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Definitive bolex figures///


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#1 Ralph Tabith

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Posted 18 October 2007 - 02:55 PM

I am planning my trip to asia soon and bringing my newly acquired rex 5. I am going to shoot tests at the weekend but maybe not in time...

I was wondering whether the following was correct: i have my sekonic 508 cine and have programmed it for 130/135 shutter angle. I have also programmed it with an increment of 0.3 + for light loss.

Thanks, hopefully I can take some nice shots
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#2 Nick Mulder

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Posted 18 October 2007 - 03:35 PM

Those are the numbers I have in mine yep - the 0.3 isn't perfect but its the closest you can get to the actual loss of 0.2somethinghigherthan5 which I calculated one rainy day last year - works fine ;)

It took me a small bit of reverse engineered math to get to it - I'm interested, how did you come by the 0.3 ?
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#3 Ralph Tabith

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Posted 18 October 2007 - 04:34 PM

It took me a small bit of reverse engineered math to get to it - I'm interested, how did you come by the 0.3 ?


You told me ! :D Should I dial in 135 degree as well as the additional increment? Thanks
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#4 Nick Mulder

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Posted 18 October 2007 - 04:54 PM

yip - the 135 deg is separate (and more important) than the prism loss
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#5 Ralph Tabith

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Posted 19 October 2007 - 01:38 PM

yip - the 135 deg is separate (and more important) than the prism loss


Would this be the same if i were using a tcs time lapse motor as well?/ thanks for the "definitive figures" !

R
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#6 Mark Heim

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Posted 04 December 2007 - 03:52 PM

So if I'm using an REX 4 with a Sekonic L-558 cine, I should set the shutter to 135 degrees and compensate the prism loss by setting the ISO 1/3 stop slower? (200 instead of 250?) Then can I set my meter to 24fps and have an accurate reading?

Thanks in advance

Mark
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#7 Nick Mulder

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Posted 04 December 2007 - 06:19 PM

Sorry Ralph ! The notification of your question must of got lost in the pile of facebook crap I get (recent acquisition I may or not continue with) - Tobin Motor, I've used it twice... the prism loss stays the same, but I think the TCS runs on its own duty cycle which is to say the motor isn't running constantly... it stops and starts creating its own virtual shutter angle - email Clive to get the full details ;)

Mark: shutter angle 135deg - yip correct

ISO 1/3 slower - no not for correct exposure - I dont know your meter but you need to find the compensation function, look up 'filter factors' in the index of the manual and you'll probably find the correct page ... The 0.3 isn't a third of a stop, its a filter factor which uses Log base2 - you have to think mathemagically to get your head around it, and in the meantime I've forgotten the exact potion to get it going on the calc here

That being said, rating your stock lower like that (above and beyond what is required to compensate for the prism) isn't a bad idea as IIRC you'll punch up the shadow detail a little (but not pull developing btw) ...

Go Team Bolex!

Edited by Nick Mulder, 04 December 2007 - 06:20 PM.

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#8 Mark Heim

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Posted 04 December 2007 - 09:10 PM

thanks Ralph for the info. I have found the compensation feature on my meter. do i want a + .3 or - .3... i would assume -.3 as I am compensating for a light loss. so if i have my shutter at 135 and a compensation of -.3 that should then allow to meter at 24fps successfully?

thanks
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#9 Nick Mulder

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Posted 04 December 2007 - 10:55 PM

thanks Ralph for the info. I have found the compensation feature on my meter. do i want a + .3 or - .3... i would assume -.3 as I am compensating for a light loss. so if i have my shutter at 135 and a compensation of -.3 that should then allow to meter at 24fps successfully?

thanks


I forget which way around it goes but a dummy check is to take a reading at 0.0 then at + or - 0.3 and see the difference in exposure - the correct 'direction' would indicate you need a larger aperture
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#10 Ralph Tabith

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Posted 17 December 2007 - 03:01 AM

thanks Ralph for the info.


actually thanks to Nick really, I gleaned it all from him. and thanks for the info on the timelapse aswell nick. i actually had been shooting with 0.3 + and it should have been 0.3 - minus, oh dear. will it make that much of a difference if i get a graded telecine?

Edited by Ralph Tabith, 17 December 2007 - 03:02 AM.

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#11 Nick Mulder

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Posted 17 December 2007 - 03:21 AM

actually thanks to Nick really, I gleaned it all from him. and thanks for the info on the timelapse aswell nick. i actually had been shooting with 0.3 + and it should have been 0.3 - minus, oh dear. will it make that much of a difference if i get a graded telecine?



none ;) - well, some ... but unless you were shooting critical high-contrast scenes in reversal (reasons etc...) you really aren't going to gain anything by shooting it all over again
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