. Your shutter will be out of synch with the refresh rate of the TV and you will see a black band move across the picture. Same concept.

Kelly

[Jeff Milligan]

Thanks Kelly for this information. What shutter speed guidelines would you recommend to avoid this effect?

This makes sense since the fluorescent lighting was the main light and the on camera light was more of a fill. I was shooting with a narrow depth of field to reduce the distractions in the background. This would raise the shutter speed.

I have shot under fluorescent lights before without this effect but not with this lighting combination for catch lights in the eyes and to open up the dark shadows under the eyes from overhead lighting.

[A. J. deLange]

Fluorescent lights go through a cycle of color temperature with each half cycle of the power line which lasts 1/120th of a second (in the US) so shutter speeds of 1/60th or 1/30th will cover more than a complete color cycle and should take care of most of the problem.

[Jeff Milligan]

Thanks A.J. for the information about shutter speed settings. I will experiment with the ND filter to see how to shoot for narrow depth of field and the shutter speeds.

[Stephanie Wilson]

Yes,

I blew a very important interview using a shutter speed of 500 while the studio fluorescent lights were on. Even though I used some additional stand lights the video looked like a freakin kaleidoscope and was totally unusable. Unless of course, the audience was on acid and might enjoy the show..... Unfortunately they weren't....

Steph

[Graham Bernard]

Stephanie? I wonder if there is a way to "pull-back" your "ditched" video work. How about making two tracks, one with reversed field order. I use Vegas, maybe putting the same event one on top of the other and reversing the field order .. just a thought . .hmmm.. maybe a Vegas script could "do" something?

Just a thought - Grazie

[Jeffrey Thayer]

I do a lot of xl2 shooting of hockey games under mercury and flourescent lighting. Every game is different and every rink is different. I use warm cards and white balancing extensively. I use the light blue and the light green cards to balance and it generally helps.

[Jean-Francois Robichaud]

Now, this is very interesting. Last saturday, I shot a scene in a fast-food restaurant, under fluorescent lighting plus my own soft light source. I was wondering why the colour phase was slowly pulsating on the final image (warm-cold-warm-cold). I now understand my mistake: I used a fast shutter speed, and I can see how using a slower one would have evened out the effect. I should have known better! I solemny swear that from now on, I shall always use 1/60, unless the situation really calls for something different.

Last June, I shot a movie in Germany with my NTSC camera, under 50Hz cheap light fixtures. The strobing effect because of frequency mismatch is horrible. I know this is different, and I can't remember if I used 1/60 or not. If I didn't, I wonder if it would have helped...

[Gustavo Godinho]

It happened to me some days ago and I was worried about the possibility of a camera problem.

I was shooting with a 300W as backlight, a 650W very diffused as key and a 650W fresnel to light the background, a little diffused. The room had some flo lights (ceiling) and after setting the white balance, the problem began. I said to the guy being the interviewed: "just a moment, I have to make a litte adjustment", and I just couldn´t find a way to fix the problem. I used the camera white balance presets and it was happening even on those modes!! Then, I changed to AUTO mode and the problem was gone. I´m not sure what was the shutter speed at the time, but I *THINK* i tested slower shutter speeds. Can´t remember now.

Do you guys think that the camera shooting a person lit with sronger lights, the flo lights on the ceiling could cause that?