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Exposure Calculator?


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#1 Rob McGreevy

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Posted 12 September 2016 - 12:54 PM

Can anyone point me in the direction of a solid online exposure calculator? I've got the Toland AC app on my phone, but it doesn't offer me all the settings I want and it's kind of malfunctioning on me anyway...I'm gaffing a feature and I need to know how many foot candles I need for exposure at 1000 ISO, 24 fps and 180 shutter...don't have f stop confirmed yet but dp tells me it'll be roughly in the 2-2.8ish range.

I've got a balloon light system coming in from L.A. that I've never worked with and before I have production throw down $ on it I need to be sure it will be sufficient.


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#2 Gregg MacPherson

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Posted 12 September 2016 - 04:43 PM

Hey Rob,

If you have something in your kit like an old analogue hand held Seconic L-28c2 you can get some quick answers.  I'm rusty,  but got about 12 foot candles in a few seconds.  Not much is it.  Maybe I boobed.  When you're sorted, let me know.

 

Without the high slide,  the top units that the needle sweeps are foot candles.  Though for these "what if" type thoughts we aren't reading anything,  just setting ASA and T stop to see the foot candles on the Low scale on the wheel.

 

Those old meters are really tough,  and cheap now

 

EDIT: 12 fc at T2.8


Edited by Gregg MacPherson, 12 September 2016 - 04:51 PM.

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#3 Brian Drysdale

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Posted 12 September 2016 - 06:50 PM

You can work it out quickly if you remember that 100ASA (ISO) 1/50 at f2.8 needs 100 footcandles.


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#4 Gregg MacPherson

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Posted 12 September 2016 - 11:33 PM

That is easier isn't it. And it will never get lost,  stolen or break down.

Still,  there's a good case for having an old analgue like the seconic in ones kit.


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#5 Rob McGreevy

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Posted 13 September 2016 - 04:41 PM

I don't have that in my kit, the Toland app was serving pretty well until my phone started having software issues...I used to try to do those calcs based on that equation, I'm just pretty bad at math especially in my head, so once it became an option to let the computer do it for me, well, I kind of forgot about those old formulas...

I was kind of hoping to find something reliable on the cyber-webs though, as I'm currently in the thick of it on a shoot out in BFE Texas and I won't be getting analogue equipment or equipment of any variety for that matter in anytime soon...


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#6 Gregg MacPherson

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Posted 14 September 2016 - 12:31 AM

If you clear your head the algebra is quite easy...

Starting with the relationship Brian gave...

100ASA (ISO) 1/50 at f2.8 needs 100 footcandles

So..

200ASA (ISO) 1/50 at f2.8 needs 50 footcandles

400ASA (ISO) 1/50 at f2.8 needs 25 footcandles

800ASA (ISO) 1/50 at f2.8 needs 12.5 footcandles

 

Have to fudge it for the 1000ASA.  (don't bother). (smiley face)


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#7 John E Clark

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Posted 14 September 2016 - 01:31 PM

If you clear your head the algebra is quite easy...

Starting with the relationship Brian gave...

100ASA (ISO) 1/50 at f2.8 needs 100 footcandles

So..

200ASA (ISO) 1/50 at f2.8 needs 50 footcandles

400ASA (ISO) 1/50 at f2.8 needs 25 footcandles

800ASA (ISO) 1/50 at f2.8 needs 12.5 footcandles

 

Have to fudge it for the 1000ASA.  (don't bother). (smiley face)

 

For 1000 ISO the Forumula is quite easy... if 100 ISO requires 100 fc... then 1000 ISO requires 10 fc @ f/2.8 @ 24 fps @ 180 deg.


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#8 Gregg MacPherson

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Posted 14 September 2016 - 04:31 PM

Hey John,

 

We may well find the algebra trivial.....new fc = 100/(new ASA) * 100......(the f/s and shutter being constant for now,  as given in the original post)

 

But non algebraically oriented folk, even very clever people actually,  under fire,  tired, will revert quickly,  with near instant mental arithmetic,  to the idea of halving the fc if the ASA is doubled.

 

Our first duty being to help Rob.


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