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class="style8" Is 23.976 A Flicker Free Frame Rate?

>Published : 26th February 2005

>Hello,

>In the middle of filming our short film (22 minutes), and we're inside a lot of buildings with the F900 that contain fluorescents.

>I'm trying to see the flicker on the field monitor, but since it's already running at 48i, I can't tell if there's a definite flicker in the lights. I've seen some pulsing in- and-out occasionally on one or two lights, but not the whole scene like I've seen with HMI flicker. Basically the flicker seems to phase in-and-out, first going away and then coming back, and I'm concerned if this is ruining the scene, or if it's just an annoying background difficulty. We have the rest of the week ahead of us for shooting, so if this is a problem, we can prevent it on further scenes down the road.

>I'm shooting with a 1/50 shutter at 23.976, is this a problem, and am I screwing things up flicker-wise? If so, what settings should I be shooting at?

>Thanks,

>Jason Rodriguez
Post Production Artist (and now Director of this little film)
Virginia Beach, VA


>Jason,

>Based on my own experience and the many posts here concerning color phasing problems in video that has been shot at shutter speeds other than 1/60 sec. I think your best bet under fluorescence is to use a 1/60 shutter speed. I think you'll have to actually use the clear scan feature and set it to 1/60th if I remember correctly.

>If you have time to search the archive on cml you should find several threads regarding a subtle, rhythmic color shift in video not shot at 1/60 sec (NTSC/U.S. standard) under fluoro’s.

Besides, when in doubt what can it hurt to shoot at 1/60 vs 1/48 or 1/50 just to be on the safe side? A quarter or fifth stop is nuthin'

>Good luck,

>Randy Miller, DP in LA


>You don't need clear scan to go to 1/60th of a second, or is there a difference in the 1/60th of the clear-scan vs. the normal 1/60th you'd select in the shutter menu?

>Has the footage I've already shot been hurt badly, and if so, how do I tell on a monitor such as a 20" Multiformat that's running at 48i and already "flickers"?

>Thanks,

>Jason Rodriguez
Post Production Artist
Virginia Beach, VA


>Hi,

>I've shot PAL video in the US and I didn't notice a colour shift, just a very subtle pulsating. I could have missed a slight green shift, I guess, but it wasn't that obvious. It was possible to tell when two different buildings were on two different phases!

>Phil Rhodes
Video camera/edit
London


>Jason Rodriguez wrote:

class="style9">>Has the footage I've already shot been hurt badly, and if so, how do I tell >on a monitor such as a 20" Multiformat that's running at 48i and already >"flickers"?

>You may not see "flicker" but "phasing" which can manifest itself as a subtle but cyclical level shift or color shift. Shoot a test, white card or grey card properly exposed in the questionable light.

>Watch luminance levels on a wfm if you have the problem you'll see the luma levels breathing usually by a few units on a regular time base.

>Mark Smith


class="style9">>You don't need clear scan to go to 1/60th

>Sorry, I couldn't remember if 1/60 was in the shutter speed range or not. Made the Clearscan suggestion just to be safe. There shouldn't be any difference.

>As for footage you've already shot it's a crap shoot whether there is noticeable color phasing in it. Depends on the fixtures, ballasts, area of frame illuminated by the fixture(s), how you were holding your mouth at the time of the shot. Mark's suggestion about using a waveform and white card is a good one.

>The other thing that is very important while shooting under mixed/crappy light is to create a clean and proper viewing environment for your monitor. Fluorescent light can contaminate the monitor and make it difficult at best to judge color and flicker.

>A couple of years ago I shot in a prop house lit completely by big fluoro’s overhead. I matched a tungsten to them with gels for a key and set up the shot. Didn't have time to flag the ambient light from the monitor. When I had a chance to look at the picture on the small HD field monitor I was horrified by how bad it looked. I spent 10 precious minutes white balancing, changing gels, re-adjusting the monitor.

>Finally had to shot and assume we could color correct in post. When the client got back to their office with the tapes I called and asked about the prop room scene. "Looks great" was the answer. In talking about this experience later with my rental house rep he said you'd be amazed by how many cameras and/or monitors "break" or go out of adjustment when moved from a proper, uncontaminated viewing environment to one with crappy fluorescent light bouncing around on the monitor's screen.

>Randy "big piece of duvateen over my head sometimes" Miller,
DP in LA


>In regard to video flicker, I have shot several 24p jobs and was told to switch to 1/60th when shooting under older magnetic ballast HMI's to get rid of a potential color phase problem.

>I thought that this was all foolish but the tech really was convinced that this problem would manifest itself.

>What are the possibilities that this is a reality?

Cheers,
Jeff Barklage, s.o.c.
US based DP
www.barklage.com
View reel : www.reelsondemand.com


>John Babl :

class="style9">>was told to switch to 1/60th when shooting under older magnetic ballast >HMI's to get rid of a potential color phase problem

>Jeff,

>I think the safest approach when shooting 24P (24, 23.98, whatever) is to use a 1/60th (U.S.) shutter. As we all know for any 24 fps speed origination format, 1/48th or 1/50th sec. shutter speed is not a safe shutter for non-flicker free HMI's or many non-continuous light sources.

>If you search cml for the word "flicker" you'll find several threads over the last few years about this issue and I've come to the conclusion that there's little if any downside to using 1/60 shutter speed under these conditions. As a reinforcement to this thinking I can say that having shot video of one kind or another for many years I never ran into a color phasing problem under fluorescents until I started shooting non-60i formats with their non-1/60th sec shutters. Just as shooting NTSC 60i CRT monitors on video was never an issue until 24P video came along.

>My 2 cents worth.

>Randy Miller, DP in LA


>Hi,

>I've also seen 60Hz iron-ballast HMIs flicker on 25i video. I have some material around somewhere which demonstrates this.

>Phil Rhodes
Video camera/edit
London


class="style9">>I'm shooting with a 1/50 shutter at 23.976, is this a problem, and am I >screwing things up flicker-wise?

>Assuming that the film is being shot in Virginia, it is worth noting that the AC power is at a frequency of SIXTY HERTZ, not FIFTY, if that's worth anything to you.

>Jeffery Haas
freelance shooter and editor
Dallas, Texas


>Okay,

>Today we just got back, and of course with more fluorescents in the scene I decided to take your guys advice and switch to 1/60th shutter-didn't seem to have any problems.

>One thing though, I did see some phasing in the shots from the last two days, but it seems as thought the HMI's are okay, and since they were about 1.5-2 stops brighter than the fluorescents, they blocked out the phasing around the subjects, only some lights in the background seem to be demonstrating some phasing-type artefacts.

>I'm not really sure if anybody will notice. Also it seemed as though only some of the lights exhibited phasing, we were shooting some windows where the fluorescent fixtures in the ceiling were clearly seen, and they didn't seem to have any phasing problems, there were only a couple lights in the back that did, and in those you could see a flicker even with your naked eyes.

>Now is this a common thing, that a light can be phasing, but because there are other sources in the scene that are overpowering these problem fixtures (such as the sun, brighter HMI, etc.) I won't see the phasing in the final picture, or when I get the footage back, will I see phasing throughout the scene?

>Jason Rodriguez
Post Production Artist
Virginia Beach, VA