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ASA For DVX100A


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#1 AJ DeRose

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Posted 23 March 2007 - 08:05 PM

How can I figure out what the ASA of the DVX100A is. I know its DV but we would like to meter scenes anyway. Thanks
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#2 David Mullen ASC

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Posted 23 March 2007 - 08:39 PM

Well, the sensitivity can be affected by diffferent factors, so you're only going to get a ballpark figure (long time ago, I tested it and came to the conclusion that it was 320 ASA at 24P with a 1/48th shutter at 0 db.)

Probably the best way is to have an 11-step chip charp and a waveform monitor, but assuming you don't, if you can set the Zebras to appear at 70 IRE, which is a light grey that is close to caucasian skintone (in theory) and find a grey scale, you'll see a light grey stripe that is one-stop (one Zone) brighter than the 18% grey zone -- that should be around 70 IRE. So set the camera at 0db, select a shutter speed, and adjust the f-stop until the light grey stripe has a Zebra pattern. Then play around with the ASA rating on a light meter, using the same shutter speed setting, until you get the same f-stop on your meter that you are using on the lens.

Now I seem to recall that the DVX100 can't do Zebras at 70 IRE, but I'm not sure.

You could do it with 100 IRE Zebras and a white card, but the problem is that the knee setting affects the exposure at the high end.

Even simpler and rougher is to set-up a monitor with color bars, expose a simple shot in flat frontal light to look "normal" in brightness (again at 0 db with a selected shutter speed) and play around with the ASA values of your meter until you get a similar reading.

But I wouldn't use a light meter to set the final exposure on a video camera. I might use it to rough in the lighting on a big scene, or to scout a location, but a video camera itself is a light meter and its important that you expose it for the details you want to hold. You're missing the point if you treat it like a film camera; since it doesn't have the latitude of color negative film, you have to place exposure information into the narrow range that the camera can handle, which means looking out for clipping, etc.
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#3 Daniel Sheehy

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Posted 25 March 2007 - 02:42 PM

Now I seem to recall that the DVX100 can't do Zebras at 70 IRE, but I'm not sure.


80 & 100 IRE.
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