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class="Paragraph" Flicker Problems With Dinos

Published : 4th April 2004


Hi Guys,

I’ve got a strange one.

Shooting with 24Ks 12Ks Dinos and 1K groundrow at 100 fps on 5218 I'm getting flicker in the red channel.

I tested yesterday after first problems and we couldn’t reproduce it, now my rushes are flickering...

Has anyone got any ideas?

I'm lost, all tungsten, no small filaments, a safe speed etc etc.

WTF is going on!

Thanks in advance

Geoff Boyle
Copenhagen biting nails.



Geoff Boyle writes :

>Shooting with 24Ks 12Ks Dinos and 1K groundrow at 100 fps on 5218 >I'm getting flicker in the red channel.

>I tested yesterday after first problems and we couldn’t reproduce it, now >my rushes are flickering...


Since it's only in the red channel, it seems that there are only two possibilities: the film itself or the transfer.

If the problem were lighting or camera based, it would affect all layers -- and therefore all channels equally. I don't see how a manufacturing problem with the film could produce a flicker that would confine itself to the film frame.

I would try a transfer on another TX machine. I have a vague recollection from the dim past of hearing about this problem before. I'm going for a TX this PM and I'll ask around to see if anyone remembers, but it really sounds very much like a transfer problem.

Bran "I hate it when things like this happen." Heller
IA 600 DP



Geoff Boyle wrote :

>Shooting with 24Ks 12Ks Dinos and 1K groundrow at 100 fps on 5218 >I'm getting flicker in the red channel.

Was the flicker random, or a steady pulse?
What was your power source, a generator or a power grid?
Were ALL of the red channel lights flickering, or just some?
If it was a generator, was the load balanced, and how close to maximum capacity was it running?

Craig Kief



What shutter angle were you shooting at?

Unless you were skinnied down, I would think it very unlikely that you were getting appreciable variance on the 1k or larger tungsten stuff, especially the Dino, since, if you are using 120v. globes in pairs, you have a nice fat filament. Also, 100 fps should be a nice fat window for any shutter angle at 50 Hz power delivery.

Assuming for the moment that this is NOT light related, this leaves camera, film, or TK

Is the nature of the variance in the red layer across the board from dim to bright objects or is it more apparent at one end of the density range than the other?

Can you look at the neg outside the image area with a densitometer or frame by frame on the TK? If this occurs outside the image area also, it could NOT be lighting related.

Is the flicker a rthymical pulsing? Can you time it to figure out the period?

If the period is constant throughout a roll, then whatever has caused it might be in the film itself caused during manufacture, due to something happening to it in the camera, or something happening to it in the lab while running through the lab film path at a constant speed.

If the rate gets steadily faster or slower through a roll, that implies something that has happened to the film while it was rolled up. If it starts slower and speeds up, it might have been something that happened to the raw stock or the feed side of the mag. If it starts faster and slows down, it would be more likely to have happened on the take-up side of the mag or to the exposed film. I do not know enough about lab practices to know whether they spool the neg from tails out to head out when they check for perf damage or splices, so I don't know whether the exposed undeveloped neg ever exists in the lab head out.

If you put the film the other way around on the TK, does the problem happen at the same places or different ones. This might help eliminate the TK or point to it as the culprit

I've shot 18 at speed with no ill effects, but I have never experienced the red-only problem you have described with any stock.

One total wild card question: if this was a 435 at 100fps, did you have the intervalometer door in or the non-intervalometer door? I can't imagine it would have made a difference, but could that little internal capping shutter have in any way contributed?

Jeez - good luck finding the answer.

Mark "Watson, not Sherlock" Weingartner



Both Brian and Mark make really good suggestions for trouble shooting your problem.

I agree that it's not a lighting/power-flicker issue because ALL the light would change density evenly, not only in one color.

The other possibilities could be something is wrong with the electronic signal between the film and your eyeball. Maybe they have a bad tape deck that was used for your first and third transfer, but not the second.

Or I've also seen several situations with where the signal of the playback monitors on set was distorted by another monitor sitting next to it on the cart with different resulting distortions each time. Once, even by the magnets in a megaphone the 1st AD had set down on top of the monitor.

Good luck.

Paul Szopa
DP Los Angeles



First of all, thanks to everyone for their help.

Second, red face time

The flicker in today’s rushes seems to have a very simple solution.

Phil my AC found it when he stuck his head into the water tank alongside the periscope.

"Do you mean the rhythmic pulsing just above the waterline Geoff?"

"Yes! what is it?"

"Well you know this 'king huge tank is full of water and you've got a couple of wave machines going like mad!

"Yeah, get on with it!"

"Well it looks to me like the key is bouncing off the waves and diluting the sky Cyc"

"expletive deleted!" repeat many times...

The Cyc, a 180 degree curved one, is lit with 12K's with CalColor Blue 30 and 15 gels and white groundrow.

The caustics from the 24K key were rippling in amongst the blue/clear overlap area and weren't visible from any position other than right in the tank with your head in the water!

It was also a case of the guys in TK being too hypercritical, when we got the rushes back only a couple of us could even see what they were commenting on.

I think the stress caused lost me a couple of years.

Cheers

Geoff Boyle FBKS
Director of Photography
EU Based
www.cinematography.net



Just back on this for a moment. Vigo my gaffer, and I were tearing our hair out on this.

All big sources, spread across 3 phases of studio supply.

Frequency measured as 50.04

B&S variation of 0.7%

How could there be any lamp flicker?

Of course, there wasn't...

Cheers

Geoff Boyle FBKS
Director of Photography
EU Based



Geoff Boyle wrote :

> I’ve got a strange one.

Have you seen it, or relying the colorist? Or relying on someone at the transfer house other than the colorist?

Was the first problem the same as the rushes? Are you transferring at 25 FPS, or is it With a meta speed or other Frame rate controller at the X-fer house?

Bad red channel cable at the transfer house?

Seeking possibilities other than transfer:

Film shipped to location from another country? Shipping or X-ray damage?

Guessing it is with an Arri 435, Arri glow on or off, or Mistimed? (If it is your camera, probably not what you want to hear). Time code burned in wrong sensitivity? Is there a time code burn in option on the camera you are using?

Really far out: is there an infrared sensor somewhere in the film path? If so, is 5218 sensitive to IR (would it register as red?), or was perhaps some flare through an IR passing window.

How fast is the flicker, what is it's frequency? Is it light leak maybe? Pressure fog on the red channel from loop not being set right (remember 5296 - wasn't it - had blue pressure flashes). Is it a fog, or over the whole frame? Every roll, or only errant light, bouncing around?

Is the intensity of the red flicker the same at different filming rates?

Really far out idea, can't be: is there an infrared sensor some where in the film path? If so, is 5218 sensitive to IR (would it register as red?), or was perhaps some flare through an IR passing window?

Hope this helps.

Steven Gladstone
Cinematographer - Gladstone Films
Cinematography Mailing List - East Coast List Administrator
Better off Broadcast (B.O.B.)
New York, U.S.A.



>The Cyc, a 180 degree curved one, is lit with 12K's with CalColor Blue >30 and 15 gels and white groundrow.

What is white groundrow?

Steven Gladstone
Cinematographer - Gladstone Films
Cinematography Mailing List - East Coast List Administrator
Better off Broadcast (B.O.B.)
New York, U.S.A.



>I think the stress caused lost me a couple of years...

Geoff

I understand you can add alcohol to reduce that problem.

Very glad to hear you've isolated and solved the problem.

Best,

Kent Hughes
DoP
SoCal



Hi guys.

Thanks for pointing out the transfer house as a probable source of the problem but... we have of-course checked the material on two independent telecines (Shadow and Spirit) both before and after tape and see identical fluctuation in the red channel. The fluctuation freq. increases with camera speed.

Any more ideas?

Kris Kolodziejski, DFL, Copenhagen.



Kris Kolodziejski writes :

>we have of-course checked the material on two independent telecines >(Shadow and Spirit) both before and after tape and see identical >fluctuation in the red channel. The fluctuation freq. increases with >camera speed. Any more ideas?

Rippling caustics bouncing over the bounding Main.

Cf: Founding Father's earlier post.

Brian "Ready for next CML quiz." Heller
IA 600 DP



Kris Kolodziejski writes :

>Any more ideas?

Hi Kris, the small flicker on the sword shot from the second day we've traced to a Source 4 575 PAR lamp that I'd used to punch up a tree in the background.

Isn't this a variation on "if in doubt blame the lab?"

It's the weirdest thing I've ever come across, it wasn't even the caustics from the key, it was very soft caustics from the 20 * 12 soft fill!!

I hope to see you on Tuesday morning when I come in to have a play.

Cheers

Geoff Boyle FBKS
Director of Photography
EU Based



Hi guys.

Thanks for pointing out the transfer house as a probable source of the problem but...we have of-course checked the material on two independent telecines (Shadow and Spirit) both before and after tape and see identical fluctuation in the red channel. The fluctuation freq. increases with camera speed.

Any more ideas?

Kris Kolodziejski, DFL, Copenhagen.



Mark H. Weingartner wrote :

>Secondly, you should get a special award for using the term caustic.

Uhhh Sorry guys . I 'm unfamiliar with the term "caustic" . Were you using Drano in the water tank? or is it something else.

Mark Smith
Oh Seven Films
143 Grand St
Jersey City, NJ 07302



>Uhhh Sorry guys . I 'm unfamiliar with the term "caustic" . Were you >using Drano in the water tank? or is it something else.

If you collect parallel light rays with a spherical reflector, the light that bounces back forms a lit area that is described as a caustic curve.

By contrast, if you collect parallel light rays with a parabolic reflector, all the rays pass through a single point. If you put a filament at the focus of a parabolic reflector, you get parallel rays coming off of it (eg. xenon lights)

If you put your filament at the radius of a spherical reflector you get a distribution that has fall off on the edges compared to the centre (Most fresnels , both HMI and tungsten, use spherical reflectors.)

When parallel rays of light hit rippling water, you get bands of light focused by the waves acting as lenses which could be considered caustics also.

Aww, jeez...who woulda thunk that all that physics would actually be good for something.

Mark "uber geek" Weingartner
LA based



It's the weirdest thing I've ever come across, it wasn't even the caustics from the key, it was very soft caustics from the 20 * 12 soft fill.

Why'd you get red caustics from a 3200K fill and blue (8000k?) background lights ."Caustics" only amplify light, like a magnifying glass, they don't change color temp.....or do they? Where did the red come from?

Nick Hoffman NY Dp



"When parallel rays of light hit rippling water, you get bands of light

>focused by the waves acting as lenses which could be considered >caustics also" ...

So Where'd the RED come from?

Nick Hoffman 600 DP



Paul Szopa writes :

>because ALL the light would change density evenly, not only in one >color.

Agreed - That's why I kept repeating "it's a long shot", but it was all that came to mind.

Geoff Writes :

>Well it looks to me like the key is bouncing off the waves and diluting >the sky Cyc.

Was the key gelled (is that a word) red, or was it some other optical phenomena?

Sorry - I deleted the earlier posts and don't remember the rundown you gave on your setup.

Brent Reynolds
DP / Producer
Tampa, FL



> "Caustics" only amplify light, like a magnifying glass,

I'm not familiar with that term. What are caustics?

Blain Brown
DP
LA



Nick Hoffman writes :

>Why'd you get red caustics from a 3200K fill and blue (8000k?) >background lights ."Caustics" only amplify light, like a magnifying glass, >they don't change color temp.....or do they?.

What we had were variations in the red channel, I'm assuming that the white light hitting the Cyc was diluting the blue causing a "negative blue" effect also the tank that the water is in is lined with Cyan, or "negative red"

Slight tweaks to the angle of things gave us perfect rushes yesterday

Way cool shots of model boats, tracking alongside them, submerging to see the screws and then coming back up for a "helicopter" shot, all in one.

>Was the key gelled (is that a word) red, or was it some other optical >phenomena?

The key wasn't gelled but the Cyc was.

Also the soft fill was bouncing odd a cyan lined tank.

Cheers

Geoff Boyle FBKS
Director of Photography
EU Based



Geoff Boyle wrote:

>"Way cool shots of model boats, tracking alongside them, submerging >to see the screws and then coming back up for a "helicopter" shot, all in >one."

What did you do to keep the lens free of water droplets....or was that part of the shot? Also what is this a toy spot? or a sequence to be cut with full size boats actors etc...

Sounds like a fun project whatever the hell it was.

Nick Hoffman NYC DP


class="Paragraph"
This is a very nice description of Caustics.

class="Paragraph" Try going to this link for more detailed info :

http://physicsweb.org/article/review/15/11/1

A single ray of light has a pathetic repertoire, limited to bending and bouncing (into water, glass or air, and from mirrors). But when rays are put together into a family - sunlight, for example - the possibilities get dramatically richer. This is because a family of rays has the holistic property, not inherent in any individual ray, that it can be focused so as to concentrate on caustic lines and surfaces.

Caustics are the brightest places in an optical field. They are the singularities of geometrical optics. The most familiar caustic is the rainbow, a grossly distorted image of the Sun in the form of a giant arc in the skyspace of directions, formed by the angular focusing of sunlight that has been twice refracted and once
reflected in raindrops."

Paul M. Zenk
DP
Los Angeles, Reno, Sacramento



>Uhhh Sorry guys . I 'm unfamiliar with the term "caustic". Were you using >Drano in the water tank? or is it something else.

To physics major Mark W's excellent explanation of caustic curves an English major might add: Caustic drain cleaner and caustic curves are both derived from the same original meaning of caustic as something which burns or creates heat. A caustic curve focuses light to a hot spot, akin to a magnifying and the sun as a fire starter, the caustic compounds in drain cleaner, etc. will burn your skin.

Caustic remarks can get under your skin...

Brian Heller
IA 600 DP



Brian Heller wrote :

>Caustic drain cleaner and caustic curves are both derived from the >same original meaning of caustic as something which burns or creates >heat.

So in other words, they were using Drano "light" in the tank

I just did this the other day in a restaurant with a candle and a glass of water, focusing the light on my daughter's face. Now I can use the word caustic rather than the "light thingy with the candle and the glass"

Mark Smith



Adding to Sam's list, one of my fav's - the Schlieren Effect.

This is the name for that which causes the heat ripples that we were talking about creating with gas or sterno or whatever.

(The guy next to me at the county science fair was doing this one.)

Mark Weingartner
LA based



>This is a very nice description of Caustics. Try going to this link for more >detailed info  http://physicsweb.org/article/review/15/11/1

Also check out "Light and Color in the Outdoors" by M.G.J. Minnaert [Springer-Verlag]

Sam Wells



>This is a very nice description of Caustics. Try going to this link for more >detailed info  http://physicsweb.org/article/review/15/11/1

Thanks for the link, very intriguing. And also reveals that the wonderful prose of your message was actually Descartes'...!

Wade K. Ramsey, DP
Dept. of Cinema & Video Production
Bob Jones University
Greenville, SC 29614



>"What did you do to keep the lens free of water droplets....or was that >part of the shot? Also what is this a toy spot?

It's a toy commercial, we used a surface tension reducing coating on the housing lens and it's come up clean every time!

It's the stuff you get for car windscreens.

Cheers

Geoff Boyle FBKS
Director of Photography
EU Based



Geoff wrote:

>...It's a toy commercial, we used a surface tension reducing coating on >the housing lens and it's come up clean every time! It's the stuff you get >for car windscreens.

Over here in the colonies that would be Rain-X. Great idea!

Wade K. Ramsey, DP
Dept. of Cinema & Video Production
Bob Jones University
Greenville, SC 29614