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Marcos del Villar

Shutter speed and lights flicker with Bolex H16 EL

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Hello everyone,

 

I will be filming a shortfilm with my H16 EL in a couple of weeks. I am planning to light one interior scene with an HMI 1,2KW and some practical lights. I live in Europe so light is 50Hz. Given that shutter angle is 170º, is there any way to avoid lights from flicker at 24fps or 25fps?

 

(24x360)/170=50,82

 

If my maths are correct, 24fps would give the closest shutter speed to 1/50.

 

Best,

Marcos

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A 170 degrees opening angle only cuts a little on the light when 172.8 degrees is the optimum.

 

The bigger task is to keep the shutter and light pulsation in synch, meaning that exposure should take place on an energy peak. You need a means for phase shift, a speed control unit. Without one, in the worst case, your shutter will be open during an energy valley which isn’t really bad. You only loose some light.

 

The H-16 EL can be run crystal controlled but that may cause slow exposure variations by interference. The crystal controlled motor can run steadier than the mains light pulsations are. To do away with that one would have a synchronous motor hooked to the same mains section as the lamps are. Crystal control is apt to sound work, not necessarily to HMI lighting.

 

You might be well off by doing a few takes. At least one of them should be fine. An other solution are DC powered lamps. You can burn 24 V, 250 W types on car batteries. Do you use colour film?

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Hello, Simon

 

Many thanks for your quick response.

 

I'll film with 250D colour film. If I only loose some light would be ok. I'm afraid of having coloured stripes in the middle of the frame like in the picture attached.

 

DC powered bulb sounds like a good solution.

 

Would be better If I use any kind of LED source instead of the HMI. I could rent some Arri L7C or similar it It's a safer choice.

 

Marcos

 

lm7HG.jpg

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Daylight colour film and incandescent lamps don’t match well, you’d need a blueish conversion filter which sucks two stops. I should have suggested a high-intensity carbon arc brute on DC but that might intimidate you. Xenon arc lamp?

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I like combining warm and cold color temperatures in frame. Not a big issue.

 

One more question, would flicker free ballast for the HMI be a better option to avoid flicker with the Bolex?

 

I'm afraid I won't find carbon arc lights at the rental house I'm in contact.

 

Best,

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Electronic ballast reduces flicker to a photographically irrelevant minimum. Magnetic ballast doesn’t.

 

Three slide projectors could also work, with or without the lens. You can place gel filters in slide frames.

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