Re: [TCML] America's Got Talent - Camera interference

[bturner@xxxxxxxx]

My own comments on this subject --

My large coil (6' discharge, 3.5KVa imput) is rather 'dirty' in some ways,
though we have YET to induce any major or significant 'video artifiacts'
into either the cameras or the video stream itself. And I have had cameras
as close as 10 feet, including ones on the gimbal'd cranes doing
'flyovers'. A lot has to do with how you are grounded. Single-point
grounds, low-impedence ground runs, etc. We also draw power from an
isolated circuit whenever possible, I also use a 5Kva isolation
transformer inline - 240:120v into conventional line filter. (Corcom)

We tell the DP (Director of Photography) and the grips to run their video
and power lines away from the coil, and to check that the grounding
(shielding) on THEIR cables is intact. Also, lighting cables (DMX control
lines) are to use opto-isolators inline, again, verifying that all ground
shielding is intact. The ONE time we had a lighting malfunction occur was
due to a disconnected shield inside one lighting unit...

We even tried using an FM mic system while sitting on the coil - it worked
just fine.

Main things are ground loops, and open grounds which can act as antennas.

- brent




> On Sat, 14 Aug 2010 06:49:03 +0800, you wrote:
>
>>After 14 TV shoots I have seen TV cameras monitors turn to hash on a
>> number
>>of occasions. (scary on a $50,000 unit). My large coil within say 20+
>> feet
>>will certainly cause a problem.
>
> Kind of OT, but I was once brought a camera (pre-CCD days; magnetic
> deflection pickup tubes) that was horribly out of registration.  It
> checked
> out on the charts just fine, and I asked, "Where were you shooting with
> this?"
> "Oh, the new lab that has a huge superconducting magnet!"
> I can't quote my exact reply...
> Don't forget, the signal from a CCD is tiny, and there's a pre-amp in the
> same module with lots of gain.  Shielding (Brits: we mean "screening") can
> do only so much...
>
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