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Angineux 5.9mm c mount


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#1 Tyler Graim

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Posted 19 March 2011 - 03:40 PM

HI,
I recently shot some footage with the 5.9mm f/1.8 Angenieux lens on a regular 16mm Bolex. It seemed like everything I shot with it was overexposed. I was curious if anyone knew if I need to adjust the f-stop because this type of lens lets too much light in for regular 16mm bolex? I am assuming it is just not made for this camera so I need to stop down a little bit to fix the exposure. If anyone has any info on this it would be appreciated.
Thanks

Edited by Tyler Graim, 19 March 2011 - 03:41 PM.

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#2 Bernie O'Doherty

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Posted 19 March 2011 - 04:11 PM

Could be that the f-stop setting has shifted. Make sure that in the f22 setting, the iris looks almost completely closed, and, of course, wide open at the widest opening.
This lens should work the same way on any camera. Did you set up your meter for 1/75 to 1/80 sec exposure at 24 frames/sec . to take account of the Bolex in-line prism ?
Make sure your variable shutter is all the way up-open. You might want to check your exposure meter also.
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#3 Tyler Graim

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Posted 21 March 2011 - 06:15 PM

Could be that the f-stop setting has shifted. Make sure that in the f22 setting, the iris looks almost completely closed, and, of course, wide open at the widest opening.
This lens should work the same way on any camera. Did you set up your meter for 1/75 to 1/80 sec exposure at 24 frames/sec . to take account of the Bolex in-line prism ?
Make sure your variable shutter is all the way up-open. You might want to check your exposure meter also.


Hi Bernie, Thanks for your response,
I set up my Meter for 24 f/s and the shutter angle is set at a 180 degree shutter. So you are saying that the Bolex needs to be corrected to shoot at a different shutter angle. Are you saying I should change the angle on my meter to correlate to 1/75 or 1/80 exposure time? Like maybe a 120 degree shutter? Tell me if I am getting this right. Thanks Tyler
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#4 Dom Jaeger

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Posted 21 March 2011 - 07:43 PM

The exposure time varies depending on what kind of H16 Bolex you have.

On early cameras (below serial no 100401) the shutter angle is 192 degrees, so at 24fps the exposure time will be 1/45 sec.

Later non-reflex cameras have a shutter angle of 144 degrees, giving an exposure time of 1/60 sec at 24 fps.

The reflex models (except the EBM and EL) have a shutter angle of 133 degrees, but also lose about a quarter of the light due to the prism, so the 'adapted' exposure time (taking into account the prism loss) is 1/80 sec at 24fps.

If your footage is overexposed, it sounds like you may have an early model with a 192 degree shutter, although the difference between 1/48 sec (which you say you calculated) and 1/45 sec should be negligible. The later cameras would actually give you underexposed footage if you measured for a 180 degree shutter. The most likely explanation is that your camera is running slow, and giving you longer exposure times than you are calculating for.

Have you used the camera with other lenses?
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#5 Tyler Graim

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Posted 21 March 2011 - 11:48 PM

Ok thanks Dom,
I found out that my Bolex was made in 1959. The serial number is 167612. I believe it is an H16 REX1. This website says that it has a 145 degree shutter: http://www.city-net....bolex/history/. This would mean about a 1/60 exposure time (exposure time=(fps x 360) / (Shutter Angle°).
If this is right I was not compensating for that. But shouldn't that mean that my footage should have been under exposed if I was exposing for a 180 degree shutter? I need to do some tests with other lenses it sounds like. Thanks for your help this enlightened me to some things about Bolex's that I didn't know.

Edited by Tyler Graim, 21 March 2011 - 11:49 PM.

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#6 Dom Jaeger

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Posted 22 March 2011 - 07:05 AM

If you've got a reflex model, don't forget you need to compensate for light loss in the beam splitting prism. If you move the turret out of the way (or remove the taking lens) you can see it behind the filter holder. The prism sits between the lens and the film plane and diverts about 1/4 of the light to the viewfinder, allowing you to see through the lens even when filming.

The first reflexes still had the 144 degree shutter angle, giving about 1/60 sec exposure time at 24 fps as you calculated, but taking into account the prism light loss the 'adapted' exposure time is about 1/75 sec, not far off the 1/80 sec 'adapted' exposure time of later reflex models.

If you look through the archives of cinematography.com in the Bolex forum you'll find plenty of discussions about how people work out their exposures for reflex Bolexes. Some use the 'adapted' exposure time, some prefer to offset the ISO setting on their meter, others just open the lens 2/3 of a stop more than their meter indicates (using a meter with frame rates and an assumed shutter angle of 180 degrees).

None of this explains your problem though. Given that you calculated for 1/48 sec exposure time, your footage should be about 2/3 of a stop underexposed, not over. Even if your camera was running extremely slow, say 18 fps when the speed dial indicated 24, the footage would still not be overexposed. Did you check the iris of the lens as Bernie suggested? Or your meter? Could you have made a mistake with the film stock speed?
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