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Tungsten flicker at 150Fps
25 replies to this topic
Posted 30 June 2007 - 12:21 PM
Has anyone ever had any problems with tungsten lights flickering at 150Fps, 180º ? Everything I had under 1Kw flickered on this comercial . I saw my life flashing before my eyes when I saw the rushes, hopefully post production managed to remove most of it. I've talked to lots of others DPs, most of them much , much more experienced than me, and everyones reaction was "What!? That's not possible!" After the shoot, we re-tested the camera with the same lights we used, in the same conditions, with dimmer, without dimmers and plugged to the genny ( as we had on the shoot ) and company electricity. The all flickered at 150 Fps... Can anyone help? ( this is just the off line + 1 light tk ) you can check the finalized film at http://web.mac.com/aszankowski1
All the best!
Posted 30 June 2007 - 01:32 PM
I can see the flicker it's slight but definitely there, i would have suggested it might be dimmers but you've allready tested that
I'm also at a loss i'm afraid! I'll phone a gaffer friend of mine see if he's got any suggestions.
Nice work BTW! Looks beautiful!
Posted 30 June 2007 - 01:45 PM
The mpeg hides it a bit, the smaller the lamp the more it had, they would actually look they were turning on and off...
Posted 30 June 2007 - 02:13 PM
I can't reach my gaffer friend he's always working! but i was just thinking, the nature of AC electricity is that it actually pulsates unlike DC which
is a constant stream, is it feasible with a high fps speed that your actually seeing this Phenomenon?
Just a thought.
Posted 30 June 2007 - 02:24 PM
Yes, at Higher speeds you will sometimes encounter flicker from small tungsten sources. To my understanding it is better to use larger tungsten units when shooting at higher frame rates as there will be less risk of flicker. What size source at which frame rates will be safe, I'm not completely sure.
I hope that the post house can fix it all for you. Looked great btw.
Posted 30 June 2007 - 02:25 PM
Well Kieran, that's the only explanation we got so far actually, cinematographer friend of mine, found out that there are some new kind of tungsten filaments that cool off faster to help with the lamps life,or lamps that are over charged to get a brighter light. if that is so, at high speeds maybe we can see the fillament fading... that's the best we have so far.. anyway, from now on i'll deal with small filament tungsten lamps just like HMI's...
Posted 30 June 2007 - 02:33 PM
Hi Matt, i know you can get flicker with high speed, but i always heard like 2000 frames and so on... My practicals where 200w lamps ( dimmerd ) and a few 45w on the first set, just above the girls hand. I also had some kinos flickering, but that can happen if the ballsts are malfunctioning... The rest was Par 64 Cans, 650w Fresnels and tree 4Kw Tungsten Helium Ballons... We excluded camera problems as it would have afected the whole image. The next day I asked a gaffer friend to order me a flicker meter...
Posted 30 June 2007 - 02:43 PM
And so will I Andre, you live and learn!
All the best
Posted 30 June 2007 - 02:44 PM
The dimmer could well be the problem, in any case small units should be avoided for high speed shooting. As always test test test.
Posted 01 July 2007 - 02:35 AM
I've seen this lots of times. Any unit under 2k run from AC flickers, its a question of degree. Most times you'll never notice it, especially in the days of projection, but when telecine came in it suddenly became noticed. People tried to nail it down to the most incredible things, even the plastic take up belts on Mitchell magazines were blamed for a long time.
AC fluctuates, its the nature of the beast, but on larger units £2k+ there is enough thermal retention to maintain light output from wave to wave.
I was 1st AC on a shoot doing high speed stuff on a treadmill, 4 x Dinos through silks were used and the flicker @120fps was amazing - so even the bigger units can suffer. We reshot from a DC power source.
It not uncommon, surprised if experienced people have not encountered it.....
Posted 01 July 2007 - 03:20 AM
It's been my experience that you'll get flicker with lights under 2k when shooting over 120fps. Something to keep in mind though is that even if you've got, for example a 9-light maxi, you're likely to still get the flicker (it's a matrix of smaller lights). You're better off getting a single 10K light for the reasons Tony Brown mentioned, "enough thermal retention to maintain light output from wave to wave". And the dimmer only adds to the problem. HMI (and as far as I know fluorescent lights) are fine up to speeds of 10,000fps so long as you use an electric ballasts. You can get what's know as "arc wander" in HMIs, but it's remedied by diffusing the light since it's a bright spot that moves around the globe.
Posted 01 July 2007 - 04:24 AM
On a shoot with the Weisscam last week me and my gaffer were told by the DIT not to use the blondes we set up next to some 10K's, because of flicker. We were shooting at 300fps.
Posted 01 July 2007 - 01:21 PM
What would be used as a DC power source as you described above? Thanks.
Posted 01 July 2007 - 03:05 PM
I did some tests with a Phantom, at 1000 fps a blonde does indeed filcker.
Posted 02 July 2007 - 01:20 AM
Even Kinos that are supposedly "flicker free" will flicker at certain shutter and speed combos.
Posted 02 July 2007 - 02:58 AM
It is for sure an effect from the dimmer!
As you posted the a question in another forum but with different information I replied there too but based on the info given there.
In this case you clearly state you dimmed the lights. This is not the right way when you shoot highspeed.
Modern dimmers work by cutting off part of the cycle of the 220volts power supply.
So if you dim your lamps you increase the "off" time considerably, a 50% setting gives you as much "off" time as "on" time and your eyes might not notice it but the combination of camera speed and shutter for sure!
The only way you can reduce the light is with scrims or nd gels.
And use big globes, 5K or better 10K and up.
Or flicker free HMI.
Posted 02 July 2007 - 12:42 PM
The light output of an incandescent -- and that includes halogen-- will have a ripple at twice the power frequency. It's brightest at the peaks, and cools and dims somewhat at the zero crossings. Triac dimmers will make it worse, because they increase the width of the 'off" time at the zero point. Higher power lamps - 5k & 10k - will flicker less, because the heavier filaments take longer to cool down. This was a huge problem back in the days of optical sound tracks and incandescent exciter lamps, because the first filter on the audio amplifiers would strip out the DC component, and they'd amplify the power frequency ripple.
Conventional flourescents have a wide "off" time, as their light output goes to nearly nothing when the mercury arc drops out and re-strikes around the zero crossing. They're much worse than incandescents. KinoFlo's use an electronic ballast to solve that problem.
It would be fun to shoot a test of a variety of light sources at, say, 2400 fps. That would give us 20 frames per pulse cycle (in 60 Hz countries), enough to see what the variation really is.
Posted 02 July 2007 - 01:21 PM
In 60hz countries, tungsten lamps will flicker over 120fps. The smaller the fixture the greater the flicker. We generally recommend 5K and above as the filiaments are so thick & hot that they can't cool noticeably between cycles. Arc wander in HMI llights is an issue and varies in bulb type, size and age.
Posted 02 July 2007 - 04:39 PM
As was said,
Anything smaller than a 5k will flicker at high frame rates on AC power. I have gotten away with mixing some 1k PAR back lights or bounce mixed with plenty of 10ks, it flickers but is not noticeable if the object is moving (i.e. a drink pour etc).
For example, from this weekend: