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Converting foot candles


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#1 Nicholas A Micros

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Posted 14 April 2011 - 03:20 PM

I'm struggling converting 550 foot candles to a f/stop at 200 iso and 180 shutter. Can anyone help me out?

Or 6000 lumens to ...

Thanks
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#2 Tom Jensen

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Posted 14 April 2011 - 04:02 PM

I'm struggling converting 550 foot candles to a f/stop at 200 iso and 180 shutter. Can anyone help me out?

Or 6000 lumens to ...

Thanks

Make it easy on yourself and just use stops. You need 100 footcandles at 100 asa to get a 2.8. So at 200 asa you only need 50 footcandles to get a 2.8. 100 to get a 4, 200 to get a 5.6, 400 to get an 8 and 800 to get an 11. So, I'm guessing its 5.6 and 1/3 at 550 with 200 asa. I think I did that right. Someone feel free to correct me if I/m wrong.
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#3 Nicholas A Micros

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Posted 17 April 2011 - 12:44 PM

Thanks tom. Your reply is very helpful. Thats all the info I needed
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#4 Gregory Andracke

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Posted 21 April 2015 - 11:50 PM

Thanks tom. Your reply is very helpful. Thats all the info I needed

 

Make it easy on yourself and just use stops. You need 100 footcandles at 100 asa to get a 2.8. So at 200 asa you only need 50 footcandles to get a 2.8. 100 to get a 4, 200 to get a 5.6, 400 to get an 8 and 800 to get an 11. So, I'm guessing its 5.6 and 1/3 at 550 with 200 asa. I think I did that right. Someone feel free to correct me if I/m wrong.

My calculation on an old Spectra Pro was more like f/8 1/3 ---  I know this is an old post, but I was looking for some other stuff on FC and ISO and stumbled across this one!


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#5 David Mullen ASC

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Posted 22 April 2015 - 12:51 AM

100 fc = f/2.8 at 100 ASA so...

100 fc = f/4 at 200 ASA

200 fc = f/5.6 at 200 ASA

400 fc = f/8 at 200 ASA

800 fc = f/11 at 200 ASA

 

So Tom was right until he somehow thought that 550 fc was less than 400 fc, not more (or he forgot he had already converted to 200 ASA) and went down to f/5.6 instead of up to f/8... 550 fc should be a bit over f/8 1/3.


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