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High speed lighting


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#1 Rick Griemink

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Posted 09 January 2017 - 01:07 PM

Hi all,

 

I am currently in a concept fase on a project. We are having plans to shoot 1.000fps in a studio (white limbo) setting. Shooting on a Miro with a base of 640 I was wondering what the minimum required of KW's is needed to lit it properly (exposed on a 2.0 t-stop, high key.) 

 

Thanks!


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#2 Stuart Allman

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Posted 09 January 2017 - 01:48 PM

Rick,

 

I don't mean to sound snobbish, but I think you may be asking the wrong question.  What you really mean to ask is how many foot-candles you'll need.  For that, use the formula fc=25*stop*stop/(ISO*shutter time).  This provides an good approximation.

 

Assuming you have a nearly 360 degree shutter angle at 1000fps your requirement equates to =25*4/(640/1000) = 156FC for standard exposure.  Double this number if you use a 180-degree shutter angle.  Use the photometric charts from the lighting vendors to determine what fixtures you need and at what distance.  If you use diffusion then you have to take that into account as well.

 

In this calculation I also assumed you're using a lens measured in T-stops.  If you're using a lens measured in f/stops then you need to compensate for optical losses in the lens, which may or may not be significant.  I also don't know how accurate the ISO sensitivity is on the Miro since I've never used it.  I've had varying degrees of ISO accuracy with different cameras.  You should test that ahead of time and apply any necessary compensation.

 

Also, you describe this as "white limbo" which may mean you need to overexpose the background and/or character.  You'll have to look at the Miro exposure range in highlights to determine how much is enough for that camera.  My guess is that you'll need to overexpose the background a stop or two at the very least.

 

Stuart Allman

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Edited by Stuart Allman, 09 January 2017 - 01:53 PM.

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#3 Albion Hockney

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Posted 09 January 2017 - 03:35 PM

I think your question is just how do you calculate how much light loss you are losing for a given frame rate. 

 

At 1000fps @ 360 Degree shutter you are effectively shooting at 1/1000sec. A 360 degree shutter seems pretty standard for high frame rate work - rather then the typical 180 degree shutter for 24fps (which results in the traditional 1/48sec shutter speed).

 

So just calculate the light loss and you can figure out how much power you need. The light output you will need will (like any shoot) depend on the size of the shots and what you are looking to achieve. Obviously a table top will take much less light then a wide shot of a car! 

 

this is a useful tool many use to sort these questions out.  http://calc.arri.de/calculator


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