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Foot candles conversion


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#1 Eugene Lehnert

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Posted 31 August 2005 - 01:09 PM

So according to Kodak's technical data on their website their 500T Vision 2 stock needs 80 ft candles to be exposed at normal. But this is based on a shutter angle of 170 degrees.

So for the Bolex with it's 133 degree shutter and prism the light exposing the film is 1/80th of a second. Which is about 1.6667 times slower than 1/48th of a second. So therefore it should take 133 ft candles to expose film on an RX5 Bolex at an f-stop of 5.6?
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#2 John Pytlak RIP

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Posted 31 August 2005 - 01:42 PM

So according to Kodak's technical data on their website their 500T Vision 2 stock needs 80 ft candles to be exposed at normal.  But this is based on a shutter angle of 170 degrees. 

So for the Bolex with it's 133 degree shutter and prism the light exposing the film is 1/80th of a second.  Which is about 1.6667 times slower than 1/48th of a second.  So therefore it should take 133 ft candles to expose film on an RX5 Bolex at an f-stop of 5.6?

<{POST_SNAPBACK}>


Yes, you need 80 footcandles with a 170 degree shutter opening and 24fps for a T-5.6 stop with a EI500T film.

So for a 133 degree shutter opening:

(170/133) x 80 = 102 footcandles.
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#3 Eugene Lehnert

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Posted 31 August 2005 - 03:34 PM

Yes, you need 80 footcandles with a 170 degree shutter opening and 24fps for a T-5.6 stop with a EI500T film.

So for a 133 degree shutter opening:

(170/133) x 80 = 102 footcandles.

<{POST_SNAPBACK}>



Yes, ok, and I'm using RX lenses so I'm not calculating for 1/80 of a second I'm calculating for 1/65.

Thanks!
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#4 Dominic Case

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Posted 31 August 2005 - 10:42 PM

the light exposing the film is 1/80th of a second. Which is about 1.6667 times slower than 1/48th of a second.

Not meaning to be picky, but 1/80th of a second is actually faster than 1/48th of a second, not slower.

Still, you are correct in saying you therefore need more light.

If a 170deg shutter is run at 24fps, then the exposure is 1/51th sec and a 133deg shutter will expose for 1/65th sec.

But you can work out the light you need just from the angles. If you need 80fc at 170 deg, then you need (80 x 170/133) = 102fc at 133 deg.
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