Foot candles conversion

[Eugene Lehnert]

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?

[John Pytlak RIP]

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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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.

[Eugene Lehnert]

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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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!

[Dominic Case]

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.