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180 deg shuttter and flicker free lighting?


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#1 James Steven Beverly

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Posted 24 January 2009 - 03:23 AM

I was just looking at an add in the classified section of the forum and noticed Frank Cook had a Arri IIC High Speed camera for sale. Well curious as I always am about 35mm equipment I took a look to see if it might be a bargain. I was looking at the ad and noticed this line:

Just need to add that this Arriflex IIC has the 172.8 degree shutter rather than the 180 to allow for flicker free use with certain lighting.

WHICH concerned me a little. ALL my Russian cameras, the Konvas-1, The Kinor 35C Rotovision 5000 and the Kinor 35PII all have 180 deg shutters. Under what conditions would the camera flicker while shooting with a 180 deg shutter? Is this problem unique to the Arri IIC or does it happen to all cameras with a fixed 180deg shutter? The fastest my cameras will run is 50 FPS. Is this a problem that is associated with high speed cinematography and not something to be concerned with at lower speeds? I know they make flicker free ballasts for HMIs (Mel has some on the truck and we've used them before, though I was to busy at the time to notice what if any difference it made to the naked eye). Does this eliminate the problem? Thanks-Steve

Edited by James Steven Beverly, 24 January 2009 - 03:25 AM.

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#2 David Mullen ASC

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Posted 24 January 2009 - 11:09 AM

If you do some math, you'll realize that 172.8 degrees shutter angle at 24 fps gives you a 1/50th shutter -- so basically 172.8 is meant to be safe for 50 Hz (Europe) lighting when shooting at 24 fps.

However, it is also safe for 60 Hz (USA) shooting at 24 fps. See:
http://www.panavisio...kerfree60Hz.htm

But this assumes 24 fps crystal sync on the camera motor and a crystal sync generator for the HMI's.
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#3 Tim Carroll

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Posted 24 January 2009 - 02:50 PM

My IIC also has the 172.8º shutter. The cameras ARRI made with the 172.8º shutter were intended for the european market.

Like David said, when shooting crystal sync at 24 fps I have had no problem with flicker here in the States (60 Hz), and I guess if I were in Europe, I would have no problem with flicker at 24 fps as well. I wonder though, if in Europe and shooting 25 fps, that would give you a shutter speed of 1/52nd shutter speed, would that cause flicker under 50 Hz lights?

Best,
-Tim
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#4 Stephen Williams

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Posted 24 January 2009 - 03:36 PM

I wonder though, if in Europe and shooting 25 fps, that would give you a shutter speed of 1/52nd shutter speed, would that cause flicker under 50 Hz lights?

Best,
-Tim


Hi Tim,

25fps in Europe is flicker free regardless of shutter angle.

Stephen
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#5 David Rakoczy

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Posted 24 January 2009 - 04:51 PM

Just need to add that this Arriflex IIC has the 172.8 degree shutter rather than the 180 to allow for flicker free use with certain lighting.


Clever clause... tho truthful.

I would be sure to purchase (if possible) a camera with a 'true' 180 degree Shutter. That was one of the selling points on the SR2 S16 conversion I purchased from Camtec.
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#6 David Mullen ASC

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Posted 24 January 2009 - 06:52 PM

Clever clause... tho truthful.

I would be sure to purchase (if possible) a camera with a 'true' 180 degree Shutter. That was one of the selling points on the SR2 S16 conversion I purchased from Camtec.


172.8 should be fine though (assuming crystal-sync on both the camera and generator) -- truth is that for 60 Hz at 24 fps, 144 degrees is the optimal shutter angle, not 180 degrees. But anything above 72 degrees should be fine, even below that is OK... but then you start to run into shot to shot exposure variations. At 144 degrees, you capture two light pulses per frame, but below 72 degrees, you capture less than a full sine wave, so every time you trigger the shutter, you may end up in sync with the valley or the peak of the light pulse. That wouldn't show up as flicker, which is variation in exposure frame by frame, but it could show up as some shots being darker than others.
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#7 James Steven Beverly

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Posted 24 January 2009 - 11:16 PM

So, a 180 deg shutter is fine at all speeds in the US, then. Makes me kinda wonder why the Russians set they shutter angle at 180 degs instead of 172.8 unless western Europe uses a different electrical standard than eastern Europe which I know uses 220 vt at I THOUGHT 50 Hz. Anyway, I'm assuming a crystal sync camera like my 35C Rotovision with 180 deg shutter WILL flicker if one uses an HMI without a sync generator, correct? (I remember Mel saying something about that but I just want to make sure I heard him right and am understanding what you all are saying) and let me ask you another question what about wild rheostat motors like the one on my Konvas-1, how do HMIs affect them?

Edited by James Steven Beverly, 24 January 2009 - 11:18 PM.

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#8 David Mullen ASC

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Posted 25 January 2009 - 12:00 AM

So, a 180 deg shutter is fine at all speeds in the US, then.


No... Did you look at the chart in the link I posted?

At 24 fps crystal-sync, most shutter angles are fine for 60 Hz lighting. There are plenty of frame rates that are NOT fine though except at specific shutter angles. Just look at the safe speeds chart.

The generator has to be crystal-sync for HMI's. I think perhaps you could get away with a non-sync generator IF the ballasts are flicker-free within limits, but I can't swear by that. But if you are using magnetic ballasts, then you definitely need to use a sync generator.

Wild and constant speed camera motors are not precise enough for HMI's using magnetic ballasts, the camera motor has to be crystal-sync. Again, if the HMI's are using electronic flicker-free ballasts, then you probably have more leeway to be off-speed.

Flicker on film results from small variations in camera speed relative to variations in the pulsing rate of the light. Hence why BOTH have to be precisely regulated in some way unless the rate of the flickering light source is incredibly high due to a flicker-free ballast.

If you've got cameras with wild and constant-speed motors and generators without crystal-sync control, then you really should be avoiding HMI's and using big tungsten lamps instead.
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#9 James Steven Beverly

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Posted 25 January 2009 - 01:22 AM

OOOHHH sorry, I somehow missed the link you posted, my bad. I don't know what we are planning to use as far as HMIs go but I will certainly heed your advice with regards to avoiding them when shooting with the little Konvas-1. I had planned on using that particular camera hand held on my steadicam as the werewolf's POV so lighting would probably be done with tungsten anyway for the most part. I WILL definitely look at the link and study it. Thanks again-Steve
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#10 James Steven Beverly

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Posted 25 January 2009 - 02:28 AM

Really GREAT site BTW, David. Do you have any more like this? It is terrific!!
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