Home of Professional Cinematography since 1996

class="style1">50-60 htz Flicker

>Published : 2nd July 2007

>I just returned from shooting musical performances in large venues in
Europe. Paris, Brussels, Rotterdam and Luxemburg.

>I was shooting with a HVX200 setup for a 720/24pn project. Film Cam and shutter angle at 180.

>In a couple of the venues, I got flicker from the carbon-arc follow spot. I tried every thing I could think of and couldn't get rid of it. Would I have needed a PAL version of the HVX200 that was a 720/25pn project? Then done some sort of frame-rate conversion back home to use the material in a 24frame project?

>All the venues were 220 - 50 hertz countries. Why would the carbon-arc flicker in some, but not in others?

>Working backstage under fluorescent lights, I had no problem. (although under mercury-vapour fixtures, the flicker was really bad.

>Jim Dollarhide
Director/Cinematographer
601-853-4252
http://www.dollarhide.net


>If you set the shutter speed at multiples of 1/50 of a second, you will not have a problem. Most NTSC cameras do not have a 1/50th setting, so you must use 1/100th.

>What you thought were carbon arcs were most likely CSI or HMI lamps, discharge sources, like mercury vapours, carbon arc followspots were rare 20 years ago and are practically non-existent today.

>Where you thought you were ok, like backstage, there must have been either

>1/- some incandescent light (or daylight) that was filling in or

>2/- the fluorescents were wired on different phases, which would have cancelled out flicker to some extent.

>Unfortunately, there's no way to fix this after the fact, and of course you can't see it on LCD monitors which don't have rasters. An expensive lesson, but you won't ever do it again. I have shot in 30 countries that are 220/50hz (even some that are 100/50hz, like the eastern half of Japan) and have never had a problem: Whenever I see any non incandescent source, fluorescents, neon, mercury or sodium vapour, I set my shutter to 1/100th.

>Similarly, if you shoot a PAL camera in the US or other 60hz country, set the shutter to 1/60th. All PAL cameras have this capability.

>Before you go, check your voltage/current at

>http://www.roadogz.com/productionoffice/voltage/index.html

>or better yet, my favourite

>http://www.kropla.com/electric2.htm

>Where they list all the plugs you'll find as well.

>Bill Megalos


>Jim, in general when you use a non-PAL framerate in a PAL country you've got to set your shutter at either 1/50 (if possible) or 1/100 sec.

>I believe you'd need to set your film-style shutter at 172.8 degrees to get a 1/50 shutter speed at 24p. Does the DVX provide that setting?

>I'm not an expert on this, but in theory you should start having flicker problems at higher shutter speeds because at either 24fps or 30fps your framerate will be out of phase with the mains frequency and the higher the shutter speed, the more your exposures will visibly reflect that phase shift.

>I suppose it's possible that the fluorescents had just enough phosphor lag to minimize your flicker problem, whereas carbon arcs and mercury-vapour lights have no lag -- they're either on or off. The length of their "on" cycle (with each alternation of the AC power) may vary with lamp temperature, voltage, spacing of arc carbons and so forth. Those are just guesses -- hopefully someone more knowledgeable will chime in...

>Dan Drasin
Producer/DP
Marin County, CA


>Daniel Drasin wrote:

class="style2">>>I believe you'd need to set your film-style shutter at 172.8 degrees to >>get a 1/50 shutter speed at 24p. Does the DVX provide that setting?

Provide, no , but can you get there, or very close, yes. In an HVX shutter ca be shifted up or down from 180 by degree increments.

Mark Smith
DP NYC


class="style2">>>I was shooting with a HVX200 setup for a 720/24pn project. Film >>Cam and shutter angle at 180.

>Interestingly, if you turn the shutter "off" in an HVX200, what you get, in any frame rate other than 60, is 1/50 second. This was apparently done to accommodate shooting under 50 Hz lighting, maybe because the HVX200 didn't support 50 fps.

>If that doesn't solve the problem, you can use the SynchroScan settings in the menu to find the correct shutter angle, as slow as close to 1/24" (24.7) in 24PN mode. About 345 degrees would be close to 1/25 and about 172.5 would be close to 1/50. Remember, the HVX200 is always based on 59.94 Hz so the numbers don't start as integers, and the SynchroScan granularity is only 0.5 degrees, so you can only get close.

>Depending on your motion content, one of these should work.

>I ran into this problem from a client a few years ago and there was a tool in After Effects that was supposed to reduce the effect. Unfortunately, my version was too old to include it so I had to apply some frame blending to somewhat reduce the flicker. Sorry, I don't remember the name of the tool.

>A quick Google search for "After Effects, flicker, tool" turned up this one.

>http://www.genarts.com/sapphire-ae.html

>I'm sure there must be more by now.

>At the time (2003), Teranex (now Silicon Optix) was working on a flicker reduction filter for their boxes. You might check to see who has a box with that software in your area.

>Cheers,

>Charles R. (C.R.) Caillouet, Jr.

>Vision Unlimited/LA
Prairieville, LA
HD production technical support since 1987
...searching for the right tools for the job...


class="style2">>>Jim, in general when you use a non-PAL framerate in a PAL country >>you've got to set your shutter at either 1/50 (if possible) or 1/100 sec. I >>believe you'd need to set your film-style shutter at 172.8 degrees to get >>a 1/50 shutter speed at 24p. Does the DVX provide that setting?

>Don,

>The HVX200 has different syncro-scan settings, depending on whether you are in Film Cam or Video Cam mode.

>In Film Cam, you can get 172.5 or 173.0. Tried those. In Video Cam, you can get 172.1, 172.9 or 173.8 Tried those. In fact I scrolled through all the shutter degree settings in both modes and could not eliminate it. The speed of the flicker would change, but not go away.

>The HVX shutter speed settings are 1/24, 1/60, 1/120. No 1/50 or 100th available.

>Bill Megalos emailed me off the list, and suggested that I would not be able to see it on an LCD, but I could in fact see it on my LCD. It was very apparent.

>I agree with his assessment of the type of instrument -- I guess I just have the name carbon-arc stuck in my head as a generic term for follow spots.

>Anyway, like I said in my original post, I tried every setting the camera offered, but couldn't get rid of it. What baffles me is that I got in two arenas, but not in two others. And under the backstage fluorescents, I had no problems in three of the arenas, but had it quite bad in one.

>The idea of daylight or incandescent "filling in" was not the case. The
lighting was bright and uniformly fluorescent.

>Anyway, I guess the lack of 1/50th or 1/100th is what killed me.

Jim Dollarhide
Director/Cinematographer
601-853-4252

http://www.dollarhide.net


>I agree with Bill that the follow spot was most likely not a carbon arc. Long throw follow spots are either xenon or HMI. Xenon's are DC, so they don't flicker. If it was an HMI follow spot and your camera was set correctly to shoot under 50Hz discharge lighting there is one other, remote, possibility. Some electronic HMI ballasts offer three output settings - flicker free, 50 Hz, AND 60 Hz. It is possible that the follow spot was incorrectly set to 60 Hz.

>On a more general note, I have a joke theory about filmmaking. Filmmaking is 90 percent logistics. Of the remaining 10 percent, it's 90 percent calibration (as in this case, and especially true in multi-camera live events). If the logistics and calibration are well executed we're left the remaining 1 percent to be creative. Of course, most of us love our jobs and chose our careers because of the last one percent! :)

>Stephen Olsen
Lighting Technician
LA


>Jim Dollarhide wrote :

class="style2">>>The HVX shutter speed settings are 1/24, 1/60, 1/120. No 1/50 or >>100th available.

>1/50th is the default "off" shutter speed.

class="style2">>>... suggested that I would not be able to see it on an LCD, but I could in >>fact see it on my LCD.

>There are different types of "flicker". You cannot see interlace flicker on a progressive display like most LCD's, but a fast LCD will definitely show you embedded lighting flicker because the video amplitude is actually changing from frame to frame.

class="style2">>>What baffles me is that I got in two arenas, but not in two others.

>It sounds like you had mixed frequency sources. This is like trying to use SynchroScan or ClearScan to remove the bars in two computer displays in the same scene. If one of your sources was typical 50 Hz and the other running from a generator or crystal controlled source at another frequency (like 60, for example), you couldn't take both out. That sounds like it could be your problem. It could have been from advanced lighting instruments, like the new projector/camera/lighting combos.

>After the fact, it's pretty hard to establish. Even on site, it is often hard to isolate the problem fixtures. Sometimes you can stop down and scan the instruments to see which ones flicker differently, but there may not be much you can do in a large venue when you don't have control of the facility. If you are setting up a shot, you can sometimes flag the offending fixtures, or just overpower them. Even then, the lighter shadows can flicker on you.

>Cheers,

>Charles R. (C.R.) Caillouet, Jr.

>Vision Unlimited/LA
Prairieville, LA
HD production technical support since 1987
...searching for the right tools for the job...


class="style2">>>In a couple of the venues, I got flicker from the carbon-arc follow >>spot. I tried every thing I could think of and couldn't get rid of it

>Jim, are you sure that the follow spot was carbon arc? Arcs are, in my experience, run off direct current, and the flicker associated with carbon-arcs in the past was visible to the eye, where the flame is interrupted due to broken or wet carbons. If it was rectified DC, then I suppose it's possible that the flame was following a 50hz cycle, but it doesn't make sense to me. Carbon-arc lamps are literally carbons burning a housing. Other types of follow spots like Super Troupers have xenon lamps, supplied by rectified DC, using a ballast. I've never seen flicker from a xenon unit. However, other lamps, like the Softsun, which are supplied by rectified DC using a ballast, can flicker and have flicker free versions.

>Fixing the shutter at 1/50th should have done the trick, or true 24fps and a 172.8 degree shutter (not possible with this camera) or 25fps (also not possible with your version of the camera) would also have worked.

>The fluorescents more than likely had high-frequency ballasts, i.e. were flicker free.

>Ted Hayash
Los Angeles, CA