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Bolex with a lightmeter - What do you set it up as?


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#1 grantsmith

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Posted 24 November 2006 - 01:11 PM

Hello,

I have a pre-reflex bolex. I want to set my lightmeter up as accurately as possible to use it with the bolex.

As the shutter is not 180, what is the best way to set it up as to get the most accurate measurement at 24fps? and 18fps?

Should I just use it as if it were a 180 shutter and over-expose by 1/3 stop? As the meter is 1/50 rather than 1/48, will this make a noticable exposure difference.

As it isn't reflex I don't have to worry about taking the prism lightloss into account.

Any ideas?

Thanks
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#2 Nick Mulder

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Posted 24 November 2006 - 03:37 PM

well, I got an old bolex out an did some rudimentary measurements of the shutter - I ended up with a result of 195deg which I thought was incorrect but according to this page:

http://www.bolexcoll...16standard.html

I was pretty close :lol: 190deg ... your shutter speed will be 1/(190/360*1/fps) eg, for 24fps

190/360 = 0.5277777...

1/24 = 0.041666666...

0.527777 * 0.041666666666 = 0.0219907407407...

1/0.0219907407407 = ~45

ie. 1/45th of a second which is just a smidgen longer than 1/48th which you'd get with a 180deg shutter...

Basically, just multiply whichever fps you want to use by 1.89 and you'll get your answer that you can use in your light meter ... 1.89 * 18 = 34 >> 1/34th of a sec
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#3 grantsmith

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Posted 24 November 2006 - 05:32 PM

Thanks Nick!,

My meter only meters 1/30 or 1/50. If shooting reversal can I get away with the difference or will I have to compensate with exposure?

Cheers,
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#4 Nick Mulder

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Posted 26 November 2006 - 05:43 PM

Thanks Nick!,

My meter only meters 1/30 or 1/50. If shooting reversal can I get away with the difference or will I have to compensate with exposure?

Cheers,


The differences between 1/45 and 1/50 and also 1/34 and 1/30 are not that great and you should get good results, you could/should affect your aperture a tad more in the right direction from the setting that the light meter recommends - shooting 24fps you would slightly over expose if you used the meter reading as is, 18fps you would slightly under expose...

The latitude of most films will accomodate this, even the reversal, but it depends on what you are going to do with the film... there are so many variables in exposures scene to scene that in some cases the difference will be important and others not worth thinking about ...


To remove any uncertainty if you have the time set up some tests
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#5 Clive Tobin

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Posted 28 November 2006 - 11:08 PM

I have a pre-reflex bolex. I want to set my lightmeter up ...

You need to be more specific. There was a substantial design change made at Serial 100401 which changed to the so-called Registration Claw with better edge guiding also, and changed the 24 FPS shutter speed from 1/45 to 1/60.

Most still camera light meters already have 1/60 so you can just use that with a newer camera.

If you have the older model Bolex, set the meter to 1/60 but rate the ASA at 1 step higher. That is, if using 100 film set the meter to ASA 125.

If you have the newer Bolex with an actual cine meter, the ASA should be set one step lower. That is, if using 100 film set the meter to ASA 80.

There is a lot of information on my site in the Identifying Your Bolex H Camera section, with lots of pictures and miscellaneous information and links.
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#6 grantsmith

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Posted 10 December 2006 - 10:51 AM

Thanks Clive,

What an interesting site you have.

I'm assuming the directions you are giving is for shooting 24fps?

My Bolex (non-reflex) SR is 159060 which seems to be inbetween the m and the rex 1. I'm pretty sure it is a bolex T however as it is like the supreme as all spec seems the same (no filter, 5 part parralax viewer).

Are the diections the same for this camera?

Anyone have any other tips for getting the best exposure possible with an incident light meter?


Thanks,

Grant
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#7 Clive Tobin

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Posted 10 December 2006 - 07:48 PM

...I'm assuming the directions you are giving is for shooting 24fps?...

Yes.
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