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Old September 4th, 2003, 09:18 AM   #1
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color shifting problem

Lately I have been doing quite a lot of legal video depositions and I have been having a recurring problem.

The important thing to understand first off is that I rarely use additional lighting because it tends to distract and bother the deposing witness so I usually have to go with existing lighting, which varies.

In one case, where the lighting was low and in other cases where I am shooting x-rays (on a backlit viewer), I get strange but regular color shifts from bluish to reddish back to bluish....It seems to occur at a regular interval.

I use Iris priority settings so that I can manually open and close the iris to fade up and back down when going on and off the record (I am afraid of using the fade custom key because of problems in the past).

Most times I cannot see the viewfinder during the deposition and have to use a cheap Varizoom monitor for referrence during the shoot (not accurate at all) because of space concerns.

Should I be using complete manual? Should I set the shutter to 1/60, leave it there and then be able just to play with the iris? Should I keep doing what I'm doing (Av mode) and lock exposure (can I press the lock exposure button again to unlock it?)? Should I use the AE shift settings more often?

This is troubling to me because it has only started happening recently and it provides some pretty bad results.

Any help or suggestions would be appreciated.

Thanks ahead of time,
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Old September 4th, 2003, 09:19 AM   #2
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also

I haven't used manual mode much.

If I set the shutter at lets say 1/60 and leave it there, will it stay at 1/60 until I change modes or turn the camera off?

Thanks,
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Old September 4th, 2003, 02:22 PM   #3
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and also...

I never use auto white balance or auto gain.

O.K....hopefully that's enough info...
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Old September 4th, 2003, 06:43 PM   #4
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The X-ray viewers use fluorescent lights. They flicker at a frequency of 60 kHz or multiple thereof. The eye usually doesn't notice the flicker, our persistence of vision. However, the camera does. You may notice the flicker less with Auto White Balance. You'll need to experiment with AWB, alternate light sources and different shutter speeds.
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Old September 5th, 2003, 12:54 AM   #5
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We had the same problem crop up a while back. I posed a question similar to yours, and here's what Don Palomaki said could have caused the trouble:

"Using aperture priority exposure mode. Check the shutter speed on the recording from the data code. You may find that the shutter speed has changed from 1/60 or 1/20 during the time of shifting color.

This might be cause by a beat between the pulsed light output of the flourescents (120 Hz arc) and the camcorder field rate (59.94) If this is the case, using shutter priority at 1/60 or perhaps 1/120 would probably avoid the problem."
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