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HMI safe shutter angles


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#1 Kirk Sade

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Posted 03 March 2008 - 06:43 PM

I want to shoot this cop scene with a 45 degree shutter angle and at a variety of speeds i.e 24fps, 36 fps and 48fps. ( this is in north america so 60hz) I'm not sure yet if my HMIs are going to be equipped with flicker free ballasts though...can anyone tell me if I'll be fine...thanks..
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#2 Jonathan Bowerbank

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Posted 03 March 2008 - 09:08 PM

Those shots are all going to look very interesting. I'd go for flicker-free, just because the name sounds less chancey given the circumstances. I haven't shot enough high-speed stuff to answer you.

Sounds like a question for Mr. Zanit.
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#3 timHealy

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Posted 03 March 2008 - 09:37 PM

I want to shoot this cop scene with a 45 degree shutter angle and at a variety of speeds i.e 24fps, 36 fps and 48fps. ( this is in north america so 60hz) I'm not sure yet if my HMIs are going to be equipped with flicker free ballasts though...can anyone tell me if I'll be fine...thanks..


This question get asked a lot. A quick search on this site or the internet will find them. Also should be in the ASC manual and the Harry Box book.


60 hertz:
basically 20,24,30,40,60,120 whole number fps. There are more with specific shutter angles.

best

Tim
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#4 David Mullen ASC

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Posted 03 March 2008 - 09:40 PM

You should get flicker-free ballasts for a 45 degree shutter shot. At 45 degrees, you are capturing less than a full single sine wave for a normal non-flicker-free 60 Hz light. So depending on when you trigger the camera, you may be in-sync with the sine wave (so no flicker problems) but be getting less exposure some takes more than others depending on whether you are in-sync with the valley or the peak of the sine wave.
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#5 timHealy

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Posted 05 March 2008 - 08:19 PM

Hey David,

I don't doubt you, but should all the "safe shooting speed at any angle" charts be changed then? Or at least have an asterisk next to them for 45 or smaller angles.

Or one may have to hook up three HMI's from every lighting position plugged into a different leg if using three phase.

Or just get flicker free ballasts as you suggest.

best

Tim
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#6 timHealy

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Posted 05 March 2008 - 08:19 PM

Hey David,

I don't doubt you, but should all the "safe shooting speed at any angle" charts be changed then? Or at least have an asterisk next to them for 45 or smaller angles.

Or one may have to hook up three HMI's from every lighting position plugged into a different leg if using three phase.

Or just get flicker free ballasts as you suggest.

best

Tim
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#7 David Mullen ASC

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Posted 05 March 2008 - 08:26 PM

Like I said, the potential problem isn't flicker, it's exposure. You shouldn't have any flicker problems with 45 degrees at the "safe" speeds.
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