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Arri 435 speed stability


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#1 Andre Szankowski AIP

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Posted 30 June 2007 - 01:55 PM

Hi! When a camera is sync tested at 25fps , does it mean it will be stable at 150fps?
I posted a "tungsten flicker" in general discussion, trying to figure out what happend...
All the best!
Andre

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#2 Stephen Williams

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Posted 30 June 2007 - 02:41 PM

Hi! When a camera is sync tested at 25fps , does it mean it will be stable at 150fps?
I posted a "tungsten flicker" in general discussion, trying to figure out what happend...
All the best!
Andre


Hi,

An Arri 435 is cristal @ 150 fps, however low wattage bulbs will flicker at higher speeds. At 500 FPS you should only use large tungsten units (10K's).

Stephen

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#3 Andre Szankowski AIP

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Posted 30 June 2007 - 02:44 PM

Thank you Stephen!
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#4 Olex Kalynychenko

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Posted 01 July 2007 - 03:58 PM

Hi! When a camera is sync tested at 25fps , does it mean it will be stable at 150fps?
I posted a "tungsten flicker" in general discussion, trying to figure out what happend...
All the best!
Andre


I wish give you a some words about problem of " flicker" too.
The matter is that, the frequency of main power can be not 50 Hz. This can be 49.5..49.8 Hz.
This is 0.5...0.2 hz can give you low frequency beating between 49.5 hz and 150.00 fps.
My idea , to measuring of real frequency of main power and choose of synchronous speed.
For example, if we have 49.5 Hz, need use of 49.5x3= 148.5 FPS.

Or will need use DC power source for lighters ,
or use three-phase supply.

A some cine cameras have possibility to syhcronization of speed of camera with real frequency of main power.
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#5 Rob van Gelder

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Posted 02 July 2007 - 02:37 AM

Just curious, are these practicals installed by your lighting crew or were they at this location already?
If the last instance, they might look like Tungsten bulbs but can contain a discharge bulb inside a "tungsten-like" glass envelope.

I have seen a similar mistake once, when they tried to dim these lamps which of course did not work.

Regarding the flicker: if the frequency of the power supply is slightly off, you will get a slow pulsing, not the rapid pulsing that i see here, in my experience.
The flicker rate that i see here, suggest a large difference in frequency, like 60 hz line frequency. If this was lighting from the building it might have been on a separate system, not 50Hz related.

Also keep in mind that the faster you shoot your film, the more accurate the frequency of the lighting has to be, so shooting 150 fps with HMI lighting without flickerfree setting (magnetic ballast) is a no-go, specially on a generator, though officially it should work. Your margin of error is so small then, you will have flicker in your highlights/glare very quickly.
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#6 Olex Kalynychenko

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Posted 02 July 2007 - 03:30 AM

I have seen a similar mistake once, when they tried to dim these lamps which of course did not work.


About control of volume of light of tungsten bulb.
You can control of volume of light by a few ways.
The first way - to control by rheostat and you change of voltage on bulb, but , the form of sinusoidal voltage not change.
This is style of control not generate of " flickers", but, to have a some shortcoming - big weight and size of high power rheostats and change of color temperature of light.

The next way of control of bulb - PWM , pulse-width modulation of output voltage.
The voltage not change, but, change of time of luminescence of bulb by every half-cycle.
This is style of bulb control can generate of " flicher" effect .
You need adjust of speed of shooting with frequency of main power.

From other side, the spiral inside of bulb have big temperature inertia and the " flicker" effect will have
more high volume, if you will have underheating of spiral ( low voltage or PWM with short pulses ).
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