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minimum lux for top exposure


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#1 Gabriel Rochette

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Posted 26 February 2007 - 06:54 PM

I'm looking for a real answer about f/stop (exposure) vs Lux. A kind of formula to be sure that the iris opening of the video camera is the best. I known the technique of ZEBRA but what is about this minimum LUX the do a sharp image without noise ?
Thank you
Gabriel Rochette
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#2 Daniel Sheehy

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Posted 26 February 2007 - 10:45 PM

Hi,

'Minimum Lux' is a phrase most often seen in advertising material, it often has very little to do with good exposure.
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#3 Michael Nash

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Posted 26 February 2007 - 11:27 PM

The "real" answer is to forget about lux. It means nothing in the real world of shooting.

You get noise in the image when the image is underexposed and you amplify it in post, or amplify the image in camera by adding gain. A dark image in camera without added gain is just a dark image. There's no more inherent noise in an underexposed image than a "properly exposed" one. Make sure any "auto gain" controls in the camera are turned off, and the gain is set to zero db.
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#4 Andrew Koch

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Posted 27 February 2007 - 01:32 AM

It's not practical to think in terms of lux unless you are dealing with very low lightlevels. One footcandle
is equal to 10.764 lux (usually rounding down to 10 works fine and it's a heck of a lot easier to do the math). Even with fast 500 ASA film at a 1.4 tstop, you need at least 5 footcandles for "normal exposure." The difference of exposure between units smaller than a footcandel becomes exponentially less significant as you increase your light levels.

I find it more useful to find a relationship between IRE units and your camera's tstops. This relationship is ofcourse dependent on the ISO of the film or the camera. Since you are talking about "zebras" I can only assume you are talking about video cameras.

To determine the ISO of your camera at a particular white balance, filter, gain, etc... setting, you need to use a waveform monitor.

This way you can use the waveform monitor with a lighteter to establish a relationship with fstops and IRE.

If the ISO of your camera is etremely high, like 2000 ISO for example, you could use lux for contrast levels for extremely dark parts of your scene, but I wonder if this is a realistic situation.

Maybe in the future, if cameras get ridiculously sensitive, lux might be more useful.

I hope this was helpful.
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#5 Gabriel Rochette

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Posted 27 February 2007 - 12:56 PM

Thank you all for information about lux
Gabriel Rochette
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