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Varicam RF Post Fix

 

Published : 8th July 2004

To anyone shooting nose-mounted Varicam aerials, be careful of stray RF from the helicopter's transponder. Yesterday, while shooting over the Gulf of Mexico, this problem raised its ugly head.

Anyway, about half of yesterday¹s footage has small horizontal spikes (most often green, but occasionally orange, only one vertical line high and no more than 1/4 of the frame wide) running intermittently through it. I¹m not an engineer, but I suspect the culprit was the transponder located less than 5 feet away. While the camera was in a fairly horizontal to slightly ³down-pointing² position, there was no problem, but when I tilted down or up more severely, we were taking hits like crazy. Though it could be due to internal components within the deck, I doubt it, since the spikes are not present when the camera was fairly horizontal (the deck mostly shielded from line of sight to the transponder).

Today, I checked out the camcorder, and everything seems perfect, so I¹m ruling out an independent problem with the recorder. I also spoke with the helicopter service company and discovered that the transponder is putting out a 1090mhz burst. Does anyone know whether or not this format or the recorder, itself, is any more sensitive to RF than a larger and slower tape format like Beta-SP?

Having shot a fair amount of aerials over the years, I¹ve never encountered this problem before, but when we shoot Beta-SP, I run the signal from the camera head to a separate BVW-50 recorder in the cockpit (for ease of review as well as tape and battery change), and when shooting film, obviously, the RF issues do not come into play.

Any tips to avoid this problem in the future, other than the obvious deactivation or location change of the transponder or recording to a separate HD deck in the cockpit? Any way to shield the camcorder better?

There is sort of a happy ending to this. Fortunately, our animator was able to use the ³Median² function in AfterEffects at the lightest setting to globally remove the spikes (since they¹re only one pixel high), but that slightly softens the image. For this particular application, which will be SD distribution, it's fine, but any help with suggested hardware or software that would remove the offending ³spikes² in post even more transparently would be much appreciated. Didn¹t Snell and Wilcox make a box a few years back that did something similar with film scratch removal?

Sorry for the lengthy post, but if the warning and/ or fix saves someone else¹s butt someday, maybe it¹s worthwhile.

Everett Gorel
Director/DP
South Coast Film and Video
Houston, Texas 77081
www.scfilmvideo.com



Everett Gorel writes :

>To anyone shooting nose-mounted Varicam aerials, be careful of stray >RF from the helicopter's transponder.

This problem is definitely not limited to the Varicam. There is probably not a video camera in commercial use that is not subject to some degree of RFI, if the source is close enough -- transponder, helo radio, etc. or powerful enough -- microwave dish, TV tower, etc.

>Having shot a fair amount of aerials over the years, I¹ve never >encountered this problem before, but when we shoot Beta-SP, I run the >signal from the camera head to a separate BVW-50 recorder in the >cockpit (for ease of review as well as tape and battery change), and >when shooting film, obviously, the RF issues do not come into play.

The best way to avoid RFI is to use a separate deck. If you are close enough to a powerful source, even film camera can be affected. Near the Empire State Building and other powerful transmitters, the RFI can overwhelm the control circuits on a 35III and a 435. Sometimes you can't turn the camera on, and sometimes you can't turn it off.

>Any tips to avoid this problem in the future, other than the obvious >deactivation or location change of the transponder or recording to a >separate HD deck in the cockpit? Any way to shield the camcorder >better?

There is a lot of good advice in the archives. With video it is really a very good idea to carefully check the tape for interference problems before moving on to the next shot.

One other thing to be aware of is that in cameras that have been repaired or serviced the internal shielding may not have been properly replaced and reconnected.

Try not to transmit on the ship's radio during a take and turn the transponder off if it's not required.

Brian Heller
IA 600 DP



>To anyone shooting nose-mounted Varicam aerials, be careful of stray >RF from the helicopter's transponder.

---It sounds like you folks have lots of experience with helicopter shots but I wonder if anyone has experienced any anomalies from static discharge from the rotor blades.

I have witnessed RFI phenomenon from static discharge in several older model cameras back in the eighties and wonder if this is still a problem.

Jeffery Haas
freelance editor, camera operator
Dallas, TX



Transponders on aircraft are not mandatory except in certain controlled airspaces ( bid city airports). Turn it off!

Wolf Seeberg



As long as you are VFR and below 18,000 feet and outside the growing numbers of controller airspace, that is true. Transponders are microwave pulsed beacon transmitters of usually between 300 and 1000 watts, and can get in to some equipment located to the propagation path. The same with any weather radar onboard.

Tom Tcimpidis
Commercial/Instrument rated pilot



I don't want to put out any bad information re: the effects of RFI, so here's an update on the aerial footage. According to Steve Mahrer at Panasonic,

Compressed formats like DVCPRO don't usually show RF hits as spike or video tearing effects. The compression and recording processes use shuffling to decorrelate the video into randomised compressed coefficients, thus if an RF hit was to somehow hit the tape or VTR, upon playback the error correction should fix it and at the same time unshuffle the hit to a sort of random noise. That noise should cause DCT blocks not lines. I suspect the cause may be more of a tape transport problem.

The fact that the footage exhibits no such DCT blocking and the transponder only transmits when queried (much more infrequently than the lines appeared) would tend to corroborate ruling out RFI; however, why would a tape transport problem be manifested only when the helicopter is running and the camera is in a non horizontal attitude? Could it be G forces, vibration, what? Again, we've practically done somersaults with the Varicam on dry land and can't make it hiccup.

BTW, someone from the list responded to me saying that he encountered this exact anomaly with some aerials he shot under similar circumstances. The cause was never discovered as the rental house, Panasonic, and the helicopter company all blamed each other. In our case, Panasonic has responded promptly and requested that we send them the original footage for review. I'll let the list know how this shakes out.

In the meantime, I didn't want to give Tyler or Panasonic a bum wrap. According to Steve Mahrer, apparently they're using Varicam's at NASA / DoD sites and those guys use LOTS of RF! No problems so far.

Everett Gorel
Director/DP
South Coast Film and Video
Houston, Texas 77081



OK Folks!

FYI-I'm doing some aerials next week with my Varicam and will consider all the great tips as well as report back with what I get out of the shoot. I'll be shooting from a helo with a mount as well as side door operation.

I can't imagine that it is a specific "Varicam " issue so lets just leave it to the woes of the digital realm.

More later.....

Larry Curtis

CURTIS PHOTOGRAPHY, INC.
P.O. BOX 900
NAPLES FL 34106 USA
www.curtisfilms.com



Good luck, Larry. We still have no definitive answer as to the cause of the "spikes" in our aerial footage. Though Panasonic's Director of Engineering suspects that it may be a tape tension issue from the sound of it, we can not simulate the problem here, even by swinging the camera around wildly in a windmill-type motion while recording.

Personally, I think it may be related to helicopter vibration, but we'll see. BTW, we've never had a problem using the Varicam and side mount together. Have a great shoot.

Everett Gorel
Director/ DP
South Coast Film and Video
Houston, Texas