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inconsistant exposure


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#1 Nicholas Fry

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Posted 23 August 2006 - 04:46 PM

I recently shot a music video for a friend with a Bolex H16 Reflex. I was a little under the levels I wanted to be at so I had all of the film pushed one stop to compensate. Unfortunately when I saw the transfer the exposure was inconsistant. It started off decent but then there are sections of the footage that fall off to almost nothing, very little detail. I taped the stop on the lens so I'm sure that the iris never changed, and to my knowledge the lighting never changed.
One person suggested that the NON crystal-synched motor was varying its speed. But it would have to be shooting at 48fps to lose just 1 stop of light, and I'm sure I would have noticed if it were going that fast. and then some of the later shots have plenty of light.
Also unfortunate is that I shot the project on reversal so it could be cross-processed. so the exposure problem is even more severe.

Could the old zoom lens labeled as a F:2 cause a dramatic loss of light when zoomed in? that's the only solution I can think of.
Any Ideas?

thanks,
nick
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#2 Satsuki Murashige

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Posted 24 August 2006 - 02:52 AM

It sounds like you had multiple camera setups within one lighting setup - how large was the space you lit, was it high-key, low-key? Chiaroschuro? Can you post some still frames so we can see what kind of exposure variation you're talking about?

What I'm getting at is that exposure variation is not necessarily the result of a camera/lens malfunction - it could very well be that the camera angles you've selected to cover the master shot required a different stop, or a lighting change. And it's near impossible to say whether that's the case without actually seeing the footage.

That said, with the Bolex, there is the manual shutter used for in-camera fades and dissolves which is very easy to bump and underexpose your footage. Also, the shutter is 135 degrees, not 180, so you lose 1/2 a stop there, and the prism loses another 1/2 stop, so you may have forgotten to take those into consideration.

The most likely culprit is the cross-processing, which can be unpredictable if you haven't tested it (especially when you're pushing the film, as well). So did you test it first? :)

Hope this was somewhat helpful.

Edited by Satsuki Murashige, 24 August 2006 - 02:54 AM.

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#3 Nicholas Fry

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Posted 24 August 2006 - 03:52 PM

thanks for replying Satsuki,
It was a local bar here in las vegas, pretty average in size, so the area wasn't too large. and it was low key. I don't have the dailies in my possession but I will try to get some still frames to look at. I see what you're saying about the different shots possibly needing different exposures. but sometimes in a wide the shot has plenty of exposure, and in a tighter shot from the same angle it is way under.
I'm pretty sure that the manual shutter never moved, but you're right, at the time I wasn't aware that the bolex wasn't 180 shutter and i didn't know about the prism. that'll teach me to do some research next time. but for the cross processing, the director decided that he didn't like the look and I didn't get to do it anyway. so that wasn't it--i was just trying to justify why I would ever shoot on reversal for something like this. It was a bad move.
if i can get some stills I'll let you know,
thanks again
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#4 Dominique Egloff

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Posted 07 November 2006 - 12:47 PM

I recently shot a music video for a friend with a Bolex H16 Reflex. I was a little under the levels I wanted to be at so I had all of the film pushed one stop to compensate. Unfortunately when I saw the transfer the exposure was inconsistant. It started off decent but then there are sections of the footage that fall off to almost nothing, very little detail. I taped the stop on the lens so I'm sure that the iris never changed, and to my knowledge the lighting never changed.
One person suggested that the NON crystal-synched motor was varying its speed. But it would have to be shooting at 48fps to lose just 1 stop of light, and I'm sure I would have noticed if it were going that fast. and then some of the later shots have plenty of light.
Also unfortunate is that I shot the project on reversal so it could be cross-processed. so the exposure problem is even more severe.

Could the old zoom lens labeled as a F:2 cause a dramatic loss of light when zoomed in? that's the only solution I can think of.
Any Ideas?

thanks,
nick


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#5 isaac_klotz

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Posted 09 November 2006 - 02:50 AM

at full zoom, its possible you would lose up to 2 stops or more. in fact, most zooms i have used lose about one-two stops at full zoom. i've seen this on film cameras and even on hd cameras like the f-900 with a fujinon hd zoom lens.

-isaac
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#6 Chris Keth

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Posted 09 November 2006 - 03:23 PM

I don't know the exact situation but it sounds like you just didn't relight or reset your stop for the other angles when you probably should have. Being on reversal, the problem is even more apparent.
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