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#1 Lucía Pérez S.

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Posted 03 January 2006 - 12:02 AM

hi,

i'm a student and i'm in a hd project.

i wanna know how is the F900 ISO, i mean, for using a light meter and have the right numbers


thanks

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#2 David Mullen ASC

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Posted 03 January 2006 - 12:15 AM

At 0 db, with a 1/48th of a second shutter, between 320 to 500 ASA.

I don't think you can use a meter to set the final exposure, only to light the sets, because you really want to base the final exposure on how the brighter highlights are holding.

Using charts, I tend to find the camera to be 320 ASA, but when I light a scene and then expose based on the zebras and how it looks on a monitor, I find I'm treating the camera closer to 500 ASA, because often it looks better to expose faces a little "down" on video, especially for night scenes.

So when I'm scouting locations or lighting sets, I set my meter to 400 ASA as a starting point. But I always set final exposure based on zebras and how it looks on a properly set-up monitor. Truth is that I hardly even take out my meter when shooting HD because the camera is a meter.
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#3 David Sweetman

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Posted 03 January 2006 - 12:34 AM

What is the method for using zebras to set exposure? stop down until there are none? or until they are minimal?
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#4 David Mullen ASC

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Posted 03 January 2006 - 12:46 AM

Depends on what you set your zebras at. If you think about a 10-step Zone System, with Zone Five, the middle, being 18% gray in luminence, and Zone Six being one stop brighter than that (I'm grossly simplifying the Zone System, excuse me) then Zone Six is also where you often place caucasian skin tones.

70 IRE is about the same thing as Zone 6, so technically if you have your Zebras set to appear at 70 IRE, then they should appear in the majority of a caucasian person's face if in frontal light and you want to expose "normally".

However, because of video's problem of handling the bright, shinier areas of skintones, you usually expose darker than that, stopping down slightly, so that the zebras appear only on the hottest spots of the face. So I stop down until the zebras JUST disappear, with them appearing now & then on the hot spots of the face, the tops of the cheeks, middle of the forehead, etc.

If you're not shooting caucasian faces, you can also think of 70 IRE as "light gray", i.e. one-stop lighter than 18% gray. So outdoors in sunlight, a cement sidewalk is about light gray and should show some zebras. Light sand too, a pale blue sky, a gray sweatshirt, etc. So look around and decide what seems like it should be light gray in luminence.

The other thing to remember is that you often to not expose "normally" or "correctly". What seems like the correct exposure for a face in sunlight may seem too bright in a night scene in a kitchen, for example. This is why I said that even though technically the camera is about 320 ASA, it seems that when you're shooting interior scenes, you often find yourself exposing more as if it were 500 ASA.

Edited by David Mullen, 03 January 2006 - 12:49 AM.

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#5 Gordon Highland

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Posted 03 January 2006 - 02:59 AM

even though technically the camera is about 320 ASA, it seems that when you're shooting interior scenes, you often find yourself exposing more as if it were 500 ASA.

Do a lot of people actually change ASA on their meter situationally? Whenever I'm going by meter, I just leave it for the ASA of the camera/film for normal exposure all the time, and just make a judgment call by eye whether I think the scene should be a little under- or over-exposed from the standard reading. On the other hand, I suppose it's no different than the fact I frequently set an "exposure compensation" (about 1/2 stop under) with my digital stills. . . speaking of, it's a little off-topic, but those LCDs are not to be trusted! Not even close sometimes. Having a histogram display is quite nice; it's kinda like a waveform monitor.
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#6 David Mullen ASC

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Posted 03 January 2006 - 12:16 PM

Do a lot of people actually change ASA on their meter situationally?


People have all sorts of odd personal habits when it comes to metering -- whatever works for them.

If I'm rating a 500 ASA stock at 320 ASA, I sometimes change it to 400 ASA when shooting night exteriors just to make sure I'm not overexposing too much for a scene I plan on printing fairly dark anyway (plus I can use the extra speed.)
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#7 Lucía Pérez S.

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Posted 03 January 2006 - 11:28 PM

thanks David...

And I must tell that, as you said, the idea is light the sets with meter and have it ready for the next shot... clearly, the last word will come from the DP after watch the monitor...
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