White Balance Woes (DV852, MX8)
 

Hey all. we were doing some prelim shots at our location for a short that's coming up this weekend and I am having some serious WB issues. Everything is on full manual and I white balanced with the manual WB setting like I have all my other projects. The little symbol flashed and then stopped, indicating that it had a set WB to work with. The location is in long cooridors that have strictly Flourescent lights all the way down. Check out these two frame grabs below (they were in fast motion so there is some distortion for frame grabs). They occured 1 second apart. Do I have to buy a flourescent filter from say BH etc. to resolve this problem? Thanks to anyone and everyone for any help you can give.....


http://www4.ncsu.edu/~berobert/Hall1.bmp


http://www4.ncsu.edu/~berobert/Hall2.bmp

Yes, looks like a problem. I never had the WB changing in the middle of a shot on my ex-MX8. Maybe your cam needs to be sent in for repairs!

From my experience, once the WB is 'locked' the colour of the light source will not change until you switch the WB. If Hall1.bmp is what you want (a little too much yellow to my taste), then Hall2.bmp should be about the same hue, that is, yellowish, too. Not gray or bluish as in your Hall2.bmp.

I doubt if a flourescent filter can help here.

And the 'streak' in Hall1 and Hall2 (white band of UFO light coming down from the flourescent light), that's quite normal to digital cams.

What was the shutter setting for these pics? Short shutter times can introduce periodic WB and exposure changes with (mains fed) fluorescents

Shutter speed was at 1500 and I was at op+12 . And I didn't necessarily want the first WB setting, but it was just to show the dramatic change in WB I was getting. I'm not sure what to do, I sure hope the cam isn't in need of repair, that whole process will take like a month probobaly and this short is really big this weekend. I just tried the manual WB settings around the APT changing from low lamp lights to a flourescent kitchen light to a natural light and the WB held steady this time. I'm going to try again today at the location with the factory "Flourescent" setting turned on and see if that helps.

Do you mean 1/1500 sec? This is a very short shutter time, better take 1/60. The reason for my concern about the shutter setting is based on the specific behavier of mains fed fluorescents. They run at 120 flashes/sec (for a 60hz net). The fluorescent material starts to emit light every time the electrical dicharge happens (=120/sec) and depending on the persistance of the fosfor(s) the light emissions last for a short while. The problem is now that most fluorescents have several fosphors mixed together...and they all have different persistance (afterglow) times. If you apply very short shutter setttings and given the fact that there is allways a small difference between your cams framerate and the mains frequency, you can end up by sampling other parts in the light flash period and finally get other "white"

Andre is probably right! I never thought about it that way, because I have always shot at the lowest shutter speed (1/50 on my PAL machine). But I do remember being told that in flourescent lighting, there is frequency mismatch problem.

Actually, there is really no need to go for faster than 1/125 (on PAL) for most video, because the footage will look very choppy, especially in dim areas. If you really want a dim look, use less digital gain or even no digital gain. As shooting in bright sunlight, an ND filter seems better than the fast shutter, as shutter of 1/50 or 1/100 (for NTSC maybe 1/60 and 1/120) will be less choppy.

Ahhhh, you guys are right, I tried it out. That's a great lesson to learn. I had the frame rate up high because I had a great deal of Glidecam work involved and didn't want any strobbing involved. When I turn the frame rate to 1/60 or one setting higher, the WB is fine, but any faster than that, and it starts to act up again. Thanks alot guys, you really saved some headaches, and anyone who reads this will learn an important fact.